Discontinuous transmission stops sending audio packets when the talker is silent, instead of wasting bandwidth encoding the sound of a quiet room. Driven by VAD, it can cut the data a typical conversation sends by 40-70%, since people are silent more than half the time in a two-way call. To keep the line from sounding dead, the encoder periodically sends a tiny descriptor of the background noise (a SID frame) so the receiver can generate matching comfort noise during the gap. DTX is especially valuable at scale — large conferences, mobile networks, paying for egress — but it must be tuned so onsets aren't clipped and the noise fill sounds natural.
The book · Volume 4 of 7
Audio for Video: A Complete Guide to Sound in Video Products: From PCM and Codecs to Loudness, Accessibility, and Real-Time Voice Processing
DTX saves a large share of call bandwidth, but tuned badly it chops word endings and makes silence feel like a dropped line. This volume covers DTX with voice activity detection, comfort noise and the Opus and speech codecs that carry it, so you can trade bitrate against how natural the pauses sound. Written by Nikolay Sapunov, CEO at Fora Soft.
Want DTX bandwidth savings in your calls without clipped words or dead-air silence?
Tell us your codec setup and network targets, and we will give you DTX and VAD settings with a test plan for clipping and comfort noise. 250+ video products shipped since 2005.
