Comfort noise
Encyclopedia
Comfort noise 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.
Some modern telephone systems (such as wireless and VoIP) use voice activity detection (VAD), a form of squelch
ing where low volume
levels are ignored by the transmitting device. In digital audio
transmissions, this saves bandwidth
of the communications channel by transmitting nothing when the source volume is under a certain threshold, leaving only louder sound
s (such as the speaker's voice) to be sent. However, improvements in background noise reduction technologies can occasionally result in the complete removal of all noise. Although maximizing call quality is a primary importance, exhaustive removal of noise may not properly simulate the typical behavior of terminals on the PSTN system.
The result of receiving total silence
, especially for a prolonged period, has a number of unwanted effects on the listener, including the following:
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. The noise generated 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 modern VoIP products, users may control whether they want comfort noise enabled or disabled.
As part of the RTP audio video profile, RFC 3389 defines a standard for distributing comfort noise information in VoIP systems.
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.
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.
Many radio stations broadcast birdsong, city-traffic or other atmospheric comfort noise during periods of deliberate silence (for example, in the United Kingdom, silence is observed on Remembrance Sunday
, and London's quiet city ambiance is used). This is to reassure the listener that the station is still 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)
Background noise
In acoustics and specifically in acoustical engineering, background noise or ambient noise is any sound other than the sound being monitored. Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations...
used in radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
and wireless
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
communications to fill the artificial silence
Silence
Silence is the relative or total lack of audible sound. By analogy, the word silence may also refer to any absence of communication, even in media other than speech....
in a transmission resulting from voice activity detection
Voice activity detection
Voice activity detection , also known as speech activity detection or speech detection, is a technique used in speech processing in which the presence or absence of human speech is detected.. The main uses of VAD are in speech coding and speech recognition...
or from the audio clarity of modern digital lines.
Some modern telephone systems (such as wireless and VoIP) use voice activity detection (VAD), a form of squelch
Squelch
In telecommunications, squelch is a circuit function that acts to suppress the audio output of a receiver in the absence of a sufficiently strong desired input signal.-Carrier squelch:...
ing where low volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
levels are ignored by the transmitting device. In digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
transmissions, this saves bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
of the communications channel by transmitting nothing when the source volume is under a certain threshold, leaving only louder sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
s (such as the speaker's voice) to be sent. However, improvements in background noise reduction technologies can occasionally result in the complete removal of all noise. Although maximizing call quality is a primary importance, exhaustive removal of noise may not properly simulate the typical behavior of terminals on the PSTN system.
The result of receiving total silence
Silence
Silence is the relative or total lack of audible sound. By analogy, the word silence may also refer to any absence of communication, even in media other than speech....
, 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 gateNoise gateA Noise Gate or gate is an electronic device or software that is used to control the volume of an audio signal. In its most simple form, a noise gate allows a signal to pass through only when it is above a set threshold: the gate is 'open'. If the signal falls below the threshold no signal is...
) 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
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
end in wireless or VoIP systems, to fill in the silent portions of transmissions with artificial noise. The noise generated 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 modern VoIP products, users may control whether they want comfort noise enabled or disabled.
As part of the RTP audio video profile, RFC 3389 defines a standard for distributing comfort noise information in VoIP systems.
A similar concept is that of sidetone
Sidetone
Sidetone is audible feedback to someone who is speaking. The term is most used in telecommunication contexts.-Telephony:In telephony, sidetone is the effect of sound that is picked up by the telephone's mouthpiece and in real-time introduced at a low level into the earpiece of the same handset,...
, 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.
During the siege of Leningrad
Siege of Leningrad
The Siege of Leningrad, also known as the Leningrad Blockade was a prolonged military operation resulting from the failure of the German Army Group North to capture Leningrad, now known as Saint Petersburg, in the Eastern Front theatre of World War II. It started on 8 September 1941, when the last...
, the beat of a metronome
Metronome
A metronome is any device that produces regular, metrical ticks — settable in beats per minute. These ticks represent a fixed, regular aural pulse; some metronomes also include synchronized visual motion...
was used as comfort noise on the Leningrad
Leningrad
Leningrad is the former name of Saint Petersburg, Russia.Leningrad may also refer to:- Places :* Leningrad Oblast, a federal subject of Russia, around Saint Petersburg* Leningrad, Tajikistan, capital of Muminobod district in Khatlon Province...
radio network
Radio network
There are two types of radio networks currently in use around the world: the one-to-many broadcast type commonly used for public information and mass media entertainment; and the two-way type used more commonly for public safety and public services such as police, fire, taxicabs, and delivery...
, indicating that the network was still functioning.
Many radio stations broadcast birdsong, city-traffic or other atmospheric comfort noise during periods of deliberate silence (for example, in the United Kingdom, silence is observed on Remembrance Sunday
Remembrance Sunday
In the United Kingdom, 'Remembrance Sunday' is held on the second Sunday in November, which is the Sunday nearest to 11 November Armistice Day. It is the anniversary of the end of hostilities in the First World War at 11 a.m...
, and London's quiet city ambiance is used). This is to reassure the listener that the station is still 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)
See also
- Background noiseBackground noiseIn acoustics and specifically in acoustical engineering, background noise or ambient noise is any sound other than the sound being monitored. Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations...
- Ambient noise
- TalkspurtTalkspurtIn digital telephony, a talkspurt is a continuous segment of speech between silent intervals, where only background noise can be heard. Segmenting speech streams into talkspurts allows bandwidth to be conserved by not sending excess data in silent intervals, and also allows synchronization,...
- Voice activity detectionVoice activity detectionVoice activity detection , also known as speech activity detection or speech detection, is a technique used in speech processing in which the presence or absence of human speech is detected.. The main uses of VAD are in speech coding and speech recognition...