A study of variable pulse allocation for MPE and CELP coders based on PESQ analysis

A novel scheme of allocating variable pulses for each frame is proposed to reduce the bit-rate of MPE and CELP coders while maintaining the same speech quality. Since speech signal is not stationary, the required pulse number in a speech coder should be variable frame by frame. In this paper we tried to approximate the optimal pulse allocation by greedy search algorithm based on the criterion of perceptual disturbance value derived by PESQ analysis. In the experiments the proposed scheme was used to reduce the pulse numbers of two standard speech coders, G.723.1 and MPEG-4 CELP. The results show that the proposed scheme can achieve over 30% bit-rate reduction in fixed codebook (FCB) and about 20% in all for both coders while maintaining the same speech quality in both objective and subjective measure. We also designed several methods to accelerate the optimal search, which could largely reduce the execution time by 120 times in the best case.