Electro-Harmonix Stereo Pulsar Tremolo Pedal Small die-cast aluminum case saves valuable pedal board spaceDepth, shape, and rate controls9V battery or optional AC operation Controls:Wave shape switch: selects between the wave triangle mode and the square wave mode Shape knob: changes the shape of the waveform that modulates the tremolo In wave triangle mode, as the shape knob is turned from the fully counter-clockwise position to the center position, the wave starts as a rising sawtooth and becomes a triangle From the center position to the fully clockwise position, the wave changes from a triangle to a falling sawtooth