Patent ID: 6470312
Filing Date: 2002-10-22
Classification: G10L,H03M

Abstract:
A speech coding apparatus which performs speech coding based on a speech production model, where a speech signal is divided into fixed-length segments for processing purposes, the apparatus comprising:an adaptive codebook which stores a series of signal vectors of a past speech signal; vector extraction means for extracting a signal vector and neighboring vectors adjacent thereto from said adaptive codebook, the signal vector being stored at a distance given by a lag parameter from the top entry location of said adaptive codebook; a long-term prediction synthesis filter with a high order which produces a long-term predicted speech signal from the signal vector and the neighboring vectors by applying long-term prediction synthesis concerning the periodicity of the speech signal; filter coefficient calculation means for calculating filter coefficients of said long-term prediction synthesis filter; a perceptual weighting synthesis filter which processes the long-term predicted speech signal to yield a reproduced coded speech signal, comprising: a linear predictive synthesis filter defined through estimation with a linear predictive coding synthesis technique that emulates a vocal tract response, and a first perceptual weighting filter which is coupled in series with said linear predictive synthesis filter and assigns perceptual weights to a signal supplied thereto according to characteristics of a human hearing system; a second perceptual weighting filter which produces a perceptually weighted speech signal by assigning perceptual weights to the speech signal; error calculation means for calculating an error of the reproduced coded speech signal with reference to the perceptually weighted speech signal; minimum error detection means for finding a minimum error point that yields the smallest error among those that said error calculation means has calculated while varying the lag parameter; and optimal value transmission means for transmitting optimal values including optimal filter coefficients and an optimal delay, the optimal filter coefficients being the filter coefficients at the minimum error point, the optimal lag parameter being the lag parameter at the minimum error point.