A backward adaptive 8 kbit/s speech coder using conditional pitch prediction

The authors present a high-quality 8-kb/s speech coder with an algorithmic delay of 2.875 ms. The proposed coder is based on the backward-adaptive CELP (code-excited linear prediction) coder. It uses two new techniques to improve the quality. One is conditional pitch prediction, where the pitch period is selected from the candidates pruned by backward pitch analysis. The other is a switchover of the synthesis filter, where one of two sets of filter coefficients for the random excitation is selected. Experiments show that the quality of the proposed coder is superior to that of a 6-b μ-law pulse-code modulation (PCM) coder. In particular, the quality of female speech coding is equivalent to that of a 7-b PCM