|
Synthesizers
Controllers
There are devices which can be used to switch instruments/patches while playing,
or which can be used to trigger MIDI, such as a
theremin
sort of thing where you just
wave your hands in the air.
But controllers, here, refer to something else.
All the while a MIDI is playing,
controllers are used by a particular synth to change settings,
change what notes do, and other things, and are referred to by number,
in a control change message.
The numbers could refer to different things, depending on manufacturer.
But these were standardized under GM
to refer to the same thing, for whatever manufacturer.
So GM compatible synths will treat the same number the same way,
so that it will control and do what is expected;
though not every synth can recognize all controllers that might
conceivably be available.
One type of control change message is used to change the
instrument (or 'patch').
Another is used to specify
RPN/NRPN.
Another refers to channel pressure.
Beyond that, GM expects certain controller numbers to
be acted upon in a certain way, for each channel, out of 16:
| |
| 1 |
the amount of modulation for the instrument: a sort of vibrato.
|
| 7 |
the overall volume: along with whatever velocity (volume) is used
for each note, and whatever the expression controller is set to.
|
| 10 |
pan: how much the instrument plays out the left or shifts over
to the right speaker, and back again.
|
| 11 |
expression: sort of a change in volume meant more to simulate
loud/soft changes in playing, without modifying the volume of
each note, or changing the overall volume for the channel.
It's useful for those loud/soft changes, literally for expression,
even fading out as a note is held, and so allows
the overall volume to be set with the volume controller.
|
| 64 |
sustain: like a piano's sustain pedal, used to hold a note
longer than it otherwise would be if based only on the specified
length of each note.
|
|
|
There are two others that may or may not be part of the GM
spec, but which should be treated alike by various synths:
| |
| 91 |
reverb: actually the level or 'volume' of the reverb.
Setting various types of reverb, and modifications, are
typically handled by
SysEx command strings.
|
| 93 |
chorus: again, the level of the chorus.
Chorus type, and variations, are set with SysEx.
|
|
|
Some synths might ignore these controllers
and make you select
reverb/chorus apart from the MIDI, as with the
soft synth, Wingroove.
[And some synths might handle either differently with regard
to each channel.
For example, the Roland GS sets the type of reverb and chorus
for all 16 channels at once, at any given time, but the XG
allows you to select the type of reverb/chorus for each channel
separately.]
These controllers are used by specifying the number, above, and
also giving a value. For all these, above, the value is from 0 through 127,
except - for pitch bend the range is -8191 to +8191.
The standard or default value for pan, for instance, would be 64,
right in the middle of 0 and 127, centered between both speakers.
The default for modulation would be 0, or none at all.
The default for pitch bend would be 0, and the amount of pitch bend
set by RPN or SysEx, but with a GM default of +/- one whole note;
meaning two whole notes from 8191 down to -8191.
The reverb, in the Roland GS for example, defaults to 40 (28 hex).
Now the defaults are what you get if you do nothing.
But of course you can change them to whatever you want, even and
often particularly as the MIDI is playing.
People sometimes like to pan back and forth between the speakers for
effect.
Pitch bend and expression are often in constant use in certain MIDIs,
modulation to a lesser degree.
CONTINUE
|
