** 376 Pages, soft cover ** Turn On, Tune In, Drift Off: Ambient Music's Psychedelic Past rethinks the history and socioaesthetics of ambient music as a popular genre with roots in the psychedelic countercultures of the late twentieth century. Victor Szabo reveals how anglophone audio producers and DJs between the mid-1960s and century's end commodified drone- and loop-based records as "ambient audio": slow, spare, spacious audio sold as artful personal media for creating atmosphere, fostering c…