Module 4: Loudness and Intensity Coding

threshold of audibility

the smallest level required for a listener to detect the presence of a sound

sensitivity to frequency

for very low and very high frequencies, the auditory system is NOT sensitive

MAF Thresholds

sound pressure levels for pure tone at absolute threshold measured in a free field, determined for listeners facing the speakers, listening with both ears at one meter from the speakers

after determining the threshold, subject leaves the room, a microphone is placed where the listeners head was to calibrate the threshold sound pressure, which are then converted to dB

MAP Thresholds

sound pressure levels for pure tone at absolute threshold measured at the level of tympanic membrane, obtained by presenting sounds over earphones (mono-aural) to listeners

after determining the threshold, the pressure that corresponds to the threshold is measured in a test cavity or coupler attached to the earphone during calibration

Shape of MAP and MAF

shape is the same

Reduced sensitivity on MAF and MAP can be found at ______ and ______

above 4000 Hz and below 1000 Hz

Sensitivity is the same/not the same across frequencies

not the same

Threshold of pain/feeling is around ___ dB in the ____ frequency region and ____ at ___ and ___ frequencies

120

mid

decreases

low and high

RETSPL

for a particular earphone and coupler combination, the threshold SPL measured in the coupler is called the Reference Equivalent Threshold Sound Pressure Levels

Standardized RETSPL

levels in dB SPL required for threshold detection of different frequencies presented via different earphones and calibrated with the appropriate coupler

a complete picture of auditory capability can be obtained by measuring….

the resolution of intensity at different frequencies and the resolution of frequency at different intensities

difference limen

smallest perceptible intensity difference or smallest change

tells us the dB difference required to determine that two tones are different

intensity difference limen or difference limen for intensity (DLI) or just noticeable difference for intensity

weber fraction (relative difference)

differential threshold can be expressed in terms of proportional or relative change

renders differential sensitivity as a ratio or percentage

JND for intensity (ΔI) / intensity (I)

has no unit

equal loudness contours

perceptional quantity most related to sound intensity, fitting formulas are based on these

vary the level of one sound until it seems as loud as another sound

curves connecting the pure tones of equal loudness, all matched to a 1000 Hz

loudness level unit

phon

phons vary depending on…

the transducer, frequency

all tones are judged to be equal in _______ although they differ in _____

loudness

SPL

at ____ intensity levels, equal loudness contours are similar to that of _____

lower

MAF

the loudness curve _____ slightly at _____ frequencies

flattens

higher

at _____ intensities, shape of ______ does not change very much

higher

loudness

the growth of loudness is ____ at ____ frequencies than at high frequencies, more nerve fibers at _____ frequencies

greater

low

low

phon curves do not show…

how loudness is related to intensity or how loudness changes with level

one way to measure loudness

present two sounds and ask the listener to give a number corresponding to how much louder one sound seems than the other (magnitude estimation)

sone scale

the loudness-intensity relationship scale

sone

unit of loudness

1000 Hz tone at 40 dB

sone scale expresses loudness as…

ratios

steven’s power law

the magnitude of perception is equal to the power of the magnitude of the stimulus

a slope of one means that the perception has a one-to-one relationship with the size of the stimulus

loudness has a slop of 0.6 which means the loudness increases at a slower rate as the intensity increases

sound intensity that exists on the basilar membrane is maintained where?

at the level of the central auditory nervous system

both the BM response function and the loudness growth function are ____ at low levels than they are at higher levels when plotted on a ______ scale

steeper

logarithmic

loudness matching

frequency

bandwidthd

effect of frequency

the loudness curve flattens slightly at higher frequencies

at higher intensities, loudness does not vary much

growth of loudness with level is greater at low-frequencies than at high frequencies

low intensity perception is different than high intensity

effect of bandwidth

increasing the overall bandwidth of a noise with fixed overall level of a noise results in an increase in loudness

loudness is related to the total activity of the basilar membrane

effect of duration

temporal summation

the longer duration → louder perception

intensity coding and the auditory system

most fibers in the auditory nerve show a background level of firing called spontaneous activity

most fibers have high spontaneous rates, producing about 60 spikes per second when no sound is present

these fibers ten to be quite sensitive and show an increase in firing rate in response to a low stimulus level

the remainiing fibers have low spontaneous rates of less than about 10 spikes per second, these fibers tend to be less senstiive

high spontaneous rate fibers have steeper rate-level functions that saturate at a much lower level (no more than about 40 dB SPL in the mid-frequency region) than do low spontaneous (high intensity) rate fibers