Phaser is a modulation effect that creates a smooth, swirling sound by splitting the signal and shifting the phase of one path before mixing it back with the original. As the phase shift is modulated, it produces moving peaks and dips in the frequency response, giving the effect its characteristic sweep.

It is commonly used to add movement and texture to guitars, keyboards, and other instruments, ranging from subtle and warm to deep and psychedelic. Phaser effects are strongly associated with classic funk, rock, and 1970s tones, but remain widely used in modern music for their fluid, musical character.