Echo cancellation and echo cancellation are methods in telephony to improve voice quality by preventing the echo from being created or deleted after it is already present. In addition to improving subjective quality, this process increases the capacity achieved by suppressing silence, preventing the echo travel through a network.
These methods are commonly referred to as acoustic echo suppression (AES) and acoustic echo cancellation (AEC), and more rarely line echo cancellation (LEC). In some cases, these terms are more accurate, as there are several types and causes of echo with unique characteristics, including acoustic echo (sounds of a speaker reflected and recorded by a microphone, which can vary substantially over time) and echo Line Electrical impulses caused, for example, by the coupling between the sending and receiving cables, impedance impedance, electrical reflections, etc., which varies much less than acoustic echo). 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. "AEC" in particular is commonly used to refer to echo cancellers in general, regardless of whether they were intended for acoustic echo, line echo or both.
Echo suppressors were developed in the 1950s in response to the first use of telecommunications satellites, but have since been largely supplanted by better-performing echo cancellers.
Although echo suppressors and echo cancellers have similar goals - including an individual who speaks of hearing an echo of their own voice - the methods they use are different:
• Echo suppressors work by detecting a voice signal that goes in one direction in one circuit and inserting a large amount of losses in the other direction. Generally, the echo suppressor at the far end of the circuit adds this loss when it detects the voice coming from the near end of the circuit. This additional loss prevents the speaker from hearing his or her own voice.
• Echo cancellation involves first recognising the originally transmitted signal that reappears, with some delay, in the transmitted or received signal. Once the echo is recognised, it can be removed by subtracting the transmitted or received signal. This technique is generally implemented digitally using a digital signal processor or software, although it can also be implemented in analog circuits.