Sound signals undergo a series of complex transformations in the early auditory system which convert the acoustic spectrum of the stimulus into an internal spectral representation, the auditory spectrum. Extensive analytical and experimental investigations [. shamma 1989 robust, Hubbard Mountain 1996,ghitza 1988.] have demonstrated the noise-robustness and perceptual relevance of the auditory spectrum. In fact, many unique features of auditory spectral analysis have already greatly influenced the design of sound detection, analysis, and recognition systems, such as the use of pseudo-logarithmic frequency axis, critical bands, and adaptive and/or automatic gain control mechanisms.