Abbey Road Studios’ Artificial Double Tracking is the most legendary of all Abbey Road tape effects and can be heard on countless historic recordings.
Over the years, many recording engineers have tried to replicate the effect, but with only partial success. This is largely because a definitive description of the exact process used at Abbey Road has, until now, been a closely guarded secret.
ADT was invented at Abbey Road Studios in the 1960s in order to meet the Beatles’ unique recording needs. As the band’s success grew, so did their desire to find new ways of working, leading Abbey Road’s engineers to experiment with new technology.
By 1966, the band had become frustrated by the need to continually re-record vocals to create multi-layered vocal effects. To solve the problem, Abbey Road engineer Ken Townsend created Artificial Double Tracking (ADT). By connecting the primary tape machine to a second, speed-controlled machine, two versions of the same signal could be played back simultaneously. And by gently wobbling the frequency of an oscillator to vary the speed of the second machine, the replayed signal could be moved around just enough to make it sound like a separate take.
The introduction of ADT was a milestone in the history of sound recording, and the technique was used heavily on many recording sessions at Abbey Road Studios. ADT became such a prominent and integral part of the production process that Abbey Road’s momentous move from 4-track to 8-track recording was postponed for several months—from May to September 1968—until the new M3 8-track tape heads could be modified to enable the independent sync output needed for achieving ADT.
John Lennon reputedly dubbed ADT ‘Ken’s Flanger,’ which some say led to flanging becoming established as a technical term in studios around the world.
"One night we had been double-tracking Paul’s voice by sending a track down to the studio via cans (headphones) and him singing over his own voice. It was a time-consuming process, and a waste of a valuable track on the tape machine. Driving home in the early hours of the morning, I came up with an idea how this could be done by sending the sync output of a Studer J37 and delaying this by using a BTR2 with the capstan motor on frequency control, then adding it to the original signal from the replay output of the Studer. I rushed back to work the following morning, tried my idea out and it worked. I demonstrated it to the Beatles the following evening and they utilized it frequently from then on. About six months later I was called up to the General Manager’s office, and told not to use it until it had been technically approved. The same evening the Beatles used it again!"
– Ken Townsend