The Development Of MPEG-4 Audio Coding System Based On Wavelet Packet Decomposing Algorithm

The MPEG audio coding standard is one of the three international audio coding commercial systems.Especially,MPEG-4 audio coding formula is instituted as international standard in 1999.It is wildly used in the areas of Interactive Multimedia in Internet,HD-DTV,Digital Movies and so on.The advantage of MPEG-4 audio coding formula is that it supports both natural sound and synthesized voice.MPEG-4 audio coding formula tries to apply to as many areas of audio using as possible,and has considered extensible demands.MPEG-4 audio coding standard institutes different coding formulas according to different subjects.The General Audio Coding,MPEG-4AAC,has extensive using among a series of audio coding formulas in MPEG-4.MPEG-4AAC bases on General Psychoacoustic Model.Its time-frequency transform module adopts MDCT.In this paper,we introduce MPEG-4 audio coding,and then discuss MPEG-4AAC process detailedly.Finally,we develop a breadth-first wavelet packet algorithm based on critical band matching to replace MDCT.Unlike wavelet transform,wavelet packet transform can not only decompose the frequency of single,but also allow a finer resolution at high frequency.So,wavelet packet transform can provide better decomposition for signals including numerous intermediate and high frequency.The advantage of wavelet packet transform is that it can implement incomplete wavelet packet decomposing and choose the best wavelet packet basis for singles.The algorithm in the paper can reduce the algorithmic complicated degree and adapt the areas of audio coding well.Then,we use it to MPEG-4AAC process and implement a new audio coding formula at last.Compare with wavelet transform algorithms,new audio compression system is able to divide frequency-band of audio signals close to the critical band as far as possible.So,it is helpful to improve the encoding quality.Moreover,we can adjust decomposing depth of wavelet packet according to coding computational complexity. It makes audio coding more flexible.These advantages are able to play an excellent role in the Internet and Multimedia Age.