A device designed to govern the supply voltage in an electronic circuit. Such a circuit could be in a computer, digital reverb, or automobile. Or it could be part of a power distribution system employed in your studio or stage rack. In all cases the idea is the same: to work with an input voltage that may vary and output a voltage that stays within a predefined range. Regulators come in many sizes, configurations, and price ranges. They do not all work the same way. Some may simply switch between different taps on a transformer (usually not a good idea for digital equipment because the switching can produce spikes on the line) while others may deploy sophisticated monitoring systems that control very complex circuits keeping output voltage at an exact fixed point as well as providing all sorts of EMI, RFI and surge suppression. Most fall somewhere in between. Voltage regulators cannot create power so if voltage falls at the input, the device must begin to draw more current from the source to be able to maintain its output voltage. You should keep this in mind when using any device that regulates voltage.