关键词: 语音编码, 低延迟, 低延迟语音编码算法, 自适应码书, 代数码书

Abstract: The 16 kb/s Low Delay Code-Excited Linear Prediction（LD-CELP） has been used in many environments，however，the high bit rate required in this work have been a handicap in using it for some condition.In this paper，a speech coder using two stages code book search schemes is proposed to improve the performance of LD-CELP and reduce its bit rate.To develop the proposed speech coder with a low bit rate，two sub code books are explored：a backward updated adaptive sub code book and a fix sub code book with algebraic structure.Second，a two stages target vector search scheme is proposed to minimize the mean squared error between the filtered excitation vector and the target vector.As a result，a 10 kb/s dual code book CELP coder is proposed with a delay of 2.5 ms in sampling rate of 8 kHz.It is shown that the proposed speech coder has a comparable speech quality to 16 kb/s G.728 in Segmented Signal-to-Noise Ratio（SSNR） and Perceptual Evaluation of Speech Quality（PESQ）.

Key words: speech coding, low delay, Low Delay Code-Excited Linear Prediction（LD-CELP）, self-adaptive codebook, algebraic codebook