Hardly anybody waiting in the sold-out SPCO Music Room for Wednesday night's performance of Reid Anderson's "The Rough Mixes" had any idea what was going to happen. The lucky few with more than an inkling had seen Tuesday's world premiere. Even Anderson, best known as the bassist for jazz trio the Bad Plus, wasn't entirely sure of the outcome.

Nor did he want to be.

While his 65-minute meditation for string trio, percussion, electronics and video included plenty of composed parts, he left ample room for improvisation. Not that you could tell — Anderson, violinists Stephen Copes and Sunmi Chang, cellist Anthony Ross, percussionist Jeff Ballard and visualist Cristina Guadalupe played together as if they'd been preparing for much longer than the few days they actually had.

His meal-ticket instrument nowhere in sight, Anderson radiated confidence and calm as he romanced worlds of sound out of a laptop, a pad-type controller and a couple other electronic devices. The Twin Cities native and longtime New Yorker avoided sonic clutter religiously, often backing away from his rig to do a little stealth conducting or simply to let a process he'd launched unfold.

Each of the piece's dozen or so sections demanded much of the instrumentalists — both in timing and technique — and very little from the audience. Anderson's strengths as a composer made their presence known from the moment the string players (all from the St. Paul Chamber Orchestra except Ross, who is principal cellist for the Minnesota Orchestra) slipped the first dose of elegant counterpoint under the simple synth melody that opened the performance. While violins and cello often lingered long in graceful legato constructs, they did plenty of fancy fast stuff, too.

But nowhere near as much as Ballard, a member of the Brad Mehldau Trio, Joshua Redman's Elastic Band, Fly, and various Chick Corea-led ensembles. Offering the performance's only hints of jazz, the drummer played heroically, often locking complex polyrhythms into the open spaces of Anderson's electronic beats to form even more complex polyrhythms.

Guadalupe's video projections complemented the music beautifully, commanding the crowd's attention without ever becoming overbearing. The New York-based architect and visual artist relied heavily on looping and processing snippets of simple nature footage — trees in a breeze, waves breaking on a beach, and the like — just enough to give the results an air of surreality. Providing a foil (literally) to all the abstraction, a woman in full fencing attire appeared repeatedly, making a final appearance as the last notes faded away and a long ovation commenced.