At some point did the show stop filming in front of an audience? I know the first few seasons they didn't. Then they did for a while. But this morning I was watching 2 episodes that both had canned laughter. One was the first Mork episode, and Richie was on it. The other had Lori Beth and Richie, and Fonzie was dating a ballerina.

There may have been certain scenes of certain episodes that had to use canned laughter because having an audience either wasn't practical or possible. I'm not sure if the two episodes you mentioned would figure into one of those scenarios. Otherwise, all episodes after season two were filmed live before a studio audience.

also, keep in mind that "canned" laughter is routinely added to sitcom soundtracks when the live audience doesn't supply the amount of reaction desired.

That's the feeling I got. It seemed like it was filmed live by the way they were acting, but the laughter was definitely canned.

The odd thing about canned laughter is that it was real recorded audience laughter at some time in the past. But the same recordings were used over and over again until it acquired a familiar sound to us.

also, keep in mind that "canned" laughter is routinely added to sitcom soundtracks when the live audience doesn't supply the amount of reaction desired.

I didn't even think about that. They probably should have employed that tactic more during the last season of Happy Days because I remember quite a few times where there were jokes that received absolutely zero reaction from the audience.