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 .