Double tracking

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.