>>55957873
The O Brother Where Art Thou soundtrack is Old-Time
I'd reccomend you check out the basics of old-time, Dock Boggs, Charlie Poole, Roscoe Holcomb, and, if you'd like a more recent artist, Frank Fairfield.
Also check out pic related, it's a four hour collection of folk, old time, and blues that's a great introduction to Americana, there's a MEGA link in the archives.