Physics Of Music Test 2

Attack and Decay

How quickly a sound rises and falls

Outer Ear

Sound energy spreads out from its sources; it spreads out according to the inverse square law; it acts as a preamp to enhance the sensitivity of hearing

What is a vocal Formant?

set of frequencies and harmonics (with varying amplitudes) that have a particular overall shape or envelope. So, even when the sound is spoken at different frequencies, the overall envelopes are similar and are recognized as the same sound.

What is the reason for the shortcomings of the decibel system?

the human ear doesn't respond equally to diff frequencies; it responds differently to high and low frequencies

Cochlea

the inner ear structure; a snail-like shel structure divided into 3 fluid filled parts. Two are canals for the transmission of pressure; the Organ of Corti is in the 3rd one

Pitch/Frequency

the perceived pitch of a sound is the ear's response to frequency

Ossicles

the three tiniest bones in the body form the coupling between the vibration of the eardrum and the forces exerted on the oval window of the ear; hammer, anvil and stirrup

Place Theory

*theory of hearing: our perception of sounds depends on where each component frequency produces vibrations along the basilar membrane *low frequencies vibrate the basilar membrane and lower frequencies travel further along the membrane before causing excitement of the membrane *unrolls the cochlea and reps the distribution of sensitive hair cells on the Organ of Corti

Three components of timbre

1. attack and decay 2. harmonic content 3. vibrato/tremolo

Proposed mechanisms for sharpening pitch perception

1.bring the peak of the excitation pattern on the basilar membrane into greater relief by inhibiting the firing of those hair cells which are adjacent to the peak 2. Since nerve cells obey an "all-or-none" law, discharging when receiving the appropriate stimulus and then drawing energy from the metabolism to recharge before firing again, one form the lateral inhibition could take is the inhibition of the recharging process since the cells at the peak of the response will be drawing energy from the surrounding fluid most rapidly 3. Inhibition of the lateral hair cells could also occur at the ganglia, with some kind of inhibitory gating which lets through only those pulses from the cells which are firing most rapidly

What is the threshold of hearing?

10-12 watts/m2; the sound level below which a person's ear is unable to detect any sound

Because of the ear's differing sensitivity, a bass musical note at 40 Hz must be about 40 decibels more intense than a 1000 Hz tone to be perceived as equally loud when they are played very softly. However, if both sounds are very loud, the ear's response is more nearly equal and the 40 Hz tone need be only 10 dB more intense to be perceived as equally loud. What is the numerical ratio of the intensities in each case? For soft sounds the low tone must be _________ times as intense, whereas for the loud sounds it must be only _________times as intense.

40dB=10 log (I/I0) 4=log I/I0 10^4 I/I0=1 10

A sound with loudness 90 phons is how many times as loud as a 60 phon sound?

90-60=30 30=10log (I/I0) 3=log (I/I0) 10^3 dB

A sound with intensity 90 dB is how many times as intense as a 60 dB sound?

90-60=30 30=10log (I/I0) 3=log I/Io 10^3 dB

How do you get around these shortcomings?

ABC Filters

Quality

Characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness

Components which amplify sound? How?

Closed tube resonance of the auditory canal enhances 2000-5000 Hz (air columns); Tympanic membrane (eardrum) has some 15x area of oval window contributing an area of amplification; ossicles (hammer, anvil and stirrup) contribute a lever-type amp when listening to soft sounds

Intensity in the decibel scale

Decibels measure the ratio of a given intensity I to the threshold of hearing intensity , so that this threshold takes the value 0 decibels (0 dB)

Loudness/Intensity

Loudness: the subjective response of the human ear Intensity: an objective measurement of wave energy

Protective mechanisms of the ear

Muscle tension tightens the tympanic membrane and, acting through the tendon connecting the hammer and the anvil, repositions the ossicles to pull the stirrup back, lessening the transfer of force to the oval window of the inner ear

Harmonic Content

The number and relative intensity tof the upper harmonics present in the sound; the ratio of sums of the powers of all harmonic components to the power of the fundamental frequency

Critical band

When two sounds of equal loudness when sounded separately are close together in pitch, their combined loudness when sounded together will be only slightly louder than one of them alone. They may be said to be in the same critical band where they are competing for the same nerve endings on the basilar membrane of the inner ear

Fast Fourier Transform

a mathematical method for transforming a function of time into a function of frequency

Vibrato

a rapid variation in pitch in singing/instruments producing a strong/richer tone

Tremolo

a wavering effect in a musical tone, produced by a reiteration of a note or by a repeated variation in the pitch of a note

Auditory Canal

acts as a closed tube resonator, enhancing sounds in the range 2000-5000 kHz

Geometric Waves

an electronically generated wave consisting of many harmonics (square, triangle and sawtooth waves)

B Filter

approx the ear for medium loud sounds (rarely used)

Semi-circular Canals

balance organs, detecting acceleration in the three perpendicular planes; hair cells detect movements of the fluid in the canals caused by angular acceleration about an axis perpendicular to the plane of the canal; tiny floating particles aid the process of stimulating the hair cells as they move with the fluid. The canals are connected to the auditory nerve

How might you artificially (electronically) create a sound using geometric waves?

by adding, subtracting and changing the amplitude of the harmonics

A classroom when no one is speaking 1,000,000 I0

dB=10log (1,000,000) db=10x6 60dB

Hearing tests compare your hearing to an average threshold of hearing for the population. If a person has to increase the intensity to 100 times the average threshold of hearing, what would be his hearing loss expressed in decibels below normal?

dB=10log (100) dB=10x2 20dB

Sound at your open window on the expressway when a truck roars by next to you 100,000,000,000 I0

dB=10log (100,000,000) dB=10x11 dB=110dB

Joe had his hearing tested and was alarmed when he was told that a certain frequency had to be boosted by a factor of 1000 above the normal threshold for him to hear it. What is Joe's hearing loss in decibels at that frequency? (Hearing aids are generally not prescribed unless hearing loss exceeds about 40 dB.). Would Joe need a hearing aid?

dB=10log (1000) dB=10x3 30dB He wouldn't need a hearing aid

Decibel Scale

dB=10log (I/I0) I0=threshold of hearing

Organ of Corti

detects pressure impulses and responds with electrical impulses which travel along the auditory nerve to the brain

C Filter

doesn't filter as much of the lows and highs as the others; approx the ear at very high sound levels and used for traffic noise surveys in noisy areas

A Filter

filters out more bass than others; designed to approx the ear at 40 phon level; useful for eliminating inaudible low frequencies

What happens to a vowel sound if the pitch is changed?

frequency ranges where the sound is enhanced by the cavity resonances of the human vocal mechanism

Rule of thumb for Loudness

intensity goes up by a factor of 10 to increase loudness by a facto of 2

Temporary Threshold Shifts

loss of hearing; a particular sound would have to be more intense for the person to hear it; can happen temporarily after hearing loud noises.

Intensity measured in phons

phon scale is modified to match the response of the human ear

Phone Scale

phons measure loudness

Tympanic Membrane (eardrum)

receives vibrations from the auditory nerve and transfers them through the ossicles to the oval window

Effects of loud sounds

temporary loss of hearing; results aren't clear if you have hearing loss

Timbre

term for the distinguishable characteristics of a tone

Fourier Transform

the extraction of the series of sines and cosines which when superimposed will produce the unction.

How do we perceive diff vowel sounds spoken at the same pitch?

the vowels differ in distribution of harmonic -formants. The ear according to place theory can detect various harmonics and amplitudes