Comfort noise
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Comfort noise (or comfort tone) is synthetic background noise used in radio and wireless communications to fill the artificial silence in a transmission resulting from voice activity detection or from the audio clarity of modern digital lines.[1]
Some modern telephone systems (such as
Issues with silence
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
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.[2]
In many VoIP products, users may control how VAD and comfort noise are configured, or disable the feature entirely.[1]
As part of the
Examples
Many radio stations broadcast birdsong, city-traffic or other atmospheric comfort noise during periods of deliberate silence. For example, in the UK, silence is observed on Remembrance Sunday, and London's quiet city ambiance is used. This is to reassure the listener that the station is on-air, but primarily to prevent silence detection systems at transmitters from automatically starting backup tapes of music (designed to be broadcast in the case of transmission link failure).[4]
During the
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
- Ambient noise
- Talkspurt
- Discontinuous transmission (DTX)
- Presence (sound recording)
- Autonomous sensory meridian response
- Sound masking
References
- ^ a b "Troubleshooting Hissing and Static: Comfort Noise and VAD". CISCO. Retrieved 18 July 2014.
- ^ US patent 7649988, Suppapola, Seth; Ebenezer, Samuel Ponvara & Allen, Justin L., "Comfort noise generator using modified Doblinger noise estimate"
- .
- ^ "RB-SD1 Silence Detect Unit". Sonifex. Retrieved 2013-05-28.
- ^ "Radio". Encyclopaedia of St. Petersburg.
- Gao Research - VAD/CNG
- Newton, Harry. Newton's Telecom Dictionary. 20th ed. 2004.