When the iconic Sister Rosetta Tharpe was asked about the phenomenal success of rock n’ roll music, she said “This is just sped up rhythm and blues - I've been doing that forever.” It’s hard to doubt her when listening to these R&B cuts from the pre-rock era. Maybe there’s a little more piano, a little less guitar - but between the rollicking party songs of Louis Jordan, the Treniers’ cheeky “Poontang,” and Lucille Bogan’s beyond-cheeky “Shave Em Dry,” all the elements of rock are already here. (Seriously, you aren’t prepared for “Shave Em Dry.”)