Flanging is an
audio effect produced by mixing two identical
signals together, one signal delayed by a small and gradually changing period, usually smaller than 20
milliseconds. This produces a swept
comb filter effect: peaks and notches are produced in the resulting
frequency spectrum, related to each other in a linear
harmonic series. Varying the time delay causes these to sweep up and down the frequency spectrum. A
flanger is an
effects unit that creates this effect. In some cases the two signals will become so close that it almost fades away to oblivion called "sucking air." It has also been called the "Darth Vader effect."