I hear everything.
Sounds like an obvious comment, but when I listen to music, it's like my mind is a multi-processor computer, with a thread for each part. I hear drums, vocals, guitar, whatever, all seperately - as if just one of them were there, but my mind is doing the mixing, not the audio track?
It's quite intense, and I don't think I've really explained it properly. Sometimes I can pick out the individual harmonics of a note, though that's very difficult. Largely though, when I hear music, and have the oppurtunity to shut my eyes, and not look like an idiot in public, I see blotches of colour on a musical canvas that rushes past my minds eye. (I've always found language other than music impossible to describe thought with.)
The two experiences that taught me most about music though, were Psilocybe mushroom trips where I did nothing but listen to classical music. For the pieces I knew best, I wasn't listening to the music - I became it. I stil have moments where that happens now. I felt like one part was coming from my chest, another from my feet, another from my lips et cetera. It was overwhelming. I recommend it.
I'm not sure if I "see" music - I think maybe it just takes me over sometimes, and pushes everything else to the side. For that reason, it's incredibly powerful, which seemingly now stops me listening to it when I'm not physically ready.
Addendum: Singing is extraordinarily poewrful - I've been known to walk out of services at the Cathedral I sing at, visibly shaking from the adrenaline rush of singing something big, and powerful.
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CARPE PECTORIS!!
There is nothing about these perplexing and morally insensitive humans that cannot be solved with the aid of a heavy machine gun.