"Revolution 9" is a sound collage, which has been described as piece of experimental and avant-garde music as well as a musique concrète work. The piece begins with a slow piano theme in the key of B minor and the voice of an EMI engineer repeating the words "number nine", quickly panning across the stereo channels. Both the piano theme and the "number nine" loop recur many times during the piece, serving as a motif. Lennon later said of the track and its production: