VAD techniques for real-time speech transmission on the Internet

We discuss techniques for voice activity detection (VAD) for voice over Internet Protocol (VoIP). VAD aids in reducing the bandwidth requirement of a voice session, thereby using bandwidth efficiently. Such a scheme would be implemented in the application layer. Thus the VAD is independent of the lower layers in the network stack (see Flood, J.E., "Telecommunications Switching - Traffic and Networks", Prentice Hall India). We compare four time-domain VAD algorithms in terms of speech quality, compression level and computational complexity. A comparison of the relative merits and demerits along with the subjective quality of speech after the pruning of silence periods is presented for all the algorithms. A quantitative measurement of speech quality for different algorithms is also presented.