It's easy to think of The xx as a fashionable band: Its members have a sleek all-in-black look, its typography and cover art is coolly and distinctively styled, and the group itself has been showered with validation, including Britain's 2010 Mercury Prize. But beneath all that tightly controlled image-making lays music that's raw and vulnerable; shy, worried tentativeness is wired into a sound that shimmers powerfully, but remains as fragile and delicate as a soap bubble. The xx's second album, Coexist, came out last fall, and it plays like a series of tensely lovely interludes, each building to a climax that never arrives. Plopped in front of Bob Boilen's desk and asked to play a few songs from the record, singer-guitarist Romy Madley Croft and singer-bassist Oliver Sim have reason to look slightly ill-at-ease: The setting and band configuration robs them of cover. No beats from member Jamie Smith, who opted to hang back at the hotel; no shroud of darkness or bright lights pointed outward to blunt the crowd's stares. Throughout their characteristically compact seven-minute performance, Croft and Sim avoid eye contact, as they visibly try to ignore the huge throng and cameras positioned maybe 10 feet away from them. What comes out of their performance is not just beauty, but humanity — the sense that, in all of The xx's songs, all the calm chilliness in the world can't quite contain an exposed heart.