Blake Shelton and Gwen Stefani recently hit No. 1 with their duet, “Nobody But You,” and Blake says he is “blown away” by her perfectionism and work ethic when it comes to recording.

 “The thing that I think that I’m blown away by with Gwen is just how hard she works when she gets in the studio. She’s not willing to take anything less than greatness.”

Blake says his girlfriend will sing a song over and over and over, even to the point of exhaustion.

Watch the behind the scenes video of the recording of “Nobody But You.”