Abbreviation for General Purpose Interface. As the name implies GPI’s can take many different forms and have different purposes. Historically they have been used in audio and video production to control devices that do not have a specific way to interface with other equipment. For example, an artist may want to turn on a particular stage lighting effect at a specific point in a sequenced performance via MIDI. To do this he would need a device that converted MIDI data (most likely MTC) into an analog (hardware) switch closure. This effectively “throws a switch” at the appropriate time in the performance. This switch can be connected to other hardware that controls the lighting effect. Devices that convert one standardized type of data (MTC, SMPTE, etc.) into a general kind of data (switch closures, pulse outputs, etc.) are known as GPI’s.