8Kbit/s low delay speech coding algorithm with adaptive codebook

This paper makes improvement in G.728 algorithm aiming at reducing coding rate and presents an 8 Kbit/s speech coding algorithm whose delay is 2.5 ms. The size of frame which is 5 samples in G.728 is extended to 20 samples. Adaptive codebook is introduced, which is composed of the recent excitation.20 dimensions normalized fixed codebook is adopted for the proposed algorithm. The exact gain of adaptive and fixed codeword are calculated and quantized. Fixed quantization is used in adaptive codebook and adaptive quantization is used in fixed codebook. The size of adaptive and fixed codeword are both 128 and their gain are both 8. The whole search mode is used to obtain the best excitation in algorithm. New algorithm's coding rate is only half of G.728 and has only 2.5 ms delay. Testing with the average segment SNR and Perceptual Evaluation of Speech Quality (PESQ), the improved algorithm is close to G.728 in speech coding quality. And it achieves desirable balance in coding rate, delay time and coding quality.