Four years ago, a group of 20-year-olds from South London who craft quiet, soulful electronic music suddenly made a huge noise. They called themselves The xx, and their debut album was an unexpected hit. Soon their music was ubiquitous — first in the UK, then in America — on soundtracks, in big-ticket commercials, and sampled by Rihanna.

The xx has now released their second album, Coexist, and if anything it's even more restrained and minimalist than the first. Oliver Sim and Romy Madley Croft, the band's founders and singers, talked to Kurt Andersen on a stop from their North American tour.

An unmistakable characteristic of The xx’s music is their hushed, intimate boy-girl vocals, but Oliver and Romy are not a couple; they’re best friends who met as three-year-olds in nursery school. When they sing their duets, “We’re both talking about different things, focusing our affections on different people or ideas,” says Romy. “It’s funny, we never thought about [sounding like lovers], and it was never uncomfortable.”

And it’s the close friendships within the band that keep these shy 23-year-olds sane in the wake of overnight stardom. “If you do start going a little bit off the rails, or start to become someone else, I’m sure Oliver would sit me down and have a word,” says Romy. The xx have learned to embrace performing on big stages, but Oliver says songwriting for other artists might be more satisfying in the long run. “I know I’m always going to want to write songs but I don’t know if I’ll always want to perform ... this is a way to stay creative.”

So if you want to see The xx live, catch the current tour before Oliver retires.