Research Of Low Bit-Rate Mobile Audio Codec

With the rapid development of mobile telecommunication and the opening of 3G、B3G trial network, the demand of innovative multimedia services such as mobile music downloading, audio broadcasting, mobile phone TV grow rapidly. Audio content relevant for these services includes music, speech, and speech mixed with diverse audio types as in sportscasts, news, and movies. Further, the bit rates available for these services may be as low as 10kbps. Therefore, efficient audio coding at very low bit rates with consistent performance over different content types is of prime importance for the success of these services. The needs of new services promote the research of low bit-rate mobile audio codec. 3GPP introduces AMR-WB+, MPEG introduces EAAC+, and the Audio Video coding Standard Workgroup of China (AVS workgroup) also starts the program of setting the AVS-M Audio standard at the end of 2005. This article concludes main techniques of low bit-rate mobile audio coding, typically studies ACELP, TCX and the hybrid ACELP/TCX coding technique. AMR-WB+ audio codec uses these techniques and provides high quality at exceptionally low rate and consistent quality over all audio types. This codec is selected by 3GPP and DVB to support low-bit-rate audio and audiovisual applications on mobile networks.The article studies Vector Quatization in AMR-WB+ and AVS-M, and proposes a new VQ codebook which designed for the scalar quantization combined with vector quantization coding algorithm in AVS-M. The principle of the code words selection is that, taking into account the capacity, the use frequency of the leader code word and the limited capacity of the codebook, trying to contain as more code words wihich are used in high frequency as possible.In the end, the article introduces the present situation of AVS-M reference C code Debug, and do some subjective listening tests and objective tests. The coding quality of AVS-M is a little worse than AMR-WB+ in several sequences. The detailed reason of the quality degradation needs to be found in the later work in order to prove the coding quality of AVS-M.