Embedded speech coding based on pyramid CELP

In this paper we investigate embedded coding of speech in the CELP (code-excited-linear-prediction) framework. Compared to other known approaches of variable bit rate speech coding, such as the adaptive multi-rate (AMR) codec, embedded coding systems allow bit rate reductions at any point along the communication network, without changes of the encoder and the decoder. Thus, the quality of the decoded speech increases with the amount of received bits. Aiming at a coding scheme, that produces such a hierarchically-structured bit stream, we focus on a decomposition of the excitation signal by means of pyramid coding. To achieve reasonable speech compression, analysis-by-synthesis (AbS) based quantization of the pyramid layers is designed in a CELP-type fashion, called P-CELP (pyramid CELP). Besides an efficient design of fixed algebraic codebooks in each pyramid layer, special attention is payed to the integration of an adaptive codebook. To achieve maximum performance, the proposed coding scheme is used for wideband (50 Hz-7 kHz) speech.