Comb filter speech coding with preselected excitation code vectors

Abstract

In a code excited speech encoder, an input speech signal is segmented into speech samples at first intervals and a spectral parameter is derived from the speech samples that occur at second intervals longer than the first intervals, the spectral parameter representing the characteristic spectral feature. Each speech sample is weighted with the spectral parameter for producing weighted speech samples. The pitch period of the speech signal is determined from the weighted speech samples. A predetermined number of excitation code vectors having smaller amounts of distortion are selected from excitation codebooks as candidate code vectors. The candidate vectors are comb-filtered with a delay time set equal to the pitch period. One of the filtered code vectors having a minimum distortion is selected. The selected filtered code vector is calculated for minimum distortion and, in response thereto, a gain code vector is selected from a gain codebook. Index signals representing the spectral parameter, the pitch period, the selected excitation and gain code vectors are multiplexed for transmission or storage.