Tom Hull’s “consumer guide” to the music of William Parker, et. al includes several links to interviews with William Parker, one of which had a few interesting pieces:

I visualized each string of the bass as a band of light, and I saw the bow of the bass as a prism and when I bowed the bass, it was like sending light through a prism. As white light, it would get broken up into different color bands. I looked at each sound. each harmonic as a different color band, and each color band could do a different thing. So I wasn’t just studying scales, I studied a method of relating these ideas of vision, color and sound, and what sound could do, like mantras and trance chants, you know, so this was my guide and my underlying aesthetic, that each sound had to have a reason and each sound had to do a specific thing.

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I also looked at the bass like a drum set, rather than just a stringed instrument. The G string which is the highest string, I looked at as a ride cymbal. My D string, I looked at as a snare. My low E string, I looked at like a gong, and my A string I looked at as a bass drum. So I developed that concept of the bass as a drum set, because I was very much influenced by drummers and the way they played, and the concept of the rhythm, sound, and melody you could get happening at once by playing the drum set. I was also looking at this concept of sound by which you were playing, but you weren’t thinking of notes. This wasn’t a note concept where you could play B and C and C# if you wanted, but of just sound, where you’re not thinking of notes, only of sound, sound vibrating. The more I studied, I realized we were dealing with the vibration of sound and understood how vibrating sound changes properties. Like when you boil water into steam — that’s how sound works. You have to just vibrate it enough so that it changes property and people perceive it in different way.

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Just the idea that the layman has about the music is wrong. There’s nothing “out” about this music. If you analyze it, you find that it has rhythm, harmony, melody. It has extended techniques. It’s influenced by music from all over the world, you know? The cell of sound is smaller. The rhythm isn’t constant, it’s more like the idea of a pulse, where you take a longer rhythm and break it up, varying smaller and longer cells. Sometimes you’re playing a chant that builds to a fever pitch. You deal with dances, the feeling of the blues. But it’s not about playing anything you want to play. It’s not even about wanting to play! It’s about having to do it, and training yourself how to go along with sound and a flow of ideas.

The passages in which Parker describes visual and sonic metaphors which motivated his musical development led me to do a quick google for “synesthesia,” a phenomena in which I’ve been interested, but about which I don’t know much real information. Here are a couple that I hope to look at more later: