Variable Data Rate Vocoder Improvements for Secure Interoperable DoD Voice Communication

One intermediate goal towards achieving universal secure voice interoperability in the Department of Defense (DoD) has been the development of a universal voice encoder (vocoder). This vocoder would seamlessly encode speech at a wide range of interoperable variable and fixed data rates to suit a wide range of DoD communication equipment. This paper describes the most important features of such a vocoder and recent advancements in achieving this goal. Specifically this paper will describe three main areas: 1) Summary of the variable data rate (VDR) algorithm and the most recent improvements to the vocoder. 2) Methods for transcoding between fixed rate and variable data rate vocoding modes. 3) Summary of heavily bit error protected, fixed-rate modes.