【作者】 张宏；

【导师】 师卫；

【作者基本信息】 太原理工大学 ， 电路与系统， 2007， 硕士

【摘要】 与数字信号相比，通过模拟信号来实现音频的处理和传递有着许多无法克服的缺点：控制性较差，易受干扰，保密性不好。音频信号的数字化是大势所趋。互联网技术的广泛应用为数字音频信号的传输提供了极大便利，通过网络进行数字音频信号的传输和交换代表了未来音频技术的发展方向。当前，大多数音频流服务器是通过PC获取数据，或者是用其它方法将采集到的数据传给PC，然后通过PC将数据传送到网上，系统成本过高，且大多只能实现单路音频的采集。随着人们需求的变化，越来越多的应用场合需要多路音频的同时采集。因此，开发一种低成本、低功耗、高性能的多路实况数字音频流服务器系统具有重大的现实意义。在查阅大量资料的基础上，本文设计出一种多路实况数字音频流服务器系统，系统采用CPLD、IP网络多播等技术，实现了四路模拟音源的同时实时采集，将模拟音频信号以44.1kHz的采样率、16位的采样精度转换为数字音频信号后，通过以太网传输到播放终端。传输过程的数字化使音频信号具有更好的可控性、保密性和抗干扰能力。系统还具有AGC(自动增益控制)功能，能够根据输入音源信号幅度大小的不同自动将其稳定在一定的水平，避免了由于音源信号强弱的变化而造成播放终端声音的忽大忽小，同时保护了终端播放设备。论文的第一部分介绍了数字音频流服务器系统的相关理论，包括音频的数字化和本文所用到的TCP／IP相关协议。第二部分介绍了硬件系统设计，包括音频采集板和网络接口板的设计。音频采集板以CPLD为核心，主要将各路模拟音频信号转换成数字音频信号，然后存入数据缓冲区。CPLD技术的应用不仅使系统具有可扩展性，易于更新和维护，而且使系统小巧、稳定、功耗低、实时性强。CPLD程序的编写采用VHDL硬件描述语言。网络接口板以网络微控制器DS80C400为核心器件，主要实现音频采集板与以太网的接口，将音频采集板采集到的各路音频数据发送到各自的多播地址。DS80C400是DALLAS公司生产的网络微控制器，以8051为核，集成了以太网MAC，片上ROM固化了完整的TCP IPv4／6网络协议栈。第三部分介绍了软件系统设计。软件系统采用汇编语言实现，虽然也可以用Java和C来编写，但是，因本系统同时采集四路音频，数据量大，要求的实时性强，实验证明，用Java和C编写的程序均不能满足系统速度上的要求。最后，根据系统设计画出电路原理图和PCB，做出了实际电路板，并调试成功。经反复测试，系统功能达到了预期要求。更多还原

【Abstract】 Compared to the digital signal, analog signal has many disadvantages that can not be overcome when it is used to dispose of and transfer the audio. Analog signal is not safe, hard to be controlled and easy to be interfered with. The digitization of the audio signal is the tendency. With the development of the internet, the transfer of the digital audio signal becomes more convenient. It is the direction of development of the audio technology to transfer and exchange the digital audio signal through the internet.Currently, the way of the most audio stream servers to get the audio data is through PC. Some applications get the data in other ways, and then transfer the data to the internet through the PC. In this way, the system is expensive. Further more, only one channel audio can be sampled. With the change of the people’s requirement, many applications need to sample the multi channel audio signal simultaneously. So, it is significative practically to develop a multi channel field digital audio stream server system with low cost, low power and high performance.Based on referring to abundant information, a multi channel field digital audio stream server system is designed. The system introduce the technology of CPLD and IP network multicast, and implement the real time sample of four channel analog audio signal simultaneously. After the conversion from analog audio signal to digital audio signal by the sampling rate of 44.1 kHz and the sampling precision of 16 bits, the audio signal is transferred to the play terminal through the Ethernet. The digitization of the transferring makes the audio signal more controllable, safer and more anti-jamming. The system has the function of AGC (Automatic Gain Control), which can stabilize the signal on the stated level according to the change of the input audio signal, preventing the audio of the terminal from changing acutely, and protecting the terminal equipment.The first section of the paper introduces the theory relative to the digital audio stream server system, including the digitization of the audio signal and the TCP/IP protocol used in this paper.The second section introduces the design of the hardware system, including the design of the sampling audio board and network interface board.CPLD is the core of the sampling audio board, which converts the analog audio signal in every channel to digital audio signal, then stores the audio data in the data buffer. The introduction of the technology of CPLD makes the system not only flexible, extensible and easy to update and maintain, but also cabinet, steady, low power, strong in real time. The program of the CPLD is written in VHDL.The network microcontroller DS80C400 is the core of the network interface board, which implement the connection between the sampling board and the Ethernet. The network interface board sends the audio data sampled by the sampling audio board to the multicast address of the network. DS80C400 is a network microcontroller manufactured by Dallas Semiconductor with the 8051 core. It integrates the Ethernet MAC on chip. A full application accessible TCP IPv4/6 network stack is provided in the ROM.The third section of the paper introduces the design of the software system, which is implemented in assemble language. Although the software of the DS80C400 can also be written in Java or C, the software written in Java or C can not meet the need in speed because of the large numbers of the audio data of four channels and the need of the real time.In the end, the schematics and PCB are drawn according to the design of the system. The print board is debugged successfully after it is manufactured. Through tested repeatedly, the system meets the prospective function.更多还原