So remember the old Modulation Wheel or the Pitch Bend? Well, let’s use the MW as an example. The message it produce is called, in terms of the MIDI protocol, a CC or continuous controller message. There are many CC messages (1 through 127) available, all of which can be used the same way as the WM message, which happens to be CC #1. When the wheel is in the original position or minimum, its data value is at 0, and when pushing the wheel to the maximum position, it’s at 127. When the wheel is moved it continuously (hence the name of the message type) generates MIDI messages. Since the CC message sent when moving the wheel is really just a stream of numbers, it can be used for anything. What I mean is that if a recipient does not utilize an actual MW, it can still respond to the numbers coming across, if programmed to do so.
The point is that MIDI is not just for Notes on or off, which a synthesizer use, but also for controlling other aspects of a MIDI performance. I am not familiar with the GR 33 per se, but considering it’s a guitar synthesizer one could imagine being able to change aspects of the sound it generates, say the filter q or maybe influence some parameter of an effect, maybe the size of the room, or the width of the chorus, etc. This could easily be done with CC messages, if the device has that sort of MIDI capability. I wouldn’t be surprised if it can respond to the WM CC out of the box. Anyways, knowing Roland’s excellent MIDI support generally, in their devices, I am sure it can be programmed to do just this type of stuff.
Another interesting application for MIDI, speaking of non-synthesizers and to get some perspective on what it can be used for, is a light synthesizer. You could have a device that responds to MIDI and that in turn controls stage lights. For example, you send a note on C2 and a particular light comes on, you let go of the key and the light goes off. You send a CC message (e.g. #1, MW) and depending on the data value received (0-127) it turns the lights softer or brighter.
Also, as an FYI, you see me referring to the range 0-127 a lot. That’s the range of a byte (as in computer byte) value within the realm of the MIDI protocol.