Chapter 2 of Moore (1989)

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Chapter 3 of Moore (1997)

Frequency Selectivity (with Stress on the Concept of Masking)

Scope

Masking and the critical band (CB), the phenomenon and the theoretical implications
Fletcher's power spectrum model.
How we come about determining the CB? (Take note, you vision scientists!!)
The shape of the auditory filter
Masking v.s. excitation patterns
Mechanisms of masking

Masking, the Definition and the Phenomena

The process (or the amount) by which the threshold of audibility for one sound is raised by the presence of another (masking) sound.
Only when the target and the masker share some properties along some dimensions can the latter masks the former (in those dimensions). <demo>
Masking can occur when the target and the masker are arranged in various kinds of temporal order (forward, backward and simultaneous masking).

The Concept of CB, and How It Can be Revealed by Masking

The peripheral auditory system behaves as if it contains a bank of bandpass filters.
The passband of a given filter can be estimated by Fletcher's band-widening experiment. (See Fig. 3.1)

Fletcher's Power Spectrum Model

When detecting a tone, the listener makes use of the filter whose center frequency is close to that of a signal.
Only a narrow band of frequencies surrounding the tone-those falling within the CB-contribute to the masking of the tone.
When the noise just masks the tone, the power of the tone, P, divided by the power of the noise inside the CB is a constant, K. (Ring a bell? Fellows?)

Estimating the CB (1): Loudness of Complex Sounds

Increase the bandwidth of a complex sound while keeping its total power constant, one would detect a loudness increment when the bandwidth exceeds the CB of the filter responsible for detecting the complex. See Fig. 3.2.
The bending point gives an estimate of the CB.

Estimating the CB (2):Subthreshold Summation

In detecting a complex sound, at the threshold level each of the componets in the complex can still be well bellow its own threshold level provided the following is true:
Two tones can only be summed together when the spacing in their frequcies falls within the CB.
The maximum spacing in freq. beween two tones that still renders subthreshold summation gives an estimate of the CB.

Estimating the CB (3): Two Tone Masking
n Target: Narrow band noise (~1CB wide)
n Maskers: Two tone at either side of the target separated by f.
n When f is within a to-be-measured CB, the threshold of the target is constant. When f goes beyond the CB, the threshold of the target drops.

Estimating the CB (4): Sensitivity to Phase

AM and FM. What's the fuss about them?
Relative phase only counts when the two components of interest are being detected by the same filter. See Figs. 3.4 & 3.5

Estimating the CB (5): Hearing out Partials in a Complex Sound

Assumption: Subjects can only hear out a partial in a complex when the partial and its neighbours are detected by different filters.
There's a slight advantage for detecting partials close to the frequency edges of the complex.

Determining the Shape of a Given Filter

(Under Construction)

Mechanisms of Masking

(Under Construction)

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