Noisy-channel performance of 16 kb/s APC coders

This paper presents the results of our optimization study of 16 kb/s APC coders operating over noisy channels. With the objective of achieving good speech quality and a robust coder performance for channel bit-error rates of up to 1%, we have investigated a number of issues including: the tradeoff between voice-data bandwidth and error-protection bandwidth; the amount of error protection for individual transmission parameters; comparison of several residual coding methods; the relative performance of the two ways of sequencing the spectral and pitch predictors; use of folded binary code for encoding the quantized residual; and smoothing of the decoded residual. Most impressive of the several interesting and useful results reported in the paper is that the final optimized, robust coder design yields speech quality that degrades only slightly as the bit-error rate is increased from 0% to 1%.