Flanger was produced by running two identical recordings at the same time and by slowing one down to create a small delay between the two, the short delay produces extra harmonic content which is where you get your classic Flanger fx from.
Flanger has a very short delay time between 0.10ms to around 11ms & also incorporate a feedback control.
Rate/ Amount /Speed - How quick the LFO (Low Frequency Oscillator) sweeps through the spectrum & extends the LFO's influence via the amount.
Feedback - Increases the intensity of the effect by focusing on the resonant frequency.
Hi pass - Filters out any frequencies below the frequency that is selected.
Width - 0% the waveform is identical to the right and left channels at 100% the waveform is in full stereo.