Chris DeVille linked to an interesting article about the music of Robert Johnson, the most influential of the Delta bluesmen and, in many opinions, the man who would birth R&B and everything that came after it. (Which is pretty much everything.)
The gist of the article wonders if Johnson's music, recorded in the late 1930s, was transferred to wax about 20 percent faster than normal. In other words, the author wonders if the 42 songs in the Johnson catalogue should sound deeper and in slightly different keys than we're used to. It's an interesting theory about the most legendary man in the history of popular music.
For instance, check out an excerpt from "Crossroad Blues," slowed down to the correct speed postulated by the author. If you're familiar with the original, this sounds much different -- and, in some ways, more realistic. There's always been an otherworldly quality about Johnson's music, and it might be the inaccurate speed of the popular songs.
It's fascinating, but I won't argue that the history of American music would've been different were these recordings disemminated at slower speeds. Why people were so mesmerized by Johnson was his soul-wrenching vocals and the intricacy of his guitar work.
Remember: People thought that there were two guitars in most Johnson solo recordings -- and that Satan was playing the second because Johnson sold his soul to the devil at a crossroads somewhere in the deep South.