Automatic double tracking imitates the effect of doubling voices or instruments using double tracking, without the need for a musician to overdub their part (they perform their part only once). I have often heard that The Beatles invented ADT using tape delay. For example, the guitar solo on "Taxman" and the vocals on "I'm Only Sleeping" are said to be double-tracked using tape delay.
Can someone please explain the tape delay setup used to achieve automatic double tracking?
[Note: It is likely that a sound engineer, working with The Beatles, invented the ADT technique -- instead of it being an invention of one of John, Paul, George or Ringo.]