Sunn O))) / Boris - 'Altar' (Southern Lord) Released 23/10/06

Descending deeper into the murky underworld explored on Sunn O)))'s monumental 'Black 1' might have been possible, but only by conducting field recordings inside a sealed tomb or converting entirely to the blood-curdling screeches, buzzsaw guitars and demonic pretensions of black metal, the oft-ridiculed sub-genre the nightmarish 2005 LP was a (black)heartfelt fan letter to. Instead, the follow-up drafts acclaimed Japanese noisenik trio Boris for an album-length collaboration that's simultaneously reassuringly familiar and fearlessly progressive, with both bands embarking on electrifying excursions far beyond their comfort zones.

Bleakness freaks need not worry. The robe-sporting US doom rock pioneers aren't exactly switching to dazzling day-glo here, although next to the relentless dreariness of its predecessor much of 'Altar' appears as strikingly vivid as blazing sunshine. 'Etna' sets the tone. A brutal aural equivalent of a fiery cauldron brewing in the belly of a volcano, complete with bone-crushing heaviness and planet-sized riff sludge stagnant enough for the living dead to bust a decomposing move to, the track's steadily escalating tension erupts into a breathtaking solo of desolate majesty that screeches ever upwards in a hail of smouldering lava. Jaw-droppingly intense as it is, this grandly gruesome beast of pulverising power is still recognisably the work of Sunn O))), which makes the total curveball that follows even more startling.

Fronted by the weary sigh of gothic Americana chanteuse Jesse Sykes, 'The Sinking Belle' is an opiated alt. country waltz, a drowsy lullaby heard through the blue-tinged haze of a half-remembered dream. The newfound fondness of tunes this spine-tinglingly spooky track showcases might not please the drone fiends and metalheads, but its unabashedly melodic loveliness - now there’s a word not commonly associated with this bunch of noise-mongers – should attract numerous new fans. Who might well be scared right off by the assault of 'Akuma No Kuma', which unleashes the berserk belch of a malfunctioning music-making robot on a rampage, its melting audio card spewing forth a flurry of synth-horns, loose-limbed percussion barrage and Melvins champ Joe Preston's vocoder-warped vocals. It's a moment of pure batshit brilliance, a triumphant procession of seemingly unrelated emissions that somehow form a perfectly cohesive union, a statement that also applies to 'Altar' as a whole.

Elsewhere, the haunting ambient crawl of 'Fried Eagle Mind', which ups the foreboding atmospherics to truly devastating levels with an electronic hiss akin to a plague of locusts, is supremely unsettling stuff, whilst 'Blood Swamp' must have sent chunks of plaster flying from the studio ceiling with its teeth-grindingly loud sludge of simmering slo-mo skronk that practically oozes with evil intention, even if the 15-minute epic never quite reaches a suitably staggering climax despite recruiting the psychedelic prowess of ex-Soundgarden guitarist Kim Thayil. But as impressive as both workouts are, they're a bit too keen to stick with the Sunn O))) hallmarks - painstakingly detailed textures, diabolical decibel overloads and layers of ribcage-rattling low frequencies - to equal the dizzy heights of what's gone before.

Even so, worshipping at this 'Altar' is not to be missed.