Backmasking

Backmasking is a recording technique in which a sound or message is recorded backward onto a track that is meant to be played forward. Backmasking is a deliberate process, whereas a message found through phonetic reversal may be unintentional.

Backmasking was popularised by the Beatles, who used backward instrumentation on their 1966 album Revolver. Artists have since used backmasking for artistic, comedic and satiric effect, on both analogue and digital recordings. The technique has also been used to censor words or phrases for "clean" releases of explicit songs.