【作者】 任军刚；

【导师】 常义林；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2006， 硕士

【摘要】 Enhanced aacPlus是目前最完美的、开放的低码率音频编码方案。为了满足移动通信、因特网流媒体以及数字广播市场新应用的需求，本文对Enhanced aacPlus编解码器的技术原理和实现方法作了深入的研究。论文首先介绍了音频编码技术的发展以及基本原理，然后详细分析研究了Enhanced aacPlus的结构框架和主要的算法模块。在尽量不降低音频质量的前提下，为了提高编解码性能，对Enhanced aacPlus编解码的算法采用了一些改进和优化措施。例如在心理声学模型中，采用CMDCT滤波器组来替代FFT滤波器组，利用谱平面法来进行音调侦测；在滤波器组模块中采用MDCT、IMDCT快速算法；在量化编码模块中采用一种新的单循环模式；对SBR和PS分别采用低能量工具和QMF滤波器组等等。实验结果显示，Enhanced aacPlus能够在低比特率下获得高质量的音频效果。更多还原

【Abstract】 Enhanced aacPlus is the state-of-the-art low bit rate open standards audio codec. In this paper, the principle and implementation method of Enhanced aacPlus codec are studied deeply in order to enabling new applications in the markets of mobile, Internet streaming and digital broadcasting. A brief introduction to the development and the fundamental principle of audio coding technology is firstly carried out. Subsequently, the standard function blocks of Enhanced aacPlus are introduced, also the main algorithm techniques of the key modules is discussed in detail. Some important algorithmic modifications and optimizations are used to improve encoding performance and speed without reducing the audio quality. For example, the modification method used CMDCT filterbank instead of FFT filerbank and employed spectral flatness measure to detect tonality for the psychoacoustic model, developed a fast MDCT algorithm for filter bank tool, designed a new single loop structure for quantization module, used a low power SBR tool and QMF-based implementation of PS codec. Finally, the test results show that Enhanced aacPlus achieved excellent audio quality at low bitrate.更多还原