Kool A.D. grew up in San Francisco-- while this is a well-known fact, it's not one that's acknowledged particularly often. It's understandable considering Das Racist have become entrenched in N.Y.'s cultural milieu in so many different ways that their music has been embraced as something like a metaphor for a certain kind of lifestyle in the city. You can ascertain Victor Vazquez's Cali roots as a matter of relativity, being that Queens native Heems is more assertive as both a rapper and as a media presence. But otherwise, outside of calling himself the "second-best rapper with glasses after E-40," it's tough to pinpoint much influence even when you know it's there. All of which makes Kool A.D.'s second mixtape of 2012, 51, a surprise and a long time coming: Recorded entirely in Oakland with a heavy presence of Bay Area producers and rappers, it's a testament to his heretofore untested malleability, a new way to hear the old Kool A.D.-- something which the admirable, if loopy outré R&B of The Palm Wine Drinkard got only half right.