An Expander is a dynamic processing tool designed to widen the gap between the loudest and quietest parts of an audio signal, effectively serving as the functional opposite of a compressor. Its primary operation involves analyzing the incoming signal level against a set threshold; in the most common downward expansion mode, any signal that drops below this threshold is attenuated further by a set ratio. This technique is invaluable for audio hygiene, gently reducing background noise, headphone bleed, or room ambience during pauses in a performance, offering a more natural decay than the hard cut-off of a dedicated Noise Gate. Less commonly, upward expansion can be used to uncramp over-compressed audio by boosting the gain of signals that exceed the threshold, attempting to restore lost transient impact.