The term silence suppression is used in
telephony
Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...
to describe the process of not transmitting information over the
network when one of the parties involved in a
telephone call
A telephone call, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party.
Telephone calls are the form of human communication that was first enabl ...
is not speaking, thereby reducing
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
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, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party.
Telephone calls are the form of human communication that was first enabl ...
. (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 to ...
mechanism called
voice activity detection (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 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 i ...
.
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 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
External links
Silence suppression and comfort noise generation (International Engineering Consortium on-line education topic)
Telephony