Celp-type speech encoder having an improved long-term predictor

Abstract

A speech signal encoder includes a speech analyzer for determining short-term prediction codes at a predetermined time interval. The prediction codes indicate frequency characteristics of a speech signal. A reverse filter is provided for calculating residual signals of first synthesis filter. The residual signals are defined by the short-term prediction codes. A residual code book stores past residual signals. Further, a plurality of delay codes, each of which represents pitch correlation of the speech signal, are predetermined. A vector generator issues, using the residual code book, delay residual vectors each of which corresponds to the delay code. A filter is provided for generating a synthesis signal using second synthesis filter which receives the delay residual vectors and which is defined by the short-term prediction codes. A distance between the speech signal and the synthesis signal is calculated. Subsequently, a pitch path estimator estimates a pitch path which varies smoothly. The pitch path thus estimated is used for determining a delay code.