Long before Justin Vernon retired into the woods of Wisconsin and hatched his solo project Bon Iver, he tinkered with indie-rock friends from around that state. And they’ve since let their creative juices flow in the group Volcano Choir.

“It’s not atypical, actually, for that to work that way around here,” guitarist Chris Rosenau says from his home in Milwaukee, within four hours of his bandmates. “It’s an open situation, with people playing in other people’s bands all the time.”

Vernon was fond of Collections of Colonies of Bees, a group that included Rosenau and other future members of Volcano Choir. They began to swap email files with song ideas that begat Unmap, released in 2009 shortly after Bon Iver’s debut, For Emma, Forever Ago, and sharing its sparse, abstract atmospheres.

“For 90 percent of the writing on Unmap, Volcano Choir didn’t exist, technically,” Rosenau says. “It was us screwing around, and we realized at some point, there’s music here.” After a tour of Japan where the musicians recast Unmap for the stage, Volcano Choir became a flesh-and-blood band beyond its name, setting up the grander textural strokes of its 2013 sophomore album, Repave.

“It’s a tightrope to figure out the correct direction for a song, and that’s where all the years of utter, implicit trust come together,” Rosenau says. “Volcano Choir, which is the largest band we’re all in, is also the one project where we all feel the most free. There’s no real genre. There are no real rules. We can bring in any idea, and it’s put through the VC crucible and deconstructed and reconstructed.”

That process took three years in the case of Repave, due to Bon Iver’s heavy touring schedule as well as other members’ music projects and day jobs. “You come back six months later, and you can approach it totally fresh,” Rosenau says. “No one’s married to any [song] parts. You can listen to a song as a whole, and the best stuff comes out.”

Repave spans a spectrum ranging from the acoustic guitar-flecked “Alaskans” to the stately march of “Byegones.” Whereas Unmap echoed Bon Iver’s eerie indie-folk, Repave reverberates in starker contrast to Vernon’s better-known project.

“Seeing him get the attention he deserved was fantastic,” Rosenau says of Bon Iver’s Grammy-winning success, but he adds, “After Unmap, there was probably a bit of that [idea] resonating, like ‘Let’s make a proper kick-ass rock ’n’ roll record and cement this shit forever, so Volcano Choir can stand as its own entity.’”

The group elevates further in concert. Vernon sings from a podium rigged with vocal-processing equipment that he triggers through keyboardist Thomas Wincek’s computer banks. Wincek similarly works with loops in his current all-instrumental outfit All Tiny Creatures —as he did in Collections of Colonies of Bees, says Rosenau, who also layers with looping effects.

“We’re very particular in executing these live performances without pre-recorded tracks,” the guitarist says. “You have the freedom to improvise and be creative within these songs because all the changes are being made in real time.”

To orchestrate all those song parts live, Volcano Choir also added a third guitarist, Andy Fitzpatrick, to a lineup completed by drummer Jon Mueller, bassist Matthew Skemp and guitarist Daniel Spack. “That’s just kind of the ethos of this band, and us as musicians,” Rosenau says. “It’s harder, but it’s way more rewarding.”

Onstage, each musician tends to blur into the fabric, performing under oblique lighting in front of a topographic relief that recalls the ocean waves on the cover of Repave. “We wanted something atmospheric and simple,” he says of the backdrop built by Michael Brown, lighting designer for the National.

Of course, that setup won’t work the same in daylight when Volcano Choir hits Boston Calling on Sept. 6, the day after the National headlines. But that doesn’t faze Rosenau. “The festival vibe in the daytime is great,” contends the guitarist, whose group recently played at Montreal’s Osheaga. “The lights and the backdrop, when we think of it, that’s just how we see it in our brains.”

Volcano Choir play Boston Calling on Sept. 6.