Masking, critical bands, and auditory filters

Define masking

the process in which one sound makes another sound more difficult to be hear or detected

Name the factors that influence masking

intensity

frequency

temporal characteristics

True or false: the initiation of effective masking level will plateau a threshold of a test signal

false; elevate a threshold of a test signal

Fill in the blank: once a masker attaints an effective level, there is a ________ relationship between masking and masker level

linear

intensity is independent from?

frequency

True or false: narrowband masking is frequency selective

true

Define upward spread of masking

increasing masking intensity affects higher frequencies more than the lows

What happens when the intensity of a masker increase?

more masking

more frequencies are masked

more upward spread of masking

What causes the upward spread of masking?

caused by the asymmetry of cochlear traveling wave and low frequency sounds can effectively mask high frequency sounds

Why can there be no downward spread of masking?

because of asymmetry of the cochlear traveling wave in the cochlea

Define critical bands

when the signal and masker are close enough in frequency and their traveling waves interact and create a more effective masking

Define equivalent rectangular bandwidth

the bandwidth of noise that is equivalent in total power to the amount of power that can pass through the auditory filter

Fill in the blank: bandwidth of the masker will elevate the threshold of the masked tone until critical band is ____________.

reached

Fill in the blank: increase in masker beyond the critical band will no longer affect the _________ _________.

tone perception

Define critical band theory

the bandwidth at which increasing the masker bandwidth no longer increases masking

True or false: frequencies outside of the critical band will not mask the signal

True :)

A signal is masked if?

power of the masker is greater than or equal to the power of the signal

A signal is not masked if?

power of the masker is less than the power of the signal

Define notched-noise method

a method that is used to estimate the shape of the critical bands

What is the procedure of the notch-noise method

two wideband noises with a spectral notch centered at the test tone frequency and the notch bandwidth is varied so that the threshold for the test tone can be measured

Fill in the blank: as the ______ notch widens, less noise passes through the critical band and threshold _________.

spectral

improves

The notched noise method can be used to determine what?

if critical bands are asymmetrical

Define auditory filters

a modern term used to describe frequency selectivity of human auditory system

Name the characteristics of auditory filters

rounded

asymmetric

level dependent

Name the characteristics of critical bands

rectangular

symmetrical

level independent

True or false: both auditory filters and critical bands show overlapping of the different regions of filters

TRUE

Define off frequency listening

a tone can be heard at its own auditory filter, but also at the tail of another auditory filter

Why does off frequency listening happen?

happens when the listener shifts to another auditory filter to improve signal to noise ration

True or false: auditory filter asymmetry decreases at higher stimulus level

false; increases

If we move the filter what happens?

it decreases the effects of the masker because it doesn’t take as much space on the bandwidth

Fill in the blank auditory filters measure at different __________ ___________.

stimulus levels

What type of bandwidth is this?

notch bandwidth

What type of bandwidth is this?

equivalent rectangular bandwidth

What type of filter is this?

auditory filter

What type of filter is this?

critical band

Name the different type of scales of filters

barker scale

equivalent rectangular bandwidth scale

Name some characteristics of the barker scale

24 critical bands in human hearing range

constant bandwidth below 500 Hz

bandwidth is approximately 1/3 octave above 500 Hz

Name some characteristics of the equivalent rectangular bandwidth

around 40 filters

has smaller bandwidth than bark scale

What scale is this?

ERB scale

True or false: the lower the frequency the more filters there are

false; higher

Define frequency lower amplification and why it is used?

it is in HAs so you can make sounds louder but it won’t be that much better because it is a dead region at the basal turn

Define a psychophysical tuning curve

a plot that shows the level of a masker needed to mask a signal as a function of the frequency of the masker

Fill in the blank: the physiological tuning curve does not require a ____________ _________

behavioral response

Define sensation level

10 dB about an individual’s threshold

What indicates a damaged auditory filter?

reduced number of auditory filters with greater bandwidth

OHC damage

decreased frequency selectivity

more asymmetry of auditory filter

more upward spread of masking

What is the auditory system’s version of the spectrum?

excitation pattern

The excitation pattern can be thought as what?

the output of the auditory filters plotted as a function of their center frequency

What does the excitation pattern show?

the degree to which different frequency components in complex sounds are resolved by the cochlea

What are the characteristics of excitation patterns in vowels?

input spectrum contain many harmonics

auditory filter output excitation pattern shows only the dominant harmonics

Fill in the blank: when there is noise there is less _________ excitation patterns

detailed

True or false: noise reduces the information available in the input spectrum

T r u e

Name the types of masking

simultaneous masking

temporal masking

• forward masking

• backward masking

What does this represent?

simultaneous masking

What does this represent?

forward or post-masking

What does this represent?

backward masking or pre-masking

Define forward masking

when the masking noise is played before the stimulus

Define backward masking

when the stimulus is played first and followed by the masking noise

Name some possible mechanisms of forward masking

peripheral and central processes such as ringing effect of the basilar membrane

Name some possible mechanisms of backward masking

central processes

Name some parameters that affect temporal masking

time gap between signal and masker

masker level

masker duration

Fill in the blank: pre-masking can occur up to ______ ms before masking noise starts

20

Fill in the blank: post-masking last up to _____ ms after masking noise stops

200

Forward masking can be found in?

cochlear implant patients

In forward masking higher quality factors can be found, why is this?

there is an absence of cochlear suppression

Fill in the blank: cochlear suppression can affect _______________ ___________ in simultaneous masking

psychophysical tuning curves

Where can two tone suppression be measured?

auditory nerve

Name some characteristics of two tone suppression

causes nonlinear response

depends of frequency and intensity

What effects will musical training have on forward and simultaneous masked psychophysical tuning curve?

musicians have better frequency selectivity in both forward and simultaneous masked psychophysical tuning curves