LOW BIT-RATE PATTERN ENCODING AND DECODING WITH A REDUCED NUMBER OF EXCITATION PULSES

In an encoder operable in response to a discrete pattern signal divisible into a succession of segments to produce an output code sequence, a pitch parameter and a spectral parameter are extracted in a parameter calculator from each segment and from a spectral interval. In an excitation pulse producing circuit, each spectral interval is divided into a plurality of subframes, namely, pitch periods with reference to the pitch parameter to divide each segment. A minor group of excitation pulses is calculated from the segment at every subframe to form a major group of the excitation pulses in the spectral interval. The excitation pulses of the major group are reduced in number with reference to adjacent ones of the minor groups in each spectral interval and are modified into a succession of modified excitation pulses. The modified excitation pulses are combined with the spectral parameter into the output code sequence. In a decoder, the modified excitation pulses and the spectral parameter are extracted from the output code sequence. The pitch parameter is recovered by the use of the extracted and mofified excitation pulses and is used to produce a reproduction of the discrete pattern signal. Alternatively, the pitch parameter may be sent from the encoder together with the spectral parameter and the modified excitation pulses as the output code sequence and extracted from the output code sequence in the decoder.