San Francisco’s Om is informed by the dark side of the ’70s—though that doesn’t necessarily separate it from the current heavy-rock pack. The duo, which consists of bassist/vocalist Al Cisneros and drummer Chris Hakius, is perhaps best known as the rhythm section of Sleep, a stoner-riffic trio that based much of its sound on Black Sabbath’s first four albums. Cisneros has even called Sabbath (another act named after an Italian horror flick) “the institution.” But unlike the dudes in hipster acts such as the Sword and Wolfmother, he and Hakius have always used Ozzy & Co. merely as a point of departure. Sleep’s swan song, 1999’s Jerusalem, transformed a handful of Iommi riffs into a single hourlong drone. Though not as conceptually extreme, Om’s output is similarly expansive.

The band’s three-song debut, last year’s Variations on a Theme, was chock full of eccentricities, chief among them Cisneros’ voice. In Sleep, the singer was predictably gruff, chanting above the din in a style appropriate to the death metal of its day. Beginning with Variations, his vocals have been delivered with little trace of affectation, something that few in metal can boast. His singing hews closely to riffs, creating a buzz ’n’ thrum that’s more folk than rock. And because Sleep producer Billy Anderson, the console man on both Om albums, situates Cisneros’ singing above everything else in the mix, listeners can actually make out the lyrics—another rarity in modern metal.

By and large, the two songs on Om’s second full-length, Conference of the Birds—a title borrowed from Dave Holland’s ’70s free-jazz classic—offer mere variations on Variations. Cisneros seems to write the same bass line over and over again, which works because, hey, it’s a really good bass line. Loopy without being static, Cisneros’ playing twists and winds and folds back on itself, making Om’s five songs to date seem less like distinctive compositions than details from a larger work. The effect is of a band always playing somewhere—probably on a mountaintop or near something monolithic. Anderson simply captures the sound in 15-to-20-minute chunks.

This sense of everlasting activity is underscored by the lyrics. He often begins verses with a verb in medias res—“rides,” “travels,” “atones”—and his hippie-spiritual verbiage would hardly sound odd coming from the likes of Pharoah Sanders or Alice Coltrane. On the Sabbath-esque “Flight of the Eagle,” he sings, “Fielded onto cohesion, geometric altar reflect the new day.” On the Pink Floyd–ian “At Giza,” he tailgates instrumental breaks with “and” after “and”: “And lighten upon day,” “And travels under twin sun rays,” and so forth.

Cisneros also mentions Lebanon repeatedly, which is less pointed than it might seem. His impressionistic references are probably just a sign of our fundamentalist-vs.-fundamentalist times—an indication of just how much the Arab world has seeped into our collective consciousness. Return of the repressed? Not exactly.

There’s no violence in Cisneros’ words, and even the soft-to-loud surge halfway through “At Giza” has a comforting effect. In horror-theory terms, that’s probably a failure. But even Ozzy used to flash a peace sign every once in a while. Until we get a doom-metal disc that’s as malignant as our doom-taunting age, Cisneros and Hakius’ conference of doves will have to suffice.