History of Backmasking

In 1877, Thomas Edison invented the phonograph, a device that allowed sound to be recorded and reproduced on a rotating cylinder with a stylus attached to a diaphragm mounted at the narrow end of a horn. Emile Berliner invented the lateral-cut disc phonograph record in 1888. His design became more popular than the Edison phonograph around the 1920's, since Berliner's patent expired in 1918. This allowed others to use his invention for their own purposes.

In addition to recreating recorded sounds by placing the stylus on the cylinder or disc and rotating it in the same direction as during the recording, you can hear different sounds by merely spinning the disc in the opposite direction. In 1878 Edison noted that, when played backwards, "the song is still melodious in many cases, and some of the strains are sweet and novel, but altogether different from the song reproduced in the right way." The backwards playing of records was suggested as training for magicians by the occultist known as Aleister Crowley. His 1913 book Magick (Book 4), alluded to the fact that an adept can "train himself to think backwards by external means." This included listening to phonograph records in reverse.

The 1950's saw the development of musique concrete, an avant-garde form of electronic music which utilizes editing together fragments of natural and industrial sounds, and the coetaneous spread of the use of tape recorders in recording studios. These trends led to tape music compositions, done on tape with techniques including reverse tape effects.

The Beatles, who included the techniques of musique concrete into their recordings, were known for popularizing the idea of backmasking. Singer John Lennon and producer George Martin both claim they discovered the backward recording technique during the recording of 1966's Revolver; more specifically the songs "Tomorrow Never Knows," "I'm Only Sleeping," and the single "Rain." Lennon stated that, while under the influence of marijuana, he accidentally played the tapes for "Rain" in reverse, and enjoyed the sound. The next day he shared the results with the other members of the band, and the effect was used first in the guitar solo for "Tomorrow Never Knows," and later in the coda of "Rain." According to Martin, the band had been testing altering the speeds of and reversing the "Tomorrow Never Knows" tapes, and Martin got the idea of reversing Lennon's vocals and guitar, which he did with a clip from "Rain." Lennon liked the effect so much he decided to keep it. Regardless, "Rain" was the very first song to include a backmasked message.

Sources: Wikipedia article on Backmasking