It's rare for an artist to return for a second Tiny Desk Concert at NPR's office, but Alt-J made sure the follow-up to their 2012 performance was special: They brought along a string section.

Performing their new singles "3WW" and "In Cold Blood" alongside two older favorites "Warm Foothills" and "Taro," this was the first time the guys had ever heard the string arrangements—but you wouldn't know it listening to the session. This is one of those magical moments where an experimental promo performance turns into something special that will live outside the studio recordings themselves. The strings add a whole new layer and breathe new life into these songs.

Check it out above and look for Alt-J's new album, Relaxer, on June 2.

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