A variable bit rate audio coder for videoconferencing

Videoconferencing requires the transmission of both video and audio information over a communication channel of fixed bandwidth. Typically, a portion of the band width is dedicated to audio and the remaining bandwidth to video. For efficient operation, it is necessary to use a variable bit rate audio codec and a variable bit rate video codec. During periods of silence less audio information is transmitted, allowing the video bandwidth and picture quality to increase by using the vacated audio bandwidth. During periods of high audio activity the bandwidth increases to maintian audio fidelity. The audio codec described here was designed for use in such a videoconferencing system. It was designed to provide 7 kHz bandwidth audio equivalent to CCITT G.722 (at 48 kbitts) for both music and speech with extremely low complexity, variable bit rate with subjec tively transparent transitions between changes in bit rate, scalability - the ability to operate as a narrow band or wide band codec. The nominal average bit rate during periods of high audio activity is 28 kbit/s, while during silence as little as 6 kbit/s.