A multimode source/channel coder which can dynamically control the balance of source and channel coding according to the channel quality is introduced. As an example of such a system, a 4.8-kb/s code excited linear predictive coder with three coding modes (A, B1, and B2), each of which has different bit assignments to source and channel coding, is presented. The optimum coding mode is selected in each frame, based on an evaluation of the spectral distortion (SNLAR) in reproduced speech. The threshold value of SNLAR for mode decision is varied according to the channel error rate. Computer simulation shows that 2 dB and 3 dB of SNRseg improvement is achieved at a bit error rate of 3×10-3 and 3×10 -2 respectively, over conventional CELP without channel coding
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Acoustics, Speech, and Signal Processing, 1990. ICASSP-90., 1990 International Conference on
Date of Conference: 3-6 Apr 1990