Grizzly Bear, Brixton Academy, London

Grizzly Bear (Getty Images)

It is Grizzly Bear vocalist Ed Droste's birthday, and the crowd break into a haphazard round of 'Happy Birthday'. This should please the Brooklyn four-piece - they publicly moaned that an audience in Newcastle was too quiet last week.

But although they're graciously appreciative throughout the evening, unlike many bands who would grin and jam along for a few bars, they don't join in. Maybe 'Happy Birthday' is just too damn simple.

For Grizzly Bear, it seems, don't do straightforward. Their output is layered and intricate, characterised by haunting harmonies and Daniel Rossen's signature pealing guitar sound, honeyed but oddly distant.

Their records - they've just released a fourth, Shields - very much fall into the 'rewards repeated listens' category, and live, with an extra keyboardist in tow, it is still music that demands your full attention.

At worst, it feels overly tinkered with, careful, calculated, merely cerebral; at its best, it's completely immersive, the accumulated details, textures and subtle shifts mounting up to an avalanche of sound that sweeps you along.

Take "Ready, Able": starting a restless thing, with chirruping guitar phrases and Droste's drifting voice, it rolls into an incredibly rich powerful track, with a pull like an underwater current.

"Speak in Rounds" begins with amped up drums, chiming guitar and Droste's (surprisingly nasal, often incomprehensible) vocals; as it concludes, a host of long-tailed lanterns rise into the air, pulsing and hovering like jellyfish - an appropriate image, given the slippery, tendrilled nature of Grizzly Bear's output.

"Lullaby" may feature twinkling glockenspiel and flute, but I dread to think what dreams you'd have if wooed to sleep by it, for its shifty melodic moves are soon unsettlingly thickened with drums and fuzz.

"A Simple Answer" starts out all strident, but before you know it you're crunching into unlikely chords, its seemingly straight up guitar-and-keyboard swaddled with a kind of warped organ noise.

Even "Knife", positively anthemic at points, with heavy drums, wide guitars and feathery harmonies, ultimately comes down on the side of dense and mysterious rather than lighters-aloft.

They finish with a seriously stripped down version of "All We Ask" – just a jazzy shuffle on a single drum, an acoustic guitar, and those gorgeous multiple voiced harmonies, as the band repeat the plaintive line “I can't get out of what I'm into with you,” over and over again. Gorgeous – and the closest you're gonna get to a singalong.