As each new note sounds, its pitch (and that of all currently sounding notes) is adjusted microtonally (based on its spectrum) to maximize consonance. The adaptation causes interesting glides and microtonal pitch adjustments in a perceptually sensible fashion. See my paper on Adaptive Tunings, and the method is decribed in great detail in Tuning Timbre Spectrum Scale.
It's 4:19 long and about 4 Megs.
To overview of Xentonality
Looking for Bill's other music? There's plenty more weird (alternately tuned) stuff, and also a bunch of "normal" stuff.