Animal Collective, Astoria 2, London

For a group whose lyrics speak of sharks and fireworks, this is a somewhat tame performance, albeit one that intermittently fizzes with invention. Animal Collective fit more original ideas into one song than most bands can conjure for an entire album, though tonight they prefer a more measured approach.

Known best in the UK for a collaboration with Vashti Bunyan, the Baltimore natives (now based in New York) are earning growing plaudits for their own distinctive sound, which has developed in an especially idiosyncratic manner. The cosy Sung Tongs album gave them an acid-folk tag, though that was followed by the ecstatic and very different Feels. The current offering, Strawberry Jam, has a title that suggests the group's innate sweetness, though not the kaleidoscopic nature of their giddy, unclassifiable idiom, which occupies a unique space between the majestic psychedelic rock of The Flaming Lips and the chaotic outbursts of the underground noise scene.

With Josh "Deakin" Dibb having taken the year off, Animal Collective perform as a trio, a line-up that at first doesn't seem to restrict their phenomenal effect. Noah Lennox, known for his own solo output as Panda Bear, and Brian "Geologist" Weitz, with a miner's lamp to light his kit, face the audience from behind messy banks of enigmatic devices, all knobs and wires – though this is far from an antiseptic electronic performance. And not only because the twitchy David "Avey Tare" Portner moves between either mike or guitar and his own lone cymbal.

The sounds the group produce come with such satisfying fuzziness that it is a wonder they form tunes at all, but tunes do emerge, sometimes as churning tides, elsewhere in more delicate threads. Strummed guitars scratch against clumsy basslines, martial drums or skittering beats. Overtop, Geologist and Panda add whispered voices, wonky percussion and eerie drones that suggest water-filled caves or enchanted forests. When a sample actually sounds like an instrument, like the penny whistle at the end of the set, the simplicity is as shocking as a cold shower. You can imagine this is what the Incredible String Band would sound like today, especially when Avey opens with a song about a dancer with flowers in her hair.

His fairy tales come with bite, though, as he interrupts his delivery with trills and screams, a counterpoint to Panda's more boyish delivery. The group gradually build tunes from component parts, like a magician showing you how his trick works. Occasionally this leaves you spellbound, though the high points are few and far between. Instead, the vocalists groan in primitive fashion, share two-man rounds or mumble mantras that never quite reach peaks of hypnotic grandeur.

At their best, Animal Collective songs pulse and evolve like living organisms, but all too often tonight they meander until they melt into another tune. It is hard to work out how much the lack of propulsion is down to Deakin's absence, or perhaps the familial distractions of Panda Bear's new life in Portugal. Certainly the band lack the fevered intensity of previous shows. The crowd themselves are unsure how to react. Some sway in time to the beat; a few raise hands to the ceiling; one even holds a flashing rave accessory. Most just watch attentively for any clue as to what is going on.

Highlights include the recognisable portions of Strawberry Jam: segments of "Fireworks", a thrilling pop song, that emerge from an extended jam, and Panda Bear's meditative version of "Chores", which suggests Brian Wilson at both his most crazed and childlike with The Beach Boys harmonising over the middle section of "Whole Lotta Love".

That, though, is not the point of the challenge that Animal Collective lay down, both for themselves and for us, when they play live. Maybe they failed to convince over an hour and 40 minutes, but signs of genius suggest that this is only a minor blip.