So you have an orchestra; and if you have an orchestra, you have some guy standing in front of everyone waving his hands in the air. It looks fairly mysterious, but evidently the people in the group understand what he is doing.
So what is it exactly that conductors do? Well, not a great deal in some cases. If they happen to be performing the "William Tell Overture," once he gets things started, the conductor’s job is pretty much over until he gives the sign to stop. Touring military bands usually play "Stars and Stripes Forever" at every concert. Major professional orchestras, whose musicians are hired full-time, have played many of the works in the standard repertoire so many times that they can almost play them in their sleep.
As a case in point, back in 1985 my wife and I traveled to New York City and my parents gave us a gift of tickets to the Metropolitan Opera. They were performing "La Bohème," which is about as much of an old war-horse as you will find among operas. The conductor was the famous tenor Placido Domingo.
I will have to say that as a conductor, Domingo was a pretty good tenor and should have stuck with it. He could have used a lot less flamboyance and a lot more precision in his motions. How the orchestra followed him I could not say. The point is, however, that the musicians did not have to follow him very much, because they have played that particular work so many times that they probably had it almost memorized.
Years ago I read an article in the Wall Street Journal about the cymbal player at the Met. Cymbalists are not the busiest members of the orchestra, and this fellow reportedly had timed the spaces between his clashes so that during the lengthier rests in his part he could slip out of the orchestra pit, exit the auditorium, walk to the pub across the street and have a drink and get back in plenty of time for his next note. That is pretty much having your performance on autopilot.
But an orchestra does need to start together and stop together and stay together throughout the piece, and that is where the conductor comes in. If they have a note that is supposed to be held for a moment, it is the conductor who determines just how long that hold will be. If they are supposed to slow down, the conductor dictates the rate at which the slowing takes place.
What you see during performances is the easy part, anyway. The conductor’s “heavy lifting” is during rehearsals. That is where the kinks get worked out, when he tells the orchestra how he wants the piece interpreted. Musicians in major orchestras are expected to have mastered the piece ahead of time. Rehearsal is not where they learn to play the music, but where they learn how the conductor wants it to be played.
All that having been said, if you have ever watched a video of a surgeon performing a delicate and lengthy operation, then you have an approximation of the level of concentration needed to conduct an orchestra in one of the more difficult major compositions. It is very intense work.
Obviously, the consequences of a surgeon’s mistakes are much greater than those of a conductor, but the effects of each are easy to detect. “Oops” is not something you want to hear either your surgeon or your conductor say.