The Science and Poetry of Music
As I have remarked elsewhere, music is one of those things that people like to define poetically. And there is an audience for that kind of definition, especially if it "resonates" with the feelings that the audience has about music.
The problem is, most poetry isn't very scientific.
Can we mix science and poetry?
Here's my best attempt:
Music perception is the perception of truths about the world which go beyond anything we can learn from our own personal experience.
The (Perception) Caveat
You'll notice that I didn't actually define music. I defined music perception. This is because my super-stimulus theory of music isn't a theory about music, it's a theory about music perception. According to the theory, music perception is a special kind of "truth perception". But music itself is false and contrived, and any "truth" or feeling of "truthfulness" propagated by music is entirely false.
Some people would say that spirituality has to do with truths that go beyond our ordinary experience of life. And some people would say that music has a spiritual aspect to it. So there could be a connection there.
A Feeling of Belief
Sometimes when I listen to strong music, while thinking about something I want to believe in, the music can create a feeling that my desired belief is true.
Unfortunately the feeling goes away when the music stops. But the fact that music even has this effect suggests that music perception has something to do with the validation of beliefs which are not completely supported by the evidence available to us directly.
Another thing I have noticed about music is that song lyrics which are slightly nonsensical "work" better than song lyrics which state a proposition and then present large amounts of hard rational evidence in favour of that proposition, as if the singer was trying to win a debate.
Again, this suggests that music perception is about believing stuff when you don't have rational reasons to believe that it is true.