Flanging

Flanging is an audio effect that occurs when two identical signals are mixed together, but with one signal time-delayed by a small and gradually changing amount, usually smaller than 20 milliseconds.It originally achieved using two reel-to-reel tape recorders playing the same program and slowing them down by pressing against the flanges of the tape reels. This audio effect originally know as "reel flanging" eventually became known as simply flanging and is used as a standard modern digital and analog audio effect.