Double bill of acclaimed Scandinavian folk bands. Jaerv is an innovative folk quintet from Sweden that plays jazz- and pop-influenced interpretations of Scandinavian folk songs, some dating back 700 years. The OK Factor is the Minneapolis crossover string duo of cellist Olivia Diercks and violinist Karla Peters that’s known for arrangements of folk tunes that blend classically-trained rigor and joyful enthusiasm. $29.