Pyramid CELP: Embedded speech coding for packet communications

In this paper we present a novel speech coding algorithm for transmission over packet networks based on CELP (Code-Excited-Linear-Prediction). While various CELP type speech coders like the ITU-T G.729 or the Adaptive Multi-Rate (AMR) codec are applicable to packet voice communication systems such as the Internet, there are some fundamental reasons that may limit their Performance in case of packet loss. We investigate the alternative of embedded coding in the CELP framework. focussing on an efficient quantization of the excitation signal to generate a hierarchically-structured bit stream by means of pyramid coding [1]. Thus, the receiver can reconstruct speech at a basic quality by decoding only a subset of the entire bit stream. The quality of the decoded speech increases with the amount of received bits. We demonstrate the performance by an experimental hierarchical wideband (0.05–7 kHz) speech coder, applied to an IP (Internet Protocol) channel simulation.