Boston string quartet Darlingside, a veteran of the 2014 and 2015 Sisters Folk Festivals, comes back to the organization for a show at the Tower Theatre on Sunday. The band brought its stripped-down second album, “Birds Say” — recorded sans founding drummer Sam Kapala — to Sisters High School in March (not that the sound was a surprise for SFF audiences — the evolution was ongoing during its previous appearances at the event). On last month’s follow-up EP, “Whippoorwill,” composed of B-sides from the “Birds Say” sessions, the foursome splits the difference between acoustic-based harmonies and its earlier folk-rock sound: Distorted guitars highlight “Blow the House Down,” while a cover of Smashing Pumpkins’ “1979” ups the rock quotient considerably. Chicago indie duo Frances Luke Accord opens the show.

Darlingside, with Frances Luke Accord: 7 p.m. Sunday; $22.50 in advance, $26.50 at the door, plus fees; Tower Theatre, 835 NW Wall St., Bend; or 541-317-0700.