Sigur Ros, Brixton Academy, London <!-- none onestar twostar threestar fivestar -->

For a band so mellifluous they seem to be at once absent and present, sigur rós make an aptly extraterrestrial entrance. Opening with the rapturous "glósóli", from their fifth and latest album, takk..., the Icelandic quartet elect to play behind a silk screen. In its ethereality, this act conjures up a sense of how adrift sigur rós are, seeming to play without anchor in anything "real", often singing in a made-up language ("Hopelandic"), and preferring a sighing drift to the "drive" of conventional songwriting.

But then the song gives way to a crescendo, the screen rises, and sigur rós emerge. The point is fittingly made: takk... has been welcomed as the band's most approachable album, due to its heavenly choruses and the singer/guitarist Jonsi Birgisson's decision to deliver his sweet coo of a voice in proper Icelandic.

The latter point may be overstated, as it's likely that few people here tonight can hear the difference. It's all Hopelandic to me, as the songs melt and slide into one another - it's not that they sound the same so much as they all come from the same strange pool of sigur rós's making.

takk... seems to have prompted the band to put on a show. For the lullaby-ish "sé lest", a brass band march and hop across the stage. Later, a screen takes up the wall behind the band, playing host to stars that flash in time with a glockenspiel, something that looks like an alien ghost trampolining in time with a trumpet, and a mannequin whose stare conveys something in the music's beauty that remains untouchable.

For a minute, though, both mannequin and music freeze, causing some of the audience to fall silent, some to scream and others to shout, "Ssssh!" You can see where the howl comes from. If sigur rós sound a little like the link between the Cocteau Twins and the post-rock bands they emerged with in the late-1990s (Mogwai, Godspeed You! Black Emperor), they also occasionally make you long for the latter two's visceral sonic ruptures.

That might be due to this rock band-favouring venue, though, and it's a measure of sigur rós's singularity that they're easier to define by what they aren't than what they are. They create a world of their own from a modest approach to majestic music. Fittingly, the set-closer sees them back behind the screen, conjuring up private reveries.

sigur rós play Brimingham Academy tonight ( www.sigur-ros.co.uk/tour)