8Kb／sLD－CELP编码器的研究

Study on LD-CELP Coder at the Bit Rate of 8 Kb/s

描述了一种８Ｋｂ／ｓ的低延迟ＣＥＬＰ编码器．这种编码器采用后向自适应技术，所使用的激励矢量长度很短，使得单向编译码延迟小于５ｍｓ，计算复杂度也由于使用了“形状－增益”码本而得到降低．这种编码算法包括：（１）用于ＬＰＣ分析的汉明窗（Ｈａｍｍｉｎｇｗｉｎｄｏｗｓ）；（２）三抽头基音预测器和１０阶ＬＰＣ预测器的级联；（３）对数增益预测器；（４）闭环搜索．

The paper presents an 8 Kb/s low delay CELP coder. With backward adaptation the coder uses small excitation vectors and then makes one way CODEC delay smaller than 5ms,and the computational complexity is reduced by a'gain-shape'codebook. The algorithm includes: (1 )a Hamming window for LPC analyses; (2) tandom of a three-tap pitch predictor and a 10-order LPC predictor; (3) a log-gain predictor; (4)closed-loop search.