ADT
During the recording of Tomorrow Never Knows, Lennon complained that he had always hated doing a second take to double the sound of his vocals, so Townsend, the studio technical manager, created the world's first ADT system by taking the signal from the playback and recording heads and delaying them slightly, thereby creating two sound images and not just one. By altering the speed and frequencies he could also create other different types of effects, which The Beatles used throughout the recording of Revolver.
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