` (UTC)  You literally record it on a separate track on the tape (or these days on the digital recorder) so you can remove it. Each mike comes through a sound board and you can add or delete it. Generally before digital you had eight tracks on a tape (four before about 1967, I think the Beatles' Abbey Road was the first professional album to use four-track) so you record different mikes on different tracks. If you keep a track free you can add a laughter track later. I would imagine it is also used for dubbing, if you record actor's voice mikes on a separate track. There must be some crossplay that it will end up as an ``echo`` on other tracks I am not an expert.    23:39, 28 January 2009`