Laugh tracks

http://www.straightdope.com/mailbag/mlaughtrack.html

I’m not so sure about this answer. I know that Warner Brothers spends a LOT of time and effort to get live audiences to watch their sitcoms being taped. They have microphones hanging above the audience. They have “comics” to keep the audience in a jovial mood and implore everyone to yuck it up during the action. They also tape every scene at least twice and tell the audience members to laugh as much the second time they see it as the first. Some shows give prizes away for the “best laugher”. They can also filter out parts of the audience where someone calls out names, etc.

Having said that I suspect they may use the laughter and feed it into a machine and play THAT at the appropriate times.