Critical bands

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Critical bands are frequency ranges in which one pitch will mask another pitch. Critical bands occur because a wave striking the basilar membrane disturbs the membrane over a small area beyond the point the wave strikes, exciting the nerve endings over that entire area. Thus, frequencies close to the original frequency do not affect the sensation of the loudness of the sound much, even if the intensity of the sound is thereby doubled.

The sensation of loudness is not affected in this way when a frequency outside the critical band is added to the mix.

[edit] See also

Loudness
Psychoacoustics, especially Masking effects

As an example, the perceived loudness of a narrow band noise source at constant sound pressure level remains constant initially as the bandwidth is increased gradually. Beyond a certain bandwidth, the loudness begins to increase significantly. The bandwidth at this point is known as the critical bandwidth.