KMTDBOURSE wrote:
Hi,
Thanks a lot for describing the vad algo it seems rather a basic algo and I am surprised it is not more sophisticated. I hear also from speex users (must be same algo?) that the vad algo is very poor and should be improved. That is what I am doing, try to improve vad and echo cancellation algorithms. I would appreciate a link where I can find data files (audio) to download on which I can perform tests. Of course I will feedback the freeswitch community in case of improvment.
best
Zelda There is a pretty good free echo canceller at www.rowetel.com, although FreeSwitch can't directly use it as it is GPL software. It does, however, mean that free and open workable algorithms for robust EC do exist.
VAD is different. It is still a research topic. You can see this from the way the VAD algorithms in things like G.729 have been revised over the codec's lifetime, as further research has been done. The algorithms G.729 and AMR use are encumbered by patents, otherwise cloning them would be excellent start. VAD for speech recognition is relatively straightforward. When you can buffer the audio, and look forwards and backwards in time, it become much easier to identify the start and end of voice bursts. It becomes hard when you can only look back in a low latency scenario. Steve