To dream that you are in an orchestra represents inner integration, resolution, and harmony. You need to incorporate various aspects of your life. Alternatively, an orchestra refers to your desires to fit in and be accepted by society. 

To hear the music of an orchestra signifies your connection to humanity. You are sympathetic and passionate about your beliefs.

To dream that you are conducting an orchestra indicates control, empowerment. or manipulation  The dream may also be a metaphor suggests that you are “orchestrating” some plan.