SPEECH CODING METHOD AND SYSTEM

A speech coding method which can code a speech. An autocorrelation of a synthesis signal synthesized from a codevector of an excitation codebook and a linear predictive parameter of an input speech signal is corrected using an autocorrelation of a synthesis signal synthesized from a codevector of an adaptive codebook and the linear predictive parameter and a cross-correlation between the synthesis signal of the codevector of the adaptive codebook and the synthesis signal of the codevector of the excitation codebook. A gain codebook is searched using the corrected autocorrelation and a cross-correlation between a signal obtained by subtraction of the synthesis signal of the codevector of the adaptive codebook from the input speech signal and the synthesis signal of the codevector of the excitation codebook.