| 摘要 |
An improved excitation signal in a low bit-rate coding device for coding a discrete speech signal sequence into an output code sequence for use in exciting a synthesizing filter, an autocorrelation function of an impulse response calculated for the synthesizing filter by using a parmeter sequence representative of a spectral envelope of the segment and a cross-correlation function between the segment and the impulse response are used to produce a sequence of excitation pulses by successively deciding locations and amplitudes of the pulses with the location of a currently processed pulse decided by the use of the locations and the amplitudes of previously processed pulses and with renewal of the previously processed pulse amplitudes carried out concurrently with decision of the currently processed pulse amplitude by the use of the previously and currently processed pulse locations. Alternatively, the currently processed pulse location and the previously and currently processed pulse amplitudes are decided by the use of the previously processed pulse locations. The parameter and the excitation pulse sequences are coded and then combined into the output code sequence. The correlation functions are preferably calculated with the segment and the impulse response weighted by weights dependent on the parameter sequence. The segment may be a frame of the speech signal sequence or a subframe of a constant or variable length.
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