Flanger is a modulation effect that creates a sweeping, jet-like sound by mixing the original signal with a slightly delayed copy that is continuously modulated. As the delay time changes, it produces a series of moving peaks and notches in the frequency response, giving the effect its distinctive whooshing character.

It is often used to add dramatic movement and texture to guitars, basses, and synthesizers, ranging from subtle shimmer to intense, psychedelic sweeps. Flanger is commonly associated with classic rock and experimental sounds, but it remains widely used wherever bold modulation and motion are wanted.