The Melp Speech Coder And The Ac-3 Audio Decoder, The Research And Its Implementation

With the development of informational society, the compression andtransmission technology of sound has already become important representation of thesocial development level. Both the speech coding/decoding technology, which is usedin human communication, and the audio coding/decoding technology, which is usedin TV and broadcast transmission, are important parts of the modem social life. Inadditional, these coding/decoding technologies play a very significant role in themultimedia, network communication and security communication.MELP(Mixed Excitation Linear Prediction) vocoder is widely applied incommercial and military speech communication because of its low-bit-rate, low-delayand low-complexity. Therefore, realizing the MELP speech coder is very useful andhas important meaning. BF561 is the new generation DSP produced by ADICorporation, which has two cores to deal with more instructions, and each core canwork at 600MHz. BF561 also has lots of peripheral interfaces. So, BF561 is an idealplatform for multimedia applications. In this thesis, we put the MELP speech coderonto this platform. Then we implement and optimize it on the BF561.The AC-3 audio standard became one part of the American HDTV standard in1995, and is widely applied in many fields, such as TV, film, broadcast etc. In China,digital TV is stepping in people's normal life, in this situation, realizing the AC-3audio decoder also has significant practical meaning. DM6446 is newly proposeddual-core DSP by TI Corporation, which possesses both ARM and DSP properties.DM6446 is very suitable for multimedia applications. We apply AC-3 decodingalgorithm on the ARM of DM6446 in order to perform fixed-point description.The thesis at first surveys the development and the current progress of thespeech coding and current audio formats. Secondly, we introduce the principle ofspeech coder, and present the important model of MELP algorithm. Thirdly, wesimply introduce MELP codec system and its platform, including the structurecharacter of the BF561, audio sampling and sending on evaluating board, softwareplatform Visual DSP, and so on. Fourthly, we introduce methods to optimize programperformance and use them in MELP speech coder. Fifthly, we introduce the flow ofAC-3 decoding algorithm, realizing platform, system framework, I/O interface settingand its fixed-point description realization on the ARM of DM6446. Then we usefixed-point description to modify the program, and optimize the memory. Finally, wepresent the conclusion and tasks in the future.