Variable Rate Coding of Speech

In this paper, we examine a number of concepts and issues concerning variable-rate coding of speech. We formulate the problem as a multistate coder (i.e., a coder that can operate at several bit rates) coupled with a time buffer. We first analyze the theoretical aspects of the problem by examining it in the context of a block processing formulation. We then suggest practical methods for implementing a variable rate coder based on a dynamic buffering approach. We also allude to a multiple user configuration of variable-rate coding for tasi-type applications. A practical example of a variable rate adpcm coder is presented and applied to speech coding. It is shown that by careful design the algorithm can be made to be as robust to channel errors as that of a fixed rate adpcm coder.