A recording technique used to build up layers of sound, frequently employed in the tape studio. The classic method of sound-on-sound recording involved using an analog tape recorder. First, a sound is recorded on the tape in the conventional manner. Then the tape is rewound, and placed into record again, but with the erase head disengaged or bypassed. The second recording becomes added to the one already on the tape. This can be repeated many times to build up layers of sound.
In the 1950s, before the invention of multi-track recorders, sound on sound techniques were used both for early electronic music and for recordings of conventional music. Guitarist Les Paul and singer Mary Ford famously used sound on sound to make one of the first mutltracked recordings: their recording of "How High The Moon" in 1951, with overdubbed guitar and bass tracks from Paul and Ford singing harmony with herself. However, this was a tricky way to record; after a number of overdubs, the sounds recorded first began to deteriorate due to the properties of analog magnetic tape recording. Further, there was no way to correct mistakes; if a mistake was made, it was necessary to start the entire process over.
The invention of multitrack tape recorders in the late '50s eliminated the need to use sound on sound for conventional music recording. However, it continued in use in the tape studio, where electronic music artists prized the technique's characteristic of sometimes producing surprising results, and the aesthetic of working with and improvising around mistakes, instead of just re-recording the part.
After 1960, sound on sound recording was nearly forgotten until 1974, when Brian Eno and guitarist Robert Fripp recorded their album No Pussyfooting using a sound on sound that Eno had devised, in which a tape was recorded on one recorder, traveled across a space to another recorder were it was played back, and the played-back audio was mixed with the live audio going into the first recorder. Fripp would practically make a second career out of recording with this method, which he dubbed Frippertronics, and a few other artists made use of the technique including Larry Fast and Richard Pinhas. But the big advance came in the mid-1980s, when computer memory became cheap enough that digital delay lines with more than four seconds of memory became practical. Fripp himself did a technology update from the tape recorders to delay lines (and guitar synthesizers); he now refers to the upgraded system as Soundscapes, and a number of other artists have taken up the technique. Dedicated looper devices are now available which allows a performer to capture a clip of audio, or a sequence of clips, which can then be looped indefinitely to perform over.