A 5.6 kb/s speech codec using a pulse codebook and improved Viterbi decoding

A low bit-rate speech codec has been developed. The speech coder employs a PCELP (CELP with pulse codebook) algorithm, which uses a pulse-train excitation codebook to enhance the quality of voiced speech. The computational complexity for the pulse codebook search is greatly reduced by using truncated impulse responses of a weighted synthesis filter. An improved Viterbi decoding method using error detecting code information instead of tail bits has also been developed to increase the effective error-correction coding rate. A 5.6 kb/s speech codec has been implemented by incorporating the PCELP speech coding algorithm with the improved Viterbi decoding. Formal listening tests show that the synthetic speech quality of this codec is equivalent to that of 5.4-bit μ-law PCM in the absence of channel errors