For MIDI instruments to communicate with one another, they need to have a common vocabulary. This is where MIDI messages come in. MIDI messages contain an array of commands, including the following:
Performance data messages: These messages consist of note-on and note-off, velocity, after-touch, vibrato, and pitch-bend messages.
MIDI performance data messages each have 128 different values. For example, each note that you play on the keyboard has a number associated with it (middle C is 60, for instance). Likewise, velocity is recorded and sent as a number between 0 and 127, 0 being the softest volume (no sound) and 127 being the loudest that you can play.
Control change messages: These are a type of performance data message. These messages contain data about expression, including modulation, volume, and pan.
System-common messages: These messages contain data about which channel the performance data is sent to and what sound in the sound library to play. System common messages also include information about timing data, master volume, and effects settings.
System-exclusive messages: These messages contain information that is exclusive to the system or device. The messages can include data transfers of new sound patches, among other things.
To use MIDI effectively, you don’t need to know all (or many, really) of the MIDI messages that a device can recognize. If you hook up your gear and play, your MIDI devices generate and respond to the messages for you.
Not all MIDI devices recognize all the MIDI commands. For example, a sound module generally can’t send performance data messages, such as after-touch messages, because a sound module doesn’t have triggering mechanisms that produce these commands.
Check your instrument’s manual for a MIDI Implementation Chart. All MIDI instruments come with this chart. In it, you can find a list of all the MIDI commands that the device can send or receive. The chart also includes information on polyphony, which refers to how many notes the instrument can play at once, and multitimbrality, or how many different sounds the instrument can produce at the same time.
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