Bob Pittman was CEO of AOL, Six Flags, and MTV before he took over at Clear Channel, and understatement has never been his style. When discussing the the future of music, few people are talking about traditional broadcast radio. But iHeartRadio, the digital arm of Clear Channel’s sprawling media empire, seems to have found a way to thrive at a time when its peers in the record industry are struggling to make the transition into the mobile age. Today Clear Channel announced that it has passed 50 million registered users, a mark it reached in less than three years, much faster than rivals like Spotify or Pandora.