How ADT (Automatic Double Tracking) Thickened David Gilmour's Vocals on The Dark Side of the Moon

The most interesting thing about the vocal sound on The Dark Side of the Moon is that Gilmour often wasn’t actually singing twice. Instead, engineer Alan Parsons used a trick called Automatic Double Tracking (ADT) — invented just a few years earlier by Abbey Road’s Ken Townsend. ADT works by splitting the vocal signal, feeding one copy to a tape machine, and playing it back a few milliseconds later alongside the live signal. That tiny delay (usually 20–50 ms) creates a natural comb-filtering effect that thickens the voice and makes it sound like two slightly different takes, without the hassle of recording a second pass.

On this album, ADT was applied heavily to Gilmour’s lead vocals, especially on “Time” and “Us and Them.” The slight pitch drift from the tape machine added a subtle, organic wobble — not enough to sound like chorus, but enough to give the voice a fuller, almost three-dimensional presence. Parsons would often dial in just the right delay