<P>PROBLEM TO BE SOLVED: To provide an optimal speech codec for solving the problem that, it is often difficult to suitably make a model of noise in a conventional method for encoding noise, resulting in undesirable interrupt, discontinuity, and during conversation, and that background noise is not suitably encoded in a speech encoder of analysis by synthesis, like a conventional code-excited linear predictive encoder particularly in a reduced bit rate. <P>SOLUTION: A speech signal is analyzed by speech sample, and parameters of CELP (code-excited linear prediction) model, that is an LP filter coefficient, and adaptive and fixed code book indexes and a gain are extracted. These parameters are encoded and transmitted. LP analysis are performed twice by frame in Block 239, and only a single LP parameter set is converted to a quantized vector by using line spectrum frequency (LSF) and predictive multi-stage quantization (PMVQ). <P>COPYRIGHT: (C)2010,JPO&INPIT 
CODEBOOK SHARING FOR LINE SPECTRUM FREQUENCY QUANTIZATION