Having found a wider audience with Soused, last year’s collaboration with Scott Walker, Seattle-based drone metal duo Sunn O))) counterintuitively rein in some of their more avant-garde tendencies (such as the choirs and brass section of 2009’s Monoliths & Dimensions) on their seventh album. This return to their roots is still defiantly uncommercial, of course. The three lengthy movements that comprise a conceptual piece about the Buddhist bodhisattva of mercy unfurl at funereal pace, Stephen O’Malley and Greg Anderson’s downtuned guitars backing the unintelligibly guttural vocals of regular collaborator Attila Csihar. The lack of any sort of beat only adds to the disorientation. And yet, played loudly enough, Kannon sounds astonishing: by turns eerie, hypnotic and thrilling.