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The xx (music group)

The xx is still quiet, just not on stage

The xx is still quiet, just not on stage

Midway through the xx's set at April's Coachella Valley Music and Arts Annual Festival in Indio, Calif., the London-based trio threw a cover song into its set: Aaliyah's smoldering 1997 single "Hot Like Fire." Solange, the R&B singer and friend of the xx, joined the band on stage to solidify one of the weekend's standout moments. Guitarist and vocalist Romy Madley Croft, 23, talks modestly about her acclaimed band, but doesn't hesitate to gush about the two R&B singers who helped make the highlight possible. "Aaliyah has been an artist I've grown up with, like an older sister," the soft-spoken Madley Croft said. "We were...