VECTOR QUANTIZER, VECTOR INVERSE QUANTIZER, AND METHODS THEREFOR

Disclosed is a vector quantizer capable of improving the quantization accuracy of vector quantization to switch over the codebook of the vector quantization of a first stage depending on the type of feature having a correlation with a vector to be quantized. In the quantizer, a classifier (101) selects a classification code vector indicating the type of feature having the correlation with the vector to be quantized from a plurality of classification code vectors. A switch (102) selects a first codebook corresponding to the type from a plurality of first codebooks. An error minimizing section (105) selects a first code vector closest to the vector to be quantized from a plurality of first code vectors constituting the selected first codebook. An additivity factor determining section (106) selects an additivity factor vector corresponding to the type from a plurality of additivity factor vectors. The error minimizing section (105) selects a second code vector closest to the residual vector between the selected first code vector and the vector to be quantized from a plurality of second code vectors by using the selected additivity factor vector.