The GM protocol defines a "mapping" of sounds, associating a certain MIDI channel to each sound. This way a MIDI score obtained by using a certain kind of keyboard or module can be played by another module without the corresponding sounds being modified. Without this specification each MIDI channel could potentially refer to any instrument. Therefore what might happen is that a drum-beat pattern recorded using a drumkit device would get played as, say, a piano, when sent to another MIDI device. With the GM protocol a standard is thus defined, which if respected avoids us experiencing this kind of inconvenience. Other specifics are also defined in the protocol, for example regarding aftertouch and other MIDI protocol parameters. A list of the mapping of the instruments can be consulted in the appendix relating to GM. [General MIDI - Format Specifications ] .