Flanger

A delayed signal is added to the original signal with a continuously-variable delay (usually smaller than 10 ms). This effect is now done electronically using DSP, but originally the effect was created by playing the same recording on two synchronized tape players, and then mixing the signals together. As long as the machines were synchronized, the mix would sound more-or-less normal, but if the operator placed his finger on the flange of one of the players (hence "flanger"), that machine would slow down.

This would cause certian frequencies to become out-of-phase , and thus cancel. and other frequencies to be in phase, creating reinforcement. If the frequency response is plotted on a graph, the result resembles a comb, and so is called a comb filter. Once the operator took his finger off, the player would speed up until its tachometer was back in phase with the master, and as this happened, the freqenucy at which the peaks and dips in the comb filter occured would change, producing a phasing effect. This phasing up-and-down the register can be performed rhythmically.