“As an experiment…” began last week’s letter from Radiohead frontman Thom Yorke and producer Nigel Godrich, announcing Tomorrow’s Modern Boxes, Yorke’s first solo album in eight years. The “experiment” was designed to solve the same problem the music industry has been grappling with since the heyday of Shawn Fanning—how to convince the digital world to pay for music. And the means were, if not exactly original, unique for an artist of Yorke’s size: a payment system managed by