In September of 1991 the MIDI Manufacturers Association (MMA) and the Japan MIDI Standards Committee (JMSC) created the beginning of a new era in MIDI technology, by adopting the "General MIDI System Level 1", referred to as GM or GM1. The specification is designed to provide a minimum level of performance compatibility among MIDI instruments, and has helped pave the way for MIDI in the growing consumer and multimedia markets.
The specification imposes a number of requirements on compliant sound generating devices (keyboard, sound module, sound card, IC, software program or other product), including that:
When MIDI first evolved it allowed musicians to piece together musical arrangements using whatever MIDI instruments they had. But when it came to playing the files on other synthesisers, there was no guarantee that it would sound the same, because different instrument manufacturers may have assigned instruments to different program numbers: what might have been a piano on the original synthesiser may play back as a trumpet on another. General MIDI compliant modules now allow music to be produced and played back regardless of manufacturer or product.
Musical Instrument Digital Interface: a specification that standardizes the interface between computers and digital devices that simulate musical instruments. Rather than transmit bulky digitised sound samples, a computer generates music on a MIDI synthesiser by sending it commands just a few bytes in length. These contain all the information a sound board needs to reproduce the desired sound - the type of instrument, the pitch, duration, volume, attack, decay, etc. are all specified by the protocol. Each channel of a MIDI synthesiser corresponds to a different instrument, or voice. Programming several channels simultaneously produces symphonic sound.