HOPING TO get away for a few moments from the noise and stench of last month's South by Southwest music conference in Austin, Texas, I ducked into a church to see a set from a Montreal art-folk band. The church's sanctuary was a large, dark, gorgeous (and gorgeous-sounding) room. The pews were filled, but the audience was silent; the only sounds were emanating from the stage. It was as marked a contrast as you could get from the drunken din taking place mere blocks away.

That band, the Barr Brothers, offered a breathtakingly good performance, perhaps one of the best I've ever seen—full of dynamics and drama and subtlety and shade. The drummer, Andrew Barr, knew when to hold back and when to thump heavily; his brother Brad played folk songs, funeral songs, American Delta blues songs, and Malian desert blues songs on his guitar. And there was a harp.

I learned later that the harpist, Sarah Page, couldn't hear a single note of what she was playing during that performance; she sounded perfect. There was a fourth member, Andres Vial, who moved around the back of the stage, seemingly playing a different instrument every number. At one point Brad pulled on a strand of nearly invisible thread woven through the strings of his guitar. The effect was stunning, like an ultra-fine bow dragging across the strings, creating a soft, echoing drone. For the final song, Brad offered either ends of the thread to two members of the audience (plants, I later found out, but it scarcely mattered) and they gently tugged back and forth on it, several feet away from the stage.

"It's just polyester sewing thread," Brad explains when I ask him about it on the phone. "I saw it done by a Romanian Gypsy group called Taraf de Haïdouks, where the old violin player tied a piece of horsehair from his bow onto the string and then just started pulling on it. I thought, 'I should be able to do that on a guitar.'"

The Barr Brothers only have one album out, but there's good reason they already soundso masterful: Brad and Andrew spent close to two decades as members of the Slip, a Boston-based band that's toured endlessly across the US. The Barr Brothers marks a new direction, as well as the brothers' move to a new country.

The Slip played a show one night in Montreal, and the club literally caught fire. Out in the street, Andrew struck up a conversation with a waitress who worked there—they stayed in touch, and Andrew moved to Montreal not long after. Brad shortly followed suit. "All these things just pointed toward going to Montreal with Andrew," he says. "I knew I liked the spirit up here in Montreal, the way that the town felt, all the cafés and neighborhoods."

In his new apartment, Brad discovered his next-door neighbor—Page—played the harp. "I would lay in bed and listen to her play the harp all morning. Her practice room was adjacent to my bedroom wall, so I would just lie there and listen to her. We sort of struck up a friendship that way. Her music sort of seeped into my subconscious, and I started imagining songs."

Those songs eventually became The Barr Brothers, and while Brad says the Slip still has a future, this new band has become their primary focus. "I'm kinda happy with whatever happens right now," he says.