One of the aspects of interpretation (for a conductor) is to read and fully understand written scores. A score can be made rich of notes and dynamic indications, but it cannot represent the mood-painting a musical is required to express. The conductor studies a great deal of the music, not just its notes, but its history, what the composer was thinking when he wrote it and expressive options hidden in the lines. The depth of this great insight is what determines the tempo, phrasing, articulation with which to approach the music and its intensity. It’s these interpretive decisions that distinguish one performance of Beethoven Fifth Symphony from another — each conductor puts forth his or her point of view, a personal slant on something that’s already known.
Gesturing.
Unlike other kinds of leaders, the conductor uses movement as his or her primary form of communication. The beat is indicated by the baton direction, the twists and turns of hands indicate crescendos and decrescendos, smaller facial expressions hint to a change in mood or energy. These non-verbal cues are read in real time and musicians are trained to follow the conductor. The clarity and authority of these gestures are crucial because they allow eighty or more musicians to respond instantaneously and together.
A good conductor knows how to balance accuracy and inspiration,
how to communicate direction while still encouraging fluid expression from the musicians.
To have Unity and Balance
The orchestra has been called a community of many voices, and like any community it needs to be in balance to thrive.
The conductor ensures the whole is greater than the sum of its parts,
with no part having another and each instrument being only a part within a larger ensemble.
As an illustration, if in a symphony the violins are carrying the tune,
the conductor might have signs to tell the brass not play too loudly so that the strings are heard okay.
The conductor can bring all sections together simultaneously in sublime unison,
to create a thunderous wall of sound for those special moments of grandeur.
These adjustments get made in real time, as rehearsals and performances unfold,
but it highlights the importance of thinking about the conductor as a technician and artist.
Inspiring the Orchestra
A conductor is not only a technical leader but also an inspirer of the musicians.
The orchestra musicians surely have their instrumental parts well under control
but is the conductor who lights them on fire facilitating a reminder that they are not playing notes, but rather a story.
A half- decent conductor could also ensure the performance would be full of desire as well.
I don’t know, and of course my view is subject to selection bias,
but what I have heard many musicians say is that they felt more a part of the music
but also to each other when there was a maestro, and this had an emotional impact on the orchestra as well.