Robust speech coding under packet-loss conditions using recovery sub-codec for broad-band IP network

A speech-coding method called "recovery sub-code (RSC)" is described that improves speech quality under packet-loss conditions, which can occur even in high-speed wide-band networks. The RSC uses a sub bit-stream as additional information in the next speech frame in addition to the main bit-stream in the current frame. The main bit-stream is coded using a low-compression high-quality main coder and the sub bit-stream is coded using a high-compression sub-coder. The internal states of the recovery sub-coder can be updated using the output from the high-quality main coder, so they are independent of previous frames and are not affected by previous packet loss. Subjective quality tests of several speech codecs based on the proposed method show that it significantly improves the concealment of packet loss, both for narrow- and wide-band speech and audio signals.