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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

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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?


Characteristics of simultaneous masking l.jpg

Characteristics of simultaneous masking

From Gelfand (1998)


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

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

From Yost (1994)


Masking and the critical band11 l.jpg

Masking and the critical band

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

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

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

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

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

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

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


Compressive response at best frequency l.jpg

Compressive response at best frequency


So far l.jpg

So far

  • 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 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

?

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(the auditory filter)

From Yost (1994)


Upward spread of masking low frequencies mask high more than high mask low l.jpg

Upward spread of masking: low frequencies mask high more than high mask low

From Yost (1994)


Masking and masker frequency24 l.jpg

Masking and masker frequency

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

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

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?

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?

From Yost (1994)


Off frequency listening l.jpg

Off-frequency listening

From Gelfand (1998)


Slide30 l.jpg

So...

  • 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

Notchednoise

Filter we’re

measuring

From Moore (1997)


Narrow v broad filters l.jpg

Narrow v. broad filters

Threshold (dB SPL)

Notch width (Hz)


Narrow v broad filters33 l.jpg

Narrow v. broad filters

Threshold (dB SPL)

Notch width (Hz)


Thresholds at different notch widths l.jpg

Thresholds at different notch widths

BROAD

NARROW

From Patterson et al. (1982)


The auditory filter l.jpg

The auditory filter

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’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

Normal

Impaired

From Glasberg & Moore (1985)


Auditory filter width v critical bandwidth l.jpg

Auditory filter width v.critical bandwidth

From Moore (1997)


Conclusions l.jpg

Conclusions

  • 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

  • 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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