phaser
An audio effect that creates a swirling, undulating tone by splitting a signal and shifting the phase of one copy.
In Depth
A phaser splits the audio signal, passes one path through a series of all-pass filters that shift its phase at different frequencies, then recombines the two paths. Where the phases cancel, notches appear in the frequency spectrum. Sweeping these notches with a low-frequency oscillator creates the characteristic swirling, spacey sound. Phasers are subtler than flangers and were hugely popular in 1970s funk, rock, and electronic music.
Eddie Van Halen's MXR Phase 90, set to a slow sweep on his overdriven guitar, created one of the most recognisable phaser sounds in rock history.