(howlround) A loud whistle or rumble heard emanating from a sound system. It is caused by a sound being amplified many times. (E.g. a sound is picked up by a microphone and amplified through the speaker. The microphone picks up this amplified sound and it is sent through the system again). Feedback can be avoided by careful microphone positioning, and can be reduced by use of Equalisation to reduce the level of the frequency band causing the feedback.