Echo suppression and cancellation

echo cancellationecho cancellerecho suppressorAcoustic Echo Cancellationecho suppressionAcoustic Echo Cancellingcancellersecho cancelerecho suppressingecho-suppression
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.wikipedia
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Silence suppression

In addition to improving subjective audio quality, echo suppression increases the capacity achieved through silence suppression by preventing echo from traveling across a network.
For further bandwidth gains, silence suppression is normally done after echo cancellation.

Videotelephony

videoconferencingvideo conferencingvideo chat
Videoconferencing is one area where full bandwidth audio is used.

Adaptive filter

Adaptive filteringadaptive signal processingadapted
This technique requires adaptive signal processing to generate a signal accurate enough to effectively cancel the echo, where the echo can differ from the original due to various kinds of degradation along the way.

Sidetone

If the delay is very small (10s of milliseconds or less ), the phenomenon is called sidetone.

G.165

Some telephone devices disable echo suppression or echo cancellation when they detect the 2100 or 2225 Hz "answer" tones associated with such calls, in accordance with ITU-T recommendation G.164 or G.165.
G.165 is an ITU-T standard for echo cancellers.

Modem

modemsdial-up modem56k modem
Echo control on voice-frequency data calls that use dial-up modems may cause data corruption.
Echo cancellation was the next major advance in modem design.

Speakerphone

speaker
These phones are much more complicated and often employ sophisticated digital signal processing algorithms to sort out the incoming sound and the sound in the room for echo cancellation.

Audio feedback

feedbackguitar feedbackacoustic feedback
Negative indicate the echo is stronger than the original signal, which if left unchecked would cause audio feedback.

Signal reflection

reflectionreflectionsreflected
When a sufficient degree of impedance matching is not practical, echo suppressors or echo cancellers, or both, can sometimes reduce the problems.

Telephony

digital telephonytelephonedigital
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.

Echo

echoesechoedechoing
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.

Telecommunications network

networkcommunication networkcommunications network
In addition to improving subjective audio quality, echo suppression increases the capacity achieved through silence suppression by preventing echo from traveling across a network.

Digital signal processor

DSPDSPsdigital signal processors
This is primarily because AECs require a fast processor, usually in the form of a digital signal processor (DSP).

Software

Computer softwareSoftware & Programmingsoftware technology

Chorus effect

choruschorus pedalchorused
If the delay is slightly longer, around 50 milliseconds, humans cannot hear the echo as a distinct sound, but instead hear a chorus effect.

Bell Labs

Bell LaboratoriesBell Telephone LaboratoriesAT&T Bell Laboratories
In response to this, Bell Labs developed echo canceler theory in the early 1960s, which then resulted in laboratory echo cancelers in the late 1960s and commercial echo cancelers in the 1980s.

Digital signal processing

DSPsignal processingdigital
Rapid advances in digital signal processing allowed echo cancellers to be made smaller and more cost-effective.

DMS-100

remote switching centreDMS-250DMS100
In the 1990s, echo cancellers were implemented within voice switches for the first time (in the Northern Telecom DMS-250) rather than as standalone devices.

Voice engine

Today's telephony technology often employs echo cancellers in small or handheld communications devices via a software voice engine, which provides cancellation of either acoustic echo or the residual echo introduced by a far-end PSTN gateway system; such systems typically cancel echo reflections with up to 64 milliseconds delay.

Public switched telephone network

PSTNpublic telephone networktelephone network
ITU standards G.168 and P.340 describe requirements and tests for echo cancellers in digital and PSTN applications, respectively.

Decibel

dBdecibelsbel
This is the ratio, expressed in decibels, of original and it's echo.

Voice over IP

VoIPVoice over Internet Protocolvoice-over-IP
In modern times, the main use of an AES (over an AEC) lies in the VoIP sector.