Tremolo is an old school effect, and can be heard on many old 60’s surf songs and some more recent ones over the years. To get an idea of of what its like listen to Midnight Oil’s “Armistice day”, the stuttering sounding guitar uses tremolo to get that sound.
An opto based device is used to modulate the volume of the guitar signal. This opto device is controlled by a low frequency oscillator which can be set to square wave or triangle / sine wave. These two modes sound quite different with square wave being more choppy or stuttering while triangle / sine wave produces gradual changes.
RATE controls the speed of the Tremolo effect from extremely slow to full on stuttering, DEPTH controls the amount of volume reduction, VOLUME adjusts the overall volume out of the pedal, and there is a switch to select between Square mode and Triangle / Sine mode. When the effect is on, the LED goes on and off with the tremolo speed allowing a visual indication of the effects operation.
The video below shows a good overview of the range of sounds available. If RATE is turned all the way up, the sound modulation becomes almost “metallic and robotic”. A slow RATE and medium DEPTH in Triangle mode gives an almost chorus like effect