一种改进的6.25 kbit/s GSM半速率语音编码方案

A Scheme of GSM Half rate Speech Coding at Speed of 6.25 kbit/s

在采用ＣＥＬＰ（码激励线性预测）作为ＧＳＭ半速率编码方案的基础上，对ＣＥＬＰ的三个主要组成部分分别进行了改进，在ＬＳＰ（线谱对）参数分析中提出了将求解和量化相结合的快速算法；在ＬＴＰ（长时预测）分析的分数延迟搜索中，采用逐步缩小搜索范围的方法；在随机码本搜索中，采用高斯重叠稀疏码本。这些措施大大降低了计算量，从而在保证合成语音质量的基础上能够采用单片ＤＳＰ实时实现整个ＣＥＬＰ编译码器。

Three main parts of CELP on which GSM half rate speech coding is based are improved respectively in this paper. A fast algorithm combined quantization with roots solving is also proposed in LSP parameters prediction. A method of decreasing the search range step by step is used in LTP with friction delay. A Gaussian over lapped and clipped codebook is used in codebook search. The improvements result in a significant reduction in calculation complexity, so that the whole CELP codec can be real time implemented with a single DSP chip without degradation of the reconstructed speech.