Low-delay vector backward predictive coding of speech

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A method of encoding speech sounds to facilitate their transmission to and reconstruction at a remote receiver. A transmitter and a receiver have identical filters and identical codebooks containing prestored excitation vectors which model quantized speech sound vectors. The speech sound vectors are compared with filtered versions of the codebook vectors. The filtered vector closest to each speech sound vector is selected. During the comparison, filtration parameters derived by backward predictive analysis of a series of previously selected filtered codebook vectors are applied to the filter. The transmitter sends the receiver an index representative of the location of the selected vector within the codebook. The receiver uses the index to recover the selected vector from its codebook, and passes the recovered vector through its filter to yield an output signal which reproduces the original speech sound sample. By applying the same backward predictive analysis technique employed by the transmitter to the same series of previously selected filtered codebook vectors to which the transmitter applied the technique, the receiver derives the same combination of filtration parameters which the transmitter applied to its filter while selecting the codebook vector corresponding to the transmitted index.