Music is a universe of it's own, similar to mathematics. Call it the musicverse. It's inhabitants are not physical things such as soundwaves, instruments or sheet music. Those are the means by which we summon the inhabitants. Soundwaves can be used to carry a melody, but the melody is not the soundwaves. In Beethoven's last movement of the Eroica symphony, the silences are as much a part of the melody as the sounds.
What are its entities? Tones, chords, rhythms, melodies, polyphony, scales. Abstract entities within a universe with it's own set of laws.
The musicverse is strange with paradoxes built in. We say a melody moves from C to G. Nothing has moved. Yet the metaphor seems unavoidable. Play a scale from C on the piano. After seven steps you arrive back at C. But nothing has returned. The two Cs have different wavelengths and the second is the farthest from where you started. Yet it is the most similar.
From these entities we can create something sublime. All we need to enter it is a mind.