Playlouder - Music is the Network

There are probably very few musical genres with their own hand gesture. But doom metal is one of them. It's a simple move. Instructions: As the last chord falls away, raise your right arm slowly before your face, gradually curling your fingers into a fist as you do so, but taking care to never fully clench. As the soundwave of the next note thunders into the empty beach of your brain, bring your hand back into your chest, while bowing your head slightly. This, ladies and gentleman, is the Doom Claw, the revolutionary minimalist dance move that's very much in evidence tonight.

There's something profoundly gratifying about the fact that it's possible to stand in one of London's largest venues for a few hours of being continuously blasted by waves of bass drone, delivered by men in monk's cowls. It's doubly satisfying that this is very much a one-off, as we're here to see Stephen O'Malley and Greg Anderson's Sunn O))) leviathan yoked to Japanese sludge specialists Boris as they perform tracks from their collaborative 'Altar' long-player.

First we're treated a superb set from Boris. It's abundantly clear from the off that the Kentish Town Forum's notoriously lousy sound has been fixed tonight. On record I've often found Boris to be a rather overly hirsute proposition, their heavy riffing sounding to me as trad as a fat bloke covered in oil under a wood-paneled station wagon. A reappraisal is due, for tonight they're on superb form, Atsuo's formidable drumming and gong attacks intertwining with Takeshi and Wata's guitars in a full, sinuous roar.

Yet it can't compare to the brilliance of Sunn O)))'s relatively short, 40-minute set. The band arrive onstage in their uniform black cloaks, with Hungarian vocalist Attila Csihar sporting a garment made of white sacking that leaves only one arm free, a white face mask, and a crown of twigs over blond hair. The spectacle is such that Sunn O))) live is a peculiarly immersive experience. There's nothing antagonistic about Sunn's music - this is not some Throbbing Gristle-esque assault on the audience's senses. Instead, it's a communion, an exploration of the possibilities of extreme sound and the collective conscious. The audience is carried on a journey via the dynamics of bass, guitar, electronics, trombone, bowed electric upright double bass and Csihar's rasp. Close your eyes and it transports you wherever you wish to go - there's certainly something base, primal and spiritual about the exalting effects of Sunn's all-consuming thunder. You could see them being booked at a meditation retreat, or making total sense to a post-apocalyptic future humanity with no received knowledge of rock & roll. On a purely technical level it's fascinating to watch them play up close, the members watching each other for the signal of when to explore the next dark bass cavern - this is incredibly simple stuff, just picked bass strings and chords, but the timing is a matter of judicious elegance.

If that performance makes for one of the very best I've seen from Sunn O))), their joint set with Boris takes things even further into the realm of one of the undoubted gigs of the year. Proving that tonight isn't just about noise, the musicians crowded onto the stage open with a sublime version of 'The Sinking Belle', with Jesse Sykes singing the delicate vocals to an awestruck, hushed room. She floats offstage, and then all fury is unleashed. 'Etna' is more the final belch of Krakatoa than the piddly Mediterranean volcano it's named for, Atsuo's drums commandeering the noise and building it into the most monumental, astounding judder. Hearing the crushing bass chords of Sunn O))) given life and mobility by his astonishing drums is like witnessing the terrible moment when Leonardo Da Vinci invented the very first tank. And then Atsuo is gone, drifting over the crowd on a forest of raised arms, doom claws become supporting palms. It’s a triumphant finale to a magnificent evening that asserts the cold hard fact that it's in this strange netherworld of capes, drones, Japanese riffage and Hungarian throat growling that some of the most ambitious, progressive and exciting music of modern times is being made.