In the 70s and 80s, guitarist and mandolinist Tim O’Brien played in the influential trad bluegrass band Hot Rize and its alter ego, Red Knuckles & the Trailblazers–the same guys in different outfits, playing eccentric, improvisational country. For the past three years, though, he’s been working in a much more intimate setting: a duo with Kentucky-born picker and veteran session man Darrell Scott, whose resume includes dates with Randy Travis, Guy Clark, and Suzy Bogguss. Last year’s Real Time (Howdy Skies) weaves together not just their complementary voices–O’Brien’s is vulnerable, Scott’s optimistic–and instrumental styles but also a handful of related genres, from bluegrass to Celtic to Appalachian folk. Recorded without overdubs (hence the title), the album faithfully captures the duo’s uncanny synergy–sometimes it sounds like both voices and all four hands are being controlled by a single superhuman intelligence. On one of the nine originals, “With a Memory Like Mine”–told in the voice of a man whose son has come home from the war in a casket–Scott sings in a high-lonesome wail charged with grief and life-affirming power; despite the tune’s grim subject, its urgent, churning rhythms sustain the hope for happiness and peace. O’Brien and Scott take Hank Sr. back to the mountains on two Williams chestnuts, “Weary Blues From Waitin'” and the spiritual “A House of Gold,” delivering renditions that call up the folk roots of country: their keening, old-timey vocal harmonies float over picked melody lines that entwine in intricate filigrees, and the two of them even manage to break their voices into spine-tingling falsettos at the same instant. On “Keep Your Lamp Trimmed and Burning,” a traditional gospel song usually associated with Blind Willie Johnson, they summon both hellfire and hope; Scott’s intense, obsessive guitar work almost seems to pursue O’Brien’s tremulous vocals, which convey the terror of damnation side by side with compassion for the lost. Even their romantic songs have a dark, tense undercurrent: on the waltz-time ballad “More Love,” cowritten by O’Brien, the singsongy lyrics about love’s healing power are deepened by a harsh minor-key chord progression that introduces an element of doubt–a reminder that desperation and faith go hand in hand. Saturday, May 5, 7 and 10 PM, Old Town School of Folk Music, 4544 N. Lincoln; 773-728-6000.