Double tracking or vocal doubling is an audio recording technique in which a performer sings or plays along with their own prerecorded performance, usually to produce a stronger or "bigger" sound than can be obtained with a single voice or instrument. It is a form of overdubbing; the distinction comes from the doubling of a part, as opposed to recording a different part to go with the first. The effect can be further enhanced by panning one of the performances hard left and the other hard right in the stereo field.
John Lennon, who particularly enjoyed using the technique for his vocals while in the Beatles, also referred to his home-studio overdubbing technique as "double tracking", but this is not standard usage, since he recorded new parts. Lennon's post-Beatles albums frequently employed doubling echo on his vocals in place of the ADT. Some critics complained that the effect gave the impression that Lennon recorded all his vocals in a bathroom, but some performers, like Black Francis and Paul Simon, value the rich echo chamber sound that it produces.