The ADT technique was developed at Abbey Road Studios by engineers recording The Beatles in the 1960s. To free John Lennon from having to sing everything twice for real double tracking they came up with an artificial replacement: they sent the original signal to another tape machine and re-recorded it. Due to the physical distance between record and playback heads the new signal was delayed. The length of the delay depends on the tape speed (the slower the tape is running the longer it takes for the signal to travel from the record to the playback head). However, due to the machine's (small amounts of) Wow and Flutter the delay time was not fixed but varied slightly, giving an additional chorus-like effect.
- Delay: the time the ADT signal is delayed, 10 - 50 ms.
- Dra Level: the level of the original signal.
- ADT Level: the level of the ADT signal.
- ADT Pan: the pan position of the ADT signal, the original signal is positioned at the opposite side.
- Wow: amount of low frequency playback speed variation, 0 - 0.2%.
- WowFreq.: low frequency playback speed variation rate, 0 - 6Hz.
- Waveform: waveform of Wow, Sine or Triangle.
- Flutter: amount of high frequency playback speed variation, 0 - 0.2%.
- FlutFreq.: high frequency playback speed variation rate, 4 - 60Hz.
- Waveform: waveform of Flutter, Sine or Triangle