Complex sounds and critical bands.

Studies of the responses of human observers to bands of noise and other complex sounds have led to the measure of what appears to be a basic unit of hearing, the critical band. When the frequency spectrum of a stimulating sound is narrower than the critical band, the ear reacts one way; when the spectrum is wider, it reacts another way. For example, experiments show that at values less than the critical bandwidth, both loudness and absolute threshold are independent of bandwidth; only when the critical bandwidth is exceeded do the loudness and the absolute threshold increase with the width (Gassier, 1954; Zwicker & Feldtkel