The recording of sounds that are then reversed when released on a musical or other work. Popularized by The Beatles on their album, Revolver (1966). In the 1980s, a few Christian groups insisted that rock musicians where including such reversed sound elements on their albums to lead people to Satanism. Although there was never any actual evidence to support the claim that backmasking coupe actually influence or “brainwash” anyone, some Christian groups and the Parents Music Resource Center claimed it did , and tried to get laws passed about it. 

With the popularity of Compact Disks, which made trying to play something backwards to listen for such messages difficult, the furor died down. New software for recording music, however, is allowing for a rebirth of interest and claims concerning the practice.