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Highly efficient low-rate audio coding methods are required for new compelling and commercially interesting applications of streaming, messaging and broadcasting services using audio media in 3rd generation mobile communication systems. After an audio codec selection phase 3GPP has standardized the extended AMR-WB (AMR-WB+) codec that provides unique performance at very low bit rates from below 10 kbps up to 24 kbps. This paper discusses the requirements imposed by mobile audio services and gives a technology overview of AMR-WB+ as a codec matching these requirements while providing outstanding audio quality.

A b s t r a c tThe application of Algebraic Code Excited Linear Prediction (ACELP) coding to wideband speech is presented. In wideband coding, a very large excitation codebook is required in order to obtain high quality speech. Ordinary CELP algorithms fail to accomodate such large codebooks due to the excessive coding complexity. In ACELP, however, an algebraic codebook with 20 bit address can be used, without any storage requirements, and more importantly, with a very efficient search procedure which allows for real-time implementation. A focused search strategy is used in which a very small portion of the codebook is searched, yet with performance very close t o that of full search. High quality speech was obtained a t bit rates below 13 kb/s.