When we ask what noise is, we would do well to remember that no single definition can function timelessly - this may well be the case with many terms, but one of the arguments of this essay is that noise is that which always fails to come into definition. Generally speaking, noise is taken to be a problem: unwanted sound, unorganised sound, excessively loud sound. Metaphorically, when we hear of noise being generated, we understand it to be something extraneous. Historically, though, noise has just as often signalled music, or pleasing sound, as its opposite. In the twentieth century, the notion of a clear line between elements suitable for compositional use (i.e. notes, created on instruments) and the world of noises was broken down. Russolo's ‘noisy machines’, Varèse and Satie's use of ostensibly non-musical machines to generate sounds, musique concrète, Cage's rethinking of sound, noise, music, silence . . .