In the rarefied world of experimental music, collaborations are legion, but rarely illuminating. More often than not you are left wondering who did what, and why: was that pinging sound amid the roaring white noise really the result of a grand meeting of the minds? Yet, the coupling of avant garde doomlords Sunn O))) with Norway's Ulver – the progressive black metal band who left the reservation years ago to explore gothy synthpop and 60s psych – isn't just greater than the sum of its parts; it's a distinct journey between two disparate musical camps. Recorded over one night in 2008, this three-song set wills itself into motion with Sunn O)))'s primordial, monolithic guitar drones, this time augmented by a brass fanfare. It floats on through Philip Glass-esque madrigals, squalls of feedback and unearthly cabaret piano-tinkling before preparing for landing with a mournful, synth-led denouement. It's long, languorous and wonderful in its invention, with Ulver lending emotional heft to Sunn O)))'s wall of tone. And, as so often in their respective careers, these iconoclasts leave their peers far behind, struggling to catch up.