Three Cameras and the Laugh
Perform in front of an audience, shoot with three cameras at once. The setup that I Love Lucy (→ Filmed TV and the Rerun) settled into place was the backbone of the sitcom for half a century. Friends ran for ten seasons and 236 episodes, from 1994 to 2004, and 52.5 million viewers watched the finale (United States, viewers as measured by Nielsen).
There is one more, quieter invention in this band: the laughter. On 9 September 1950, when a certain comedy went out on a network, a trade paper noted it as an innovation in the soundtrack — there was no audience in the studio, yet laughter was on the film. It is valuable to have a record of people at the time feeling that this was new.
The machine that supplied that laughter was developed by an engineer, Charley Douglass. He is said to have been able to make anything from a small reaction like a whistle to a full belly laugh. In 1992 he received an Emmy in engineering development.
The story often told is that he kept the machine in a locked box and showed it to no one. That anecdote, though, could not be found in the records of the industry body, of public radio, or of the museums. This map writes only as far as could be confirmed: the machine existed, it is credited to him, and it was given an award. And we know there was at least one engineer who worked alongside him and could speak about the machine in detail.
Human laughter became, at some point, a device for carrying the sense that someone else is there into the living room. The story of it disappearing is the section next door.