Method and apparatus for converting a digital speech signal into linear prediction coding parameters and control code signals and retrieving the digital speech signal therefrom

Abstract

Analog speech signals are coded as digital signals before transmission over a transmission medium and then are decoded at their destination. The coder is of the linear predictive type (LPC) and includes an LPC analyzer for adjusting an analysis filter, which receives the digital signal and generates a residual signal representative of error content. The parameters by which the filter is adjusted by the analyzer and the residual signal together represent the digital signal. The residual signal is split into segments and, per segment, several first pulse train signals are generated, each having a different starting time position within the segment. The first pulse train signal which is most closely related to the residual signal is selected and compared to second pulse train signals stored in a codebook. A location in the codebook belonging to a second pulse train signal that exhibits the greatest degree of correspondence to the selected first pulse train signal and the starting position of the selected first pulse train signal, together, represent the residual signal and are transmitted into and through the transmission medium in addition to the LPC parameters. At the receiving location a synthesizer filter is controlled by a modified output of a duplicate codebook.