In 1927, the record industry split American music in two and sold it to separate audiences. We've believed the split ever since. Groundwater is a music history podcast that follows the current underneath — the blues, running from Congo Square to the South Bronx, from Robert Johnson to Aretha Franklin to hip-hop. Each episode traces a moment the industry tried to keep apart: the soul sessions at Stax and Muscle Shoals that crossed every line; Louis Armstrong working race and commerce from New Orleans to Chicago; the Great Migration carrying Muddy Waters and the Delta sound up the Illinois Central to Memphis, Chicago, and Detroit; and the state's long campaign against the singers who got political, from Billie Holiday to the Dixie Chicks. If you want to understand why American music sounds the way it does, start here and follow the water.