Flanging is an audio effect produced by mixing two identical signals together, with 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 resultant 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 

The scheme of FIR flanger 

The difference equation is y(n)=x(n)+ax(n-D(n)), where 

 D(n)=d/2(1-cos(2pFn)), F - deviation speed (about 1 Hz), d - deviation rate. 

The modulation of delay time causes dynamic changes in dips and peaks position. Additional effect is time stretching of audio signal. The time delay varies between 1ms and 100 ms. 

Flanger Controls 

Modulation 

Specifies the Flanger Frequency 

Delay 

Retrieves and sets the number of milliseconds the input is delayed before it is played back in the EffectsFlanger structure 

Phase Invert 

Specifies whether the added Signal should be Inverted.