There’s a new fusion genre emerging in folk music, so far without a name. You could call it chamber folk, by analogy with chamber pop, a streak of quiet indie rock that uses orchestral instruments. Some of it turned up on A Prairie Home Companion a few weeks back, with the prodigiously talented mandolinist Chris Thile joining the Appalachian Journey bassist Edgar Meyer in arrangements that gave Meyer, bowing the bass, a lot to do.

Folk, jazz, and pop are longtime partners. The new fusion adds classical music to the mix, with intricate arrangements that make the accompanying instruments into full participants in the texture. In the pairing of Scots fiddler Alasdair Fraser and American cellist Natalie Haas, the new music seems full of possibilities.

The genre’s roots are in the progressive bluegrass and new acoustic music of the American West Coast, but the variant developed by Fraser, a giant of tradition-based Scots fiddling, has the advantage of being able to lay the emotion on a bit thicker. The duo typically deploy Fraser on a traditional-sounding tune (actually, most of their music is original), with Haas adding a syncopated rhythm and then taking off into melodic counterpoint or jazzy elaboration propelled by the basic rhythmic contrast. But they leave plenty of room to circle back to lyrical interludes played in long-note harmonies, and the slow pieces have a fine dose of sentiment missing in music by the likes of Darol Anger.

Fraser and Haas offer a combination of cool sophistication and traditional ethos that has gained them a growing cadre of fans. Drive around the Northeast, where folk music holds a bigger slice of the public radio schedule than it does here, and you’ll likely hear Fraser and Haas often.

Fraser came from Scotland to California and started a Scots fiddling school called Valley of the Moon, where Haas, a graduate of the Juilliard School, became his student. They’ve been at this for about five years, long enough to know the ins and outs of each other’s musical minds. Fraser points out that the use of a fiddle and cello together in Scots music was actually common in the eighteenth century, when the first efforts to collect Scotland’s heritage of melody were in flower. So it may be that, as with other musicians and scholars from the British Isles, he found a deeper layer of the tradition by coming across the sea.

Alasdair Fraser and Natalie Haas come to the Ark on Saturday, January 24.