Research On Optimal Design And Implement Of DSP Program Of MPEG-4 AAC Coder

The coding standard of MPEG-4 AAC(Advanced Audio Coding) is the latest and most efficient Hi-Fi digital audio coding method among all the existing perceptive audio coding standards. It stands for the most advanced audio coding technology, providing high compression ratio, excellent rebuilt timbre, flexible sound track configuration and diverse algorithm complexities for applications in different levels. Thus, the MPEG-4 ACC will be widely used in domains such as digital audio broadcast, digital voice reservation, home theater and network transmission. BF533, the fixed-point chip of the Blackfin series product by American Analog Devices, Inc., has high speed clock, unique hardware architecture and high collateral instruction set,which makes it possible to implement MPEG-4 ACC encoder on single DSP chip. This theme introduces the audio coding standard and the algorithm principle of the encoder in MPEG-4 ACC, discusses the key technologies and implemental schemes of the ACC audio encoder, and presents the software implementation on PC platform as well as optimal design and implemental method based on DSP chips. The encoder is composed of various module such as psychoacoustic model, filterbank, frequency prediction, Temporal Noise Shaping, and quantization. The algorithm of encoder has high complexity, and requires large memory and processing capability. So, the emphases of this theme are presented as follows: The first is optimizing the psychoacoustic model,which costs the biggest calculating quantity, as well as the filterbank and quantization module. The second is transforming floating-point programs into fixed-pointing programs and implementing them with assemblers. The third is implementing a MPEG-4 ACC coder with Low Complexity Profile on BF533. The experimentation shows that, with the above measures, the implemental complexity of MPEG-4 ACC has been reduced, the operative speed of the procedure has been enhanced and the satisfied rebuilt audio quality of the encoder based on BF533 has been acquired . At last, this theme also gives analysis and evaluations of the DSP results with the above fixed-point algorithm, demonstrating the fact, both theoretically and practically, that the proposed fixed-point algorithm can assure the quality of rebuilt audio signals with high compression ratio at the same time.