She's the firebrand frontwoman of Yeah Yeah Yeahs. He's the guy with a finger in some of the greatest albums of the last 20 years. Now, the two New Yorkers have joined forces on 'Lux Prima', a conceptual album that reveals a different side to each artist. Rhian Daly meets Karen O and Danger Mouse in Manhattan to hear about the eight-years-in-the-making collaboration.