Comfort Noise

Comfort noise

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Comfort noise (or comfort tone) is artificial background noise used in radio and wireless communications to fill the silence in a transmission resulting from voice activity detection or from the clarity of modern digital lines.

Some modern telephone systems (such as wireless and VoIP) use voice activity detection (VAD, or VOX), a form of squelching where low volume levels are ignored by the transmitting device. In digital transmissions, this saves bandwidth of the communications channel by transmitting nothing when the source volume is under a certain threshold, leaving only louder sounds (such as the speaker's voice) to be sent.

The result of receiving total silence, especially for a prolonged period, has a number of unanticipated effects on the listener, such as:

• the listener may believe that the transmission has been lost, and therefore hang up prematurely
• the speech may sound "choppy" and even be hard 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 receivingend in wireless or VoIP systems, to fill in the silent portions oftransmissions with artificial noise. The noise generated is at a lowbut audible volume level, and can vary based on the average volumelevel of received signals to minimize jarring transitions.

In modern VoIP products, users may control whether they want comfort noise enabled or disabled.