A trick used in music production. The vocalist sings the same phrase twice, then the two tracks are overlaid onto each other.

Advantages

  1. It serves as a kind of averaging filter to get rid of vocal errors.
  2. It adds presence to the voice.
  3. It makes the voice seem louder.
Drawbacks
  1. It sounds mushy.
  2. You have to sing in time and cannot do any improvisation, because otherwise your hard sounds such as 'B', 'D', and 'T' will appear to have been spoken twice.
  3. It sounds less intimate.
Extensive use of double tracking is a sign that the vocalist is not all that talented, and DT must be used to correct errors. More experienced vocalists will eschew the practice, but it is commonly used on the chorus of many songs, just to accentuate it.

The best and most obvious example of double tracking that I can think of is the entire song Gotta Have Faith, by George Michael.