Formulate a flanger
The simplest and most classic modulation effect, the humble flanger is created by delaying a signal and then modulating the delay time. Set your delay’s Dry/Wet to 50%, and make sure you keep the delay time quick – about 10 milliseconds to start off with. Now modulate the delay time with an LFO, at a rate below a second (ie, under 1Hz). Keep the delay amount low as well – you don’t really want delay time to go over 20ms at its highest excursion. Experiment with delay timing and modulation timing. and for a stronger effect and more ‘whoosh’, crank the delay’s feedback control up.