Introduction into MIDI
MIDI stands for Musical Instrument Digital Interface and has been the rage among electronic musicians throughout its six year existence. It is a powerful tool for composers and teachers alike. It allows musicians to be more creative on stage and in the studio. It allows composers to write music that no human could ever perform. But it is NOT a tangible object, a thing to be had. MIDI is a communications protocol that allows electronic musical instruments to interact with each other.
All too often I have seen misinformed customers browsing through a music store: "Where do you keep your MIDIs?" "I'd like to get a MIDI for my home computer." "I need to get two MIDIs so they can talk to each other, right?" Explaining to customers that they cannot just get a MIDI becomes frustrating to the salesman. Fortunately, the average consumer is learning more about the concept of MIDI through articles such as this one. To have a complete understanding of how MIDI works, though, one should learn its history.
The Method of MIDI
Much in the same way that two computers communicate via modems, two synthesizers communicate via MIDI. The information exchanged between two MIDI devices is musical in nature. MIDI information tells a synthesizer, in its most basic mode, when to start and stop playing a specific note. Other information shared includes the volume and modulation of the note, if any. MIDI information can also be more hardware specific. It can tell a synthesizer to change sounds, master volume, modulation devices, and even how to receive information. In more advanced uses, MIDI information can to indicate the starting and stopping points of a song or the metric position within a song. More recent applications include using the interface between computers and synthesizers to edit and store sound information for the synthesizer on the computer.
The basis for MIDI communication is the byte. Through a combination of bytes a vast amount of information can be transferred. Each MIDI command has a specific byte sequence. The first byte is the status byte, which tells the MIDI device what function to perform. Encoded in the status byte is the MIDI channel. MIDI operates on 16 different channels, numbered 0 through 15. MIDI units will accept or ignore a status byte depending on what channel the machine is set to receive. Only the status byte has the MIDI channel number encoded. All other bytes are assumed to be on the channel indicated by the status byte until another status byte is received.