Low complexity forward error correction for CELP-type speech coding over erasure channel transmission

Abstract

One of the well-known problems of Code-Excited Linear Prediction (CELP)-type codec is its vulnerability to a frame erasure. When a frame is erased, the inter-frame dependency introduced by the Long Term Prediction causes a desynchronization of the Adaptive Codebook (ACB) which introduces in its turn an error propagation through the correctly received frames. In this paper, we propose a media-specific Forward Error Correction (FEC) method using a Pitch-Pulse Codebook (PPCB)-based approach to model the ACB contribution for voiced frame (frame onset) determined under Zero Crossing Rate constraint. The PPCB uses a single pulse optimized by Multipulse Maximum Likelihood Quantization algorithm to model the pitch-like contribution at the encoder side while the quantized version of that pulse will be sent as FEC information to resynchronize the ACB at the decoder side after a frame erasure. Through this approach a noticeable improvement of the synthesis speech quality is achieved under adverse channel conditions with the advantage of low computational complexity while the legacy bit-rate of the codec is kept unchanged.