An abrupt change in a quantity, characterized by a rise and a decline, typically occurring over a short time interval in comparison to the time scale of interest. Typically in our applications this refers to a sharp variation of a current or voltage having a normally constant value. A clock signal is sometimes considered a pulse, though it is usually more like a square wave. A square wave differs from a pulse in that it may maintain its high or low state for some relatively long period of time. A pulse will very abruptly change from low to high and back to low again (or vice versa). Pulses are generated and used by all sorts of electronic equipment. In music production pulses and clock signals have been used a lot over the years to synchronize equipment together, particularly old sequencers and drum machines prior to MIDI. Once MIDI arrived on the scene, its digital precision rendered analog pulses and clock signals obsolete as a method of communicating between devices.