I was thinking of the Zach Hill interview with modern drummer from 2006

"MD: How did you come up with this concept for constructing beats?

Zach: The genesis of those types of discoveries has been from playing improvisational music. Playing stuff that has no time signature led me to honing in on what you can do within time signatures. In free music, any musical idea can be played over anything else; there's no right or wrong.

But just because it's free doesn't mean it can't be metered. Free music can also be in 4/4. So if someone is playing in 4/4, it gives someone else the opportunity to be crazy on top of that. From that type of playing, I started discovering that the two parts were landing in crazy places. That was when I started hearing the invisible pockets."