Speech analyzer comprising circuits for calculating autocorrelation coefficients forwardly and backwardly

Abstract

A speech analyzer with improved pitch period extraction and improved accuracy of voiced/unvoiced decision comprises circuits for calculating autocorrelation coefficients forwardly and backwardly with respect to time. Reference members for the forward and the backward calculation are those successively prescribed ones of windowed samples of a signal representative of speech sound which are placed in each window period farther from a trailing and a leading end thereof, respectively. Members to be joined to the respective reference members for forward and backward calculation of each autocorrelation coefficient are displaced therefrom by a joining interval farther from the leading and the trailing ends, respectively. The joining interval is varied between a shortest and a longest pitch period of the speech sound stepwise by a spacing between two successive windowed samples. One of the joining intervals for which the greatest of the autocorrelation coefficients is calculated during each window period gives a better pitch period for that period than ever obtained. The circuits may comprise a circuit for calculating a rate of increase of an average power of the speech sound in each window period and an autocorrelator for carrying out the forward and the backward calculation when the rate is less and greater than a preselected value, respectively. Alternatively, the circuits may comprise two autocorrelators, one for the forward calculation and the other for the backward calculation.