The Beatles ADT on YouTube.
Hi, welcome to an episode of “Thinking Inside the Box” on Noah’s Ark. In the video, we’re going to talk about ADT, also called Automatic Double Tracking or Artificial Double Tracking.
ADT was invented in 1966 by Ken Townsend, technical engineer at Abbey Road Studios at the time. It was conceived as a means to tackle a demand from John Lennon to alleviate the vocal recording process of double tracking. As you may know recording several takes of the same vocal part can reinforce the performance and Lennon asked Townsend to come up with an automatic way of doing this tedious task.
So how did Townsend conceive the ADT effect? Well, during the recording process of let’s say a vocal track you have a tape machine recording the signal. In addition to that, you need a second machine to double the part and this is how you wire the two machines together. You tap the signal from the record head of the first machine into the second one and you combine the signals from the reproduce heads of both machines.
So technically at this point you must have the exact same signal synced and doubled in amplitude. But here’s the trick, if you control the speed of the second machine with a varispeed, you can make the duplicate signal fluctuate in speed. As you change the speed from faster to slower, the signal will become out of phase at certain points and especially when crossing the null point due to the inherent delay between the two machines. And this is going to produce the famous phased and flanged ADT sound.
To find out more about the Beatles ADT effect, you can watch the video above or on YouTube here.