Nippon Telegraph and Telephone Corporation

Hitoshi Ohmura

Takehiro Moriya

Shigeaki Sasaki

Kazunori Mano

Naoki Iwakami

Satoshi Miki

In a CELP coding scheme, p-order LPC coefficients of an input signal are transformed into n-order LPC cepctrum coefficients c.sub.j (S.sub.2), which are modified into n-order modified LPC cepstrum coefficients c.sub.j ' (S.sub.3). 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 corresponding orders of the LPC cepstrum coefficients is calculated, and the modification in step S.sub.3 is carried out on the basis of the relationship. The modified coefficients c.sub.j 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.

Growing community of inventors

Higashimurayama, Japan

Hitoshi Ohmura