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MIDI Supplement: Appendix B
QuadraSynth Plus Piano Reference Manual 182
MIDI Message Basics
The are two main types of MIDI messages. Channel messages, which are
channel-specific, consist of Voice and Mode messages. System messages, which
do not have a channel number and are received by all units in a system, include
Common, Real Time, and Exclusive messages.
Channel Messages: Mode Messages
There are two messages that determine the MIDI mode (i.e., how a
device will receive MIDI data). The “Omni” message determines how
many channels will be recognized. Omni On means that data from all
channels will be received; Omni Off limits the number of channels,
usually to one.
The “Mono/Poly” message deals with voice assignment within the
synthesizer. In Mono mode, only one note at a time plays in response to
voice messages; in Poly mode, as many voices can play notes as are
available to play notes.
Channel Messages: Voice Messages
A synthesizer’s voice is the most basic unit of sound generation. Usually,
each voice plays one note at a time, so the number of notes you can play
at one time will be limited by the available number of voices. MIDI
messages that affect voices include:
Note On. Corresponds to a key being pressed down; values range from
000 (lowest note) to 127 (highest note). Middle C is 60.
Note Off. Corresponds to a key being released; values are the same as
note on.
Velocity. Corresponds to dynamics; values range from 001 (minimum
velocity) to 127 (maximum velocity). A velocity of 000 is equivalent to a
note-off message.
Pressure. Indicates the pressure applied to a keyboard after pressing a
key. Mono pressure (Aftertouch) represents the average amount of
pressure applied by all keys. Poly Pressure produces individual pressure
messages for each key.
Program Change. Sending a Program Change command from a
sequencer or other MIDI keyboard can change synth patches
automatically. There are 128 Program Change command numbers.
Also note that not all units number programs consistently. Some number
them as 000-127, others as 001-128, and still others arrange programs in
banks of 8 programs (such as A1-A8, B1-B8, C1-C8, etc.).
Pitch Bend. This “bends” a note from its standard pitch.