The Music Director
The music director is the last participant to join the orchestral process and comes aboard after after the composer and the orchestrator have completed most of their work. Thus, the music director needs to read through the score, interact with the orchestrator and composer and understand all nuances before starting to work with the orchestra. This is the point in rehearsals when the music director and orchestra find out why a diva is considered to be temperamental. Does the key need to be changed? Is the high note unflattering? Does the tempo interfere with the vocal artistry? Quite often the music director is a mediator, trying to find common ground.
As we look back at the beginnings of the American musical, we need to understand that, for many musicians, the first move away from playing an instrument was to conduct other musicians. No matter how well trained in academic study, the musician needed experience to learn the craft of composition in performance. Quite often, we will see musicians move from being music directors or conductors into orchestration and perhaps into composition.