From an article on the Yardbirds, from April 2009
http://www.goldminemag.com/tag/eric-clapton
According to future Savoy Brown and Fleetwood Mac frontman Dave Walker, who recorded his own album-length tribute to Williamson in 2004 (Mostly Sonny), “There was a simplicity to Sonny Boy … the same as Jimmy Reed, it was just a shuffle, but it was a beautiful shuffle. Some of those old guys, you listen to the records and they’re out of tune, or you can’t understand them. But Sonny Boy’s records were so warm and so exciting.”