Comfort noise

The result of receiving total silence, especially for a prolonged period, has a number of unwanted effects on the listener, including the following: • the listener may believe that the transmission has been lost, and therefore hang up prematurely • the speech may sound "choppy" (see noise gate) and difficult to understand • the sudden change in sound level can be jarring to the listener. To counteract these effects, comfort noise is added, usually on the receiving end in wireless or VoIP systems, to fill in the silent portions of transmissions with artificial noise. ==Noise==

Generated comfort noise is at a low but audible volume level, and can vary based on the average volume level of received signals to minimize jarring transitions. In many VoIP products, users may control how VAD and comfort noise are configured, or disable the feature entirely. During the siege of Leningrad, the beat of a metronome was used as comfort noise on the Leningrad radio network, indicating that the network was still functioning. ==Related concepts==

A similar concept is that of sidetone, the effect of sound that is picked up by a telephone's mouthpiece and introduced (at low level) into the earpiece of the same handset, acting as feedback. ==See also==