It happens about once a year in hip-hop production: someone invents or perfects a sound, someone figures out how to get a weird noise out of some piece of technology not designed to make that noise, someone figures out a way to make a drum machine say the same old thing with a different accent and the whole rap world tilts on its axis. If you manage to change the beat — if your sound drifts upstream from mix tapes to pop radio, if it becomes the only thing anybody wants to hear — you can change hip-hop.