It's often suggested that free-improvising musicians be judged on how composed their spontaneous musings sound. The Boston quartet Debris aggressively blur the distinctions between improvised and composed music, crafting their work with equally generous portions of each. While reminiscent of both Anthony Braxton's zigzagging saxophone and the complex precision of the 70s British rock band Henry Cow, Debris' snaking music most recalls the labyrinthine compositions of New York composer-saxophonist Tim Berne, at least to judge from their demanding but rewarding album last year, Terre Haute (Ratascan). Whether cooperating or playing against each other, the sax of Steve Norton and the electric guitar of Arthor Weinstein form a jagged, relentless front line of melodic, timbral, and harmonic exploration--on the CD Matt Turner's cello only raises the stakes, but he's been replaced by a bassist--while strong-willed percussionist Curt Newton mirrors the action and prods it along. Debris' compositions are consistently knotty and dense, packed with hard turns and unexpected twists; these surprises often open the door to inspired improvisations that range from contemplative gentle nudges to full-blown sonic squalls. Last December Newton was in town for a duet performance with Ken Vandermark; so it seems appropriate that Debris shares this bill with the Vandermark Quartet (see Critic's Choice). Friday, 9 PM, HotHouse, 1565 N. Milwaukee; 235-2334.