The Beatles "Carnival of Light" (1967 Unreleased Experimental Track)

On January 5th, 1967, shortly after vocal overdubbing sessions took place for Penny Lane, The Beatles (on request) recorded an experimental track for use in a then-upcoming art, light and sound festival titled The Million Volt Light and Sound Rave, that was to be held at the Chalk Farm Road Roundhouse Theatre in London on both the 28th January and the 4th February 1967. The track is said to be 13:48 minutes in length, and besides the two original events in which the track was played, it has never been heard by the general public.

The song's origins began in December 1966 when designer David Vaughan (after having painted a psychadelic design on Paul McCartney's piano) asked McCartney if he would be willing to submit a track for  The Million Volt Light and Sound Rave, organised, in part, by Vaughan himself. Much to his surprise, McCartney agreed, and the track was recorded the very next month.

Beatles expert Mark Lewisohn (who was personally allowed to listening to the song in 1987, while compiling his book The Complete Beatles Recording Sessions) has been quoted as saying that the song included "distorted, hypnotic drum and organ sounds, a distorted lead guitar, the sound of a church organ, various effects (water gargling was one) and, perhaps most intimidating of all, John Lennon and McCartney screaming dementedly and bawling aloud random phrases like 'Are you alright?' and 'Barcelona!'".

Others who have heard the song, such as McCartney biographer Barry Miles added in his 1997 publication Paul McCartney: Many Years from Now have added that the song had "no rhythm, although a beat is sometimes established for a few bars by the percussion or a rhythmic pounding piano. There is no melody, although snatches of a tune sometimes threaten to break through". McCartney himself described, in a November 2008 interview, the song's production, saying "I said 'all I want you to do is just wander around all the stuff, bang it, shout, play it, it doesn't need to make any sense. Hit a drum, then wander onto the piano, hit a few notes and just wander around'".

The base track consists of an organ playing bass notes and drums, and was recorded in fast motion, as to create a slower, more droaning sound when played in realtime. The song's instruments make heavy use of reverb, and it contains many vocal samples from Lennon and McCartney, from audible samples such as Lennon shouting 'Electricity!', to distorted gasps, coughs and the final echo soaked sample (heard just before the songs end) of McCarntney asking "Can we hear it back now?". Other instruments heard throughout the track include bursts of guitar feedback, gushy cinema organ and fragments of clinking pub piano.

McCartney tried to have the track released in 1996, intended to include it on their compilation record The Beatles Anthology 2, although George Harrison voted against it, stating that he "didn't like avant garde music", and the track never made it to the compilation. In the same year McCartney also claimed that he had been working on a photo collage film in which he intended to use Carnival of Light in the soundtrack, although the project has never been seen, and the last time McCartney spoke of it was in 2002.

McCartney confirmed himself in the same November 2008 interview that he was indeed still in possession of the master tapes, and was still eager to release it, saying that he felt as though "the time has come for it to get its moment. I like it because it's the Beatles free, going off piste", although he also stated that such a release would require consent from the groups estate (Lennon's widow, Yoko Ono, and George Harrison's widow, Olivia Harrison, as well as Ringo Starr). As of 2013, the song has not been released, and McCartney hasn't mentioned it since 2008.