【作者】 杨永祥；

【导师】 汪国有；

【作者基本信息】 华中科技大学 ， 模式识别与智能系统， 2005， 硕士

【摘要】 计算机和网络技术的发展,促进了音视频技术在多媒体、网络、可视电话、监控、道路等领域的应用。MPEG4 AAC(Advance Audio Coding)作为MPEG-4 标准的高质量音频压缩编解码的核心,能够在每通道64kbps 下提供高质量音频压缩编解码,在压缩音频流中支持多于48 个音频通道,16 个低频有效通道,16 个多配音多种语言通道和16 个数据流,因此在许多领域中发挥了重要作用。德州仪器(TI)公司的DM642定点多媒体DSP 具有高速时钟,高度并行化指令集,使得在DSP 上实现MPEG4 AAC实时解码器成为了可能。本文首先介绍了MPEG4 AAC 解码器的无噪声解码、反量化、应用比例因子、联合立体声解码、瞬时噪声整形、长时预测和反滤波器组等模块的基本原理,详细探讨了针对DM642 评估板硬件的特点,阐述了DSP 算法设计与实现的优化技术。为了能使AAC 解码应用到多媒体、网络、可视电话、监控、道路和IPTV 等领域当中,如何提高程序执行效率和运算速度,保证实时性,成为了本文最关心的问题。为此,在不影响音质的前提下,本文给出了通过优化程序结构和简化模块运算的方法,并在DM642 上实现了MPEG-4AAC 实时解码器。最后,本文给出了解码器算法在DM642 上的实现结果分析和AAC 编解码器的音频质量客观评价的性能指标,试验表明解码后的信号与原始信号在主观上基本“无差别”,而且在客观上与MOS 分相似较好。可以看出AAC 解码器具有一定的实用价值。更多还原

【Abstract】 The development of computer and network improves the technique of audio-videoapplied in the multi-media, network, visual telephone, monitor ,road etc. MPEG4AAC( Advance Audio Coding), as the kernel of MPEG-4 audio standard, can encode anddecode high quality under 64kbps. It support over 48 audio channels,16 low frequencychannels, 16 multi-dub and multi-language channels, and 16 data streams.so it play a keyrole in many fields.The DM642,which is a multimedia DSP, posses highly clock, highlyparallel instruction set, these performances make possible of realizing MPEG4 AACreal-time decoder. The algorithms of MPEG4 audio standard are discussed. And the AAC decoder isrealized on the DM642. First, we introduce the principle of MPEG4 AAC standard, anddiscussed the key decoding modules; Then we introduce hardware system of DM642 EVM; Third, we introduce the correlative optimize technique; Last, from the objectivity estimateaspect, we make analyse the audio quality of the output of AAC decoder. MPEG4 AAC decoder is made of Noiseless decoding, inverse quantity, apply scalefactor, union stero decoding, temporal noise shaping, long term predict, inverse filter bankevery modules has quite large operations. In order that AAC can be applied to network,visual telephone, IPTV domain, that how to improve efficiency and sunning speed is thekey point. Finally we implement the AAC decoder on the DM642 EVM by programoptimizing. Finally, we give the realized results, analyze and technique target of the decoderalgorithms on the DM642, including the audio objective evaluation. The Experiments showthat there no difference between decoded signal and original subjectively, and similar withMOS objectively. The decoder has certain applied value.更多还原