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This paper describes an efficient Code-Excited Linear Predictive (CELP) Coder for bit rates between 6 and 16 kbills, and new effective algorithms for the selection of the excitorion signor Then we propose a chss of binary codebooks having interesting properties in terms of performance, robustness against transmission errors and &xibili@ in the choice of the bit rate. Due to the optimal structure of the coder and to the fast algorithms fur selecting the excitation signal, a real time implementation has been made possible on one 32 bits floating-point digital signal processor.

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In this paper, an algorithm for coding 20 Hz -15 kHz speech signals at 64 kbit/s with a very low delay (frame of 0.16 ms) is presented. To achieve a quality near to transparency, we propose adapting the Low-Delay CELP coder [1] to the 15 kHz bandwidth and suggest a new noise shaping method based on a psychoacoustic model. In this way we take advantage of linear predictive coding and masking properties of the human perception system. Finally, an algebraic codebook is proposed, allowing an important reduction of coder computational complexity, without decreasing the perceived quality of signals.