Low bit-rate CELP speech coder with low delay

This paper presents a speech coding algorithm for a low bit-rate backward prediction coder with a bit-rate of less than 4 kbit/s, and a codebook design with a closed-loop training procedure. The coding system proposed is based on the backward prediction algorithm in LD-CELP and results in a 13.5 ms coding delay, which is 1/7 the length of delay in conventional forward prediction coders at the same transmission bit-rates. The codebook design is carried out in a closed-loop training process to generate the codebook so that we can represent harmonic portions of voiced speech appropriately. Finally, we carried out a simulation for the performance of the low-delay coder system trained in closed-loop method with the proposed initial codebook. We evaluated the effectiveness of the initial codebook with the optimal assignment and found that its reconstructed speech was clear enough to understand though it contained a slight element of noise. (C) 1999 Elsevier Science B.V. All rights reserved.