Method for the modification of LPC coefficients of acoustic signals

Abstract

In a CELP coding scheme, p-order LPC coefficients of an input signal are transformed into n-order LPC cepctrum coefficients cj (S2), which are modified into n-order modified LPC cepstrum coefficients cj' (S3). Log power spectral envelopes of the input signal and a masking function suited thereto are calculated (Figs. 3B, C), then they are subjected to inverse Fourier transform to obtain n-order LPC cepstrum coefficients, respectively, (Figs. 3D, E), then the relationship between each corresponding orders of the both LPC cepstrum coefficients is calculated, and the modification in step S3 is carried out on the basis of the relationship. The modified coefficients cj are inversely transformed by the method of least squares into m-order LPC coefficients for use as filter coefficients of a perceptual weighting filter. This concept is applicable to a postfilter as well.