A Flanger effect is created when two similar audio signals are mixed together with one signal being delayed ever so slightly using an LFO. As the sound starts to swirl around it creates peaks and troughs in the frequency band.
By varying the time delay slightly, these peaks and troughs sweep up and down the frequency band to create the flanging effect. Usually, a section of the output signal is sent back to the input which produces a resonance effect to give more intensity to the swirling peaks and troughs.
Flanging can be used to great effect when creating synth pads, without the flanger your pads can still sound beautiful and airy. However, adding flanging effects to your pads will leave the end result a lot livelier and it will feel as though the music is evolving as it swirls around.
Flanging has come a long way since it was first introduced in the 1950s and 1960s. The original technique used two tape machines that played back the same audio simultaneously. During playback, the “flange” or outer edge of the tape would be slightly obstructed to cause a delay.
As the obstructed tape would finally get back in sync with the other, the flanging sound could then be heard. It was an expensive and long-winded process, but digital technology has now been able to replicate the process in an easier and cheaper format.