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Figure 3.4 Critical Bandwidths of the Ear (Kinsler et al., 1982)

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can have a region of influence on a higher pitched sound, but not vice versa unless the sounds are quite close in frequency.

The phenomenon of critical bands is of great significance for many aspects of human hearing. They play a role in music by defining regions of consonance and dissonance. They influence the calculation of loudness by determining the method of combination used for multiple tones. They are critical to the phenomenon of masking, explaining many of the varied masking experiments.

Consonance and Dissonance

When two tones are played together, there is a frequency range over which they sound rough or dissonant (Fig. 3.5). Hermann von Helmholtz in his famous book, On the Sensations of Tone, hypothesized that the phenomenon of consonance was closely related to the frequency separation of tones and their harmonics. He thought that when two tones or their partials had a difference frequency of 30 to 40 Hz, this caused unpleasant beats. Subsequent experiments by Plomp and Levelt (1965) added some additional factors to his hypothesis.

Plomp's experiments revealed that the maximum dissonance occurs at about 25% of the critical bandwidth. Figure 3.6 gives a graph of consonance and dissonance as a function

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