NYC's finest pugilist fight-poppers, Sleigh Bells, for their last record (Reign Of Terror) took a turn for the serious. Not especially so, but as the record was more a coping mechanism for death and disease, the tone was dark and intense, as opposed to the grandiose bar-brawl anthemics of their debut, Treats.

On their forthcoming LP, Bitter Rivals, the duo showcase a self-described 'celebratory side' - it's a way of emerging from the macabre crevice and depressive spiral of grief. It's not a record that just channels an emotional change, but a physical one too - there's been a detox of sorts, multi-instrumentalist Derek Miller has retired the shades, and they've begun boxing. Yep, boxing. Watch out Pacquiao.

The pair, comprising vocalist Alexis Krauss and Miller, via a gaffe by Amazon, erupted back onto the main stage with new single 'Bitter Rivals'. With sampled canines snarls, an unsheathing of sabres and blithe acoustic chords, it begins rather PG-rated, almost like Matilda-OST '90s pop-rock, which is a major step away from the usual shitstorm of merciless, brutal noise-pop we've come to rather enjoy. Swiftly however, and with the familiar saccharine yowl of "I've stubbed my toe,"-level fury, Krauss roars (not like a Katy Perry roar, like a proper, guttural apoplexy). They're back. Miller's grinding axe riffs cajole finger-snaps into a sweet melange, and while Krauss vents rage at her nemesis - "You are my bitter rival, but I need you for survival!" - you can't help feeling that amongst the banterous verbal duel, faux-rage and swaggering clicks, that this is more akin to a gloriously gory retelling of West Side Story.

It doesn't stop there. Where once a sheer battle royal of knuckle-duster licks, noggin-splittin' beat(down)s and violence ruled the claret-stained roost, a nonchalance reigns supreme now. Obviously the figurehead of Sleigh Bell's distinctive sound is still raucous chip-on-shoulder belligerence - Bitter Rivals wouldn't really be a Sleigh Bells record without it - but even in the scrappy scrums, you get the impression that they're not fighting for something, rather, they're fighting for pleasure. They're still entirely up for smacking you upside the mandible, but they'll do it with a coy grin.

The violence is no longer born from wrath - it's born of bloodlust, sadism and a terrifying callousness; and frankly, it's bloody excellent, as it's a fresh palette of noises to delve into. We've got handclaps by the dozen, whistling mercenaries, R&B suavity, chiptune sugar and utterly sublime pop hooks. Where before, even with their tinges of pop, Treats or Reign Of Terror could be slotted into rock or indie categories, this is unabashed Top 40 material.

'Love Sick' sounds like something that could've featured on Taylor Swift's RED. Krauss' voice is a glossy, almost MKS croon; Miller's fretwork is as frayed as ever, but when the actual sleigh bells are brought out, and reverb-doused Robert Smith guitars pervade Krauss' humming, you can't help but see them vying for the number one spot. 'To Hell With You', featuring grazed strings and the festering scabs of electroclash, is largely a ballad - yes, a Sleigh Bells ballad. It swoons and withers and could even be described as 'graceful' - perhaps in the same way as Courtney Love in a ballgown might fleetingly be.

'Young Legends', an ode to the unlucky who never get a break, has ferocious rhythmic stabs, but there's none of the weight behind it; it's just chirpy and bouncy, rather than abrasive. '24' is rife with 8-bit-aping melodies and '80s six-stringers with an almost Smiths-ian vibe. The whole of Bitter Rivals lunges into new grounds and displays sonic threads you would never associate with Sleigh Bells, and that's its beauty. It's repeatedly surprising, and not in a "Holy mackerel, what is that?" kind of way, but in a considerably more mind-blowing way.

Bitter Rivals follows the mission statement perfectly. It is indeed celebratory; it is a lurch into unknown waters, and it is nothing like their previous full-lengths. Sleigh Bells have a formula, generally applied to aggressive tones, which they've here plastered onto R&B, bubblegum rock and J-pop. Every track double-taps you; one noisy, riotous cartridge ignites a kegger in your gut, another instigates single-minded glee in your brain. It's more Miley Cyrus than it is Black Flag, and far from being career suicide, it's probably the best thing they've done.