Ever listen to the opening guitar riff of Van Halen’s “Aint Talkin’ Bout Love” and wonder what that wonderful swooshing effect was? The late, great EVH was a keen proponent of the flange effect and used it to great effect on this track and a great many more of his biggest hits.
EVH wasn't the only one who loved a bit of flange. Many tracks by The Cure feature bass soaked in it and the instantly recognisable riff of heart’s “Barracuda” just wouldn't be the same without it.
A flanger pedal creates a modulation effect akin to that of a phaser or filter pedal. It splits your signal into two before using Low-Frequency Oscillation to apply a rhythmic sweeping pattern to each of them. It then recombines the signals together, with one signal fractionally out of time. This results in a swept comb filter effect, and by changing the speed and depth of the modulation, you can create some awesome cyclical whooshing effects.