In common with their Icelandic compatriot Björk, Amiina make up their own rules. They are four women in their 20s who play bells, saw, harp, violin and a host of other instruments. Here, they begin with unearthly, bowed xylophone notes - the kind of sounds you imagine people mean when they talk about the music of the spheres. The piece, Boga, builds gradually to a sparse, glacial, baroque tone, breathtaking in its poise.

It is this kind of strange, beautiful, gentle sound that makes the listener fiercely protective of Amiina. But there is nothing fey or twee about their music: it feels both homely and domestic, yet powerfully other. It is not just the odd, keening sounds that make you think of the Clangers; the music has a magical blend of playfulness and melancholy, redolent of Oliver Postgate's DIY fairytale worlds; of childhood and its end.

Virtually beatless, and with only a few, non-verbal vocal passages (for instance, the gorgeous, folkish harmonies of Lupina), the music feels egoless, too. Ammaelis has a ludicrously plastic, tinkly-bonk drum pattern, as if sending up the oppressiveness of the omnipresent 4/4 beat. The pieces might be lullabies if they weren't so ecstatic - although it is an ecstasy measured out with awestruck, delicate precision.

Amiina keep exalted company: with Peggy Lee's underrated Sea Shells album, with Ryuichi Sakamoto at his most ethereal, and, to a lesser degree, with experimental groups such as Clogs, who have their feet planted more firmly in the world of post-rock. At the end of the short set, there is a sense that the audience feel privileged to have been present. It is a rare and wonderful thing.