Alesis GT Reference Manual page 126

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.
Like many other affordable keyboards, the DPM 2 does not include
pressure.
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.
Continuous Controller Footpedals, breath controllers, and modulation
wheels can vary sounds as you play, thus adding expressiveness. MIDI
allows for 64 continuous controllers (these act like potentiometers in
that you can choose one of many different values) and 58
continuous/switch controllers (these can act like continuous controllers
but some are assumed to choose between two possible states, such as
on/off).
Each type of controller is stamped with its own controller identification
number. Not all controller numbers have been standardized for specific
functions, but the following indicates the current list of assigned
controllers. Numbers in parenthesis indicate the controller range.
1 Modulation Wheel (0-127)
2 Breath Controller (0-127)
3 Early DX7 Aftertouch (0-127)
4 Foot Controller (0-127)
5 Portamento Time (0-127)
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