PURPOSE:To form a vector quantizer guaranteeing the asymtotic performance of a quantized vector with respect to an input vector by calculating the amplitude and retrieving a code vector for one stage only, and calculating the amplitude with respect to a code vector prepared in advance in response to the code vector of the 1st stage as to the calculation of the 2nd and succeeding stages. CONSTITUTION:Vector quantizers 2, 7-10 are connected in multi-stage by the number of dimensions of a vector, and the code vector is retrieved and its amplitude is calculated up to the number of optional stages of the vector quantizers 2, 7-10. Then the code vector prepared in advance is used in response to the representative code vector before the number of optional stages to calculate the amplitude after the number of optional stages, and the amplitude for the number of dimensions of the vector and the code vector index of the number of optional stages are subject to quantization. This method differs from a conventional technology in that a code vector prepared in advance in response to the representative code vector at a 1st stage 2 in the vector quantization on and after a 2nd stage 7 of the vector quantizer and the code vectors are set so as to form an orthogonal system. Thus, the asymtotic performance of the quantized vector with respect to the input vector is obtained.
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