This technique is generally implemented digitally using a digital signal processor or software, although it can be implemented in analog circuits as well. Once the echo is recognized, it can be removed by subtracting it from the transmitted or received signal.
In practice, however, the same techniques are used to treat all types of echo, so an acoustic echo canceller can cancel line echo as well as acoustic echo. In some cases, these terms are more precise, as there are various types and causes of echo with unique characteristics, including acoustic echo (sounds from a loudspeaker being reflected and recorded by a microphone, which can vary substantially over time) and line echo (electrical impulses caused by, e.g., coupling between the sending and receiving wires, impedance mismatches, electrical reflections, etc., which varies much less than acoustic echo). Echo suppressors were developed in the 1950s in response to the first use of satellites for telecommunications.Įcho suppression and cancellation methods are commonly called acoustic echo suppression ( AES) and acoustic echo cancellation ( AEC), and more rarely line echo cancellation ( LEC). In addition to improving subjective audio quality, echo suppression increases the capacity achieved through silence suppression by preventing echo from traveling across a telecommunications network.