Named for the original effects technique where a second audio tape playback deck was slowed by a thumb on the reel flange, flanging is a special audio effect where a delayed version of a signal is mixed with the original signal, creating a swooshing sound. This is caused by the fact that when the time delay is different for the two combined signals, there will be frequencies where the phase-shift is 180? and the signals will cancel, causing deep dips or holes in the frequency response curve called the comb filter effect. As the speed is varied, the frequency of the dips is swept across the frequency range, giving the swooshing sound. Electronic flangers contain an adjustable electronic delay line. If the time delay is very short, the effect is called phasing. See also notch filter.