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Frequency selectivity 2. Masking and the auditory filter. Masking. 60 dB SPL. 80 dB SPL. And he said, “ I know how to study the soul! ”. So on October 22, Fechner sat up in bed…. Definitions. Masking is the reduction in audibility of one sound caused by the presence of another sound.

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Frequency selectivity 2 l.jpg

Frequency selectivity 2

Masking and the auditory filter


Masking l.jpg
Masking

60 dB SPL

80 dB SPL

And he said, “I know how to study the soul!”

So on October 22, Fechner sat up in bed…


Definitions l.jpg
Definitions

  • Masking is the reduction in audibility of one sound caused by the presence of another sound.

  • The amount of masking is the difference between the threshold for the target sound with no masker and the threshold for the target sound with the masker.


Why does simultaneous masking occur l.jpg

swamping”

suppression

Why does simultaneous masking occur?



When a tone is masked by a broadband noise masked threshold l.jpg
When a tone is masked by a broadband noise, masked threshold

Increases slightly at higher probe frequencies

Decreases dramatically at higher probe frequencies

Is exactly the same at all probe frequencies

Can be lower than absolute threshold

0

Answer Now


Growth of simultaneous masking l.jpg
Growth of simultaneous masking

10 dB increase in masker level leads to a 10 dB increase

in masked threshold (amount of masking)

From Gelfand (1998)


What does a person do when they are trying to detect a tone in noise l.jpg
What does a person do when they are trying to detect a tone in noise?

Level

(dB)

1.0 1.1 1.26

Freq (kHz)

Relative

amplitude (dB)

794 1000 1260 1588

Frequency (kHz)


Masking and masker bandwidth l.jpg
Masking and masker bandwidth in noise?

Level

(dB)

Level

(dB)

25

25

1.0 1.1 1.26

1.0 1.1 1.26

Freq (kHz)

Freq (kHz)

Relative

amplitude (dB)

Relative

amplitude (dB)

794 1000 1260 1588

794 1000 1260 1588

Frequency (kHz)

Frequency (kHz)

Level

(dB)

25

Level

(dB)

25

1.0 1.1 1.26

1.0 1.1 1.26

Freq (kHz)

Freq (kHz)

Relative

amplitude (dB)

Relative

amplitude (dB)

794 1000 1260 1588

794 1000 1260 1588

Frequency (kHz)

Frequency (kHz)


Masking and the critical band l.jpg
Masking and the critical band in noise?

From Yost (1994)


Masking and the critical band11 l.jpg
Masking and the critical band in noise?

The filter through which we listen to sounds is called

the auditory filter.

From Gelfand (1998)


Masking and masker frequency l.jpg
Masking and masker frequency in noise?

Level

(dB)

1.0 1.1 1.26

Freq (kHz)

Relative

amplitude (dB)

794 1000 1260 1588

Frequency (kHz)


Masking and masker frequency13 l.jpg
Masking and masker frequency in noise?

Level

(dB)

1.0 1.1 1.26

Freq (kHz)

Relative

amplitude (dB)

794 1000 1260 1588

Frequency (kHz)


The frequency of the signal was l.jpg

0 in noise?

Answer Now

The frequency of the signal was

  • 250 Hz

  • 500 Hz

  • 1000 Hz

  • 2000 Hz


What is changing as the curve moves up to higher amounts of masking l.jpg

0 in noise?

Answer Now

What is changing as the curve moves up to higher amounts of masking?

  • The level of the signal

  • The frequency of the signal

  • The level of the masker

  • The frequency of the masker


Slide16 l.jpg

0 in noise?

Answer Now

When the masker frequency equals the signal frequency, increasing the level of the masker by 20 dB increases the amount of masking by

  • 5 dB

  • 10 dB

  • 15 dB

  • 20 dB


Slide17 l.jpg

0 in noise?

Answer Now

True or false?If the masker frequency does not equal the signal frequency, increasing the level of the masker by 10 dB increases the amount of masking by 10 dB

  • True

  • False



So far l.jpg
So far in noise?

  • Frequency selectivity gives us a good representation of the amplitude spectrum and helps us to hear what we want to hear in noisy conditions.

  • Cochlear filtering is reflected in some neurons throughout the auditory pathway.

  • Masking is the reduction in audibility in one sound caused by the presence of another sound.


So far continued l.jpg
So far (continued) in noise?

  • In general, a 10 dB increase in masker level leads to a 10 dB increase in simultaneous masking.

    • but this only works if the signal frequency is part of the masker

  • In a broadband masker, only the band of noise around the signal frequency does the masking.

  • Then-- psychophysical tuning curves


Another masking experiment l.jpg

20 in noise?

?

20

?

Level (dB SPL)

Level (dB SPL)

1000 1200

800 1000

Frequency (Hz)

Frequency (Hz)

Another masking experiment

masker

masker

probe

probe

?

Masker level (dB SPL)

1000

Masker frequency (Hz)


Psychophysical tuning curve the auditory filter l.jpg
Psychophysical tuning curve in noise?(the auditory filter)

From Yost (1994)



Masking and masker frequency24 l.jpg
Masking and masker frequency than high mask low

Level

(dB)

1.0 1.1 1.26

Freq (kHz)

Relative

amplitude (dB)

794 1000 1260 1588

Frequency (kHz)


Masking and masker frequency25 l.jpg
Masking and masker frequency than high mask low

Level

(dB)

1.0 1.1 1.26

Freq (kHz)

Relative

amplitude (dB)

794 1000 1260 1588

Frequency (kHz)


Which would mask a 1000 hz tone at the lowest level l.jpg

1000-Hz tone than high mask low

500-Hz tone

2000-Hz tone

0

Answer Now

Which would mask a 1000 Hz tone at the lowest level?


Which would mask a 1000 hz tone at the lowest level27 l.jpg
Which would mask a 1000 Hz tone at the lowest level? than high mask low

2000-Hz tone

500-Hz tone

4000-Hz tone

0

Answer Now


Is the auditory filter the peripheral filter l.jpg
Is the auditory filter the peripheral filter? than high mask low

From Yost (1994)


Off frequency listening l.jpg
Off-frequency listening than high mask low

From Gelfand (1998)


Slide30 l.jpg
So... than high mask low

  • Psychophysical tuning curve and critical bandwidth measures of frequency resolution don’t control for off-frequency listening.

  • (People will use whatever information is available to them to detect that tone.)


Auditory filter width experiment l.jpg
Auditory filter width experiment than high mask low

Notchednoise

Filter we’re

measuring

From Moore (1997)


Narrow v broad filters l.jpg
Narrow v. broad filters than high mask low

Threshold (dB SPL)

Notch width (Hz)


Narrow v broad filters33 l.jpg
Narrow v. broad filters than high mask low

Threshold (dB SPL)

Notch width (Hz)


Thresholds at different notch widths l.jpg
Thresholds at different notch widths than high mask low

BROAD

NARROW

From Patterson et al. (1982)


The auditory filter l.jpg
The auditory filter than high mask low

Attenuation (dB)

Notch width

From Moore (1997)


What would happen to the auditory filters of a person who lost his outer hair cells l.jpg

They wouldn than high mask low’t change

They would get broader

They would get narrower

0

Answer Now

What would happen to the auditory filters of a person who lost his outer hair cells?


Effects of cochlear hearing loss on auditory filters l.jpg
Effects of cochlear hearing loss on auditory filters than high mask low

Normal

Impaired

From Glasberg & Moore (1985)


Auditory filter width v critical bandwidth l.jpg
Auditory filter width v. than high mask lowcritical bandwidth

From Moore (1997)


Conclusions l.jpg
Conclusions than high mask low

  • The results of masking experiments suggest that the auditory filter is established in the inner ear.

  • The width of the auditory filter largely determines how well we can hear sounds in noise (which is almost always).

  • People will use whatever information is available to them, even when the task is as trivial as detecting a tone.


Text sources l.jpg
Text sources than high mask low

  • Gelfand, S.A. (1998) Hearing: An introduction to psychological and physiological acoustics. New York: Marcel Dekker.

  • Glasberg, B. & Moore, B.C.J. (1985). Auditory filter shapes in subjects with unilateral and bilateral cochlear impairments. J. Acoust. Soc. Am., 79(4), 1020-1033.

  • Moore, B.C.J. (1997) An introduction to the psychology of hearing. (4th Edition) San Diego: Academic Press.

  • Patterson, R.D., Nimmo-Smith, I., Weber, D.L., & Milroy, R.. (1982). The deterioration of hearing with age: Frequency selectivity, the critical ratio, the audiogram, and speech threshold. J. Acoust. Soc. Am., 72, 1788-1803.

  • Yost, W.A. (1994) Fundamentals of hearing: an introduction. San Diego: Academic Press.


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