At the Bartlett: Mandolin Orange enjoying fuller sound of backing band

The rustic sounds of Mandolin Orange, mostly sweet and solemn and a little melancholy, make for a perfect soundtrack to the opening grace notes of autumn. It’s the kind of music that evokes images of small Southern towns and long country roads and bluegrass bands playing old gospel songs on sprawling front porches.

Mandolin Orange is the musical project of Andrew Marlin and Emily Frantz, who stop by the Bartlett on Sunday night. Based out of Chapel Hill, North Carolina, Marlin and Frantz, who are also a couple, have been writing and performing music together since 2009.

“We met playing bluegrass through mutual friends of ours, so that was a lot of the first music we were playing together, Bill Monroe covers and Stanley Brothers covers,” Frantz said. “Little by little, we started working in more and more original tunes that Andrew was writing, so that became the bulk of what we were doing. But we still spend a lot of time playing those old-timey bluegrass tunes.”

Marlin remains the duo’s primary songwriter, with Frantz contributing vocal, guitar and fiddle lines, and their collaboration has produced four albums of haunting, melodic roots music.

“I think one of the things that’s always made it really easy on us is that we both engage with music really differently. We play different roles,” Frantz said. “I’m not a songwriter at all, so there’s no real conflict there. … I definitely chime in on arrangement and the broader questions of musical direction. We do such different things, which makes it easier for us to join forces. The lyrical writing, the melody and the form of the song are really personal for (Andrew), and I like to absorb it as it’s happening.”

The band’s latest album, titled “Blindfaller,” is less spare and sonically richer than many of the band’s earlier releases. Marlin and Frantz are still front and center on the new LP, but they’re accompanied by a backing band, which Frantz said opened up Marlin’s songs for wider interpretation.

“We approached it really differently,” Frantz said. “We just allowed the songs to breathe and come into their own in the studio, which was a really fun way to do it. … Our biggest goal was for the songs to have a looser form that was going to allow more improvisation. I think one of the things we were excited about, playing with drums and bass and another guitar player, was being able to be in the song in the moment a little bit more.

“If we’re feeling a two-minute solo section, we can go there, which we can’t really do when it’s just the two of us.”

Mandolin Orange’s upcoming Bartlett show will feature the same lineup that appeared on “Blindfaller,” which is a change of pace from the two-person affairs of Marlin and Frantz’s earlier tours.

“There’s some duo stuff in the set and some trio stuff and a lot of full band stuff, especially on the new songs,” Frantz said. “It’s been really fun for us getting a feel for the ebb and flow throughout the set. … (The energy) is different, but it’s kind of a nice change of pace. Andrew and I can still focus in on each other when we need to, but it’s sometimes nice to be able to sit back in that pocket of bass and drums instead of driving everything with the acoustic guitar.”