Leprecon LD-360 - Manual (Page 7)

Page 7
LD-360M Appendix 1
:MIDI Basics
The MIDI (Musical INSTRUMENT Digital Interface) protocol is a very well developed and versatile
"language" which was originally developed to allow synthesizers from different manufacturers to
communicate with each other. By means of a simple cable connection, a keyboardist could play a "slave"
keyboard remotely from a master keyboard controller. But MIDI has rapidly expanded into the realm of
effects processors, drum machines, sound consoles, personal computers, and-of-course-lighting consoles,
and now the possibilities for creating an integrated system of music, lighting, and computer
equipment are virtually endless. .
What passes through the MIDI cables is a seemingly endless string of digital commands-binary ones and
zeros-that reflect what each MIDI device in the system is doing. Each combination of these ones and
zeros is a specific command, telling a device to perform a specific function. Though many of the MIDI
commands are geared toward keyboard functions (such as note-on and note-off, pitch bend wheel, etc.),
the designers of the MIDI protocol were farsighted enough to make the "language" easily adaptable to a
wide range of products. In the case of the LM-850, many keyboard-oriented commands serve completely
different functions. For instance, if a synthesizer is connected via MIDI to the LM-850, turning the synth'
s modulation wheel forward will cause channel 2 of the console to increase in level. Stepping on the
keyboard's sustain pedal will effectively "press" the bump button of channel 5. This is because the MIDI
command isn't really saying "press the sustain pedal," it is saying "raise the value of this particular
parameter to this particular level." In this instance, that parameter -is "continuous controller number 64,"
which to a keyboard means "sustain pedal" and to the LM-850 means "channel 5 bump button. ..
Many controls on MIDI devices, such as synthesizer modulation wheels or lighting channel faders,
operate over a wide range of values, allowing for smooth transitions from one setting to the next.
Be
cause of this, they are called "continuous controllers". The MIDI Specification calls for 128
continuous controllers, with each having a range of 128 possible values (0 to 1-27). A basic switch
function, such as a sustain pedal or bump button, can be a continuous controller as well, by using a value
of fully off (0)
to be an "Off' setting, and a value of fully on (127) to represent "On", values in
between these two ex tremes are simply not used. It is these continuous controllers that form the basis of
the LM-850's MIDI implementation. Nearly every fader and button on the console's front panel acts like a
MIDI continuous controller; moving that control will send out MIDI data, and MIDI data that is received
will mimic that control, duplicating its function remotely.
There are 16 MIDI "channels", and like a television set, a unit won't receive a particular message unless it
is set to the correct channel. To control a slave device remotely, the master controller must send out data
on the same MIDI channel that the slave is set to receive on. If the slave is set to "OMNI mode", then it
responds to messages on all MIDI channels (a device can only transmit on one channel, however). While
most devices send and receive data on the same channel, some-like the LM-850-0ffer the
added versatility of being able to send and receive on separate channels.
.
Also prevalent in the MIDI data stream are note-on and note-off messages, usually used to tell a keyboard
to play a particular note at a particular velocity. (The velocity of the note, or how hard the key is struck,
usually relates to how loudly the note should be played.) There are 128 notes defined by MIDI,
with a
128 step range in velocity values. The LM-850 can use either note data or continuous controller
-
data to control dimmers through its MIDI Dimmer Outs; this choice is made in Console mode. In either
situation, Leprecon MIDI dimmers will respond to the data as channel fader commands. In note mode,
the MIDI note number designates which dimmer channel the data is addressed to, and the velocity data
tells the dimmer the correct brightness. For some unusual applications, this data can just as easily be sent
to a keyboard or other MIDI device that responds to note data. Since the LM-850 can only address the
108 dimmer channels, it can only send (and receive) MIDI notes 0 through 107.
Program changes are another common type of MIDI data. By sending a program change to a synthe-