Before Grimes bursts onto stage at the Brixton Academy, there’s a sense that she’s compensating for something: we would usually expect the venue to be playing the usual warm-up mix of inoffensive R&B and indie pop – the standard fare for off-piste artists like Grimes, who straddle populism and experimentalism – but tonight they’ve opted for a succession of classical string pieces. There’s something deliberate about it. Following the release of her breakout third LP, Visions, which catapulted her onto the world stage, Grimes was subject to oppressive amounts of scrutiny, from professionals and public alike; in a since-deleted tumblr post, she hit back: “I’m tired of men who aren’t professional or even accomplished musicians continually offering to ‘help me out’ (without being asked), as if I did this by accident”, she wrote, “I’m tired of being considered vapid for liking pop music.”

So perhaps the strings are a means of Grimes asserting herself before she’s even glimpsed; it’s a reflection of her magpie-esque approach to music, with a range of tastes encompassing both Mariah Carey and Stravinsky, without feeling the need to posit them as polar opposites. The message Grimes seems to be sending out tonight is clear: she’s done being patronised, it’s time to break out into her own sonic sphere.

And what a sphere it is: ebullient with optimism, Grimes channelled her energy into her recent LP, Art Angels, an album that manages to be dizzyingly complex and off-piste, but still has killer hooks, perfect for screaming along to. A majority of the songs have been adapted for the live performance, adding to their intensity: Art Angels highlight ‘Flesh Without Blood’ ends with a drum machine breakdown, going out with a bang; ‘Venus Fly’, her duet with Janelle Monaé, is ratcheted up to the nth degree, dragging contrasting sections apart, and allowing the build-up to ricochet into a ground-shattering climax; and she opts for the album version of ‘Realiti’ over the previously released demo, featuring heavier basslines and drums with more kick – fans may have complained about the new version online, but those ensconced by the warm bath of sound in Brixton are lapping it up.

At her last London gig, way back in 2012, my friend said that watching Grimes was like “watching an infant play with Fisher-Price toys”. Uncharitable, perhaps, but there is a modicum of truth in it: like all artists heavily reliant on computers and synthesisers, it is difficult for Grimes to do much more than sway in the centre of the stage, surrounded by a myriad of flashing buttons and knobs. But she’s come a long way since then, bringing along two ninja-like dancers, who twirl ribbons and at one point switch to pairs of sharp blades, accentuating the music. In a nice touch, backing vocals are provided by the support act HANA, an American artist whose music is well produced, but a tad familiar, resembling a smoothed over version of Purity Ring, or a less upbeat Chvrches; like Grimes, she uses a high register, and at points in the gig their voices become indistinguishable. Despite having to repeatedly leap back to her central command station of laptops and keyboards, Grimes manages to spend most of the gig prowling around the stage, jumping and caterwauling like an escaped hyena in an astonishing display of vigour.

However, such action can only be maintained for so long, and at points the overwhelming energy of the songs collapses into a general cacophony; this is not at all helped by the dodgy sound mixing, which elevates the bass above all other sounds in the room, resulting too often in a sludgy mess. Taiwanese rapper Aristophanes isn’t available to perform her part on ‘Scream’, so Grimes takes over, offering to rap in Russian; unfortunately, what had been pinpointed Mandarin bars on the album, spat out like poison darts, becomes completely indecipherable – a clutter of shouting and wailing.

Since Visions, made on a copy of Apple’s GargeBand, Grimes has relentlessly expanded her musical vocabulary, teaching herself the guitar, ukulele, drums, and violin in preparation for _Art Angels_’ precisely-produced tidal wave of sound. With this vast armoury, she has begun the process of rearranging the songs from Visions, allowing them to fit in better with her new direction. But all translators are traitors, and by trying to fit the minimalist structures of her earlier songs around the framework of her newer stuff, she stretches the material too thin. Songs like ‘Be a Body’ and ‘Symphonia IX (My Wait is U)’ have been distorted beyond belief, their bass-lines subsuming Grimes’ vocals, which have dropped an octave or two. The magic of these songs was their intimacy: Grimes, alone in her bedroom, was reaching out across the sonic divide to each individual listener. Reinterpreting the songs for the Brixton audience, however, has robbed them of this magical power.

But there are gems here too: Grimes has had the good sense to not mess with the classics too much. ‘Genesis’ and ‘Oblivion’, the two most popular tracks from Visions, have been preserved pretty much intact, much to the delight of the cheering audience. In her scatter-brained, eclectically chatty manner, she tells the audience that she doesn’t like the process of going off and back on for an encore, and will just play it straight away instead. In her last song, ‘Kill V Maim’, the heady bass proves no match for the electrified audience, chanting away with the evil-cheerleader style chorus, and the gig ends on a triumphant note.

The concert at Brixton seems to mark Grimes out as being at a junction: the gap between the impressionistic subtleties of Visions, and the bombastic maximalism of Art Angels is a difficult one to straddle. When things all come together, it’s like she’s riding a wave of dynamism, buoyed on by the audience; but the dodgy sound mixing, and the insistence on contorting old material to fit her present sound does her no favours. Brixton was a statement of intent: Grimes has moved on from her old material, and is ready to set off on a new bombastic course. Who knows what the destination will be; but the journey will sure be interesting.