At a time when post-rock peers like Tortoise were stretching the rhythmic and abstract limits of guitar-based music, the duo of David Grubbs and Jim O'Rourke were more liable to rip holes in its space/time continuum, creating elliptical relationships between psych folk, ambient soundscapes, and musique concrète. You can hear Gastr's oppositional aesthetics play out on 1994's “Work From Smoke,” which, over its 13-minute duration, mutates from fingerpicked avant-flamenco into a haunting dronescape. But for 1998's Camoufleur, the pair muted their harsher frequencies for a set of wondrous prog-folk epics like the fiddle-whipped “Black Horse.”