The term silence suppression is used in
telephony
Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
to describe the process of not transmitting information over the
network
Network, networking and networked may refer to:
Science and technology
* Network theory, the study of graphs as a representation of relations between discrete objects
* Network science, an academic field that studies complex networks
Mathematics ...
when one of the parties involved in a
telephone call
A telephone call is a connection over a telephone network between the called party and the calling party.
First telephone call
The first telephone call was made on March 10, 1876, by Alexander Graham Bell. Bell demonstrated his ability to " ...
is not speaking, thereby reducing
bandwidth usage.
Voice is carried over a digital telephone network by converting the analog signal to a digital signal which is then
packetized and sent electronically over the network. The analogue signal is re-created at the receiving end of the network. When one of the parties does not speak, background noise is picked up and sent over the network. This is inefficient as this signal carries no useful information and thus, bandwidth is wasted.
Given that typically only one party in a conversation speaks at any one time, silence suppression can achieve overall bandwidth savings in the order of 50% over the duration of a
telephone call
A telephone call is a connection over a telephone network between the called party and the calling party.
First telephone call
The first telephone call was made on March 10, 1876, by Alexander Graham Bell. Bell demonstrated his ability to " ...
. (While both parties may sometimes speak at the same time, there are times when both parties are silent.)
Silence suppression is achieved by recognizing the lack of speech through a
speech processing
Speech processing is the study of speech signals and the processing methods of signals. The signals are usually processed in a digital representation, so speech processing can be regarded as a special case of digital signal processing, applied ...
mechanism called
voice activity detection Voice activity detection (VAD), also known as speech activity detection or speech detection, is the detection of the presence or absence of human speech, used in speech processing. The main uses of VAD are in speech coding and speech recognition. I ...
(VAD) which dynamically monitors background noise and sets a corresponding speech detection threshold. This technique is also known as speech activity detection (SAD).
A similar principle is used for
Discontinuous Reception and
discontinuous transmission
Discontinuous transmission (DTX) is a means by which a mobile telephone is temporarily shut off or muted while the phone lacks a voice input.
Misconception
A common misconception is that DTX improves capacity by freeing up TDMA time slots for us ...
in GSM mobile telephone systems.
For further bandwidth gains, silence suppression is normally done after
echo cancellation
Echo suppression and echo cancellation are methods used in telephony to improve voice quality by preventing echo from being created or removing it after it is already present. In addition to improving subjective audio quality, echo suppression ...
.
Drawbacks
Background noise detection may be difficult in some circumstances (relatively low speech level, or relatively high background noise level, for example).
When silence suppression is active, the line appears to have gone dead at the other (egress) end of the call. For this reason, so-called ''
comfort noise
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.
...
'' needs to be generated to compensate for the lack of background noise. The ingress end must therefore signal the egress end that silence suppression is in effect. For best results, the level of comfort noise being generated on egress should match that of the background noise at the ingress end.
Speech activity detection must occur very quickly, otherwise
clipping
Clipping may refer to:
Words
* Clipping (morphology), the formation of a new word by shortening it, e.g. "ad" from "advertisement"
* Clipping (phonetics), shortening the articulation of a speech sound, usually a vowel
* Clipping (publications ...
might occur.
Speech activity detection does not work well on non-speech calls (fax or modem communication, for example).
Thus, silence suppression is generally an optional feature on telephony devices. In some cases, it is automatically turned on based on the characteristics of a call.
See also
*
Comfort noise
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.
...
*
Talkspurt
*
Voice activity detection Voice activity detection (VAD), also known as speech activity detection or speech detection, is the detection of the presence or absence of human speech, used in speech processing. The main uses of VAD are in speech coding and speech recognition. I ...
External links
Silence suppression and comfort noise generation (International Engineering Consortium on-line education topic)
Telephony