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The performance of an echo canceller is measured in echo return loss enhancement (ERLE), [3] [9] which is the amount of additional signal loss applied by the echo canceller. Most echo cancellers are able to apply 18 to 35 dB ERLE. The total signal loss of the echo (ACOM) is the sum of the ERL and ERLE. [9] [10]
Delay is an audio signal processing technique that records an input signal to a storage medium and then plays it back after a period of time. When the delayed playback is mixed with the live audio, it creates an echo-like effect, whereby the original audio is heard followed by the delayed audio.
Adaptive feedback cancellation originated during the evolution of the hearing aid. The hearing aid became digital, and as such feedback cancellation was needed. In 1980 a directional microphone was introduced in the digital hearing aid, and adaptive feedback cancellation was created to block external noise that the microphone picked up. Today ...
Latency refers to a short period of delay (usually measured in milliseconds) between when an audio signal enters a system, and when it emerges.Potential contributors to latency in an audio system include analog-to-digital conversion, buffering, digital signal processing, transmission time, digital-to-analog conversion, and the speed of sound in the transmission medium.
A noise-cancellation speaker emits a sound wave with the same amplitude but with an inverted phase (also known as antiphase) relative to the original sound. The waves combine to form a new wave, in a process called interference , and effectively cancel each other out – an effect which is called destructive interference .
Due to the short delay, this cannot be considered to be a real long-delayed echo. For completeness it is still included here. Radio waves of frequency less than about 7 MHz can become trapped in magnetic field-aligned ionization ducts with L values (distance from the center of the Earth to the field line at the magnetic equator) less than about 4.
The digital canceller must process both linear and non-linear signal components, producing about 50 dB of cancellation. Both the analog and digital cancellers consist of a number of “taps” composed of attenuators, phase shifters, and delay elements. The cost, size, and complexity of the SIC solution is primarily determined by the analog stage.
The speed of light imposes a minimum propagation time on all electromagnetic signals. It is not possible to reduce the latency below = / where s is the distance and c m is the speed of light in the medium (roughly 200,000 km/s for most fiber or electrical media, depending on their velocity factor).