Hari Kunzru takes a road trip through the Deep South to figure it out. “It is extraordinary music, if you can really hear it. I’ve been making playlists of songs originally recorded on 78rpm shellac discs in the years before the second world war, songs that sounded like the work of ghosts. The voices of the old singers were distant in time, muffled by crackle and hiss, and yet somehow immediate.”