From Hydrogenaudio Knowledgebase
Human hearing system processes perceived sound in non-equal width subband called critical bands. In each critical band sound is analysed independently. Each band corresponds with an equal section of cochlea (about 1.3 mm). Critical band width differs within the frequency range. Below 500Hz bandwidths are constant, equal 100Hz. over 500Hz the width of each next critical band is 20% larger than that of the band below. See also bark.