Vocoder system and method for performing pitch estimation using an adaptive correlation sample window

Abstract

An improved vocoder system and method for estimating pitch in a speech waveform. The method comprises an improved correlation method for estimating the pitch parameter which more accurately disregards false correlation peaks resulting from the contribution of the First Formant to the pitch estimation method. The vocoder performs a correlation calculation on a frame of the speech waveform to estimate the pitch of the frame. According to the invention, during the correlation calculation the vocoder performs calculations to determine when a transition from unvoiced to voiced speech occurs. When such a transition is detected, the vocoder widens the correlation sample window. The present invention thus determines when a transition from unvoiced to voiced speech occurs and dynamically adjusts or widens the sample window to reduce the effect of the First Formant in the pitch estimation. Once this frame and the next have been classified as voiced, the correlation sample window can be reduced to its original value. Therefore, the present invention more accurately provides the correct pitch parameter in response to a sampled speech waveform.