Hexagrama is a circular music sequencer based on "sacred geometry" that triggers notes on a virtual plugin instrument; here is a video demo (hat tip dataisnature). It's intriguing to watch for a couple of minutes as you puzzle out the connections between image and sound. With your eyes closed the music gets less interesting; likewise, with the sound off, there's not much doing with the clockwork graphics. The confluence of sight and sound is thus giving you pleasurable fake insights--because the sum is more than the parts you think you're learning about structural relationships in music but you're really not.
Michel Chion's book Audio-Vision discusses momentary sound/image correspondences in film, true hybrid experiences that can't be reduced to their components and that I believe are mostly accidental. Having made a few videos with sound I kind of came to loathe the search for those magic crossing-over points. They happen and can be exciting but then there's the other 80% of the video where the music and image are just bobbing along with absolutely no reason to be together.
Am slowly drifting to the conclusion that the music you hear in your head when looking at a painting, and the images you see behind your eyelids when listening to music are phenomena more worth pursuing and thinking about than any actual conjunction, and that sound and image are ultimately most valuable to us in their zones of maximum competence, to borrow an idea from the dreaded Clement Greenberg. Contrary to his argument, this doesn't mean you have to work in those zones; compartmentalizations are choices we make.
Update: Minor edits.