【作者】 谢争捷；

【导师】 胡贯荣；

【作者基本信息】 华中科技大学 ， 计算机应用技术， 2006， 硕士

【摘要】 音频系统在嵌入式领域中有着广泛的应用,各种嵌入式产品对音频系统的要求也各不相同。对于通讯类产品,在性能方面对音频系统的要求则非常高。网络视频公话终端产品的音频系统是基于ADI公司的ADSP-BF561双核处理器芯片和完全开源的uClinux操作系统实现的。利用ADI公司Blackfin系列处理器公用的调试工具及集成开发调试环境Visual DSP++开发。在网络视频公话终端产品中,音频系统需要实现语音采集、编码、解码、输出和网络传输五种功能。为了充分利用双核处理器的双核特性,达到更好的系统性能。采取了双核心并行运行,音频系统各功能模块分别运行于两个核心上的策略。同时设计了双核间的软件通讯机制。并在现有的开发环境下,实现了音频系统的各功能模块,包括语音采集、语音编码器、语音解码器及uClinux操作系统下的音频驱动程序-UDA1380设备驱动。在音频系统的实现过程中,针对音频传输中经常出现的时延、抖动、回音及分组丢失等问题,做了些优化处理。握手时语音编码的选择,主要是利用握手选择措施找到最合适的、对资源需求最小的编码方式。在编码和解码过程中设置了循环缓冲区,对语音数据进行了有效的缓冲,解决了延时和抖动的问题。采用了回音抵消策略,解决了通话中的回音问题。还采取了加时间戳的音视频同步措施。这些措施的采用使得网络视频公话终端产品达到了较好的通话效果。更多还原

【Abstract】 Audio system is applied in field of embedded system widely, and the requirement for it varies extremely. For communication products,the needs in performance is more strict than any other products. In network video telephone terminal, audio system’s realization is based on Analog Device incorporation’s dual core processor ADSP-BF561 and open sourced uClinux operation system. The audio system is developed with ADI’s debug tool in Visual DSP++ integrated developing environment, which is designed for Blackfin series processors.In network video telephone terminal, audio system needs to perform 5 functions, i.e. voice gathering, encoding, decoding, exporting and network transmission. In order to make full use of the dual core’s characteristic of ADSP-BF561, and reach better performance, the dual cores run parallelly, and every module are set to run in either blackfin core. At the same time, realize the audio system’s all modules, including voice gathering, audio decoding, audio encoding and audio driver in uClinux-UDA1380 equipment driver.In the course of audio system’s realization, some questions such as delay, dither, echo and package dropping could appear in audio’s sending. So many procedures have been used to make the system or design as effective or functional as possible. The audio encoder’s selection in handshake of calling, mostly base on the selecting measure to receive the most perfect encoder. Setting the circular buffer in encoding and decoding, valid buffer for voice data, resolving the questions of delay and dither in audio’s transferring. Echo counteracting policy’s realization solves the problem of echo in talking. And adding the time stamp realizes the audio and video data stream’s synchronization. All the measures let the network video telephone terminal reach better performance.更多还原