It starts with a thunder-crack snare hit and a galloping drum-beat, a frantic percussive workout that sounds like it should be accompanying visuals of someone running for their life. Then comes the guitar, a shredding, hyper-speed metallic riff circling around and around the drums like a spirograph pattern, followed by a repeated keyboard scale that weaves its way into the few remaining spaces. Thirty seconds into Both Lights, the third full-length offering from Portland experimentalists AU, you're already reeling, and then - suddenly - the sensory bombardment stops. A momentary pause, then a thunderous, buzzing bass-line heralds a cacophonous return; more keyboard arpeggios, then brass and a brief blast of saxophone. Over the course of just three and a half minutes, what started off as the soundtrack to some imagined chase scene has transformed, magically, into a triumphant climactic escape theme. The song is called 'Epic', and you're unlikely to hear a more fittingly-titled track this year.

AU (pronounced "ay-yoo") is the brainchild of classically-trained pianist Luke Wyland who, on 2007's eponymous debut and the following year's Verbs, assembled sprawling teams of friends and session musicians to bring to life the cosmic folk-flavoured symphonies in his head. Since whittled down to a more stable core line-up of himself and Dana Valatka, a drummer with a background in punk and metal bands, Wyland here sings and plays keyboards, guitar, lap-steel, banjo, melodica and more, as well as adding after-the-fact digital dressing via laptop and samplers. There are a few important assists though: Nick Sweet (trumpet) and Alex Milsted (trombone) contribute subtle swells and jazzy fanfares, whilst guest vocalists Sara Winchester and Holland Andrews make 'Get Alive''s Beirut-esque melody line soar and turn the droning, dulcimer-led ‘Crazy Idol’ into an ethereal, almost operatic, folk chorale.

Another notable guest is Colin Stetson: it’s his saxophone you can hear on ‘Epic’, but he really shines on album highlight 'Solid Gold'. Marrying a celebratory campfire vocal to a punked-up funk rhythm and blaring Afro-jazz horns, it’s an unholy, wholly heavenly noise. Inspired by their remix for last year's Tradi-Mods Vs Rockers compilation, its part-Congotronics, part-Animal Collective, part-Naked City vibe sums up Both Lights’ nomadic charms quite nicely. Here is a group that doesn’t seem to know where it fits; it can’t decide whether it wants to rack itself freak-folk, or avant-noise, or post-rock, or even neo-classical. But it also understands that, actually, you don’t have to choose. The album finishes with a four-song suite that runs the gamut of AU's stylistic range, starting with the manic thrash of 'Why I Must' and the beautiful, shimmering ‘Go Slow’ before moving on to ‘Old Friend’, a stripped-down piano ballad featuring an understated Winchester lead vocal and closer ‘Don't Lie Down’, a slow-burning stew of crackling, acid-fried psych guitar and crashing cymbals. Each flows effortlessly into the next, proof that some boundaries are better left undefined.