Predictive coding of pitch lag in a speech coder

摘要

A speech coding device capable of delivering a speech signal of excellent sound quality at a low bit rate is disclosed. The disclosed device is characterized by a method of calculating lag corresponding to pitch period and a speech signal coding method. Lag is calculated as follows: A speech signal is divided into frames; one- frame is divided into a plurality of subframes; for each frame, subframes in which lag of a speech signal is expressed in the form of a differential relative to lag of a previous subframe and subframes in which lag is expressed in the form of an absolute value, i.e., the lag value itself, are established; a plurality of bit allocation patterns are established for each frame that allocate bits for expressing lag as an absolute value or a differential in each of the plurality of subframes; for each bit allocation pattern, pitch predictive distortion is calculated for every subframe; accumulated distortion is calculated by accumulating the pitch predictive distortion over a predetermined plurality of subframes in the frame; a bit allocation pattern is selected so as to minimize the accumulated distortion. The lags in the subframes of the selected pattern are determined as the lags in the subframes of interest.