改进的嵌入式CELP固定码本快速搜索方法

Improved Method of Fixed Codebook Fast Search in the Embedded CELP

G.729.1是ITU-T近年来提出的一种嵌入式宽带变速率的语音编码标准.它可以根据信道的特征随时调整编码速率取得更好的宽带语音质量,这使得该编码算法具有很高的复杂度.在G.729.1标准中,固定码本搜索约占算法总复杂度的25%,为降低固定码本搜索算法的复杂度,提出一种分级并简化脉冲替换的方法.该算法依据似然估计向量大小对脉冲位置重新排序,利用两级搜索同时对第二级简化搜索来改善脉冲替换搜索的效率,从而减少搜索次数.实验结果表明,改进后的方法可使固定码书搜索次数降为G.729.1中全局脉冲替换方法的42.72%,并且保持了与其几乎相同的语音质量.

In recent years,ITU-T puts forward a kind of embedded variable bit-rate wideband speech codec standard which can adjust the coding rate according to the characteristics of channel at any time and can get a better wideband speech quality. Therefore, G. 729. 1 has a high complexity in the encoding algorithm. The fixed codebook search algorithm accounts for about 25 percent of total complexity in G. 729. 1. To reduce the complexity of the fixed codebook search, a method of the graded and simplified pulse replacement is proposed in this paper. This algorithm reorders the pulse position in terms of the size of the pulse-position likelihood-estimate vector. And that the efficiency of the pulse replacement is improved by using two-stage searches and simplifying second-level search. The experimental results show that the proposed method can make the search times of fixed cedebook down to 42. 72% of global pulse replacement search method, and that the quality is degraded slightly compared with the original global pulse replacement search method.