A musical performance is not about playing the piece correctly. If it were, a computer would be able to perform better than any human being.
No, a musical performance is all about interpretation. The same piece played by two different musicians would sound completely different. And in the case of an orchestral performance, the conductor is the musician; the orchestra is his/her musical instrument.
An interesting article from today’s NY Times - Demystifying Conducting: The Connection between gesture and music. Alan Gilbert, of the New York Philharmonic, is shown in motion capture and interview, working on the Grand Chorale from Stravinsky’s ‘A Soldier’s Tale’.
Speaking as a guy with a BA in Music, that pretty much sums it up.
This is what is known as “conducting badly.” Most conductors have a specific visual cue to when they think the beat occurs: they change the direction of the cue. So, at the very bottom of the swing, that’s the beat, like dropping a basketball on the ground: when you hear it hit, that’s when the beat is. A less clear conductor “feels” the beat happening some time other than when he shows it via the cue, and the musicians just have to learn to read a little ahead or behind whatever he’s conducting so they play when he wants them to. It’s kinda frustrating, really.
I think a marching band is one of the few times an average person is going to encounter a situation where the difference between the speed of light and the speed of sound (in air) is actually an issue. When we had really spread out drill, occasionally the people in the very back would have to actually lag behind the conductors by a very small fraction of a second. Very obnoxious. There’s no way we would have figured that out without a conductor there to listen.
Though I’ll grant that nobody really consciously slowed down by any specific amount, it was one of those things where the conductor complained we were off and we reflexively ended up trailing the conductor a little bit. The interval is so short you can’t really quantify how much to trail, it’s mostly reflex and muscle memory.
There is a reality show on Swedish television right now where a number of celebrities compete against each other in conducting. I asked a member of the orchestra how much attention they actually paid to the conductors and he said that they were instructed to follow them blindly, no matter how good or bad they were at it. He also said that last season there had been a girl who had been very good, but it turned out that she had studied music at the university, which may explain it.