The importance of the British collective AMM for any of today's radical music cannot be overstated. Their brand of freely improvised sound set the stage for industrial, noise rock, and ambient 30 years ago, and they successfully brought together strands from free jazz and experimental classical music, yielding an altogether new agglomeration. Meanwhile, AMM actively sought to bridge the perceived gap between the physical and psychological materials of sound and the social practices of music making--to give the lie to the supposed elitism of abstraction. Their concerts were sprawling adventures in real time. (No pious artistes, these--a few years ago I saw an AMM concert at which audience members were encouraged to come and leave as they liked, with none of the conventional discomfort at leaving when bored.) Now, after more than three decades of intense audio investigation, AMM live on as the longest continuing ensemble in free music, turning acoustics into a tool for deep inquiry. Since their first records in the 60s--including the currently available AMMUSIC 1966 (Cuneiform) and The Crypt--12th June 1968 (Matchless)--AMM have deployed a unique kind of improvising built on a steady accumulation of textures, simultaneous sounds (including long tones, drones, scrapes, and oscillations), and the singular musical vocabularies of the ensemble's participants. Once fittingly described as "laminar," AMM create a dense, noise-saturated set of stratified layers. Over the last decade or so, the group's core personnel has consisted of Keith Rowe on guitar and percussionist Eddie Prevost (both founding members, along with the late composer, pianist, and music philosopher Cornelius Cardew) and virtuoso avant-garde classical pianist John Tilbury. Rowe virtually invented the "tabletop" approach to guitar--imagine a combination of John Cage's prepared piano and Leon McAuliffe's lap steel--a tool now being intently explored by Chicago's own Kevin Drumm. Last time I saw them, though, AMM's secret weapon was Tilbury. In the midst of Rowe's electric sound-sheets and Prevost's rolling toms, brittle snare, and bowed cymbals, the pianist somehow slipped in a genuinely harmonic statement, his fingers spiderlike as they slinked one sly melodic line after another. AMM very rarely come to town; their 1984 visit to the Arts Club resulted in the recently reissued Combines and Laminates (Matchless). In the superb acoustic environs of Goodspeed Recital Hall, this promises to be an event not to miss. Saturday, 7 PM, Goodspeed Recital Hall, University of Chicago, 1010 E. 59th; 702-8670.