Research And Realization On Crucial Aspects Of VoIP Telephone Conference System Mixing Module

With the development of the communication technology, computer technology and network, the creation of conference telephone network is developing fast. At present, the conference telephone technology moves forward to multimedia conference communication, which based on the internet, i.e. the visualized IP telephone conference system. The telephone conference system is a communication method between two or more locations via IP network, which uses computer, multimedia technology and apparatus. In the telephone conference system, the audio module is important, and is also a standard to measure a quality of a system.The audio module controls the locus say-so traditionally, i.e. only one person is allowed to speak in a moment. A chairman will be selected in a meeting first, and others have to applied to the chairman for the right to speak, and release the right after finishing his speech. Therefore, the communication of the members is limited tremendously, but the audio mix technology solves that problem. More members are able to speak in the same time, and deliver one's information to all members, this is audio mixing.The passage simply introduces the operation principle of VOIP, some basic application mode and key technology. Then introduces an audio mixing algorithm of VOIP telephone conference system, and further bring up an advanced audio mixing algorithm that suits the said system. The algorithm is not only enhanced the audio mixing speed, but also apply the "soft clipping" in analog circuit, which can soft the overflow peak. It is proved that the said algorithm is easier than the self adapting weight algorithm. In windows XP system, CPU is Celeron(R)/2.4GHz, memory 256M, dealing with 5.5S audio mixing, the said algorithm saves 0.4 ms than the self adapting weight algorithm, when the VOIP telephone meeting system server serves for multiple telephone conference, the 0.4 ms advantage is quite obvious. In addition, the quality of the audio mixing is better than other algorithms, especially in understandable and clarity of the voice. The mix result can be replay to the members that have not attended the record, and feedback through the inquiry papers.As the voice active detect portion of the terminal affects the audio mixing obviously, so the voice active detect portion is also researched in this theme. The VOIP telephone conference system supports various terminals such as phones, mobile phones, software phones, so finally select an advanced mute check algorithm, which fits the short time energy algorithm as well as zero crossing algorithm. The signal is judged as mute only the short time signal and zero crossing rate are both below the threshold.