It was commissioned for the Million Volt Light and Sound Rave, an event held at the Roundhouse in London on 28 January and 4 February 1967.

Recorded during a session for the song "Penny Lane", "Carnival of Light" is nearly 14 minutes long and contains distorted, echo-laden sounds of percussion, keyboards, guitar and vocals.

For McCartney, the piece came to hold significance in his efforts to be recognised as the first Beatle to fully engage with the avant-garde, over a year before John Lennon recorded "Revolution 9".

With their August 1966 album Revolver, the Beatles broke new ground in pop by departing from the genre's conventional notions of compositional form, instrumentation and engineering; in musicologist Walter Everett's description, it was also "an innovative example of electronic music".

[4] The latter was an electronic music group whose members included composers Delia Derbyshire and Brian Hodgson from the BBC Radiophonic Workshop and synthesizer pioneer Peter Zinovieff.

There, Zinovieff played them an experimental composition "at such intense decibel frequencies", according to Edwards, "that many parts of my anatomy (including internal organs) began to perform an involuntary dance.

[2] With reference to McCartney's credit on the poster for the rave, author Steve Turner says that as a "musical freak-out" by the four Beatles, "Carnival of Light" "wasn't so much 'composed' by Paul as initiated by him".

[18] The band first created a basic track of drums and organ recorded at a fast speed, which made them sound deeper in pitch and slower in tempo.

The two also recorded Native American war cries, whistling, close-miked gasping, genuine coughing and fragments of studio conversation.

[2] Miles suggests that the piece "most resembles 'The Return of the Son of Monster Magnet'", composed by Frank Zappa, from the Mothers of Invention's Freak Out!,[19] an album that he had given to McCartney in 1966 and which resounded with the latter's initial ideas for Sgt.

[20] Miles continues: "except there is no rhythm and the music here is more fragmented, abstract and serious ... [A] beat is sometimes established for a few bars by the percussion or a rhythmic pounding on the piano.

[22] He outlined the contents of the four-track tape: The piece concludes with McCartney asking the studio engineer in an echo-soaked voice, "Can we hear it back now?

"[21] Lewisohn wrote that a rough mono mix was given to Vaughan,[4] while Miles stated that the mixdown had "full stereo separation".

[27] McCartney was angry with the organisers when he learned that the tape had been allowed to play on past the agreed point, thereby giving the crowd a preview of "Fixing a Hole".

[30] Since 1967, "Carnival of Light" has only been heard by "Abbey Road insiders", according to author Mark Brend, and has not circulated on bootlegs.

Pepper period, it was Lennon who came to be identified as the band's revolutionary avant-gardist through "Revolution 9" and other collaborations with Ono, including their 1968 album Two Virgins.

[31] Harrison also became publicly associated with avant-garde experimentalism, with his late-1960s solo albums Wonderwall Music and Electronic Sound,[32] as did Ringo Starr, through his championing of Apple artist John Tavener; by comparison, according to music critic Richie Unterberger, McCartney retained "the straightest public image of the four".

[33] When asked about "Carnival of Light" in his interview for Lewisohn's 1988 book, McCartney likened the track to Harrison's forays into Indian music with the Beatles, and said he had recently renewed his interest in such experimental work.

[37][nb 3] George Martin, who helped evaluate all the Beatles' recordings for inclusion on the Anthology CDs,[38] also considered "Carnival of Light" unworthy of release.

"[47] In Ian MacDonald's opinion, unlike the sensitivity AMM brought to their work, "the Beatles merely bashed about at the same time, overdubbing without much thought, and relying on the Instant Art effects of tape-echo to produce something suitably 'far out'.

[12][50] Music journalist Michael Gallucci has described "Carnival of Light" as "the holy grail of lost Beatles recordings".

"[27] In a 2016 interview, McCartney stated that he was toying with the idea of releasing previously-unissued Beatles recording takes, including "Carnival of Light".