Research And Implementation Of MPEG-2 AAC Audio Processing

As one of the most advanced standards of digital audio compression, MPEG-2 AAC has been applied widely in the transmission and storage of digital audio signal. Compared with MPEG-1 audio coding, it has better audio compression quality and more flexible configuration beside it's complicated computation and bad real time feature. Therefore, research on real time compression technology base on MPEG-2 AAC has become a hot research area. The thesis introduces the development and the fundamental principle of audio coding technology. It studies and analyzes the standard function blocks of MPEG-2 AAC and the algorithm of each function block. After the analysis of the algorithms model of MPEG-2 AAC, the thesis optimizes some blocks with great computation of Psychoacoustic Model, Filter banks and Quantization coding, etc. It omits some function blocks which have much computation and avail little to the gain of coding, for example, prediction in time domain, TNS, etc. It also adopts some fast algorithms to reconstruct some model for the reason of real time characteristic. Because the complexity of encoding is greater than decoding as for MPEG-2 AAC, the thesis uses VC++6.0 to implement a software decoder of MPEG-2 AAC LC profile to testify the system. As for the encoding part with greater complexity, taking the system's real time feature and the demand of performance-price ratio into accounted, the thesis adopts digital signal processor TMS320C54x DSP as main control chip to implement the optimized coding algorithms of MPEG-2 AAC LC profile. The optimized algorithms implement the encoding and decoding of MPEG-2 AAC stereo audio basically. After repeatedly debugging and modification, experimentation result shows that not only the computing speed is improved but also the quality of compressed audio is well ensured. The algorithm is an effective one which is suitable for improve the real time feature of the audio compression algorithms. The thesis gives details to some important techniques used in the process of implementation of the MPEG-2 AAC encoding and decoding system, including point fixing of AAC, application of table consultation, compiling language embeds in C language programme and DMA using, etc. Because MPEG-2 AAC coding involves complicated computation, it needs a large storage space of data and programme. We have to pay attention to the problem how to reduce the storage space of the data and programme so as to implement it on a DSP. A good programme structure is significant in saving data storage space and speeding up the computation. Therefore, in order to improve the real time feature of encoding and decoding, we have to adopt these techniques to speed up the computation of some nonlinear process, such as exponent and logarithm.