“After Leonard Bernstein passed away,” he says, “a memorial concert was given by players from orchestras he had worked with in Vienna, London, New York, and so on. I gave my downbeat and they came in with about six different attacks, because there was no agreement where ‘now’ was. We know from their auditions that the YouTube musicians play with great heart and skill, but it isn’t clear what is going to happen when we put them together.”