feedback

In music, a continuous tone, usually a high-pitched squeal, caused by the overloading of circuits between electric guitar and amplifier as the sound of the speakers is fed back through the guitar pickup. Deliberate feedback is used in rock music.

The electric guitar innovator Les Paul used feedback in recording, as in ‘How High the Moon’ (1954), but it was generally regarded by producers as an unwanted noise until the Beatles introduced it on ‘I Feel Fine’ (1964). Both live and in recording, feedback was employed especially by the Who, Jimi Hendrix, and the Velvet Underground in the 1960s, and by noise and grunge bands in the 1980s and 1990s.