The Research Of MPEG-4 AAC Real-time Coding And Decoding System Based On Fixed-point DSP

MPEG-4 AAC (Advanced Audio Coding) is an audio coding standard with high quality. Its characteristics are high compression ratio, good rebuilding quality, modularized coding and decoding procedure and flexible track configuration. It is increasingly applied to many fields such as Internet, wireless network and digital broadcasting network because of these advantages.Despite DSP has some disadvantages such as small storage capacity, limit precision and limit dynamic range, it is still suitable for audio signal manage for its higher operation rate and lower price. So, it should be feasible to achieve the AAC real-time coding and decoding with DSP.The general principal of audio coding and the common audio compression approach are introduced in this paper. The perception model, TDAC and Huffman algorism that will be used in AAC coding and decoding are also narrated.The optimization of coding and decoding algorism is the main concern in this paper. Among the standard algorisms of MPEG-4 AAC, the MDCT and IMDCT algorisms have the largest operating amounts, and the Huffman algorism is used frequently. So, if the operating time of these algorisms can be reduced, it is enough for DSP to run these algorisms. A new algorism of MDCT and IMDCT is deduced. This algorism is efficient and the operating amounts can be reduced largely.The hardware system design of AAC real-time coding and decoding is another concern in this paper. According to the requirement of real time and products available, the scheme of hardware system is presented. The detail designs of hardware module and bus interface are also illustrated. The hardware simulation of AAC real-time coding and decoding is performed with C language on a test platform based on TMS320C54 x EVM.The results from simulation and theoretic analysis show that: the AAC real-time decoding has been achieved; the compression quality and rebuilding quality of audio are satisfying.