Effects of Channel Errors on the Signal-to-Noise Performance of Speech-Encoding Systems

Abstract

The signal-to-noise ratios of different speech-encoding schemes have been measured in the case where the channel contains errors. Those types and probabilities of errors have been considered that are of interest for mobile telephone applications. Most encoding schemes use an adaptive three-bit quantizer with an explicit transmission of the step-size information. A scheme with an adaptive prediction algorithm has also been studied. It has been assumed in all cases that the side information about the quantizer step size and the predictor coefficients is transmitted in an error-protected format. Measurements were made by simulating the coding schemes and the noisy channel on a digital computer. The results include upper bounds of the improvements that can be reached with error protection of the most significant bits.