Carl Martin's Vintage Flanger has 4 knobs to control Speed, Depth, Pre-delay and Feedback, plus a dual speed mode that is foot-switchable. There are no rules with a Flanger, just plug this versatile modulation pedal in and play, play, play.The Carl Martin Classic flange pedal's Bypass switch turns the effect on and off. The Classic Flange is not "true bypass," it has high-quality buffer circuitry. The Green LED lights up when the flange pedal is activated. The Carl Martin Classic Flanger offers two settings of speed, fast/slow select on the footswitch. The fast/slow settings share the same speed knob, therefore when changing the speed setting in fast mode, it will also change the speed in slow mode. The effect pedal's Speed knob controls the speed of the Flanger's sweep. In fast mode it can go very fast, sounding reminiscent of a Leslie rotating horn. At slowest, the speed provides a sweep that stretches very wide, good for alternate rhythm figures. The Depth goes from subtle to extreme, and works in tandem with the feedback control. The pre-delay sets the short delay time in which the Flanger operates, set to the extreme left it is the shortest time available, and to the extreme right it is the longest time available. The Carl Martin pedal's Pre-Delay controls what frequencies the Flanger accentuates, as it is a moving filter that sweeps up and down following the Speed control. In other words, it sets the flavor of the Carl Martin Flanger pedal's tone, from very swirly to rising and sinking curve, and everything in between.