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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

Frequency selectivity 2

Masking and the auditory filter

masking
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
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.
when a tone is masked by a broadband noise masked threshold
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
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
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
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 band11
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
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
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

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

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

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

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
so far
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
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

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)

masking and masker frequency24
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
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 level27
Which would mask a 1000 Hz tone at the lowest level?

2000-Hz tone

500-Hz tone

4000-Hz tone

0

Answer Now

off frequency listening
Off-frequency listening

From Gelfand (1998)

slide30
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
Auditory filter width experiment

Notchednoise

Filter we’re

measuring

From Moore (1997)

narrow v broad filters
Narrow v. broad filters

Threshold (dB SPL)

Notch width (Hz)

narrow v broad filters33
Narrow v. broad filters

Threshold (dB SPL)

Notch width (Hz)

thresholds at different notch widths
Thresholds at different notch widths

BROAD

NARROW

From Patterson et al. (1982)

the auditory filter
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
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
Effects of cochlear hearing loss on auditory filters

Normal

Impaired

From Glasberg & Moore (1985)

conclusions
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
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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