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Echo Cancellation

Definition - What does Echo Cancellation mean?

Echo cancellation is a method used in telephony and telecommunication to improve voice quality by preventing echos from being captured or created, or possibly removing it in post-processing. The aim is filter the echo that is either produced by acoustic means or a hybrid echo produced by line echo, electrical reflections or impedance mismatch.

Techopedia explains Echo Cancellation

Echo cancellation aims to remove the echo that is heard when talking on the phone, either via landline or digital communication such as VoIP. The echo is one's own voice being transmitted back from the other end due to various reasons. Echo can be very disruptive to a conversation; it can impair call quality and even increase used bandwidth. This is because more data gets transmitted because of additional sound information that has to be processed, and even when the transmission is supposed to be one way because only one person is talking and transmitting, echo from the other end causes the listener to also transmit the echo and additional static. A process called “silence suppression” is used to prevent this.

Types of echo and how they are cancelled:

  • Acoustic echo – This occurs on the listener’s end when the microphone picks up the sound coming from the speakers which the one talking hears on the other end as echo. This is often the result of a very sensitive microphone, loud speakers or sound reflection from walls, especially in a confined space. To prevent this, a special microphone with very narrow pickup directions can be used. These microphones will only pick up sound directly in front of it and will usually not be able to pick up sounds coming from other directions, resulting in less echo. The speakers could also be turned down or headphones can be used.
  • Hybrid echo – This is the result of the conversion from a two-wire system, which is the case for customer premises, to a four-wire system in the telco’s PBX office. The conversion from two to four wires does not usually perform good impedance matching, resulting in echo. To cancel the echo, proper impedance matching or an echo cancellation engine can be used, or a circuit that reads the original signal and then cancels any signal that is very similar to it following shortly after is utilized.

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