Sean Booth and Rob Brown, the Mancunian duo known since 1992 as Autechre, have produced some of the most challenging and influential electronic music of the last decade. Their early releases on Warp Records spun elements of Miami bass, Afrika Bambaataa, and Mantronix into an abstract strain of robot dance music, but by 1994, when they released Amber, they had submersed all points of reference in a dense landscape of shifting rhythms and moody but simple synthesizer melodies. That same year they also put out an EP, Anti, which was in part a protest against English legislation that prohibited public gatherings accompanied by music with repetitive beats. On the track called "Flutter," they strung together 65 different rhythmic patterns so that no part was ever repeated. On Tri Repetae (1995), Chiastic Slide (1997), and LP5 (1998) the patterns became increasingly complex and more fractured, the production more claustrophobic and distorted, and the melodies more fleeting and spooky. Autechre proved that electronic music need not reflect the precision of its process--their elaborate programming reveals the human thought behind it. Unfortunately, like most groundbreakers, they've spawned a legion of imitators, and while some, like Miami's Phoenecia and Germany's Funkstšrung, have their own twists on the sound, too many have adapted Autechre's innovations like so much computer software. Perhaps in response, the duo have reinvented themselves on the new Confield, which arrives in stores this week. It's their most difficult, abstract album yet--some of the beats fall into steady patterns, but more often than not they squirm through the brain like frogs through oiled gloves--and it's sure to send everyone else back to the lab. Tonight's gig is the group's long-awaited Chicago debut, and reportedly their set will feature all new music. Local guitar and electronics whiz Kevin Drumm is also on the bill. Friday, May 11, 10 PM, Metro, 3730 N. Clark; 773-549-0203.