To reduce echoes caused by transmission delays, special devices known as “Echo Cancellers” are used. These devices when operating efficiently can almost eliminate all traces of echo during a conference. Room acoustics and microphone positions also affect the level of echo. If a microphone is moved or its sensitivity is altered during the conference, echo could be introduced until the echo canceller has realigned itself to the new environment. A good echo canceller is dynamic in operation and is able to continually monitor the situation and alter the correction as a conference is taking place to reduce echo to a minimum. They are an essential element of high quality videoconferencing.