Reseach And Implementation On IP-based Real-time Audio Transmission Technology

Traditional live audio transmission technology uses analog cable and patch panels to build transmission system, the lack of it is cumbersome connection and complex configuration. With the rapid development of digital audio technology and network technology, there has been Audio-over-IP technology which uses IP net to transmit real-time audio. Using IP net to transmit live real-time audio has a great advantage on transmission capacity, network configuration and resource sharing. It also provides a scalable platform for future development in areas such as HD-Radio, data services etc. Researching IP-based real-time audio transmission technology has important practical significance.Using IP network to transmission real-time audio has many advantages. However, problems such as clock does not match and delay uncertainties are also exist.Clock synchronization and low latency has been a professional audio field primary problem.This paper presents a IP-based real-time audio transmission scheme, in order to get sub-microsecond clock synchronization and low latency, we launched the hardware and software platform to research and implement it.We have done detailed work as follows:1. We analyzed the relevant principles of Audio-over-IP technology and present an IP-based real-time audio transmission scheme. In order to complete synchronization, the scheme adopted the IEEE1588 Precision Time Protocol, and use hardware technology to get PTP timestamps. The theoretical synchronization precision can be achieved nanosecond. Meanwhile, in order to complete the real-time transmission of audio, we use RTP protocol to transfer data and we package the audio data according to the RTP format. It can effectively reduce the data transmission delay jitter.2. We designed the hardware platform of the IP-based audio transmission system. This hardware platform uses an ARM9 microprocessor chip(S3C2440A) as its core, uses DM9000 E as a network MAC extension. The hardware platform also adds a DP83640 chip as the PTP hardware module, this module will used as a support for IEEE1588 protocol. Meanwhile, in order to generate synchronized audio clocks, we designed DP83640+FPGA audio clock generation module. We also completed the key chip’s driver of the audio transmission system.3. We designed software code for the audio transmission system, completed the PTP code of precision clock synchronization protocol. We design the RTP code for transmit real-time audio, completed using RTP format to Package data.This paper finally achieved sub-microsecond clock synchronization enough to meet the needs of professional audio, achieved a good real-time transmission performance. Finally, the delay jitter has been effectively controlled.