VIEWED THROUGH a wide-angle lens, the line that runs through Bill Rieflin's projects seems to follow the trend of many musicians who came out of the punk era. There's the furious, angst-driven beginning that coasts steadily downward into calmer, more middle-of-the-road fare.

In the case of Rieflin, the 53-year-old musician made a name for himself in the late '80s when he joined forces with industrial-rock carpet bombers Ministry and Revolting Cocks, while also helping form the equally brutal collective Pigface. So his moving into the world of straightforward rock like the Minus 5 and R.E.M. (he was their drummer from 2003 until the band split up in 2011) might seem like he's gone soft in his later years.

"I think if you know me, it's not that much of a surprise," Rieflin says, softly and matter-of-factly. "I would finish playing with Ministry and go home and listen to Simon & Garfunkel and Kate Bush."

A closer inspection of his discography over the past two decades also reveals some more daring musical interests. In the late '90s, Rieflin collaborated with King Crimson members Robert Fripp and Trey Gunn on two albums of supple prog jams. And in 2001, he collaborated with friend Chris Connelly on a delicate collection of gorgeous, keyboard-driven balladry.

One project that goes even further is Slow Music, an all-improvisational group with an awe-inspiring lineup: Fripp and Peter Buck on guitar, Rieflin on keyboards, drummer Matt Chamberlain, and bassist Fred Chalenor.

The project was born from work Rieflin had been doing at his home studio, creating abstract sound experiments using synthesizers and tone generators. "The nature of that kind of music is that it's often made by computers," he says. "I wondered what would happen if this were made live by people. What would that be like? So basically I called the best guys that I know and threw the idea at them. Everybody said, 'Yeah.'"

As with the best groups playing improvised music like this, no one in the quintet tries to dominate the sound. Instead, all five musicians find an expansive and beautiful common ground that, as heard on the live recordings available for download, resembles a vintage icy ambient-jazz album on ECM Records.

"I really want it to be as 'in the moment' as possible," Rieflin says of Slow Music performances. "I want to create conditions that cultivate deeper listening and greater attention among the musicians and audience. When that works, there's an incredible energy that builds up."

Both he and the audience will have ample time to build up a head of steam, as Rieflin will also play bass with opening act the Humans, a glammed-up pop outfit that features Fripp's wife, Toyah Willcox, on vocals. (Their performance will also feature a little Portland flavor, as local hero Dave Depper will sit in, playing guitar, keyboards, and drums.)

Beyond this quick run of West Coast dates, Rieflin will continue his work as a sought- after musician. He just finished recording with singer/songwriter Chuck Prophet and will be back in town with Fripp next month, this time fronting the Orchestra of Crafty Guitarists for a performance at the First Congregational United Church of Christ on May 24. If that weren't enough, Rieflin also spent a long stretch in England preparing for a September tour as the newest drummer for prog-rock colossus King Crimson.

"I spent about a half hour attempting to talk [Fripp] out of it," says Rieflin, "asking him, 'Are you sure you know what I do?' But if it works and it sounds like music, then I guess I'm happy."