Modeling the precedence effect for speech using the gamma filter

The ability of the human auditory system to localize the direction of a sou nd source in a reverberant environment extends from simple clicks to comple x speech signals. The perceived location of the auditory event is dominated by the direct sound, for small enough rime intervals between the direct so und and reflection-a phenomenon known as the precedence effect. In this pap er we present a computer simulation of the precedence effect for speech, im plemented using Matlab and tested with speech signals from the TIMIT databa se. The model is based on the biological assumption that the rate of change of a signal (onset) is critical in triggering the precedence effect. The m odel demonstrates the precedence effect on speech signals, as opposed to pr ior models that have only been tested on clicks. In addition, a novel onset enhancement method is described and implemented using the gamma filter, a new class of linear systems for adaptive signal processing. This method can either use fixed coefficients and obtain similar results to prior methods of onset enhancement, or use an adaptive framework. The adaptive framework is promising in its ability to enhance onsets and to reduce the steady stat e portions of the signal. (C) 1999 Elsevier Science Ltd. All rights reserve d.