Sound on Sound Glossary

Magnetic Shielding

Also called magnetic compensation (which is usually a more accurate description). A means of restricting the radiation range of the stray magnetic field from a drive unit's permanent magnet which might otherwise interfere with the correct operation of moving-coil meters or CRT television monitors. While it is possible to enclose a magnet in a soft-metal case to prevent a stray magnetic field this becomes very expensive for large magnets, and so a more common approach is to affix additional small external magnets with opposite polarities to cancel out the unwanted stray field.

AFL

After Fade listen. A system used within mixing consoles to allow specific signals to be monitored at the level set by their fader. Aux sends are generally monitored AFL rather than PFL (see PFL).

Proximity Effect

Also known as 'Bass tip-up'. The proximity effect dramatically increases a microphone's sensitivity to low frequencies when placed very close to a sound source. It only affects directional microphones — omnidirectional microphones are immune.

Stereo

By convention, two channels of related audio which can create the impression of separate sound source positions when auditioned on a pair of loudspeakers or headphones.

Aux Return

Dedicated mixer inputs used to add effects to the mix. Aux return channels usually have fewer facilities than normal mixer inputs, such as no EQ and access to fewer aux sends. (cf. Effects Return)

Active

Describes a circuit containing transistors, ICs, tubes and other devices that require power to operate, and which are capable of amplification.

Glitch

Describes an unwanted short term corruption of a signal, or the unexplained, short term malfunction of a piece of equipment.

Figure of Eight

Describes the polar response of a microphone or loudspeaker that is equally sensitive both front and rear, yet rejects sounds coming from the sides. Also called Bipolar.

Instrument Level

The nominal signal level generated by an electric instrument like a guitar, bass guitar or keyboard. Typically around -25dBu. Instrument signals must be amplified to raise them to line-level.

Frequency

The number of complete cycles of a repetitive waveform that occur in 1 second. A waveform which repeats once per second has a frequency of 1Hz (Hertz).

Bit Rate (see also Sample Rate)

The number of data bits replayed or transferred in a given period of time (normally one second). Normally expressed in terms of kb/s (kilo bits per second) or Mb/s (mega bits per second). For example, the bit rate of a standard CD is (2 channels x 16 bits per sample x 44.1 thousand samples per second) = 1411.2 kilobits/second. Popular MP3 file format bit rates range from 128kb/s to 320kb/s, while the Dolby Digital 5.1 surround soundtrack on a DVD-Video typically ranges between 384 and 448kb/s.

Sample rate

The number of times an A/D converter samples the incoming waveform each second.

Sweet Spot

The optimum position for a microphone, or for a listener relative to monitor loudspeakers.

Continuous Controller

Type of MIDI message used to translate continuous parameter changes, such as from a pedal, wheel or breath control device.

Amp (Ampere)

Unit of electrical current (A).

Watt (W)

Unit of electrical power.

Bus

(Also sometimes referred to as a buss) An electrical signal path along which multiple signals may travel. A typical audio mixer contains several (mix) busses which carry the stereo mix, subgroups, the PFL signal, the aux sends, and so on. Power supplies are also fed along busses.

Buffer Memory

A buffer is essentially a short term data storage facility used to accommodate variable data read or write periods, temporarily storing data in sequence until it can be processed or transferred by or to some other part of the system.

Byte

A collection of digital data comprising eight bits.

Bit

A contraction of Binary digit, which may either be 1 or 0.

Binary

A counting system based on only two states: 1s and 0s. It is ideal for electronic equipment where it can be represented as high and low voltages, light on/off, N-S or S-N magnetic domains, etc.

Arpeggiator

A device (or software) that allows a MIDI instrument to sequence around any notes currently being played. Most arpeggiators also allows the sound to be sequenced over several octaves, so that holding down a simple chord can result in an impressive repeating sequence of notes.

Bass Tip-up

see Proximity Effect.

Program Change

A MIDI message designed to change instrument or effects unit patches.

Logic

A type of electronic circuitry used for processing binary signals comprising two discrete voltage levels.

Ferric

A type of magnetic tape coating that uses iron oxide.

File

A container for stored digital data that usually has a meaningful name. For example, a Standard MIDI File is a specific type of file designed to allow sequence information to be interchanged between different types of sequencer.

Pan-pot

A control found on mixers to move the signal to any point in the stereo soundstage by varying the relative levels fed to the left and right stereo outputs.

EuCon

A control protocol developed by Euphonix which operates at high-speed over an Ethernet connection. It is used between control surfaces and DAW computers to convey information about the positions of faders, knobs, and buttons and to carry display information.

Safety Copy

A copy or clone of an original tape for use in case of loss or damage to the original.

Linear

A device where the output is a direct multiple of the input with no unwanted distortions.

AES

Acronym for Audio Engineering Society, one of the industry's professional audio associations.

Power Amplifier

A device which accepts a standard line-level input signal and amplifies it to a condition in which it can drive a loudspeaker drive unit. The strength of amplification is denoted in terms of Watts of power.

Bias

A high-frequency signal used in analogue recording to improve the accuracy of the recorded signal and to drive the erase head. Bias is generated by a bias oscillator.

Sibilance

A high-frequency whistling or lisping sound that affects vocal recordings, due either to poor mic technique or excessive HF equalisation.

Open Sound Control

A high-resolution networked communication protocol for computers, synthesizers and other audio devices.

Flutter

A high-speed variation in replay speed causing rapid 'fluttering' pitch variations. See Wow and Flutter or Scrape Flutter

Cut and Paste Editing

The ability to copy or move sections of a recording to new locations.

Fidelity

The accuracy or precision of a reproduced acoustic sound wave when compared to the electrical input signal.

Pulse-width Modulation

A means of modulating the duty cycle (mark/space ratio) of a pulse wave. This changes the timbre of the basic tone; LFO modulation of pulse width can be used to produce a pseudo-chorus effect.

Fukada Tree

A 7-microphone array surround-sound, broadly equivalent to the stereo Decca Tree. Conceived by Akira Fukada when he worked for the Japanese state broadcaster NHK. The front Left, Centre and Right outputs are generated from a trio of mics arranged in a very similar way to a Decca Tree, with the left and right outriggers spaced 2m apart, and the centre mic 1m forward. The Rear Left and Rear Right channels come from mics spaced 2m apart placed and 2m behind the front outriggers. Instead of using omni mics like a Decca Tree, all five mics are usually cardioids, aimed 60 degrees outwards to maximise channel separation. These five mics are usually supplemented with an extra pair of omni outriggers placed midway between the front and rear mics.

DVS

'Digital Vinyl System' is a way of controlling and manipulating the playback of digital audio files in a computer by using conventional analogue turntables as the interface, thus maintaining a traditional 'disk-jockey' style of hands-on 'turntablism' control, including scratching. The system is based upon using special vinyl discs which carry standard timecode signals. The output of the vinyl replay chain is routed into the computer via an audio interface in the usual way, and the software is then able to analyse the timecode to determine changes in playback speed, direction, and position of the pickup on the vinyl disc, and apply that timing and speed information to the reproduction of a digital audio file. Some latency is inevitable in such a system, but it is usually very short.

Unbalanced

A 2-wire electrical signal connection where the signal conductor is surrounded by a screen which provides a 0V reference and also guards against electrical interference.

MIDI Multitimbral Module

A MIDI Sound Source capable of producing several different sounds at the same time and controlled on different MIDI channels.

Thru

A MIDI connector which passes on the signal received at the MIDI in socket.

Thunderbolt

A bi-directional computer interface based on the PCI Express protocol, used for both data transfers and to connect display monitors (it supports DVI, HDMI, and VGA monitors via adapters). Introduced by Apple in 2011, Thunderbolt 1.0 supports bi-directional data transfers at 10Gbit/s, while Thunderbolt 2.0 (launched in 2013) operates at twice that speed. This means a Thunderbolt 2.0 interface (20Gbit/s) is five times faster than USB3.0 and 25 times faster than FireWire 800. The physical Thunderbolt port is the same as Apple's mini-DisplayPort connector, and can be used to integrate FireWire, USB and Ethernet connections via appropriate adapters or hubs. Thunderbolt 3.0 uses the USB-C connector to carry up to 40Gbit/s, and has a 100W power transfer capability with appropriate cables.

Open Circuit

A break in an electrical circuit that prevents current from flowing. (see Short Circuit)

MIDI Implementation Chart

A chart, usually found in MIDI product manuals, which provides information as to which MIDI features are supported. Supported features are marked with a 0 while unsupported feature are marked with a X. Additional information may be provided, such as the exact form of the Bank Change message.

Oscillator

A circuit designed to generate a periodic electrical waveform.

Passive

A circuit with no active elements.

Way (as in, 2-way, 3-way)

A colloquial way of denoting how many separate frequency bands are reproduced by a loudspeaker. Most are two-way systems with a woofer and tweeter, but some are three way with a woofer, midrange and tweeter.

Jack Plug

A commonly used audio connector, usually ¼ inch in diameter and with either two terminals (tip and sleeve known as TS) or three (tip, ring, sleeve called TRS). The TS version can only carry unbalanced mono signals, and is often used for electric instruments (guitars, keyboards, etc). The TRS version is used for unbalanced stereo signals (eg for headphones) or balanced mono signals.

Overtone

A component of a complex sound which has a higher frequency than the fundamental frequency, but which is not necessarily related by a simple integer multiple (cf. harmonics)

Contact Cleaner

A compound designed to increase the conductivity of electrical contacts such as plugs, sockets and edge connectors. (cf. De-Oxidising Compound)

Convolution Reverb

A computationally demanding, but very accurate method, of creating artificial reverberation derived from real acoustic spaces with all their natural complexity. In essence, a reverberant space is measured to obtain its unique impulse response. That impulse response is then convolved with a 'dry' (reverberant-free) source signal to create an output signal which contains the original (dry) source signal with the desired room's reverberation characteristics imposed upon it. The convolution process is performed in the digital domain and involves multiplying each individual sample of the source signal with the impulse response of the convolving signal. The same technique can be employed to impose the characteristics of any other audio signal processing or signal-shaping device onto a source signal, such as the characteristics of legacy equalisers, compressors, tape recorders and so forth.

FireWire

A computer interface format based upon the IEEE 1394 standard and named FireWire by Apple computers (Sony's i.Link format is also the same interface). FireWire is a serial interface used for high speed isochronous data transfer, including audio and video. FireWire 400 (IEEE 1394-1995 and IEEE 1394a-2000) or S400 interface transfers data at up to 400Mb/s and can operate over cables up to 4.5metres in length. The standard 'alpha' connector is available in four and six-connector versions, the latter able to provide power (up to 25V and 8 watts). The FireWire 800 format (IEEE 1394b-2002) or S800 interface uses a 9-wire 'beta' connector and can convey data at up to 800Mb/s.

Memory

A computer's memory (RAM) used to store programs and data. This data is lost when the computer is switched off and so must be stored to disk or other suitable archive media.

Ground Loop / Ground Loop Hum

A condition created when two or more devices are interconnected in such a way that a loop is created in the ground circuit. This can result in audible hums or buzzes in analogue equipment, or unreliability and audio glitches in digital equipment. Typically, a ground loop is created when two devices are connected together using one or more screened audio cables, and both units are also plugged into the mains supply with safety ground connections via the mains plug earth pins. The loop exists between one mains plug, to the first device, through the audio cable screen to the second device, back to the mains supply via the second mains plug, and round to the first device via the building's power wiring. If the two mains socket ground terminals happen to be at slightly different voltages (which is not unusual), and small current will flow around the ground loop. Although not dangerous, this can result in audible hums or buzzes in poorly designed equipment. Ground loops can often be prevented by ensuring that the connected audio equipment is powered from a single mains socket or distribution board, thus minimising the loop. In extreme cases it may be necessary to disconnect the screen connection at one end of some of the audio cables, or to use audio isolating transformers in the signal paths. The mains plug earth connection must NEVER be disconnected to try to resolve a ground loop problem as this will render the equipment potentially LETHAL.

Unity Gain

A condition where the output signal is the same amplitude as the input signal; the overall system gain is then x1 or unity.

Hysteresis

A condition whereby the state of a system is dependent on previous events or, in other words, the system's output can lag behind the input. Most commonly found in audio in the behaviour of ferro-magnetic materials such as in transformers and analogue tape heads, or in electronic circuits such a 'switch de-bouncing'. Another example is the way a drop-down box on a computer menu remains visible for a short while after the mouse is moved.

Stage Box

A connection box terminating a multicore cable (see Snake) which is usually placed on a stage for the easy connection of individual microphone cables.

Port

A connection for the input or output of data.

DIN Connector

A consumer multi-pin connection format used for vintage microphones, some consumer audio equipment, and MIDI cabling. Various pin configurations are available.

Wow & Flutter

A cyclical variation in replay speed which affects the pitch of the recorded material. Wow is a low-speed variation (nominally below 4Hz) which typically occurs once per revolution of the device and may be caused by an off-centre hole on a vinyl record, or a sticking tape on a reel-reel machine. Flutter is a higher speed variation (nomninally above 4Hz) and can often be perceived as a form of intermodulation distortion.

Sound Card

A dedicated interface to transfer audio signals in and out of a computer. A Sound Card can be installed internally, or connected externally via USB2 or FireWire, and they are available in a wide range of formats, accommodating multiple analogue or digital audio signals (or both) in and out, as well as MIDI data in and out.

MIDI Sync

A description of the synchronisation systems available to MIDI users - MIDI Clock and MIDI Time Code (MTC).

Compressor

A device (analogue or digital) which is designed to reduce the overall dynamic range of an audio signal either by attenuating the signal if it exceeds a set threshold level according, or by increasing the level of quiet signals below a threshold. The amount of attenuation is defined by a set ratio, while the speed of response (attack) and recovery (release) can usually also be controlled.

CD-R Burner

A device capable of recording data onto blank CD-R discs.

Expander

A device designed to increase the dynamic range, typically by reducing the volume of low level signals (below a set threshold), or to increase the volume of high level signals (above a threshold). (See Compressor.)

Processor

A device designed to treat an audio signal by changing its dynamics or frequency content. Examples of processors include compressors, gates and equalisers.

Pitch-shifter

A device for changing the pitch of an audio signal without changing its duration.

Transducer

A device for converting one form of energy to another. Microphones and Loudspeakers are good examples of transducer converts between mechanical and electrical energy.

Sequencer

A device for recording and replaying MIDI data, usually in a multitrack format, allowing complex compositions to be built up a part at a time.

De-esser

A device for reducing the effect of sibilance in vocal signals.

Single-ended Noise Reduction

A device for removing or attenuating the noise component of a recording or transmission system without pre-conditioning the signal. Most digital noise-reduction systems are of the Single-ended type.

Decoupler (also isolator)

A device intended to prevent the transmission of physical vibration over a specific frequency range, such as a rubber or foam block.

Isolator (also decoupler)

A device intended to prevent the transmission of physical vibrations over a specific frequency range, such as a rubber or foam block. The term can also be applied to audio isolation transformers, used to provide galvanic isolation between the source and destination, thus avoiding ground loops.

MIDI Merge

A device or sequencer function that enables two or more streams of MIDI data to be combined.

Pop Shield

A device placed between a sound source and a microphone to trap wind blasts — such as those created by a vocalist's plosives (Bs, Ps and so on) — which would otherwise cause loud popping noises as the microphone diaphragm is over- driven. Most are constructed from multiple layers of a fine wire or nylon mesh, although more modern designs tend to use open-cell foam.

Ring Modulator

A device that accepts and processes two input signals in a particular way. The output signal does not contain any element of the original input signals but instead comprises new frequencies based on the sum and difference of the input signals' frequency components. The best known application of Ring Modulation is the creation of Dr Who's Dalek voices, but it may also be used to create dramatic instrumental textures. Depending on the relationships between the input signals, the results may either be musical or extremely dissonant - for example, ring modulation can be used to create bell-like tones. (The term 'Ring' is used because the original circuit which produced the effect used a ring of diodes.)

Interface

A device that acts as an intermediary to two or more other pieces of equipment. For example, a MIDI interface enables a computer to communicate with MIDI instruments and keyboards.

Breath Controller

A device that converts breath pressure into MIDI controller data.

MIDI Analyser

A device that gives a visual readout of MIDI activity when connected between two pieces of MIDI equipment.

Slave

A device under the control of a master device. Often used to refer to synchronised recorders, or digital clocking devices.

Mixer

A device used to combine multiple audio signals together, usually under the control of an operator using faders to balance levels. Most mixers also incorporate facilities for equalisation, signal routing to multiple outputs, and monitoring facilities. Large mixers are also known as 'desks' or 'consoles'.

Microphone

A device used to convert an acoustic sound wave into an electrical signal.

Loudspeaker (also Monitor and Speaker)

A device used to convert an electrical audio signal into an acoustic sound wave. An accurate loudspeaker intended for critical sound auditioning purposes.

Monitor (also Loudspeaker)

A device used to convert an electrical audio signal into an acoustic sound wave. An accurate loudspeaker intended for critical sound auditioning purposes. Also used to refer to a computer display screen (VDU), or the act of auditioning a mix or a specific audio signal.

Opto-electronic Device

A device where some electrical parameter changes in response to a variation in light intensity. For example, variable photo-resistors are sometimes used as gain control elements in compressors where the side-chain signal modulates the light intensity.

DI Box, Direct Injection, or Direct Instrument Box.

A device which accepts the signal input from a guitar, bass, or keyboard and conditions it to conform to the requirements of a microphone signal at the output. The output is a mic-level, balanced signal with a low source impedance, capable of driving long mic cables. There is usually a facility to break the ground continuity between mic cable and source to avoid unwanted ground loop noises. Both active and passive versions are available, the former requiring power from internal batteries or phantom power via the mic cable. Active DI boxes generally have higher input impedances than passive types and are generally considered to sound better.

Audio Interface

A device which acts as the physical bridge between the computer's workstation software and the recording environment. An audio interface may be connected to the computer (via FireWire, USB, Thunderbolt, Dante, AVB or other current communication protocols) to pass audio and MIDI data to and from the computer. Audio Interfaces are available with a wide variety of different facilities including microphone preamps, DI inputs, analogue line inputs, ADAT or S/PDIF digital inputs, analogue line and digital outputs, headphone outputs, and so on. The smallest audio interfaces provide just two channels in and out, while the largest may offer 30 or more.

Equaliser (cf. Filter)

A device which allows the user to adjust the tonality of a sound source by boosting or attenuating a specific range of frequencies. Equalisers are available in the form of shelf equalisers, parametric equalisers and graphic equalisers — or as a combination of these basic forms.

Computer

A device which can be instructed (or programmed) to carry out arithmetic or logical operations. Although mechanical 'analogue' computers do exist, most are now electronic and digital, and process digital data.

Master

A device which controls slave devices. Often used to refer to synchronised recorders, or digital clocking devices.

A/D [A-D] Converter

A device which converts an analogue audio signal into a digital representation.

MIDI Thru Box

A device which splits the MIDI Out signal of a master instrument or sequencer to avoid daisy chaining. Powered circuitry is used to 'buffer' the outputs so as to prevent problems when many pieces of equipment are driven from a single MIDI output.

Converter

A device which transcodes audio signals between the analogue and digital domains. An analogue-to-digital (A-D) converter accepts an analogue signal and converts it to a digital format, while a digital-to-analogue (D-A) converter does the reverse. The sample rate and wordlength of the digital format is often adjustable, as is the relative amplitude of analogue signal for a given digital level.

AES3

A digital audio interface which passes two digital audio channels, plus embedded clocking data, with up to 24 bits per sample and sample rates up to 384kHz. Developed by the Audio Engineering Society and the European Broadcasting Union, it is often known as the AES-EBU interface. Standard AES3 is connected using 3-pin XLRs with a balanced cable of nominal 110 Ohm impedance and with a signal voltage of up to 7V pk-pk. The related AES3-id format uses BNC connectors with unbalanced 75 Ohm coaxial cables and a 1V pk-pk signal. In both cases the datastream is structured identically to S/PDIF, although some of the Channel status codes are used differently.

Digital Delay

A digital processor that generates delay and echo effects.

Digital Reverberator

A digital processor which simulates acoustic reverberation.

R-DAT

A digital tape machine using a rotating head system and a tape cassette.

Metering

A display intended to indicate the level of a sound signal. It could indicate peak levels (eg. PPMs or digital sample meters), average levels (VU or RMS meters), or perceived loudness (LUFS meters).

Colouration

A distortion of the natural timbre or frequency response of sound, usually but not always unwanted.

A-Type Plug

A domestic and semi-pro form of jack plug, also known as TS or TRS and widely used for electric instruments, headphones and line-level connections on semi-pro equipment. (cf. B-Type Plug)

Moving Coil Microphone

A dynamic microphone where the diaphragm supports a coil of wire which moves within a magnetic field. When sound causes the diaphragm to vibrate a small electrical current is generated within the coil. The same technology is used in reverse for a moving coil loudspeaker, in which a powerful current is passed through the coil, causing the diaphragm (cone) to move in response.

Ribbon Microphone

A dynamic microphone where the sound capturing element is a thin metal ribbon diaphragm suspended within a magnetic field. When sound causes the ribbon to vibrate, a small electrical current is generated within the ribbon.

Matrix

A facility found mostly in live-sound mixing consoles used to create separate mixes which can be sent to many different output destinations. Essentially, a Matrix creates 'a mix of mixes' since derived from pre-mixed output signals such as subgroups, auxes or main outputs. This is in contrast to the normal console mixing facilities which are derived from input channel signals. A matrix can be any size, and is usually described in terms of numbers of inputs and outputs, such as 2x2 or 8x8, or 8x6 etc with a level control at each junction of the matrix so that the desired amount of any source can be sent to any output — and it is this feature that makes a Matrix more versatile than a conventional subgrouping system. Matrix sends might be used to create appropriate feeds for disparate destinations like PA front fills, green-room foldback, camera recorders, and so on.

Band-pass Filter (BPF)

A filter that removes or attenuates frequencies above and below the centre frequency at which it is set, and only passes a specific range of frequencies. Band-pass filters are often used in synthesizers as tone shaping elements.

High-Pass Filter (HPF)

A filter which passes frequencies above its cut-off frequency, but attenuates lower frequencies.

Low-Pass Filter (LPF)

A filter which passes frequencies below its cut-off frequency, but attenuates higher frequencies.

Gooseneck

A flexible tube often used to support microphones or small lights. Sometimes also known as a 'Swan Neck'.

Decca Tree

A form of 'spaced microphone' arrangement in which three microphone capsules (usually, but not always, with omnidirectional polar patterns) are placed in a large triangular array roughly two metres wide, with the central microphone one metre further forward. Sounds approaching from different directions arrive at each capsule at different times and with slightly different levels, and these timing and level differences are used to convey the directional information in the recording. The timing differences between channels can result in unwanted colouration if they are combined to produce a mono mix.

Y-Lead

A form of adapter cable that passively splits the output of a source to feed two or more destinations. Y-leads may also be used in unbalanced console insert points in which case a stereo jack plug at one end of the lead is split into two monos at the other for separate send and return connections. A Y-lead must never be used to combine signals.

FET-Compressor

A form of audio compressor in which an FET is used to provide variable signal attenuation. FET compressors are fast-acting in comparison to opto-compressors.

PWM Compression

A form of audio compressor which uses Pulse Width Modulation to detedmine the energy in the aduio signal over time. In essence, the audio signal is chopped up at a very high rate and the width of the resulting pulses is adjusted to control the average energy over time, and thus provide signal attenuation. When done well, this is the fastest form of compressor with the lowest distortion artefacts.

Diode-Bridge Compressor

A form of audio compressor which uses a diode-bridge (sometimes known as a diode-ring) arrangement as the variable gain-reducing element. The design was popular in the 1960s as it provided faster responses than typical opto-compressors, and less distortion than many FET designs. However, noise can be an issue as the audio signal has to be attenuated heavily before the diode-bridge, and considerable (~40dB) gain added subsequently. The diodes also need to be closely matched to maintain low distortion.

DANTE

A form of audio-over-IP (layer 3) created by Australian company Audinate in 2006. DANTE is an abbreviation of 'Digital Audio Network Through Ethernet'. The format provides low-latency multichannel audio over standard ethernet intrastructures. it has been widely adopted in the broadcast, music studio, and live sound sectors.

True Peak Meter

A form of digital audio meter which is capable of determining the absolute amplitude value of a digital signal by using oversampling to fully reconstruct the waveform.

C-Weighting

A form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies at high sound pressure levels (notionally 100 Phons or about 87dBA SPL). Essentially, the filter rolls-off the low frequencies below about 20Hz and the highs above about 10kHz. This filtering is often used when making measurements of high-level sounds, such as when calibrating loudspeaker reference levels. (See also A-Weighting and K-Weighting)

A-Weighting

A form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies at low sound pressure levels (notionally 40 Phons or about 30dBA SPL). Essentially, the filter rolls-off the low frequencies below about 700Hz and the highs above about 10kHz. This filtering is often used when making measurements of low-level sounds, like the noise floor of a device.

K-Weighting

A form of electrical filter which is designed to mimic the relative sensitivity of the human ear to different frequencies in terms of pereceived loudness. It is broadly similar to the A-Weighting curve, except that it adds a shelf boost above 2kHz. This filter is an integral element of the ITU-R BS.1770 loudness measurement protocol. (See also A-Weighting and C-Weighting)

Potentiometer (Pot)

A form of electrical potential divider in which the ratio of the upper and lower resistances can be changed either with a rotary control or slider (eg. a fader).

Back Electret

A form of electrostatic or capacitor microphone. Instead of creating an electrostatic charge within the capacitor capsule with an external DC voltage, an electret microphone employs a special dielectric material which permanently stores a static-electric charge. A PTFE film is normally used, and where this is attached to the back plate of the capsule the device is called a 'back electret'. Some very early electret microphones used the dielectric film as the diaphragm but these sounded very poor, which is why later and better designs which used the back electret configuration were specifically denoted as such. Designs which attach the PTFE film to the diaphragm are known as Front Electrets. Modern electret capsules compare directly in quality with traditional DC-biased capacitor capsules, and are available in the same range of configurations — large, medium and small diaphragm sizes, single and dual membrane, fixed or multi-pattern, and so on.

Tremolo

A form of modulation of the amplitude of a sound using an LFO. (cf. vibrato)

Intermodulation Distortion

A form of non-linear distortion that introduces frequencies not present in and musically unrelated to the original signal. These are invariably based on the sum and difference products of the original frequencies.

MTC — MIDI Time code

A format used for transmitting synchronisation instructions between electronic devices within the MIDI protocol.

Local On/Off

A function to allow the keyboard and sound generating section of a keyboard synthesizer to be used independently of each other.

Acoustic Treatment

A generic term embracing a range of products or constructions intended to absorb, diffuse or reflect sound waves in a controlled manner, with the intention of bestowing a room with an acceptable reverberation time and overall sound character.

Portamento

A gliding effect that allows a sound to change pitch at a gradual rate, rather than abruptly, when a new key is pressed or MIDI note sent.

Waveform

A graphic representation of the way in which a sound wave or electrical wave varies with time.

Wah Pedal

A guitar effects device where a bandpass filter is varied in frequency by means of a pedal control.

Solid-state Drive (cf. Hard Disk Drive)

A large capacity solid-state memory configured to work like a conventional hard disk drive. Some computers are now available with solid state flash drives instead of normal internal hard disk drives. Also used in digital cameras and audio recorders in formats such as SD and CF2 cards, as well as in 'pen drives' or 'USB memory sticks'.

Flash Drive (see 'solid-state drive')

A large capacity solid-state memory configured to work like a conventional hard drive. Used in digital cameras and audio recorders in formats such as SD and CF2 cards, as well as in 'pen drives' or 'USB memory sticks'. Some computers are now available with solid state flash drives instead of normal internal hard drives.

Monitor Controller

A line-level audio signal control device used to select and condition input signals for auditioning on one or more sets of monitor loudspeakers. Some monitor controllers also incorporate facilities for studio talkback and artist cue mixes.

Menu

A list of choices presented by a computer program or a device with a display window.

Active Loudspeaker or Monitor

A loudspeaker system in which the input signal is passed to a line-level crossover, the suitably filtered outputs of which feed two (or more) power amplifiers, each connected directly to its own drive unit. The line-level crossover and amplifiers are usually (but not always) built in to the loudspeaker cabinet.

Passive Loudspeaker or Monitor

A loudspeaker which requires an external power amplifier, the signal from which is passed to a passive cross-over filter. This splits and filters the signal to feed the two (or more) drive units.

Dolby Noise-Reduction

A manufacturer of analogue and digital audio equipment in the fields of tape noise-reduction systems and cinema and domestic surround-sound equipment. Dolby's noise-reduction systems included types B, C and S for domestic and semi-professional machines, and types A and SR for professional machines. Recordings made using one of these systems must also be replayed via the same system. These systems varied in complexity and effectiveness, but essentially they all employed the principlals of spectral noise-masking in ever-more complex ways using multiband encode/decode processing to raise low-level signals during recording, while reversing the process during playback.

DBX

A manufacturer of audio processing equipment, most notably compressors and tape noise reduction systems. The DBX NR systems were commercial encode/decode analogue noise-reduction processors intended for consumer and semi-pro tape recording. Different models varied in complexity, but essentially DBX compressed the audio signals during recording and expanded them by an identical amount on playback.

Insulator

A material that does not conduct electricity. (Also see conductor)

Conductor

A material that provides a low resistance path for electrical current.

Convolution

A mathematical process whereby the characteristics of one function (or signal) are imposed upon a second function (signal) , to produce a third function which combines both of their characteristics. (See Convolution Reverb). This process is performed in the digital domain by multiplying each individual sample value of a source signal with the impulse response of the wanted effect signal, so that the characteristics of the latter are imposed on the former.

Coincident

A means of arranging two or more directional microphone capsules such that they receive sound waves from all directions at exactly the same time. The varying sensitivity to sound arriving from different directions due to the directional polar patterns means that information about the directions of sound sources is captured in the form of level differences between the capsule outputs. Specific forms of coincident microphones include 'XY' and 'MS' configurations, as well as B-format and Ambisonic arrays. Coincident arrays are entirely mono-compatible because there are no timing differences between channels.

Near-coincident

A means of arranging two or more directional microphone capsules such that they receive sound waves from the directions or interest at slightly different times due to their physical spacing. Information about the directions of sound sources is captured in the form of both level differences between the capsule outputs, generated by aiming directional polar patterns in different directions, and the timing differences caused by their physical spacing. Specific forms of near-coincident microphones include the ORTF and NOS arrangements.

Spaced Array

A means of arranging two or more microphone capsules such that they receive sound waves from different directions at different times — these timing differences being used to convey information about the relatice directions of those sound sources. The technique is usually used with omnidirectional microphones, although directional mics can also be employed. The best known form of spaced array is the Decca Tree. Mono-compatibility is often reduced because the timing differences between channels often results in comb-filtering colouration when the channels are summed to mono.

Direct Coupling

A means of connecting two electrical circuits so that both AC and DC signals may be passed between them.

Parallel

A means of connecting two or more circuits together so that their inputs are connected together, and their outputs are all connected together.

Equivalent Input Noise

A means of describing the intrinsic electronic noise at the output of an amplifier in terms of an equivalent input noise, taking into account the amplifier's gain.

Aftertouch

A means of generating a control signal in a synthesizer based on how much pressure is applied to the keys of a MIDI keyboard. Most instruments that support this do not have independent pressure sensing for all keys, but rather detect the overall pressure by means of a sensing strip running beneath the keys. Aftertouch may be used to control such functions as vibrato depth, filter brightness, loudness and so on.

dB/Octave

A means of measuring the slope or steepness of a filter. The gentlest audio filter is typically 6dB/Octave (also called a first-order slope). Higher values indicate sharper filter slopes. 24dB/octave (fourth order) is the steepest normally found in analogue audio applications.

Effects Return

An additional dedicated mixer input channel, usually with minimal facilities, designed to accommodate the output from an effects unit. (cf. Aux Return)

Quantiser

A means of moving notes recorded in a MIDI sequencer so that they line up with user defined subdivisions of a musical bar, for example, 16s. The facility may be used to correct timing errors, but over-quantization can remove the human feel from a performance.

Phantom Power

A means of powering capacitor and electret microphones, as well as some dynamic microphones with built-in active impedance converters. Phantom power (P48) provides 48V (DC) to the microphone as a common-mode signal (both signal wires carry 48V while the cable screen carries the return current). The audio signal from the microphone is carried as a differential signal and the mic preamp ignores common-mode signals so doesn't see the common-mode power supply (hence the ghostly name, phantom). This system only works with a balanced three-pin mic cables. Two alternative phantom power specifications also exist, with P12 (12V) and P24 (24V) options, although they are relatively rare.

Digital (cf. Analogue)

A means of representing information (eg audio or video signals) in the form of binary codes comprising strings of 1s and 0s, or their electrical or physical equivalents. Digital audio circuitry uses discrete voltages or currents to represent the audio signal at specific moments in time (samples). A properly engineered digital system has infinite resolution, the same as an analogue system, but the audio bandwidth is restricted by the sample rate, and the signal-noise ratio (or dynamic range) is restricted by the word-length.

Common Mode Rejection

A measure of how well a balanced circuit rejects an interference signal that is common to both sides of the balanced connection.

SPL — Sound Pressure Level.

A measure of the intensity of an acoustic sound wave. Normally specified in terms of Pascals for an absolute value, or relative to the typical sensitivity of human hearing. One Pascal is 94dB SPL, or to relate it to atmospheric pressures, 0.00001 Bar or 0.000145psi!

THD, Total Harmonic Distortion.

A measure of the linearity of a device. The THD+N measurement includes the noise contribution as well and is an indication of the quality of an audio product.

Shockmount

A mechanical isolator intended to prevent the transfer of vibrations which may be transmitted through a microphone stand from reaching a microphone where they would otherwise produce unwanted low frequency sound.

Boom

A mechanical means of supporting a microphone above a sound source. Many microphone stands are supplied with a 'boom arm' affixed to the top of the stand's main vertical mast. The term may also be applied to larger, remotely controlled microphone supports used in film and TV studios, or even to the handheld 'fishpoles' used by film and TV sound recordists.

Truss Rod

A metal bar within a guitar neck which is tensioned so as to counteract the tendency for the neck to bend under the tension of the strings.

PPM, Peak Programme Meter.

A meter designed to register the approximate peak amplitude of a signal, rather than the average level indicated by, for example, a VU meter. However, PPMs have a defined integration time (typically 10ms) which means that they actually under-read on the fastest transient peaks. (cf. VU Meter)

Double-ended Noise Reduction

A method for removing or attenuating the noise component of a recording or transmission system, in which the signal is pre-conditioned in a specific way which is reversed on playback. Most analogue noise-reduction systems are of the double-ended type, such as the Dolby and DBX systems.

Copy Protection

A method used by software manufacturers to prevent unauthorised copying.

Close-Miking

A mic technique which involves placing a microphone very close to a sound source, normally with the intention of maximising the wanted sound and minimising any unwanted sound from other nearby sound sources or the room acoustics. In classic music circles the technique is more often known as 'Accent Miking'.

Omnidirectional

A microphone or loudspeaker polar pattern with equal sensitivity in all directions (often abbreviated to Omni). Also the MIDI mode where data on all channels is recognised.

High Resolution

A misnomer, but used to refer to digital formats with long word-lengths and high sample rates, eg. 24/96 or 24/192. Audio resolution is infinite and identical to analogue systems in properly configured digital systems. Word-length defines only the system's signal-to-noise ratio (equivalent to tape width in analogue systems) , while sample rate defines only the audio bandwidth (equivalent to tape speed in analogue systems).

Group

A mixed collection of signals within a mixer that are combined and routed through a separate fader to provide overall control. In a multitrack mixer several groups are provided to feed the various recorder track inputs.

Eurorack

A modular synthesizer format developed by Doepfer in the mid-1990s for its A‑100 system, but which has since become a standard format embraced by most modular synth manufacturers. It uses 3U high panels to accommodate standard Eurocard-sizes electronics, with 3.5mm plugs for patching and a +/-12V dual-rail power supply (sometimes with a separate 5V rail) connected via a ribbon cable.

Line-level

A nominal signal level which is around -10dBV for semi-pro equipment and +4dBu for professional equipment.

Loom

A number of separate cables bound together for neatness and convenience.

Side-chain

A part of an audio circuit that splits off a proportion of the main signal to be processed in some way. Compressors use a side-chain process to derive a control signals to adjust the main path attenuation.

SysEx (System Exclusive)

A part of the MIDI standard that allows manufacturers to define their own specific message formats, commonly used to dump and load a specific product's patch data.

Comb Filter

A series of deep filter notches created when a signal is combined with a delayed version of itself. The delay time (typically less than 10ms) determines the lowest frequency at which the filter notches start.

Capacitor

A passive, two-terminal electrical component which stores energy in the form of an electrostatic field. The terminals are attached to conductive 'plates' which are separated by a non-conductive dielectric. Capacitance is measured in Farads. If a voltage is applied across the terminals of a capacitor a static electric field develops across the dielectric, with positive charge collecting on one plate and negative charge on the other. Where the applied voltage is an alternating signal, a capacitor can be thought of as a form of AC resistance that reduces with increasing signal frequency. The old-fashioned term is a 'condensor'.

Channel

A path carrying for audio or data. In the context of a mixing console a channel is a single strip of controls relating to one input. In the context of MIDI, Channel refers to one of 16 possible data channels over which MIDI data may be sent. The organisation of data by channels means that up to 16 different MIDI instruments or parts may be addressed using a single cable.

Drive unit

A physical device designed to generate an acoustic sound wave in response to an electrical input signal. Drive units can be designed to reproduce almost the full audio spectrum, but most are optimised to reproduce a restricted portion, such as a bass unit (woofer) or high-frequency unit (tweeter). A range of technologies are employed, with most being moving-coil units, but ribbon and electrostatic drive units also exist, each with a different balance of advantages and disadvantages. Also known as a 'driver'.

Boundary

A physical obstruction to sound waves, such as a wall, or a large solid object. When sound waves reach a boundary they create a high pressure area at the surface.

Driver

A piece of software that handles communications between the main program and a hardware peripheral, such as a soundcard, printer or scanner. Also a term used to refer to a physical loudspeaker drive unit — eg bass driver.

Powered Loudspeaker or Monitor

A powered speaker is a conventional passive loudspeaker but with a single power amplifier built in or integrated with the cabinet in some way. The amplifier drives a passive crossover, the outputs of which connect to the appropriate drive units.

Sticky Shed Syndrome

A problem affecting some brands of analogue tape after a long time in storage. A breakdown of the binder causes the oxide to shed, and the tape tends to adhere to the tape heads and guides when played. A short term cure can be affected by baking the affected tape.

Format

A procedure required to ready a computer disk or digital tape for use. Formatting organises the medium into a series of 'electronic pigeon holes' into which data can be stored. Different computers often use different formatting systems.

Off-line

A process carried out while a recording is not playing. For example, some computer-based processes have to be carried out off-line as the computer isn't fast enough to carry out the process in real time. Also used to refer to a remote-controlled machine which is not currently active.

Modelling

A process of analysing a system and using a different technology to replicate its critical, desired characteristics. For example, a popular but rare vintage signal processor such as an equaliser can be analysed and its properties modelled by digital algorithms to allow its emulation within the digital domain.

White Noise

A random signal with a flat (constant) power spectrum density, ie. equal power within any frequency band of fixed width. White noise sounds very bright (cf. Pink Noise).

Pink Noise

A random signal with a power spectral density which is inversely proportional to the frequency. Each octave carries an equal amount of noise power. Pink noise sounds natural, and resembles the sound of a waterfall. (cf. White Noise)

Inductor

A reactive component that presents an increasing impedance with frequency. (Also see Capacitor.)

CD-R

A recordable type of Compact Disc that can only be recorded once - it cannot be erased and reused. The CD-R's technical characteristics are defined in the 'Orange Book'

Multitrack

A recording device capable of recording several 'parallel' parts or tracks which may then be mixed or re-recorded independently.

Project Studio

A relatively small recording studio facility, often with a combined recording space and control room.

Pad

A resistive circuit for reducing signal level.

Backup

A safety copy of software or other digital data. A popular saying is that unless data exists in three physically separate locations at the same time, it hasn't been backed up properly!

Chromatic

A scale of pitches rising or falling in semitone steps.

Plug-in

A self-contained software signal processor, such as an Equaliser or Compressor, which can be 'inserted' into the notional signal path of a DAW. Plug-ins are available in a myriad of different forms and functions, and produced by the DAW manufacturers or third-party developers. Most plug-ins run natively on the computer's processor, but some require bespoke DSP hardware. The VST format is the most common cross-platform plug-in format, although there are several others.

Auxiliary Sends (Auxes)

A separate output signal derived from an input channel on a mixing console, usually with the option to select a pre- or post-fader source and to adjust the level. Corresponding auxiliary sends from all channels are bussed together before being made available to feed an internal signal processor or external physical output. Sometimes also called effects or cue sends.

Isolation Room

A separate room or enclosure designed to provide acoustic isolation from external noise. Often used alongside a studio's main live room to record vocals or drums, for example, without spill from other instruments.

Algorithm

A sequence of instructions describing how to perform a specific task. Algorithms are often implemented in a computer language and compiled into a computer program. In the context of effects units, algorithms usually describe a software building block designed to create a specific effect or combination of effects.

Modes (room)

See Room Modes

Crossover

A set of audio filters designed to restrict and control the range of input signal frequencies which are passed to each loudspeaker drive unit. A typical two-way speaker will employ three filters: a high-pass filter allowing only the higher frequencies to feed the tweeter, a low pass filter that allows only the lower frequencies to feed the woofer, and a second high-pass filter that prevents subsonic signals from damaging the woofer.

Rider

A set of requests/demands that an artist or band (or their management) ask of the hosting venue as criteria for performing. A Technical Rider would typically specify the size and layout of staging, required equipment for lighting (truss weight limits, power requirements, numer of follow-spots, lighting plots or designs, etc) and sound (input channel counts, PA power, number of monitors, effects, DI boxes, backline amps and instruments, quality of equipment etc) and possibly also the operating and rigging staff provided. A Hospitality Rider is a list of requests to ensure the comfort of the artist(s), such as the number of dressing rooms, private bathroom/shower, food and beverage requirements, a number of complimentary (comp) tickets for guests, security arrangements, and so on. There may also be additional riders covering other aspects such as a Merchandise Rider detailing the space and stands provided for selling merchandise, the rates, exclusivity rights, and so forth.

Patch Cord

A short cable used with patch bays.

Post-fade

A signal derived from the channel path of a mixer after the channel fader. A post-fade aux send level follows any channel fader changes. Normally used for feeding effects devices.

Pre-fade

A signal derived from the channel path of a mixer before the channel fader. A pret-fade aux send level is unaffected by channel fader changes. Normally used for creating Foldback or Cue mixes.

Vocoder

A signal processor that imposes a changing spectral filter on a sound based on the frequency characteristics of a second sound. By taking the spectral content of a human voice and imposing it on a musical instrument, talking instrument effects can be created.

Wet

A signal that has effects added. (cf. Dry)

Dry (cf. Wet)

A signal that has had no effects added.

Mono

A single channel of audio.

Boost/Cut Control

A single gain control which allows the range of frequencies passing through a filter to be either amplified or attenuated. The centre position is usually the 'flat' or 'no effect' position.

Chip

A slang term for an Integrated Circuit or IC.

Fader

A sliding potentiometer control used in mixers and other processors.

Nut

A slotted plastic or bone component at the headstock end of a guitar neck used to guide the strings over the fingerboard, and to space the strings above the frets.

Normalise

A socket is said to be normalised when it is wired such that the original signal path is maintained unless a plug is inserted into the socket. The most common examples of normalised connectors are the insert points on a mixing console.

MIDI Module

A sound generating device with no integral keyboard.

Pitch-bend

A special control message specifically designed to produce a change in pitch in response to the movement of a pitch bend wheel or lever. Pitch bend data can be recorded and edited, just like any other MIDI controller data, even though it isn't part of the Controller message group.

Bass Trap

A special type of acoustic absorber which is optimised to absorb low frequency sound waves.

Microprocessor

A specialised IC at the heart of a computer which performs calculations and other data manipulations, following software instructions.

Boundary Layer Microphone

A specialised microphone where the diaphragm is placed very close to a boundary (eg. wall, floor or ceiling). In this position the direct and reflected sound adds constructively, giving a 6dB increase in sensitivity. It also avoids the comb-filtering that can occur when a conventionally placed microphone captures the direct sound along with strong first reflections from nearby boundaries. Also known as PZM or Pressure Zone Microphone.

M-S (Mid-Side)

A specialist form of coincident microphone array which, when decoded to left-right stereo, creates an equivalent XY configuration. In the MS array one microphone is pointed directly forward (Mid) while the second is arranged at 90 degrees to point sideways (Side). The Mid microphone can employ any desired polar pattern, the choice strongly influencing the decoded stereo acceptance angle. The Side microphone must have a figure-eight response and be aligned such that the lobe with the same polarity as the Mid microphone faces towards the left of the sound stage. Adjusting the relative sensitivity of the Mid and Side microphones affects the decoded stereo acceptance angle and the polar patterns of the equivalent XY microphones.

Bank

A specific configuration of sounds or other parameters stored in memory and accessed manually or via MIDI commands.

NOS

A specific form of near-coincident microphone array devised by the Nederlandse Omroep Stichting (NOS), the Dutch national broadcaster. The technique employs a pair of small-diaphragm cardioid microphones mounted with a mutual angle of 90 degrees and spaced apart by 30cm. The theoretical stereo recording angle is 81°.

ORTF

A specific form of near-coincident microphone array devised by the Office de Radiodiffusion Télévision Française (ORTF) at Radio France, the French national broadcaster. The technique employs a pair of small-diaphragm cardioid microphones mounted with a mutual angle of 110 degrees and spaced apart by 17cm. The theoretical stereo recording angle is 96 degrees.

Cardioid

A specific form of polar response of a unidirectional microphone or loudspeaker. It is an inverted heart-shape which has very low sensitivity at the back (180 degrees), but only slightly reduced sensitivity (typically between 3 and 6dB) at the sides (90/270 degrees).

MIDI Bank Change

A type of controller message used to select alternate banks of MIDI Programs where access to more than 128 programs is required.

Cone

A specific shape of drive unit diaphragm intended to push and pull the air to create acoustic sound waves. Most bass drivers use cone-shaped diaphragms, where the electromagnetic motor of the drive unit is connected to the point of the cone, and its outer diameter is supported by some form of flexible membrane.

Dome

A specific shape of drive unit diaphragm intended to push and pull the air to create acoustic sound waves. Most tweeters use dome-shaped diaphragms which are driven around the circumference by the drive unit's motor system. 'Soft-domes' are made of a fabric — often silk — while metal domes are constructed from a light metal like aluminium, or some form of metal alloy.

Subwoofer

A specific type of efficient loudspeaker system intended to reproduce only the lowest frequencies (typically below 120Hz).

Acoustic Foam

A specific type of open-celled expanded polyurethane foam that allows sound waves to enter and flow through the foam, absorbing their energy and preventing them being reflected. The density and depth of the foam affects the frequency range over which it is effective as an absorber.

X-Y

A specific way of mounting two directional microphone capsules such that they both receive sound waves from any direction at exactly the same time. Information about the direction of a sound sources is captured in the form of level differences between the two capsule outputs. Commonly, the two microphones in an XY array are mounted with a mutual angle of 90 degrees, although other angles are sometimes used. The two capsules will have the same polar pattern, the choice of which determines the stereo recording angle (SRA). The XY configuration is entirely mono-compatible because there are no timing differences between the two channels.

Rack Mount

A standard equipment sizing format allowing products to be mounted between vertical rails in standardised equipment bays.

MIDI File

A standard file format for storing song data recorded on a MIDI sequencer in such a way as to allow it to be read by other makes or model of MIDI sequencer.

Standard Midi File

A standard file format that allows MIDI files to be transferred between different sequencers and MIDI file players.

DCC

A stationary-head digital recorder format developed by Philips, using a bespoke cassette medium similar in size and format to Compact Cassettes. It used an MPEG data reduction system to reduce the amount of data that needs to be stored.

RMS, Root Mean Square.

A statistical measure of the magnitude of a varying quantity. Its name comes from its definition as the square root of the mean of the squares of the values of the signal.

Test Tone

A steady, fixed level tone recorded onto a multitrack recording, or passed over a signal connection to test the signal path and act as a reference when matching levels.

Blumlein Array

A stereo coincident microphone technique devices by Alan Blumlein in the early 1930s, employing a pair of microphones with figure-eight polar patterns, mounted at 90 degrees to each other with the two diaphragms vertically aligned.

Transparency

A subjective term used to describe audio quality where the high frequency detail is clear and individual sounds are easy to identify and separate.

Warmth

A subjective term used to describe sound where the bass and low mid frequencies have depth and where the high frequencies are smooth sounding rather than being aggressive or fatiguing. Warm sounding tube equipment may also exhibit some of the aspects of compression.

De-Oxidising Compound

A substance formulated to remove oxides from electrical contacts. (cf. Contact Cleaner)

Dropout

A sudden brief loss of signal level. In analogue recording tape this is often caused by a defect in the oxide layer caused by damage (eg. creasing) or by a temporary clogging of the replay head, and typically affects the high-frequencies most. The effect is less likely and less noticable with wider and faster tape formats.

Surge

A sudden increase in mains voltage.

Square Wave

A symmetrical rectangular waveform. Square waves contain a series of odd harmonics.

Triangle Wave

A symmetrical triangular shaped wave containing odd harmonics only, but with a lower harmonic content than the square wave.

Gate (CV)

A synthesiser control signal generated whenever a key is depressed on an electronic keyboard and used to trigger envelope generators and other events that need to be synchronised to key action.

Bi-Timbral

A synthesizer than can generate two different sounds simultaneously (see multi-timbral).

Poly-Synth

A synthesizer that can play more than one note at a time (eg. eight or sixteen notes), each with an independent signal chain of oscillators, filters, and envelope generators.

Mono-synth

A synthesizer that can play only one note at a time (see also poly-synth and paraphonic)

Expander Module

A synthesizer with no keyboard, often rack mountable or in some other compact format.

Multi-timbral

A synthesizer, sampler or module that can play several parts or different sounds at the same time, each under the control of a different MIDI channel.

Drum Pad

A synthetic playing surface which produces electronic trigger signals in response to being hit with drum sticks.

Talkback

A system designed to enable voice communication between rooms.

Pre-emphasis

A system for applying high frequency boost to a sound before processing. When the corresponding de-emphasis is applied any noise contribution from the processing is reduced.

Ducking

A system for controlling the level of one audio signal with another. For example, in a broadcast radio context a music track can be made to 'duck' or reduce in volume whenever there's a voice over.

DCA Group

See VCA Group

Additive Synthesis

A system for generating audio waveforms or sounds by combining basic waveforms or sampled sounds prior to further processing with filters and envelope shapers. The Hammond tonewheel organ was one of the first additive synthesizers.

Foldback

A system for making one or more separate mixes audible to musicians while performing, recording and overdubbing. Also known as a Cue mix. May be auditioned via headphones, IEMs or wedge monitors.

Sync

A system for making two or more pieces of equipment run in synchronism with each other.

Step Time

A system for programming a sequencer in non-real time.

Noise Reduction

A system for reducing analogue tape noise or for reducing the level of hiss present in a recording. (See DBX and Dolby).

Analogue Synthesis

A system for synthesizing sounds by means of analogue circuitry, usually by filtering simple repeating waveforms.

Patch Bay

A system of panel-mounted connectors used to bring inputs and outputs to a central point from where they can be routed using plug-in patch cords. Also called a Jackfield.

Jackfield

A system of panel-mounted connectors used to bring inputs and outputs to a central point from where they can be routed using plug-in patch cords. Also called a patchbay.

Encode/Decode

A system that modifies a signal prior to recording or transmission, and subsequently restores the signal on playback or reception.

Audio Data Reduction

A system used to reduce the amount of data needed to represent some information such as an audio signal. Lossless audio data reduction systems, (eg. FLAC and ALAC) can fully and precisely reconstruct the original audio data with bit-accuracy, but the amount of data reduction is rarely much more than 2:1. Lossy data audio reduction systems (eg. MPeg. AAC, AC3 and others) permanently discard audio information that is deemed to have been 'masked' by more prominent sounds. The original data can never be retrieved, but the reduction in total data can be considerable (12:1 is common).

Active Sensing

A system used to verify that a MIDI connection is working. It involves the sending device sending frequent short messages to the receiving device to reassure it that all is well. If these active sensing messages stop for any reason the receiving device will recognise a fault condition and switch off all notes. Not all MIDI devices support active sensing.

PFL, Pre-Fade Listen.

A system used within a mixing console to allow the operator to audition a selected signal, regardless of the position of the fader controlling that signal.

Noise-shaping

A system using spectrally-shaped dither to improve the perceived signal-to-noise performance of a digital audio system.

Dither

A system whereby low-level noise equivalent to one quantising level is combined with a digitised audio signal in such a way as to perfectly linearise the digital system. Dither must be employed whenever the wordlength is reduced, otherwise quantising distortion errors will manifest.

De-emphasis

A system which restores the spectral balance to correct for pre-emphasis.

Open Reel

A tape machine where the tape is wound on spools rather than housed within a cassette.

Chase

A term describing the process whereby a slave device attempts to synchronise itself with a master device. In the context of a MIDI sequence, Chase may also involve chasing events — looking back to earlier positions in the song to see if there are any program change or other events that need to be acted upon.

Machine Head

A term describing the tuning mechanism of a guitar.

DAW (Digital Audio Workstation)

A term first used in the 1980s to describe early 'tapeless' recording/sampling machines like the Fairlight and Synclavier. Nowadays, DAW is more commonly used to describe Audio+MIDI 'virtual studio' software programs such as Cubase, Logic Pro, Digital Performer, Sonar and such-like. Essentially elaborate software running on a bespoke or generic computer platform which is designed to replicate the processes involved in recording, replaying, mixing and processing real or virtual audio signals. Many modern DAWs incorporate MIDI sequencing facilities as well as audio manipulation, a range of effects and sound generation.

Snake

A term used to describe a cable used to carry multiple individual audio signals, typically between a stage and mixing console in live sound applications.

MIDI Controller

A term used to describe the physical interface by means of which the musician plays the MIDI synthesizer or other sound generator. Examples of controllers are keyboards, drum pads, wind synths and so on.

Red Book CD

A term used to imply a standard audio CD. The name comes from the fact that the original specifications documents for the audio CD created by Sony and Philips had a red cover! Recordable CD-Rs are described as 'orange book' for similar reasons.

Non-linear Recording

A term which describes digital recording systems that allow any parts of the recording to be played back in any order with no gaps. Conventional tape is referred to as linear, because the material can only play back in the order in which it was recorded.

Effect

A treatment applied to an audio signal in order to change or enhance it in some creative way. Effects often involve the use of delays, and include such treatments as reverb and echo.

MIDI Program Change

A type of MIDI message used to change sound patches on a remote module or the effects patch on a MIDI effects unit.

Isopropyl Alcohol

A type of alcohol commonly used for cleaning and de-greasing tape machine heads and guides.

BNC

A type of bayonet-locking, two-terminal connector used for professional video and digital audio connections. (See AES3-id)

PZM (Pressure Zone Microphone)

A type of boundary layer microphone.

Dynamic Microphone

A type of microphone that works on the electric generator principle, such as moving Coil and ribbon mics. An acoustical sound waves impact the microphone diaphragm which then moves an electrical conductor within a magnetic field to generate a current, the amplitude and polarity of which reflects the acoustic signal.

Switching Power Supply (Also SMPS)

A type of power supply that uses mains power to drive directly a high frequency oscillator so that a smaller, lighter transformer may be used. These power supplies are commonly used because they can be made to accept a wide range of mains supply voltages, and are thus universal.

TRS

A type of quarter-inch jack plug with three contacts (Tip, Ring and Sleeve), used either for stereo unbalanced connections (such as on headphones) or mono balanced connections (such as for line-level signals). Physically compatible in size with the TS (Tip, Sleeve) quarter-inch jack plug used for electric guitars and other instruments.

Power supply

A unit designed to convert mains electricity to the DC voltages necessary to power an electronic circuit or device.

GM Reset

A universal SysEx command which activates the General MIDI mode on a GM instrument. The same command also sets all controllers to their default values and switches off any notes still playing by means of an All Notes Off message.

General MIDI

A universally agreed subset of the MIDI standard, created to enable manufacturers to build synthesizers, synth modules and plug-in instruments that exhibit an agreed minimum degree of compatibility.

Parameter

A variable value that affects some aspect of a device's performance.

Control Voltage

A variable voltage signal typically used to control the pitch of an oscillator or filter frequency in an analogue synthesizer. Most analogue synthesizers follow a one volt per octave convention, though there are exceptions. To use a pre-MIDI analogue synthesizer under MIDI control, a MIDI to CV converter is required.

Short-Circuit

A very low resistance path that allows electrical current to flow. The term is usually used to describe a current path that exists through a fault condition. (See Open Circuit)

XLR

A very robust and latching connector commonly used to carry balanced audio signals such as the outputs from microphones or line level devices. An XLR is a type of connector developed by US manufacturer, Cannon, and used widely in professional audio systems. The company's original X-series connector was improved with the addition of a latch (Cannon XL) and a more flexible rubber compound surrounding the contacts to improve reliability (Cannon XLR). The connector format is now is available in numerous configurations, from many different manufacturers, and with several different pin configurations. Standard balanced audio interfaces — analogue and digital — use three-pin XLRs with the screen on pin 1, the 'hot' signal on pin 2 and the 'cold' signal on pin 3.

Anti-alias Filter

A very steep low-pass filter used to limit the frequency range of an analogue signal prior to A/D conversion so that the maximum frequency does not exceed half the sampling rate.

Dynamics

A way of describing the relative levels within a piece of music.

ADAT Lightpipe

A widely used eight-channel optical digital audio interface developed by Alesis as a bespoke interface for the company's digital eight-track tape machines in the early 1990s (Alesis Digital Audio Tape). The interface transfers up to eight channels of 24-bit digital audio at base sample rates (44.1 or 48kHz) via a single fibre-optic cable. This 'lightpipe' is physically identical to that used for the TOSlink optical S/PDIF stereo interface found on many digital consumer hi-fi devices, but while the fibre itself can be used interchangeably for either format, the S/PDIF and ________ interfaces are not compatible in any other way. The interface incorporates embedded clocking, and padding zeros are introduced automatically if the word length is less than 24 bits.

M

Abbreviation for mega, meaning a multiplier of 1,000,000 (one million). Used as a prefix to other values to indicate magnitude, eg. 1MOhm = 1,000,000 Ohms or 1000k Ohms.

m

Abbreviation for milli, meaning a multiplier of 1/1000 (one thousandth). Used as a prefix to other values to indicate magnitude, eg. 1mA = 0.001A.

Room Modes

Acoustic resonances within an enclosed space or room. These occur at specific frequencies where the source sound is reflected from the room's boundaries to reinforce and/or cancel with itself to create standing waves. This results in some areas in the room with very boomy or exaggerated pitches, and others where the pitch may be almost completely absent. The resonant frequencies involved relate directly to the sound wavelength and room dimensions, and is particularly prevalent at low frequencies.

MIDI Control Change

Also known as MIDI Controllers or Controller Data, these messages convey positional information relating to performance controls such as wheels, pedals, switches and other devices. This information can be used to control functions such as vibrato depth, brightness, portamento, effects levels, and many other parameters.

Bantam Plug

Also known as TT or Tiny Telephone Plugs. A professional form of miniature jack plug derived from the telecommunications industry and widely used for balanced mic and line-level connections on professional patch bays. (cf. B-Type Plug)

Capacitor Microphone

Also known as a 'condenser microphone'. This is a specific form of electrostatic microphone which operates on the principle of measuring the change in electrical voltage across a capacitor. The capacitor is formed from two metal electrodes, one fixed (the back-plate) and the other a thin conductive membrane that flexes in response to sound pressure. (See also Back Electret, and RF Capacitor Microphone.)

Valve

Also known as a 'tube' in America. A thermionic device in which the current flowing between its anode and cathode terminals is controlled by the voltage applied to one or more control grid(s). Valves can be used as the active elements in amplifiers, and because the input impedance to the grid is extremely high they are ideal for use as an impedance converter in capacitor microphones. The modern solid-state equivalent is the Field Effect Transistor or FET.

Double-lapped Screen

Also known as a Reussen screen. The signal-carrying wires in a microphone cable are protected from external electrostatic and RF interference by a 'screen' which is a surrounding conductor connected to earth or ground. The Reussen screen is a specific form of cable screen, comprising two overlapping and counter-wound layers which are unlikely to 'open up' if the cable is bent, yet remain highly flexible

Application (App)

Alternative term for computer program.

ASCII

American Standard Code for Information Interchange. An internationally recognised code used to represent computer keyboard characters.

AES17

An AES standard that defines a method of evaluating the dynamic range performance of A-D and D-A converters.

AES11

An AES standard that defines the use of a specific form of AES3 signal for clocking purposes. Also known as DARS (Digital Audio Reference Signal).

AES10

An AES standard which defines the MADI interface (serial Multichannel Audio Digital Interface). MADi can convey either 56 or 64 channels via single coaxial or optical connections.

AES42

An AES standard which defines the connectivity, powering, remote control and audio format of 'digital microphones.' The audio information is conveyed as AES3 data, while a bespoke modulated 10V phantom power supply conveys remote control and clocking information.

AES59

An AES standard which defines the use and pin-outs of 25-pin D-sub connectors for eight-channel balanced analogue audio and bi-directional eight-channel digital interfacing. It conforms fully with the established Tascam interface standard.

Amp/Amplifier

An Amplifier is an electrical device that typically increases the voltage or power of an electrical signal. The amount of amplification can be specified as a multiplication factor (eg. x10) or in decibels (eg. 20dB).

DI

An abbreviation for 'Direct Instrument' or 'Direct Inject' — the two terms being used interchangeably. Used when an electrical sound source (eg electric guitar, bass or keyboard) is connected directly into an audio chain, rather than captured with a microphone in front of a amp/loudspeaker.

OSC

An abbreviation for 'oscillator' or 'Open Sound Control'.

RF

An abbreviation for Radio Frequency.

RAM

An abbreviation for Random Access Memory. This is a type of memory used by computers for the temporary storage of programs and data, and all data is lost when the power is turned off. For that reason, work needs to be saved to disk if it is not to be lost.

ROM

An abbreviation for Read Only Memory. This is a permanent or non-volatile type of memory containing data that can't be changed once programmed. Operating systems are often stored on ROM as the memory remains intact when the power is removed.

Mult

An abbreviation of 'multiple output' (also known as a 'parallel-strip' in BBC parlance). Refers to a line-level signal splitting or distribution facility typically found on patchbays in which three or more sockets are wired together to allow an input signal to be shared with multiple destinations. As an entirely passive facility the operation relies on a very low source impedance and high destination (bridging) impedances to minimise the loss of signal level. Microphone 'mults' tend either to use transformers with multiple secondary windings or active buffer or distribution circuitry.

DAT

An abbreviation of Digital Audio Tape, but often used to refer to DAT recorders (more correctly known as R-DAT because they use a rotating head similar to a video recorder). Digital recorders using fixed or stationary heads (such as DCC) are known as S-DAT machines.

DDL

An abbreviation of Digital Delay Line, used to create simple delay-based audio effects.

Disk

An abbreviation of Diskette, but now used to describe computer floppy, hard and removable data storage disks.

IC

An abbreviation of Integrated Circuit, a collection of miniaturised transistors and other components on a single silicon wafer, designed to perform a specific function.

Speaker (also Loudspeaker and Monitor)

An accurate loudspeaker intended for critical sound auditioning purposes.

Non-registered parameter Number

An addition to the basic MIDI spec that allows Controllers 98 and 99 to be used to control non-standard parameters relating to particular models of synthesizer. This is an alternative to using System Exclusive data to achieve the same ends, though NRPNs tend to be used mainly by Yamaha and Roland instruments.

RF Capacitor Microphone

An alternative form of capacitor microphone which uses the capacitive capsule as the tuning element of a radio-frequency oscillator. Sound waves arriving at the capsule change its capacitance, which varies the frequency of the RF oscillator to produce an FM signal. This is immediately demodulated by the microphone's internal circuitry to produce the audio output. The advantage of this approach is that the capsule works in a very low-impedance environment (as opposed to the very high-impedance environment of a traditional DC-biased capacitor mic), making it immune to the effects of humidity which can cause unwanted noise in conventional capacitor mics. This technology was invented by Sennheiser and is used in their MKH range of microphones.

Pressure

An alternative term for Aftertouch.

MIDI Splitter

An alternative term for MIDI Thru box.

Patch

An alternative term for a Program, referring to a single programmed sound within a synthesizer that can be called up using Program Change commands. MIDI effects units and samplers also have patches. (see also Bank)

Capsule

An alternative term for a transducer which converts acoustic sound waves into an electrical signal.

Console

An alternative term for mixer (See also Desk).

Desk

An alternative term for mixer (See also console).

Ground

An alternative term for the electrical Earth or 0 Volts reference. In mains wiring, the ground cable is often physically connected to the planet's earth via a long conductive metal spike.

VCA, Voltage Controlled Amplifier

An amplifier in which the gain (or attenuation) is controlled by an external DC voltage. VCA's are used in a wide range of audio and musical equipment, such as fader-automation systems in large format mixing consoles, audio compressors, and synthesizers.

Daisy Chain

An arrangement of sharing a common data signal between multiple devices. A 'daisy chain' is created by connecting the appropriate output (or through) port of one device to the input of the next. This configuration is often used for connecting multiple MIDI instruments together: the MIDI Out of the master device is connected to the MIDI In of the first slave, then the MIDI Thru of the first slave is connected to the MIDI In of the second slave, and so on... A similar arrangement is often used to share a master word clock sample synchronising signal between digital devices.

Click Track

An audible metronome pulse which assists musicians in playing in time.

Vari-Mu Compressor

An audio compressor that employs a valve (tube) as the variable audio attenuator. Mu is an engineering term for gain, so this is a variable-gain compressor. In essence, the side-chain signal continuously adjusts the bias o the valve to alter its gain appropriately. Vari-Mu compressors are fast and smooth, with low distortion.

Phono plug (RCA-phono)

An audio connector developed by RCA and used extensively on hi-fi and semi-pro, unbalanced audio equipment. Also used for the electrical form of S/PDIF digital signals, and occasionally for video signals.

K-Metering

An audio level metering format developed by mastering engineer Bob Katz which must be used with a monitoring system set up to a calibrated acoustic reference level. Three VU-like meter scales are provided, differing only in the displayed headroom margin. The K-20 scale is used for source recording and wide dynamic-range mixing/mastering, and affords a 20dB headroom margin. The K-14 scale allows 14dB of headroom and is intended for most pop music mixing/mastering, while the K-12 scale is intended for material with a more heavily restricted dynamic-range, such as for broadcasting. In all cases, the meter's zero mark is aligned with the acoustic reference level.

VU Meter

An audio meter designed to interpret signal levels in roughly the same way as the human ear, which responds more closely to the average levels of sounds rather than to the peak levels. (cf. PPM)

Real-time

An audio process that can be carried out as the signal is being recorded or played back. The opposite is off-line, where the signal is processed in non-real time.

Enhancer (cf. Exciter)

An audio processor designed to brighten audio material using techniques such as dynamic equalisation, phase shifting and harmonic generation.

Exciter (cf. Enhancer)

An audio processor that works by synthesizing new high frequency harmonics.

Limiter

An automatic gain-control device used to restrict the dynamic range of an audio signal. A Limiter is a form of compressor optimised to control brief, high level transients with a ratio greater than 10:1.

Sound On Sound

An early recording technique pioneered by Les Paul and others which was a simple form of overdubbing to build up a mix of sources. Also, the world's best recording technology magazine (see www.soundonsound.com).

Chorus

An effect created by doubling a signal and adding delay and pitch modulation, intended to make a single source sound more like an ensemble.

Flanging

An effect which combines a modulated delay with the original signal, using feedback to create a dramatic, sweeping sound.

Phaser

An effect which combines a signal with a phase-shifted version of itself to produce creative comb-filtering effects. Most phasers are controlled by means of an LFO.

Preset

An effects unit or synth patch that cannot be altered by the user.

Transformer

An electrical device in which two or more separate and electrically isolated coils of wire are wound around a common ferromagnetic core. Alternating Current passing through one coil creates a varying magnetic field which induces a corresponding current in the other coil(s). In audio applications transformers are often used to convey a signal without a direct electrical connection, thus providing 'galvanic isolation' between the source and destination. Winding a transformer with different numbers of turns for each coil allows the output voltage to be increased or decreased in direct proportion - a feature widely employed in mains power-supply transformers to reduce the mains voltage to something more appropriate for the circuitry, for example, or in microphone preamp step-up transformers.

Load

An electrical load is a circuit that draws power from another circuit or power supply. The term also describes reading data into a computer system.

Signal

An electrical representation of an audio event.

Envelope generator

An electronic circuit capable of generating a control signal which represents the envelope of the sound you want to recreate. This may then be used to control the amplitude of an oscillator or other sound source, though envelopes may also be used to control filter or modulation settings. The most common example is the ADSR generator.

Filter (cf. Equaliser)

An electronic circuit designed to attenuate a specific range of frequencies. (See low-pass, high-pass and band-pass.)

Gate

An electronic device (analogue or digital) designed to mute low level signals so as to improve noise performance during pauses in the wanted material. (Also see Expander.)

Synthesiser

An electronic musical instrument designed to create a wide range of sounds, both imitative and abstract.

Transients

An element of a sound where the spectral content changes abruptly. Most natural sounds start with a transient element before settling into something more steady-state, and it is often that transient element that provides most of the recognisable character of the sound source.

Compander

An encode-decode device typically employed to pass a wide dynamic range signal over a channel with a lower dynamic range capability. The source signal is compressed in the encoder to reduce the dynamic range, and subsequently expanded by the decoder to restore the original dynamics. The Dolby noise reduction codecs are examples of companders.

Parameteric EQ

An equaliser with separate controls for frequency, bandwidth and cut/boost.

Clone

An exact duplicate. Often refers to digital copies of digital tapes.

Graphic Equaliser

An form of equaliser whereby multiple narrow segments of the audio spectrum are controlled by individual cut/boost faders. The name comes about because the fader positions provide a graphic representation of the EQ curve.

Effects Loop

An interface system, usually involving separate send and receive connections, which allows an external signal processor to be connected into the audio chain. (cf. Insert Point)

Floppy Disk

An obsolete computer disk format using a flexible magnetic medium encased in a protective plastic sleeve.

Low Frequency Oscillator (LFO)

An oscillator used as a modulation source, usually operating with frequencies below 20Hz. The most common LFO waveshape is the sine wave, though there is often a choice of sine, square, triangular and sawtooth waveforms.

Cabinet Resonance

Any box-like construction will resonate at one or more frequencies. In the case of a loudspeaker, such resonances are likely to be undesirable as they may obscure or interfere with the wanted sound from the drive units. Cabinets are usually braced and damped internally to minimise resonances.

Arming

Arming a track or channel on a recording device places it in a condition where it is ready to record audio when the system is placed in record mode. Unarmed tracks won't record audio even if the system is in record mode. When a track is armed the system monitoring usually auditions the input signal throughout the recording, whereas unarmed tracks usually replay any previously recorded audio.

Scrape Flutter

As analogue recording tape moves across the heads or other non-moving parts in the tape path it can vibrate at a high frquency (typically above 100Hz) due to a rapid stick-slip action, and this causes a form of intermodulation distortion. Often mechanical dampers and rollers are placed in the tape path to prevent scrape flutter.

Zipper Noise

Audible steps that can occur when a parameter is being varied in a digital audio processor.

Hum

Audio Signal contamination caused by the addition of low frequencies, usually related to the mains power frequency.

AC, Alternating Current

Audio signals are represented in the electrical domain as currents flowing alternately forward and back in the circuits as an analogue of the compression and rarefaction of acoustic air pressure. (cf. DC)

BPM

Beats Per Minute

CPU

Central Processing Unit — the number-crunching heart of a computer or other data processor.

VDU

Computer display screen (See also Monitor).

Plug-in Power

Consumer recorders, such as MP3 recorders, are often equipped with a microphone powering system called 'Plug-In Power'. This operates with a much lower voltage (typically 1.5V) and is not compatible with phantom powered mics at all.

Audio Random Access (ARA)

Developed by Celemony and PreSonus in 2011, ARA relates to a data-exchange extension for DAW plug ins like AU, VST and RTAS, to pass information relating to an entire track, rather than just about a specific moment in time — such as pitch, tempo, rhythm etc. ARA v2 was announced in 2018 with an extended feature set including integrated undo synchronisation. Most of the popular DAWs are now compatible with ARA v2, but the only plug-ins that use it at present are Melodyne and Revoice Pro.

DSP

Digital Signal Processor. A powerful microchip used to process digital signals.

DCA

Digitally Controlled Amplifier. The digital equivalent of a VCA often found in digital synthesisers and mixing consoles.

DCO

Digitally Controlled Oscillator. Used in digitally-controlled synthesizers.

DMA

Direct Memory Access. Part of a computer operating system that allows peripheral devices to communicate directly with the computer memory without going via the central processor or CPU.

Off/On-axis

Directional microphones are inherently more sensitive to sound from one direction, and the direction of greatest sensitivity is referred to as the principle axis. Sound sources placed on this axis are said to be 'on-axis', while sound sources elsewhere are said to be 'off-axis'

DDP

Disc Description Protocol. A data description format used for specifying the content of optical discs including CD, and used almost universally now for the delivery of disc masters to duplication houses. A DDP file contains four elements: the Audio image (.DAT); the DDP identifier (DDPID), the DDP Stream Descriptor (DDPMS); and a subcode descriptor (PQDESCR). Often an extra text file is also included with track titles and timing data. Many DAWs and audio editing programs can now create DDP files.

DOS

Disk Operating System. Part of the operating system of PC and PC compatible computers

Dolby Surround-Sound

Dolby's surround sound systems started with an analogue 4:2:4 phase-matrix system with a very elaborate active-steering decoder called ProLogic, before moving into the digital realm with Dolby Digital, Dolby Digital Plus, Dolby True HD, and others.

Sample

Either a defined short piece of audio which can be replayed under MIDI control; or a single discrete time element forming part of a digital audio signal.

Galvanic Isolation

Electrical isolation between two circuits. A transformer provides galvanic isolation because there is no direct electrical connection between the primary and secondary windings; the audio signal is passed via magnetic coupling. An opto-coupler also provides galvanic isolation, as the signal is passed via light modulation.

E-PROM

Erasable Programmable Read Only Memory. Similar to ROM, but the information on the chip can be erased and replaced using special equipment. (See ROM)

Cloud

Essentially an internet communications network (either a Wide Area Network [WAN] or a private network) in which a data-centre performs a range of services such as data storage (cloud storage) or remote apps and programs (cloud computing). The term comes from the way network engineers used to draw system diagrams with a cloud symbol to simplify a very complex (and irrelevant) network of routers, switches, drives and cables into something that just showed the relevant external connection points.

MIDI Note Number

Every key on a MIDI keyboard has its own note number ranging from 0 to 127, where 60 represents middle C. Some systems use C3 as middle C while others use C4.

FET

Field Effect Transistor. A solid-state semiconductor device in which the current flowing between source and drain terminals is controlled by the voltage on the gate terminal. The FET is a very high impedance device, which makes it highly suited for use in impedance converter stages in capacitor and electret microphones.

VCA Group

Found in large mixing consoles. The fader levels of a number of separate channels assigned to the VCA group can be adjusted together by the VCA Group fader but without mixing their signals together. Usually referred to as a DCA Group in a digital console.

Sub-bass

Frequencies below the range of typical monitor loudspeakers. Some define sub-bass as frequencies that can be felt rather than heard.

FSK

Frequency Shift Keying. An obsolete method of recording a synchronisation control signal onto tape by representing it as two alternating tones. (Also see timecode)

GUI

Graphical User Interface (pronounced 'Gooey'). A software program designer's way of creating an intuitive visual operating environment controlled by a mouse-driven pointer or similar.

Subcode

Hidden data within the CD and DAT format that includes such information as the absolute time location, number of tracks, total running time and so on.

Harmonic

High frequency components of a complex waveform, where the harmonic frequency is an integer multiple of the fundamental.

Event

In MIDI terms, an event is a single unit of MIDI data, such as a note being turned on or off, a piece of controller information, a program change, and so on.

IEM

In-Ear Monitor. A wirelessly-connected foldback monitoring system, often used by musicians on stage with in-ear earpieces.

IPS

Inches Per Second. Used to describe tape speed. Also the Institute of Professional Sound (www.ips.org.uk)

Data

Information stored and used by a computer.

IRQ

Interrupt Request. Part of the operating system of a computer that allows a connected device to request attention from the processor in order to transfer data to it or from it.

Dolby HX

Invented by B&O and licensed to Dolby. HX (often marketed as HX Pro) stands for 'Headroom eXtension' and it is a record-processing system used on some analogue open-reel and cassette tape-recorders (there is no complementary replay processing). Dolby HX Pro varies the amount of recording bias depending on the strength of high-frequencies in the audio signal itself to avoid magnetic saturation and over-biasing. This makes it possible to record with a higher overall fluxivity on the tape.

LSB

Least Significant Byte. If a piece of data has to be conveyed as two bytes, one byte represents high value numbers and the other low value numbers, much in the same way as tens and units function in the decimal system. The high value, or most significant part of the message is called the Most Significant Byte or MSB. Lightpipe — see ADAT Lightpipe.

LED

Light Emitting Diode. A form of solid state lamp.

LCD

Liquid Crystal Display.

LFO

Low Frequency Oscillator, often found in synths or effects using modulation.

MIDI Mode

MIDI information can be interpreted by the receiving MIDI instrument in a number of ways, the most common being polyphonically on a single MIDI channel (Poly-Omni Off mode). Omni mode enables a MIDI Instrument to play all incoming data regardless of channel.

Mineral Wool

Made from natural or synthetic minerals in the form of threads or fibres tangled together to form a moderately dense 'blanket' which permits but impedes air flow and is useful in the creation of sound absorbers, often employed as a cheaper and more efficient alternative to polyurethane form.

MB

Megabyte. Nominally 1,000,000 (one million) bytes of data, but in fact, because computer memory works in with binary, the actual value is 1,048,576 bytes (220).

MDM

Modular Digital Multitrack. An obsolete term for hardware digital recorders that can be used in multiples to provide a greater number of synchronized tracks than a single machine.

MADI

Multichannel Audio Digital Interface. Originally specified by the Audio engineering Society (AES) as AES10 in 1991. This unidirectional digital audio interface shares the same core 24-bit audio and status data format as AES3, but with different 'wrapping' to contain 56 or 64 synchronous channels at base sample rates, or 28 channels at 96kHz. It can be conveyed over unbalanced coaxial cables, or via optical fibres.

MIDI

Musical Instrument Digital Interface. A defined interface format that enables electronic musical instruments and computers to communicate instructional data and synchronise timing. MIDI sends musical information between compatible devices, including the pitch, volume and duration of individual notes, along with many other aspects of the instruments that lend themselves to electronic control. MIDI can also carry timing information in the form of MIDI Clock or MIDI Time Code for system synchronisation purposes.

Hub

Normally used in the context of the USB computer data interface. A hub is a device used to expand a single USB port into several, enabling the connection of multiple devices. Particularly useful where multiple software program authorisation dongles must be connected to the computer.

Paraphonic

Often used to descibe a multi-oscillator mono-synth which can be configured to allow the oscillators to be controlled independently from the keyboard, allowing two or more notes to be played simultaneously.

Cycle

One complete vibration (from maximum peak, through the negative peak, and back to the maximum again) of a sound source or its electrical equivalent. One cycle per second is expressed as 1 Hertz (Hz).

Monophonic

One note at a time.

Detent

One or more physical click-stops which can be felt when a rotary control is moved. Typically used to identify the centre of a control such as a pan or EQ cut/boost knob, or to give the impression of preset positions on a gain control.

Resistance

Opposition to the flow of electrical current. Measured in Ohms.

Compact Cassette

Originally conceived as a recording format for dictation machines in the early 1960s, it became a mainstream music release format in the form of the Musicassette. A plastic shell protected 3.81mm wide (1/8-inch) recording tape which ran at 4.75cm/s. A stereo track was recorded in one direction, and the tape could be turned over to play a second stereo track recorded in the opposite direction.

BIOS

Part of a computer operating system (basic input-output system) held on ROM rather than on disk. This handles basic routines such as accessing the disk drive.

Sustain

Part of the ADSR envelope which determines the level to which the sound will settle if a key is held down. Once the key is released, the sound decays at a rate set by the Release parameter. Also refers to a guitar's ability to hold notes which decay very slowly.

Quantisation

Part of the process of digitising an analogue signal. Quantisation is the process of describing or measuring the amplitude of the analogue signal captured in each sample, and is defined by the wordlength used to describe the audio signal — eg. 16 bits.

PCI Card

Peripheral Component Interconnect: an internal computer bus format used to integrating hardware devices such as sound cards. The PCI Local Bus has superseded earlier internal bus systems such as ISA and VESA, and although still very common on contemporary motherboards has, itself, now been superseded by faster interfaces such as PCI-X and PCI Express.

Vibrato

Pitch modulation using an LFO to modulate a VCO. (cf. Tremolo)

PQ Coding

Process for adding Pause, Cue and other subcode information to a digital master tape in preparation for CD manufacture.

SCSI

Pronounced SKUZZY, an abbreviation for Small Computer Systems Interface. An obsolete interfacing system for using hard drives, scanners, CD-ROM drives and similar peripherals with a computer. Each SCSI device has its own ID number and no two SCSI devices in the same chain must be set to the same number. The last SCSI device in the chain should be terminated, either via an internal terminator or via a plug-in terminator fitted to a free SCSI socket.

Hiss

Random noise caused by random electrical fluctuations.

Overdubbing

Recording new material to separate tracks while auditioning and playing in synchronism with previously recorded material.

Timbral

Referring to the tones that can be created by a synthesizer (see multi-timbral and bi-timbral)

Initialise

Resetting a device to its 'start-up' state. Sometimes used to mean restoring a piece of equipment to its factory default settings.

Standing Waves

Resonant low frequency sound waves bouncing between opposite surfaces such that each reflected wave aligns perfectly with previous waves to create static areas of maximum and minimum sound pressure within the room. (See also Modes and Modal Frequencies)

GS

Roland's own extension to the General MIDI protocol.

S/MUX

Sample Multiplexing (see ADAT ).

Booth

See Isolation Room

Drum Booth

See Isolation Room

Vocal Booth

See Isolation Room

LKFS

See LUFS

Comping

Short for 'compilation.' The process of recording the same performance (e.g. a lead vocal) several times on multiple tracks to allow the subsequent selection of the best sections and assembling them to create a 'compilation' performance which would be constructed on a final track.

Pre-amp

Short for 'pre-amplification' : an active gain stage used to raise the signal level of a source to a nominal line level. For example, a microphone pre-amp.

Reverb

Short for Reverberation. The dense collection of echoes which bounce off acoustically reflective surfaces in response to direct sound arriving from a signal source. Reverberation can also be created artificially using various analogue or, more commonly, digital techniques. Reverberation occurs a short while after the source signal because of the finite time taken for the sound to reach a reflective surface and return — the overall delay being representative of the size of the acoustic environment. The reverberation signal can be broadly defined as having two main components, a group of distinct 'early reflections' followed by a noise-like tail of dense reflections.

Flutter Echoes

Short time-span sound echoes which can be created when sound waves bounce between opposite walls in a small or moderately sized room. A shorter version of the 'slapback' echo whch can be experienced in a larger hall when sound from a stage is reflected strongly from the rear wall.

FX

Shorthand term for Effects.

Audio Frequency

Signals in the range of human audio audibility. Nominally 20Hz to 20kHz.

Pulse Wave

Similar to a square wave but non-symmetrical. Pulse waves sound brighter and thinner than square waves, making them useful in the synthesis of reed instruments. The timbre changes according to the mark/space ratio of the waveform.

Bug

Slang term for a software fault or equipment design problem.

Crash

Slang term relating to malfunction of computer program.

Sawtooth Wave

So called because it resembles the teeth of a saw, this waveform contains both odd and even harmonics.

Intermittent

Something that happens occasionally and unpredictably, typically a fault condition.

SPP

Song Position Pointer (MIDI).

S/PDIF

Sony/Philips Digital Interface. Pronounced either 'S-peedif' or 'Spudif'. A stereo or dual-channel self-clocking digital interfacing standard employed by Sony and Philips in consumer digital hi-fi products. The S/PDIF signal is essentially identical in data format to the professional AES3 interface, and is available as either an unbalanced electrical interface (using phono connectors and 75ohm coaxial cable), or as an optical interface called TOSlink.

Jargon

Specialised words associated with a specialist subject.

Q

The 'quality-factor' of a filter which defines its bandwidth and indicates a filter's resonant properties. The higher the Q, the more resonant the filter and the narrower the range of frequencies that are allowed to pass.

Impedance

The 'resistance' or opposition of a medium to a change of state, often encountered in the context of electrical connections (and the way signals of different frequencies are treated), or acoustic treatment (denoting the resistance it presents to air flow). Although measured in Ohms, the impedance of a 'reactive' device such as a loudspeaker drive unit will usually vary with signal frequency and will be higher than the resistance when measured with a static DC voltage. Signal sources have an output impedance and destinations have an input impedance. In analogue audio systems the usually arrangement is to source from a very low impedance and feed a destination of a much higher (typically 10 times) impedance. This is called a 'voltage matching' interface. In digital and video systems it is more normal to find 'matched impedance' interfacing where the source, destination and cable all have the same impedance (eg. 75 Ohms in the case of S/PDIF). Microphones have a very low impedance (150 Ohms or so) while microphone preamps provide an input impedance of 1,500 Ohms or more. Line inputs typically have an impedance of 10,000 Ohms and DI boxes may provide an input impedance of as much as 1,000,000 Ohms to suit the relatively high output impedance of typical guitar pickups.

Filter Frequency

The 'turnover' or 'corner' frequency of a high- or low-pass filter. Technically, the frequency at which the signal amplitude has been attenuated by 3dB.

MIDI Port

The MIDI connections of a MIDI-compatible device. A Multiport, in the context of a MIDI Interface, is a device with multiple MIDI output sockets, each capable of carrying data relating to a different set of 16 MIDI channels. Multiports are the only means of exceeding the limitations imposed by 16 MIDI channels.

MIDI Out

The MIDI connector used to send data from a master device to the MIDI In of a connected slave device.

MIDI Note On

The MIDI message sent when note is played (key pressed).

MIDI Note Off

The Message sent when key is released.

Hz

The SI symbol for Hertz, the unit of frequency.

SMPTE

The Society of Motion Picture and Television Engineers (www.smpte.org) an American standards body. The term is also used to refer to a form of time code developed for the film industry but now extensively used in music and recording. SMPTE is a real-time digital code describing hours, minutes, seconds and film or video frames. Usually conveyed as an audible warble.

Polyphony

The ability of an instrument to play two or more notes simultaneously. An instrument which can only play one note at a time is described as monophonic.

Near Field

The acoustic zone close to a sound source or microphone. Often used to describes a loudspeaker system designed to be used close to the listener - although some people prefer the term 'close field'. The advantage is that the listener hears more of the direct sound from the speakers and less of the reflected sound from the room.

SATA

The acronym stands for 'Serial Advanced Technology Attachment' and is a computer interface employed for connecting standard ATA hard drives to a computer motherboard. The SATA interface supersedes the PATA (parallel ATA) interface which has been used since the 1980s. A variant of the SATA interface, called eSATA (with the 'e' standing for 'external'), permits the connection of external hard drives. it uses a slightly different connector but is otherwise a very similar interface.

Gain Staging

The act of optimising the signal level through each audio device in a signal chain, or through each section of a mixing console, to maintain an appropriate amount of headroom and keep the signal well above the system noise floor.

Punch-in

The action of placing an already recorded track into record at the correct time during playback, so that the existing material may be extended or replaced.

Punch-out

The action of switching a tape machine (or other recording device), out of record after executing a punch-in. With most multitrack machines, both punching in and punching out can be accomplished without stopping the tape.

Harmonic Distortion

The addition of harmonics that were not present in the original signal caused by non-linearities in an electronic circuit or audio transducer.

Gain

The amount by which a circuit amplifies a signal, normally denoted in decibels.

Dynamic Range

The amplitude range, usually expressed in decibels, between the loudest signal that can be handled by a piece of equipment and the level at which small signals disappear into the noise floor. (See AES17)

Stereo Recording Angle

The angle over which sound sources can be captured by a microphone array. For a stereo array with a _____________ of 90 degrees, sound sources can be placed ±45 degree relative to the array's centre front axis, with a source at the extreme angle appearing fully left or right in the stereo image.

Headroom

The available 'safety margin' in audio equipment required to accommodate unexpected loud audio transient signals. It is defined as the region between the nominal operating level (0VU) and the clipping point. Typically, a high quality analogue audio mixer or processor will have a nominal operating level of +4dBu and a clipping point of +24dBu — providing 20dB of headroom. Analogue meters, by convention, don't show the headroom margin at all; but in contrast, digital systems normally do — hence the need to try to restrict signal levels to average around -20dBFS when tracking and mixing with digital systems to maintain a sensible headroom margin. Fully post-produced signals no longer require headroom as the peak signal level is known and controlled. For this reason it has become normal to create CDs with zero headroom.

Operating System

The basic software that enables a computer to load and run other programs.

Voice

The capacity of a synthesizer to play a single musical note. An instrument capable of playing 16 simultaneous notes is said to be a 16-voice instrument.

Modal Distribution

The characteristic distribution of resonant low frequency sound waves within a confined space such as a room.

Resonance

The characteristic of a filter that allows it to selectively pass a narrow range of frequencies. See Q.

Tweeter

The colloquial term to describe a loudspeaker drive unit optimised for the reproduction of high frequencies. (See Woofer).

Partials

The combination of fundamental and overtones together are called particals. (cf. harmonic)

Optimisation (of computer)

The concept of configuring a computer in such as way as to maximise its performance for certain tasks. In the context of a machine being used as a DAW, optimisation might involve disabling sub-programs that access the internet regularly or intermittently, such as email hosts, automatic program update checkers and so on. It might also include the structure of the hard drive, or the separation of program data to a system drive and audio data to a separate drive to minimise access times and maximise data throughputs.

Damping

The control of a resonant device. In the context of reverberation, damping refers to the rate at which the reverberant energy is absorbed by the various surfaces in the environment. In the context of a loudspeaker it relates to the cabinet design and internal acoustic absorbers.

Hard Disk Drive (cf. Solid-state Drive)

The conventional means of computer data storage. One or more metal disks (hard disks) hermetically sealed in an enclosure with integral drive electronics and interfacing. The disks coated in a magnetic material and spun at high speed (typically 7200rpm for audio applications). A series of movable arms carrying miniature magnetic heads are arranged to move closely over the surface of the discs to record (write) and replay (read) data.

Synthesis

The creation of artificial sound.

Multi-sample

The creation of several samples, each covering a limited musical range, the idea being to produce a more natural range of sounds across the range of the instrument being sampled. For example, a piano may need to be sampled every two or three semitones in order to sound convincing.

dB

The deciBel is a method of expressing the ratio between two quantities in a logarithmic fashion. Used when describing audio signal amplitudes because the logarithmic nature matches the logarithmic character of the human sense of hearing. The dB is used when comparing one signal level against another (such as the input and output levels of an amplifier or filter). When the two signal amplitudes are the same, the decibel value is 0dB. If one signal has twice the amplitude of the other the decibel value is +6dB, and if half the size it is -6dB. When one signal is being compared to a standard reference level the term is supplemented with a suffix letter representing the specific reference. 0dBu implies a reference voltage of 0.775V rms, while 0dBV relates a reference voltage of 1.0V rms. The two most common standard audio level references are +4dBu (1.223V rms) and -10dBV (0.316V rms). The actual level difference between these is close to 12dB. The term dBm is also sometimes encountered, and this relates to an amount of power rather than a voltage, specifically 1mW dissipated into 600 Ohms (which happens to generate a voltage of 0.775V rms). When discussing acoustic sound levels, 0dB SPL (sound pressure level) is the typical threshold of human hearing at 1kHz.

Polar Pattern

The directional characteristic of a microphone (omni, cardioid, figure-eight, etc).

Lay Length

The distance along the length of a cable over which the twisted core wires complete one complete turn. Shorter lay lengths provide better rejection of electromagnetic interference, but make the cable less flexible and more expensive.

Output Impedance

The effective internal impedance (resistance which many change with signal frequency) of an electronic device. In modern audio equipment the output impedance is normally very low. Microphones are normally specified with an output impedance of 150 or 200 ohms, although some vintage designs might be as low as 30 Ohms.

DC, Direct Current.

The form of electrical current supplied by batteries and the power supplies inside electrical equipment. The current flows in one direction only.

Cut-off Frequency

The frequency above or below which attenuation begins in a filter circuit.

Crossover frequency

The frequency at which one driver ceases to produce most of the sound and a second driver takes over. In the case of a two-way speaker the crossover frequency is usually between 1 and 3kHz.

Formant

The frequency components or resonances of an instrument or voice sound that doesn't change with the pitch of the note being played or sung. For example, the body resonance of an acoustic guitar remains constant, regardless of the note being played.

Bass Response

The frequency response of a loudspeaker system at the lower end of the spectrum. The physical size and design of a loudspeaker cabinet and the bass driver (woofer) determine the low frequency extension (the lowest frequency the speaker can reproduce at normal level) and the how quickly the signal level falls below that frequency.

Early Reflections

The initial sound reflections from walls, floors and ceilings following a sound created in an acoustically reflective environment.

Input Impedance

The input impedance of an electrical network is the 'load' into which a power source delivers energy. In modern audio systems the input impedance is normally about ten times higher than the source impedance — so a typical microphone preamp has an input impedance of between 1500 and 2500 Ohms, and a line input is usually between 10 and 50k Ohms.

I/O

The input/output connections of a system.

Overdrive

The intentional use of overloaded analogue circuitry as a musical effect.

USB-C

The latest (2014) incarnation of a Universal Serial Bus interface, carrying bidirectional data at speeds of 10Gb/s. USB-C is not compatible with previous generations (USB 1.1, 2.0, 3.0, 3.1) as it has a very different 24-pin connector which is symmetrical and employed at both ends of a free cable, and all devices have the same socket. Power is optionally available over USB-C conenctions at 5V with a current capacity of either 1.5A (7.5W) or 3A (15W)

Maximum SPL

The loudest sound pressure level that a device can generate or tolerate.

Low-range (low, lows)

The lower portion of the audible frequency spectrum, typically denoting frequencies below about 1kHz.

Fundamental

The lowest frequency component in a harmonically complex sound. (Also see harmonic and partial.)

Motherboard

The main circuit board within a computer into which all the other components plug or connect.

Peak

The maximum instantaneous level of a signal.

Mid-range (mid, mids)

The middle portion of the audible frequency spectrum, typically denoting frequencies between about 300Hz and 3kHz.

Poly-mode

The most common MIDI mode that allows and instrument to respond to multiple simultaneous notes transmitted on a single MIDI channel.

Diaphragm

The movable membrane in a microphone capsule which responds mechanically to variations in the pressure or pressure gradient of sound waves. The mechanical diaphragm vibrations are converted into an electrical signal usually through electromagnetic or electrostatic techniques such as ribbon, moving coil, capacitor or electret devices.

Pitch

The musical interpretation of an audio frequency.

Output Sensitivity

The nominal output voltage generated by a microphone for a known reference acoustic sound pressure level. Output sensitivity is normally specified for a sound pressure level of one Pascal (94dB SPL), and may range from about 0.5mV/Pa for a ribbon microphone, to 1.5mV/Pa for a moving coil, and up to 20 or 30mV/Pa for a capacitor microphone.

Mic Level

The nominal signal level generated by a microphone. Typically around -50dBu. Mic level signals must be amplified to raise them to line-level.

Analogue (cf. Digital)

The origin of the term is that the electrical audio signal inside a piece of equipment can be thought of as being 'analogous' to the original acoustic signal. Analogue circuitry uses a continually changing voltage or current to represent the audio signal.

Session Tape

The original tape recording made during a recording session.

Zenith

The parameter of tape head alignment relating to vertical alignment head and whether it is leaning forward or back relative to the tape path. (cf. Azimuth and Wrap)

Wrap

The parameter of tape head alignment which relates to the rotation angle of the head in a vertical axis which determines how the tape arrives and leaves the head gap.

Pickup

The part of a guitar that converts the string vibrations to electrical signals. Also the stylus/cartridge assembly used to replay vinyl records.

Head

The part of a tape machine or disk drive that reads and/or writes information magnetically to and from the storage media.

Tape Head

The part of a tape machine that transfers magnetic energy to the tape during recording, or reads it during playback.

Loudness

The perceived volume of an audio signal.

Mutual Angle

The physical angle between two microphones, used to specify various microphone array configurations (eg. 90 degrees for a Blumlein pair, or 110 degrees for an ORTF array).

Cabinet

The physical construction which encloses and supports the loudspeaker drive units. Usually built of wood or wood composites (although other materials are often used including metal alloys and mineral composites). Cabinets can be 'sealed' or 'vented' in various ways, the precise design influencing the bass and time-domain characteristics.

Zero Crossing Point

The point at which a signal waveform crosses from being positive to negative or vice versa.

Mirror Points

The positions on the walls or ceiling where, if the surface was covered with an optical mirror, one or both loudspeakers could be seen in the reflection. The mirror point is essentially any position on a boundary where sound waves from a sound source — usually a monitor loudspeaker — will be reflected directly to the listening position. This is therefore the ideal location to place an acoustic absorber to prevent audible reflections.

Loudness-Normalisation

The practice of matching the perceived loudness of different material to a given target loudness value. To accommodate varying peak levels, the medium requires an approporiate headroom margin. Loudness-normalisation is now the default form for HDTV broadcasts, as well as most audio streaming services, although the target loudness level currently varies between different platforms. Loudness-normalisation is measured using the LUFS or LKFS scale. (See LUFS, Peak-Normalisation, Mastering, Loudness Wars).

Stripe

The practice of recording a time code signal onto one track of a multitrack tape machine to facilitate subsequent synchronisation.

Peak-Normalisation

The practice of removing all headroom to maximise the peak level of an audio signal on a particular medium. So all peak-normalised material will have the same maximum peak value, but the perceived loudness is likely to vary between different tracks. The technique became popular and commonplace with the advent of digital formats such as CD, where the signal level was typically engineered to reach 0dBFS. (See also Loudness-Normalisation, Mastering and Loudness Wars)

Dubbing

The practice of transferring material from one medium to another, or of adding further material to an existing recording (cf. Over-Dub).

Loudness Wars

The practice of trying to make each new commercial music release sound subjectively louder than any previous release, on the misguided notion that louder is more exciting and results in more sales. A relationship between the average loudness of 45rpm singles and sales was noticed in America from jukebox plays, and that led to the first loudness war. However, the advent of the CD really ramped up the situation, with music becoming ever-more dynamically compressed to squeeze the average level higher and higher towards the 0dBFS peak level. This desctructive trend is, thankfully, now being slowly reversed with the ubiquity of loudness normalisation adopted by most online audio streaming services and broadcasters.

Word Clock

The precise timing of digital audio samples is critical to the correct operation of interconnected digital audio equipment. The 'metronome' that governs sample timing is called the Word Clock (sometimes conjoined to 'Wordclock', or abbreviated to 'Wclk'). However, word clock does more than merely beat time; it also identifies the start and end of each digital word or sample, and which samples belong to the left or right channels. Digital interfaces such as the AES3 and S/PDIF embody clock signals within the data stream, but it is often necessary to convey a discrete word clock between equipment as a square wave signal running at the sampling rate. Dedicated word clock inputs and outputs on digital equipment generally use BNC connectors.

Fragmentation (cf. defragment)

The process by which the available space on a disk drive gets split up into small, sometimes unusable, sections due to the storing and erasing of files.

Clocking

The process of controlling the sample rate of one digital device with an external clock signal derived from another device. In a conventional digital system there must be only one master clock device, with everything else 'clocked' or 'slaved' from that master.

Subtractive Synthesis

The process of creating a new sound by filtering and shaping a raw, harmonically complex waveform.

Loop

The process of defining a portion of audio within a DAW, and configuring the system to replay that portion repeatedly. Also, a circuit condition where the output is connected back to the input.

Bouncing

The process of mixing two or more recorded tracks together and re-recording these onto another track.

Defragment

The process of rearranging the files on a hard disk so that all the files are as contiguous as possible, and that the remaining free space is also contiguous.

Tracking

The process of recording individual tracks to a multichannel recorder. Tracking is also often discussed in the context of MIDI guitar synthesizers or controllers where the MIDI output attempts to track the pitch of the guitar strings.

Decay

The progressive reduction in amplitude of a sound or electrical signal over time, eg. The reverb decay of a room. In the context of an ADSR envelope shaper, the Decay phase starts as soon as the Attack phase has reached its maximum level.

Insert Points

The provision on a mixing console or 'channel strip' processor of a facility to break into the signal path through the unit to insert an external processor. Budget devices generally use a single connection (usually a TRS socket) with unbalanced send and return signals on separate contacts, requiring a splitter or Y-cable to provide separate send (input to the external device) and return (output from external device) connections . High end units tend to provide separate balanced send and return connections. (cf. Effects Loop)

Bandwidth

The range of frequencies passed by an electronic circuit such as an amplifier, mixer or filter. The frequency range is usually measured at the points where the level drops by 3dB relative to the maximum. (See also Q)

Roll-off

The rate at which a filter or equaliser attenuates a signal once it has passed the turnover frequency.

Velocity

The rate at which a key is depressed. This may be used to control loudness (to simulate the response of instruments such as pianos) or other parameters on later synthesizers.

Tempo

The rate of the 'beat' of a piece of music measured in beats per minute.

Signal-to-noise Ratio

The ratio of nominal or maximum signal level to the residual noise floor, expressed in decibels.

Phase

The relative position of a point within a cyclical signal, expressed in degrees where 360 degrees corresponds to one full cycle. (Also see Polarity)

Ambience

The result of sound reflections in a confined space being added to the original sound. Ambience may also be created electronically by some digital reverb units. The main difference between ambience and reverberation is that ambience doesn't have the characteristic long delay time of reverberation; the reflections mainly give the sound a sense of space.

Signal Chain

The route taken by a signal from the input of a system to the output.

Nyquist Theorum

The rule which states that a digital sampling system must have a sample rate at least twice as high as that of the highest audio frequency being sampled in order to avoid aliasing and thus reproduce the wanted audio perfectly. Because anti-aliasing filters aren't perfect, the sampling frequency has usually to be made slightly more than twice that of the maximum input frequency — which is why the standard audio rate of 44.1kHz was chosen for a nominally 20kHz audio bandwidth.

MIDI Thru

The socket on a slave unit used to feed the MIDI In socket of the next unit in line.

MIDI In

The socket used to receive information from a master controller or from the MIDI Thru socket of a slave unit.

k (lower-case k)

The standard abbreviation for kilo, meaning a multiplier of 1000 (one thousand). Used as a prefix to other values to indicate magnitude, eg. 1kHz = 1000Hz, 1kOhm = 1000 Ohms.

Hertz (Hz)

The standard measurement of frequency. 10Hz means ten complete cycles of a repeating waveform per second.

LUFS

The standard measurement of loudness, as used on Loudness Meters corresponding to the ITU-TR BS1770 specification. the acronym stands for 'Loudness Units (relative to) Full Scale. Earlier versions of the specification used LKFS instead, and this label remains in use in America. The K refers to the 'K-Weighting' filter used in the signal measurement process.

PCM, Pulse Code Modulation

The technique used by most digital audio systems to encode audio as binary data.

Slate

The term comes from the silent film practice of writing the scene, take and shot numbers with chalk on a slate and holding it up in front of the camera before the action starts, so that the film editor can identify the material. A role now replaced by the 'clapper-board' which adds an audio synchronisation marking facility as well. In an audio context, a slate is a verbal identification recorded just before each take to help identify it subsequently. This is normally achieved by using a talkback microphone routed to the main, group and/or direct outputs of a mixer. The console slate function often mixed a low frequency tone in with the microphone signal to help make locating the start of each take much easier when fast-winding the tape against the playback head. Each slate ident would be heard as a short, steady mid-frequency tone.

Track

The term dates back to multitrack tape where the tracks are physical stripes of recorded material, located side by side along the length of the tape.

Delay

The time between a sound or control signal being generated and it auditioned or taking effect, measured in seconds. Often referred to as latency in the context of computer audio interfaces.

Latency (cf. Delay)

The time delay experienced between a sound or control signal being generated and it being auditioned or taking effect, measured in seconds.

Release

The time taken for a signal level or processor gain to return to normal. Often used to describe the rate at which a synthesized sound reduces in level after a key has been released. Also used to describe the time taken for a compressor top restore unity gain after a signal has fallen below the threshold. Also known as 'recovery time .'

Attack

The time taken for a sound to achieve its maximum amplitude. Drums have a fast attack, whereas bowed strings have a slow attack. In compressors and gates, the attack time equates to how quickly the processor can reduce the signal level.

Reverberation Time

The time taken for sound waves reflecting within a space to lose energy and become inaudible. A standard measurement is 'RT60' which is the time taken for the sound reflections to decay by 60dB.

Impulse Response

The time-domain equivalent of the much more familiar frequency (and phase) responses in the frequency-domain. A very brief click (technically, a Dirac delta function) which theoretically contains all frequencies at equal amplitude, is passed through the device under test. The resulting output is the 'impulse response' of that device and uniquely describes its signal processing behaviour. Impulse responses are very convenient for digital signal processing applications as the source impulse is very similar to a single digital sample value.

Timbre

The tonal 'colour' of a sound.

Print-through

The undesirable process that causes some magnetic information from a recorded analogue tape to become imprinted onto an adjacent layer. This can produce low level pre or post echoes.

Ohm

The unit of electrical resistance.

High-range (highs)

The upper portion of the audible frequency spectrum, typically denoting frequencies above about 1kHz.

Soundproofing

The use of materials and construction techniques with the aim of preventing unwanted sound from entering or leaving a room.

Surround

The use of multiple loudspeakers placed around the listening position with the aim of reproducing a sense of envelopment within a soundstage. Numerous ___________ formats exist, but the most common currently is the 5.1 configuration in which three loudspeakers are placed in front of the listener (at ±30 degrees and straight ahead), with two behind (at ±120 degrees or thereabouts), supplemented with a separate subwoofer.

Frequency Response

The variation in amplitude relative to the signal frequency. A measurement of the frequency range that can be handled by a specific piece of electrical equipment or loudspeaker. (Also see Bandwidth)

Sine Wave

The waveform of a pure sinusoidal tone with no harmonics.

Amplitude

The waveform signal level. It can refer to acoustic sound levels or electrical signal levels.

Reflection

The way in which sound waves bounce off surfaces.

Envelope

The way in which the amplitude of a sound signal varies over time.

Polarity

This refers to a signal's voltage above or below the median line. Inverting the polarity of a signal swaps the positive voltage to negative voltage and vice versa. This condition is often referred to (incorrectly) as 'out-of-phase'.

Balance

This word has several meanings in recording. It may refer to the relative levels of the left and right channels of a stereo recording (eg. Balance Control), or it may be used to describe the relative levels of the various instruments and voices within a mix (ie. Mix balance).

Chord

Three or more different musical notes played at the same time.

Overload

To exceed the maximum acceptable signal amplitude of an electronic or electrical circuit. Overloading a device results in a noticeable increase in distortion but this may be deemed musically beneficial and desirable, or completely unacceptable and inappropriate, depending on context and intent. Overloading an analogue device typically results in the waveform peaks becoming flattened (so tending towards a square wave) and a consequent rapid increase in odd-order harmonic distortion where the distortion products appear at higher frequencies than the source signal fundamentals, but remain musically related to them. In contrast, overloading a digital system inherently contravenes the Nyquist Theorem, since he generated harmonic distortion products generally extend far above half the sampling frequency, and so become aliased and actually appear at lower frequencies than the source fundamentals with a non-musical relationship. This is why digital overloads sound so obvious and unpleasant in comparison to analogue overloads.

Unison

To play the same melody using two or more different instruments or voices.

Attenuate

To reduce the signal amplitude or level.

Erase

To remove recorded material from an analogue tape, or to remove digital data from any form of storage media.

Write

To save data to a digital storage medium, such as a hard drive.

Transpose

To shift a musical signal by a fixed number of semitones.

Dump

To transfer digital data from one device to another. A SysEx dump is a means of transmitting information about a particular instrument or module over MIDI, and may be used to store sound patches, parameter settings and so on.

Mastering

Traditionally the sequencing of individual recordings to form a cohesive album of material, and to apply corrective equalisation and dynamics processing to ensure a consistent sound character and to optimise playback on the widest possible range of sound systems. Appropriate signal processing may also be applied to make the mastered material suitable for its intended medium (such as controlling transient peaks and dynamics and mono-ing the bass for vinyl records, etc).

USB

Universal Serial Bus. A computer interface standard introduced in 1996 to replace the previous standard serial and parallel ports more commonly used. The USB1.1 interface operated at up to 12Mb/s, but this was superseded in 2000 by USB2.0 which operates at up to 480Mb/s. Most USB interfaces can also provide a 5V power supply to connected devices. USB3.0 was launched in 2008 and is claimed to operate at rates up to 5Gb/s, but it is only now (2011) starting to appear on hardware. USB conncetors can be indentified by having a blue insert in the Type-A sockets and the letters SS (SuperSpeed). The latest edition, USB3.1 (launched in 2013) offers transfer rates of 10Gb/s, approaching that of the first generation of Thunderbolt interfaces. Like earlier USB interfaces, the USB3 format provides a 5V power supply, but the current rating has been increased from USB2.0's 200mA (1.0 Watts) to 900mA (4.5 Watts), and sockets designated as charging sockets can manage 1500mA (7.5 Watts).

RF Interference

Unwanted interference into an audio system from external RF signals.

Spill

Unwanted sound picked up by microphones on one instrument from other nearby instruments.

PPQN, Pulsed Per Quarter Note

Used in the context of MIDI Clock derived sync signals.

Disc

Used to describe vinyl discs, CDs and MiniDiscs.

Sample and Hold (S&H)

Usually refers to a feature whereby random amplitude values are generated at regular intervals and then used to control another function such as pitch or filter frequency. Sample and hold circuits were also used in old analogue synthesizers to 'remember' the note being played after a key had been released.

VCA Compressor

VCA compressors tend to be fast-acting (at least in comparison to opto-compressors), a wide dynamic range, and low distortion.

Octave

When a frequency or pitch is transposed up by one octave, its frequency is doubled.

Aliasing

When an analogue signal is sampled for conversion into a digital data stream, the sampling frequency must be at least twice that of the highest frequency component of the input signal. If this rule is disobeyed the sampling process becomes ambiguous as there are insufficient points to define each cycle of the waveform, resulting in unwanted enharmonic frequencies being added to the audible signal.

Clipping

When an audio signal is allowed to overload the system conveying it, clipping is said to have occurred and severe distortion results. The 'clipping point' is reached when the audio system can no longer accommodate the signal amplitude -either because an analogue signal voltage nears or exceeds the circuitry's power supply voltage, or because a digital sample amplitude exceeds the quantiser's number range. In both cases, the result is that the signal peaks are 'clipped' because the system can't support the peak excursions — a sinewave source signal becomes more like a squarewave. In an analogue system clipping produces strong harmonic distortion artefacts at frequencies above the fundamental. In a digital system those high frequency harmonics cause aliasing which results in anharmonic distortion where the distortion artefacts reproduce at frequencies below the source fundamental. This is why digital clipping sounds so unlike analogue clipping, and is far more unpleasant and less musical.

ADSR

When creating artificial waveforms in a synthesizer, changes in the signal amplitude over time are controlled by an 'envelope generator' which typically has controls to adjust the Attack, Sustain, Decay and Release times, controlled by the pressing and subsequent release of a key on the keyboard. The Attack phase determines the time taken for the signal to grow to its maximum amplitude, triggered by the pressing of a key. The envelope then immediately enters the Decay phase during which time the signal level reduces until it reaches the Sustain level set by the user. The signal remains at this level until the key is released, at which point the Release phase is entered and the signal level reduces back to zero.

Stems

When mixing complex audio material it is often useful to divide the tracks into related sections and mix those sections separately before combining the whole. In mixing film soundtracks, the material would often be grouped as a dialogue stem, a music stem, and an effects stem. Each stem might be mono, stereo or multichannel, as appropriate to the situation. In music mixing, stems might be used for the rhythm section, backline instruments, frontline instruments, backing vocals, lead vocals and effects — or any other combination that suited the particular project.

Transmission-Line

When the length of an electrical cable is shorter than about 10% of the wavelngth of the signal it conveys, the voltage and current are effectively the same at all points along the cable. However, if the cable is longer than 10% of the can be considered to propogate as electromagnetic waves along the cable, and this condition is referred to as a 'transmission-line'. At 20Hz the electrical wavelength is well in excess of 2000 miles, and even at 20kHz it is over six miles, so there is no need to consider transmission line theory in normal audio interconnections. However, it is very important in radio-frequency installations as the relevant cable length is about 20cm for 100MHz signals, and just 20mm at 1GHz. A transmission-line can be constructed in many different physical forms, such as spaced parallel wires or coaxial cables, but all are generally of uniform cross-sectional area and have a defined 'characteristic impedance' per unit length. To prevent the signal being reflected from the end of the cable it musty be terminated at both ends in source and destination impedances which match the characeteristic impedance. The term is often also used (usually erroneously) to describe a form of loudspeaker cabient design in which the lowest frequencies are guided down an open-ended tube of considerable length lined with materials which allow the lowest frquencies to pass but absorb the higher frequencies.

Balanced Wiring

Where protection from electromagnetic interference and freedom from earth references are required, a balanced interface is used. The term 'balanced' refers to identical (balanced) impedances to ground from each of two signal carrying conductors which are enclosed, again, within an all-embracing overall screen. This screen is grounded (to catch and remove unwanted RFI), but plays no part in passing the audio signal or providing its voltage reference. Instead, the two signal wires provide the reference voltage for each other — the signal is conveyed 'differentially' and the receiver detects the voltage difference between the two signal wires. Any interference instils the same voltage on each wire (common mode) because the impedance to ground is identical for each, and as there is therefore no voltage difference between the signal wires, the interference is ignored completely by the receiver. Signals conveyed over the balanced interface may appear as equal half-level voltages with opposite polarities on each signal wire — the most commonly described technique. However, modern systems are increasingly using a single-sided approach where one wire carries the entire signal voltage and the other a ground reference for it. Some advantages of this technique include less complicated balanced driver stages, and connection to an unbalanced destination still provides the correct signal level, yet the interference rejection properties are unaffected. Effective interference rejection requires both the sending and receiving devices to have balanced output and input stages respectively.

Post-production

Work done to a recording.

XG

Yamaha's alternative to Roland's GS system for enhancing the General MIDI protocol so as to provide additional banks of patches and further editing facilities.

Electret Microphone

see Back Electret

TT Plug

see Bantam Plug

Condenser Microphone

see Capacitor Microphone

Out-of-Phase

see Polarity

eSATA

see SATA

SSD

see Solid-state Drive

SRA

see Stereo Recording Angle

SMPS

see Switching Power Supply

Tube

see Valve

Decibel

see dB