Optimizing gain codebook of LD-CELP

This paper combines the Jayant adaptive quantization and G.728's gain prediction to propose a scheme fit for designing gain coodbook of LD-CELP, in which the exact gain value was adaptively predicted and adaptively quantized. In this method, for adaptive quantization gain of 3 bit and 4 bit, the SNR have been increased by 0.5 and 6 dB separately than that of G.728. If adopting 4-bit adaptive quantization and the shape codebook of 64 codevectors, the complexity of G.728 could be reduced by 20% while SNR had 1 dB improvement than G.728. When the order of synthesis filter is reduced from 50 to 30, SNR isn't changed and the complexity of G.728 is decreased by 40%.