用子波包算法改善低速声码器性能

本文引入子波包算法，在语音信号的子波包子空间里判决语音的基音，从而可以有效避开有色噪声（如低频噪声）等的干扰，正确提取语音的基音。这种方法不仅能提高低速率声码器在无噪环境下的语音质量，而且能在很强的有色噪声环境下保持原有的声码器音质，从而有效地克服低速声码器抗噪能力差的缺点。

Improve the Performance of Low Rate Vocoders Using Wavelet Packet Algorithm

The Wavelet Packet Algorithm is introduced in this paper to determine the pitch of speech in its wavelet packet subspaces.This method can avoid the interference of color noise such as low frequency noise and determine the pitch correctly.This algorithm can not only improve the quality of low rate vocoders in noiseless environment,but also keep the speech quality of the original vocoders under very strong color noise environment to overcome the weakness of shortage of noise immunity in low rate vocoders.