When a musical is done live, it's reasonable to assume that, for better or worse, the vocals are live. Yes, people will make mistakes. Lines will be flubbed. Reeds will break. Mics cues will be missed. Lights will come on early. But at least the audience is getting a consistent listening experience.
The immense challenge of capturing this same energy and consistency in a filmed musical, for television or cinema, is not falling into the default mode of the commercial music industry and tweaking performances until they sound like they were spit out by a computer.
I was reminded of this challenge watching the season premiere of Glee last night. Everything felt pretty much the same (maybe a bit closer to good episodes of Popular than I remembered, which isn't a bad thing) except the performances sounded distracting. See if you can pick up where the actors are no longer recorded live and instead lipsync to studio recordings:
If you guessed "As soon as the first girl starts singing, Robert," then you are correct.
I'm not suggesting that musicals should film the vocal performances live. John Cameron Mitchell insisted on this for every single production number in Hedwig and the Angry Inch, and the results were clearly worth it:
Makes it seem more organic and consistent, no? But it's a filming nightmare. One thing goes wrong and you have to go back to the start. The actors need more breaks to rest their voices and if someone gets sick: forget it.
So how do you avoid having an outdoor scene, ala Down to the River to Pray in O Brother Where Art Thou?, not sound like it was recorded in a tin can and tossed in the footage? Simple. Don't record it in the usual way. A scene in a big classroom is not going to sound like a recording booth. It should not be autotuned to the point that you doubt whether or not very talented singers are fakes. It should not be mixed to sound like an album. There are ways to manipulate audio to recreate certain conditions, such as a cavernous church or a shower stall, that don't put the abilities of the cast in question.
It was every song in Glee that did this. Every single one. You go to the message boards, and people are convinced the three cheerleaders got away with lipsycing and tricked the teacher. Yet the recording sounded just like Gold Digger and Take a Bow and Le Freak and Push It, all featured in the episode.
It's obviously too late now to fix this for the season. All 13 episodes are in the can. But maybe, in the future, we can settle for production values a bit more realistic than your average live performance on So You Think You Can Dance?.