The xx, Audio, Brighton

In an era where stadium-sized rock bands such as Muse create towering symphonies and sing in a register of permanent panic, the south-west London four-piece the xx trade refreshingly in subtlety and understatement.

Few bands in recent years have conflated electronica and indie rock so sparingly and beautifully. On their deceptively sophisticated self-titled debut album, every sound is accounted for – a grinding Joy Division-style bass hook here, a digital handclap there. The same rules apply to the vocals of Romy Madley Croft and Oliver Sim. Theirs is a breathy, minimal style, revealing an easy intimacy born from a friendship that began in early childhood.

This is the xx's first headline tour and if they don't exactly look like pop's hottest prospect – they come dressed entirely in black, with sickly complexions and expressions locked into a sulk – it hardly matters. With a heavy dyed-black fringe drawn down over one eye, Madley Croft looks like a cross between Yazoo-era Alison Moyet and Kelly Osbourne. Meanwhile, Sim, discernible by his black polo neck, gold chains and magnificent greased pompadour, looks more like a French film star, his sculptural features exuding an air of tragic intensity.

Shyness is rarely a quality in pop singers, but Madley Croft and Sim's reticence somehow adds to the atmosphere in this small subterranean venue. Showmanship clearly isn't the point here, which is lucky since Madley Croft and Sim look about as capable of playing egocentric rock stars as Bono is of keeping a low profile. Their wary eyes implore us not to look but to listen, to stand and bask in the dark romanticism of their sound. Chords and choruses don't seem to feature high on their to-do list either. Odd as it sounds, it's what the xx leave out that makes them so beguiling.

That said, there are rare occasions where they veer dangerously into chill-out territory. The words "coffee-table" have killed off many a promising career and the last thing that the xx need is to find themselves on the next Café del Mar compilation. They are at their best when they speed things up a little, using pummelling electro beats as a backdrop to their vocal ruminations on love and loneliness.

For ones so young – they have just turned 20 – their record collections appear impressively wide-ranging. Post punk, goth rock, electro and ambient dance are all discernible here. They're not above throwing in the odd curve-ball either. A cover of Womack & Womack's "Teardrops" might seem an odd choice of song with which to flesh out their modest back catalogue until you hear what they do with it. Having slowed it down and stripped it to its bones, they bring haunted desolation and icy melancholy to lines like "Whenever I hear goodbyes, remind me baby of you, I break down and cry, next time I'll be true." With this, the xx provide a beguiling lesson in how less can be so much more.