I toured a facility recently and saw a number of abbreviated side workstations connected to one man mixing suites with a mysterious red button cabled box. I asked my tour guide if it was the mixer chair ejection button. The tour guide said that it was for the "laugh man." He said that a laugh man comes in and sweetens production laugh tracks for sitcoms with a collection of SFX he carries with him that contains incredible variations of crowd reactions without identifiable language. (Thus, it can also be used as the M&E laugh track as well.) He says they take about an 1.5 hours to sweeten a 30 minute show and then they are done.
I would have assumed the laugh track would have been created in editorial by the sound editor. I have certainly been charged with that mission before.
Have you ever been a laugh man? Where does one get this mysterious ubiquitous walla? How do you use that red button. Tell me more.