What you get with bassist Michael Formanek and his quartet is outside, to be sure… but only just. What you hear in his music is fully formed melody and arrangement, but expressed in Formanek’s unique harmonic language. His splendid band members—-alto saxophonist Tim Berne, pianist Jacob Sacks, drummer Gerald Cleaver—-have mastered that language so surely that it seems likely they inspired it to some level (at least in the sense that Formanek tailored his approach for his musicians). You hear it quite clearly in their improvisations, too; they’re more freeform than they might be in some bands, but less so than in others—-open, but careful, explorative, punctilious. In other words, it’s experimental jazz but within a thoughtfully structured context. It’s an excellent fit for those who want to venture onto the edges of the music, but need something constructed to hold onto. Better yet, it’s an excellent fit for those who don’t care what form the good stuff takes, as long as it’s the good stuff.The Michael Formanek Quartet performs at 8 p.m. at the Atlas Performing Arts Center, 1333 H St. NE. $25.