 Backmasking has been used as a recording technique since the 1960s . In the era of magnetic tape sound recording , backmasking required that the source reel @-@ to @-@ reel tape actually be played backwards , which was achieved by first being wound onto the original <unk> reel , then reversing the reels so as to use that reel as the source ( this would reverse the stereo channels as well ) . Digital audio recording has greatly simplified the process . 
