Rappers have traditionally overshadowed DJs as the public face of hip-hop, but DJs and turntablists have made inroads in attaining mainstream success and recognition. The terrific documentary Scratch paid homage to the art of turntablism, while supergroup X-Ecutioners released the crossover-hungry Built From Scratch, which introduced turntablism to the masses, albeit in a somewhat watered-down, radio-friendly form. Working from the success of both Scratch and Built From Scratch, X-Ecutioners' new mix-CD Scratchology takes listeners on a tour of the genre's history, beginning with some quick definitions of relevant terms and continuing on to such epochal moments as Grandmaster Flash's kaleidoscopic "The Adventures Of Grandmaster Flash On The Wheels Of Steel" and Herbie Hancock and GrandMixer DXT's "Rockit." Old-school tracks from DJ Cash Money & Marvelous Marvin and Grand Wizard Theodore share space with more recent tracks from DJ QBert and Dilated Peoples, featuring J-Rocc, Rhettmatic, and Melo-D, but the members of X-Ecutioners slice and dice with such abandon that it can be hard to tell where one track ends and the next begins. It would be nice to hear many of these seminal tracks in their entirety, or in their original forms, but a tribute to DJs without cutting, scratching, and mixing would be like an all-instrumental ode to rapping. The history of DJing warrants a full box set, but until one arrives, Scratchology should more than suffice as a fun, accessible crash course in the art form's dazzling evolution.