Multi-pulse type coding system with correlation calculation by backward-filtering operation for multi-pulse searching

Claim 1

A multi-pulse type coding system for coding a speech signal into a plurality of pulse signals, comprising: means for producing one set of parameters indicative of a spectral envelope of said speech signal for each search frame period; means, coupled to said parameter producing means and responsive to a plurality of sets of parameters, each of said sets of parameters belonging to adjacent search frame periods, for producing a plurality of sets of interpolated parameters during each search frame period; means for extracting a segmented speech signal from said speech signal and for delivering said segmented speech signal in backward time sequence, said segmented speech signal having a period corresponding to said each search frame period; means for filtering said segmented speech signal in accordance with a filtering characteristic defined by said set of parameters and said plurality of sets of interpolated parameters during said each search frame period and for directly producing a cross-correlation signal representative of a transition of cross-correlation between said segmented speech signal and an impulse response defined by said set of parameters and said sets of interpolated parameters during said each search frame period, said filtering characteristic being varied during said each search frame period in accordance with a backward time sequence of said set of parameters and said plurality of interpolated parameters, said segmented speech signal being received in backward time sequence; and means for generating said plurality of pulse signals in response to said cross-correlation signal.