The release party for About Group's third album, Between The Walls, is marked from the get-go by the absence of founding member, Charles Hayward. The former This Heat drummer decided to split from the group just after they'd finished recording the new album, leaving a hole in the line-up recently likened by Alexis Taylor to Tyondai Braxton's departure from Battles. The analogy is apt as, in the cases of both groups, the loss initially seemed fatal yet ultimately proved benign. About Group as an entity is more than its mere constituent pieces. They follow a philosophy of music-making that pulls inspiration from a bottomless well fuelled by improvisation, while the sound itself is merely coloured by whoever is playing at any given moment.

Between The Walls is the group's most consistently listenable album, showing a maturation and understanding for exactly what they're about. Their debut was a noisy and free-flowing instrumental jam session, and follow-up Start & Complete was an occasionally samey and syrupy session of subdued Rhodes and organ-led tunes, spontaneously recorded. Between The Walls balances the band's two extremes, all the while maintaining their modus operandi of spontaneously navigating their songs' arrangements. The way in which its arrangements come into being asks the question: what exactly makes the definitive version or performance of a song? Are About Group's arrangements for Alexis Taylor's tunes and lyrics mere twisted simulacra? Accordingly, their latest album's version of Bacharach and David's 'Walk On By' bears no real resemblance to the song save a few words. Yet the soul of the song comes through, even if it exists as a mutant clone.

With a mess of synths, amps, pedals and leads crowding the knee-high stage in the dark recesses of the Dalston Vic's back room, it's Pat Thomas who wordlessly ushers in the start of About Group's set. Clambering over the mess of musical toys to his own modest setup at the back - a Yamaha S03 synth perched on a hastily borrowed pub table - the calm, collected and bespectacled Thomas launches into an attack of full-palmed keyboard smashing, knob twisting and button stabbing, unleashing a bed of hazy synthesised noise that continues throughout the set. John Coxon and Alexis Taylor take to the stage amidst the noise along with the group's newest members, Susumu Mukai (Zongamin) ostensibly as bassist and Rupert Clervaux (Sian Alice Group) on drums. The group gradually stutter from Thomas' abstract freeform noise into a rising two-chord pulse. Coxon begins strumming his guitar with the same relentless pound that brought to life Spiritualized's late-90s freakouts, before Alexis Taylor suddenly breaks into song. Belting out 'I Just Don't Know What to Do With Myself', the group are suddenly morphing another Bacharach/David classic into a fuzzed out overture.

In a move that repeats throughout the set, the song dissipates and somehow finds its way into the next. Several tunes from both Between The Walls and Start & Complete reveal themselves in this manner. The almost Al Green levels of laid back soul in 'Nothing But Words' give way to a synth battle between Taylor and Thomas during a passage of Neu!-like motorik jamming, which in turn morphs into 'All Is Not Lost'.

The duo of Coxon and Mukai prove brilliantly mailable, trading instruments and getting as much unreal aural variety out of their semi-acoustic instruments as Thomas and Taylor's synths. Indeed, it's the seeming clairvoyance of the group that makes the experiment work. The gentle sway of Taylor's About Group songs could easily feel subdued to the point of banality. Yet - in a manner not dissimilar to Lou Reed's early-80s Quine/Saunders backing bands - potentially monochromatic and meagre tunes become dynamic and colourful. Taylor's voice too remains a powerful asset; bittersweet, note perfect and truthful. The almost traditional and often romantic content of the songs ("sometimes I think it beautiful, sometimes I think it's absurd") is hammered home all the more strongly by Taylor's brutally honest, boyish soprano.

The penultimate 'Lay Me Down' eventually descends into musical anarchy, while Taylor sings the final verses seemingly unaware of the noodling and mad scientist electronics taking hold of his backing band. Bookending the show, 'I Just Don't Know What to Do With Myself' re-emerges to dramatic effect, this time taking the form of a throbbing crescendo. The second reading of the song feels almost akin to Faust's 'It's A Rainy Day (Sunshine Girl)' - a song whose relentless pounding was once described as being "not so much 4/4 as 1/1". It proves a fitting end, as the song is yet again re-characterised, far removed from the ponderous poppy romance of the original, and morphed into an angst-ridden tribal cry for mercy.

From free noise to Bacharach covers: few bands could tread as much ground in an hour. They're musical adventurers, their music awash with countless varied sounds, and never certain as to where they'll go next. Tonight, About Group evolve their music right before our very eyes, yet equally benefit from Taylor's skeletal songwriting and singing, which prevents them from completely vanishing off into outer space. What they do is far too free to be described as giving renditions, yet similarly too rooted to be purely improvisation. No matter how much or little was prewritten, the music comes to life on the spot. The lyrics, or a melody, or a rhythm, can all form the basis of any piece of music, yet it's in the playing that we find the soul, and this approach amplifies the very liveness of this music. The punch that About Group pack as a live entity is pretty astonishing in comparison to their characteristically pensive introversion in the studio. Four years since their first meeting, three albums in, and one founding member down, it feels like About Group are only just stepping into their stride, and it's impossible to say just into what they'll evolve next.