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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]
Long-latency connections also benefit; in the case of satellites orbiting distant planets, retransmission due to errors would create a delay of several hours. FEC is also widely used in modems and in cellular networks. FEC processing in a receiver may be applied to a digital bit stream or in the demodulation of a digitally modulated carrier.
However, any uncancelled hybrid leakage will cause echo when the associated transmission path has delay, so the effect on the system is reduction of echo.) Hybrids and cancellers are sometimes combined with echo suppressors. These work on the assumption that usually only one of the two parties to a conversation is speaking at a given time.
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).
The Internet Control Message Protocol provides an echo functionality, where a special packet is transmitted that always produces a reply. Tools such as ping, traceroute, MTR and PathPing use this protocol to provide a visual representation of the path packets are taking, and to measure packet loss at each hop. [b]
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, from a general point of view, is a time delay between the cause and the effect of some physical change in the system being observed. Lag, as it is known in gaming circles, refers to the latency between the input to a simulation and the visual or auditory response, often occurring because of network delay in online games.
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