Animusic is the name of a company that specializes in the 3D visualization of MIDI based music. Check out their website here
In their words:
"Both music and visuals are entirely digitally synthesized. We “invent” imaginary Virtual Instruments by building computer graphics models of objects that appear to create the sound of the corresponding synthesized music track"
In their videos, the music drives the animation. Their animated models are created first then programed to follow the music. Many of the instruments appear to be robotic - some actually are animated robots - or play themselves using curious methods to produce and visualize the original compositions. The animations typically feature dramatically-lit rooms or landscapes.
Animusic featuring the percussion piece Pipe Dream 2 here