Research On Algorithm Of Audio Coding Based On MPEG-4AAC

Digital audio coding technology is widely used in audio storage and networktransmission，it meets people’s needs for audio information．There are many audiocoding compression algorithms， and there are many differences among theircomputational complexity，compression quality and compression ratio．In recent years，people have designed the coding algorithms of the high compression and the high fidelityusing the hearing system principle about the human ear，and much progress have beenmade．This coding algorithm is called perception audio coding．MPEG-4AAC audio coding is the most advanced and the most popular perceptionaudio encoding technology，in the guarantee of the audio coding quality it provided thehigh compression ratio．But the algorithm of AAC audio coding standard has pretty highcomplexity，which can not meet the need of real-time audio coding．So throughresearching the mpeg-4AAC audio coding standard and on the premise of ensuring thecoding quality，this paper puts forward some effective improving measures．First，this paper introduces the basic principle of AAC encoder，including threeencoding frame models provided by the AC coding standard、coding process of the AACencoder、psychoacoustic model、analysis filter、Joint stereo、quantitative coding and bitallocation，and the introduction of the related algorithm of these modules．Second，the calculation of the psychological acoustic parameters occupies a largeproportion in mpeg-4AAC encoder．In the psychoacoustic model Ⅱstandard，thecalculation of the masking properties(Especially masking effect of the calculation ofcritical band)has a lot of repeated computation process．Through researching the processthis paper puts forward an algorithm which can reduce the calculation process，thealgorithm improved the coding efficiency without influencing the coding quality．Finally，the quantization module calculation is the most time-consuming calculationof the AAC audio encoder．The dual-loop mode proposed by Brandenburg is used，andbetter coding quality and compression ratio is received． However， when codingpractically，slow convergence and even deadlock exist because of its excessive use ofiterations．Based on deep analysis of the MPEG-4AAC quantization algorithm，a scalefactor algorithm which can calculate each scale factor band swiftly is proposed in thispaper．The proposed algorithm reduced the quantization module calculation work througheffectively cutting down the outer loop calculation process and ensuring that thequantization distortion of each scale factor below the allowable value．...