音频信号的频率范围是从20 Hz到20,000 Hz。音频环绕声系统能以较低的码率带给倾听者良好的临场感、包围感与空间感。针对音频信号的特点，音频信号处理有着其独特的方法：感觉音频编码方法。论文采用多声道和虚拟环绕技术两个方向对音频环绕声系统进行了实验研究。 论文首先研究了多声道环绕声系统的历史与发展，对其中重要的DolbyAC-3、MPEG标准以及DTS系统进行了以下方面分析：[1]编解码结构：主要是个标准的编解码流程与使用到的工具；[2]主要的技术特点：主要是针对特殊编码工具的效用的分析。其中特别对于符合感觉音频编码的AC-3标准和MPEG标准分析了主要的模块算法。基于对多声道技术和MPEG AAC标准的算法研究，并参考ISO/IEC 13818-7标准中的设计原则与部分开放源码，在软件环境中实现了AAC编码算法。这一工作对于后续多声道技术的研究提供了一个很好的基础平台，并有利于AAC算法向DSP硬件平台上的移植与实时实现。 论文的另一方面是对虚拟环绕技术的研究与实现。通过对虚拟环绕声产生的原理的研究，总结了主要的方法，并逐一进行了算法实现。从得到的结果中总结出了一套行之有效的虚拟环绕声产生算法。根据非正式的听音测试的结果，还可以对该系统进行进一步的修正。论文工作中，将包括混响、均衡和虚拟环绕等音效在内多种音频信号后处理方法在DSP硬件平台上进行了实时实现。 最后，提出了一种音频环绕声编解码系统的新结构。该结构针对目前多声道环绕声系统中普遍存在的难点，将多声道技术的工具、编解码方法与虚拟环绕技术相结合，发挥了各自的特点，将有效的消除非对称声道之间的信息冗余度，从而能够降低整个环绕声系统的码率，并且适合在不同环境中采用不同编解码器结构。
The frequency range of audio signal is 20~20,000 Hz. With low bit rate, Audio surround sound system can give audients the feelings like in the theater, and the feelings of surround and space. For its characteristic, audio signal can be processed by perceptual coding. In present dissertation, experimental studies include multichannel and virtual surround technique.The history and progress of multichannel surround sound system were discussed at first. For Dolby AC-3, MPEG audio, and DTS, the discussed topics are coding structures in the program and coding tools, and main technique for the use of coding tools. Especially, for the perceptual audio coding standards, such as AC-3 and MPEG audio, their arithmetic of important module were discussed. Based on the study of multichannel technique, MPEG AAC standard, and source codes from Internet, the coding modules were implemented in software. It will contribute to the study of multichannel and real-time implementation in DSP.In the other hand of present dissertation, the theories of virtual surround sound were studied. After this study, main methods of producing virtual surround effects were obtained, and implemented in arithmetic. According to informal subjective evaluation result, some corrections will be done for better audio effects. Furthermore, audio effects including reverberation, equalizer and virtual surround were real-time implemented on a Motorola DSP.At last, a new scheme was given for audio surround coding systems. This scheme focuses on the difficulty of surround sound systems, connects multichannel technique and coding methods with virtual surround technique. We hope the new scheme could efficiently remove the redundancies between Not-Pair-Channels, and therefore reduce the bit rate of whole surround sound system. Based on this scheme, different structures can be used in different cases.
