This Ableton tutorial walks through how the Flanger and Doubler modes in the Phaser-Flanger device work, showing what each does to a signal and how their controls shape the result.
The Flanger duplicates the input signal, delays it by a short amount, and mixes it back in with the original. The overlap creates an interference pattern, the classic comb-filtering sweep. Feedback intensifies the effect, and the LFO keeps the delay time moving so the sweep stays animated.
The Doubler works on the same principle but pushes the delay time much further, starting at a minimum of 20 milliseconds. Where the Flanger produces tonal interference, the Doubler starts to feel like stacked copies of the signal layered on top of each other. Adding feedback multiplies those copies, and the LFO can be brought in to give the whole stack movement.