Kutzner D.

This article is concerned with a new model of the sound envelope analysis in the auditory system. The basis of the model is the classical modulation filters concept, MFB, which assumes that there is some kind of a spectral analysis of the sound envelope at the higher stages of the auditory system. The MFB is thought to be a set of linear, band-pass, overlapping filters which are tuned to different envelope changes. In other words, it is assumed that there are two filtering stages in the auditory system: the auditory filters functioning in the audible frequency domain and the modulation filters which work analogously to the cochlear filters, but in the modulation rate domain. Despite this theory of the auditory amplitude modulation processing, the model proposed by the author argues that the hypothetical modulation filters, if they existed, could not be band-pass systems. This is due to the fact, that the sound envelope (the modulus of the so-called analytic signal) and its neural representation (period histogram of action potentials), are non-negative functions. Therefore, the impulse response of the hypothetical modulation filters, should be also non-negative signal. Such filters have been called as non-negative impulse response, NNIR, modulation filters. Consequently, due to a strong DC-component of the impulse response, the frequency characteristics of the modulation filters should not be purely band-pass functions and the MFB could be composed of some pseudo-filters of combined transfer functions. The results of the model investigation are compared to the outcomes of psychoacoustical measurements related to modulation masking phenomenon. The effect of tuning in the modulation rate domain was examined and simulated for various carriers and stimulus duration. A high correlation between the results of the model and empirical investigations was found.