ITU-T RECOMMENDATION-G.729 ANNEX-B - A SILENCE COMPRESSION SCHEME FORUSE WITH G.729 OPTIMIZED FOR V.70 DIGITAL SIMULTANEOUS VOICE AND DATAAPPLICATIONS

article describes the recently adopted Annex B to ITU-T Recommendation G.729. Annex B defines a low-bit-rate silence compression scheme desi gned and optimized to work in conjunction with both the full version o f G.729 and its low-complexity Annex A. To achieve good quality low-bi t-rate silence compression, a robust frame-based voice activity detect or module is essential to detect inactive voice frames, also called si lence or background noise frames. For these detected inactive voice fr ames, a discontinuous transmission module measures the changes over ti me of the inactive voice signal characteristics and decides whether a new silence information descriptor frame should be sent to maintain th e reproduction quality of the background noise at the receiving end. I f such a frame is needed, the spectrum and energy parameters describin g the perceptual characteristics of the background noise are efficient ly coded and transmitted using 15 biframe. At the receiving end, the c omfort noise generation module regenerates the output background noise using transmitted updates or previously available parameters. The syn thesized background noise is obtained by linear predictive filtering o f a locally generated pseudo-white excitation signal of a controlled l evel. This method of coding the background noise enables the achieveme nt of bit-rate savings for coded speech at average rates as low as 4 k b/s during normal speech conversation while maintaining reproduction q uality.