C963 ratchet sequencer, from Club of the Knobs
A sequencing technique in which some mechanism is used to generate a finite number of gate or trigger signals very quickly, often with an accelerando or decelerando effect. The resulting gate or trigger is often used to produce a sharp, quick percussion sound, producing an effect sometimes referred to as the "squeaky door sound". Tangerine Dream was known for creating ratchet effects by feeding a sequencer with multiple clock lines running at different speeds and rapidly switching from one to the other, but dedicated ratchet generator devices are also available.