General MIDI

General MIDI (also known as GM or GM 1) is a standardized specification for electronic musical instruments that respond to MIDI messages. GM was developed by the American MIDI Manufacturers Association (MMA) and the Japan MIDI Standards Committee (JMSC) and first published in 1991. The official specification is available in English from the MMA, bound together with the MIDI 1.0 specification, and in Japanese from the Association of Musical Electronic Industry (AMEI). GM imposes several requirements beyond the more abstract MIDI 1.0 specification. While MIDI 1.0 by itself provides a communications protocol which ensures that different instruments can interoperate at a fundamental level — for example, that pressing keys on a MIDI keyboard will cause an attached MIDI sound module to play musical notes — GM goes further in two ways. First, GM requires that all compliant MIDI instruments meet a certain minimal set of features, such as being able to play at least 24 notes simultaneously (polyphony). Second, GM attaches specific interpretations to many parameters and control messages which were left unspecified in the MIDI 1.0 specification. For example, assigning one of the 128 possible MIDI Program Numbers selects an instrument. With MIDI 1.0, the assignment could be to an arbitrary instrument; but with GM, a program number assigns a specific instrument name. This helps ensure that playback of MIDI files sounds more consistently between different devices compliant with the GM specification. However, it still leaves the actual sounds of each instrument up to the supplier to implement; one manufacturer's French horn, say, could be brighter, or more mellow, than another's. The GM 1 specification was superseded by General MIDI 2 in 1999; however, GM 1 is still commonly used. General MIDI was widely supported by computer game developers in the 1990s.