Believe it or not, just ten years ago, MONO ONLY instruments were still being made and sold successfully! These days, MONO mode is just one facet of an instrument's abilities. This takes us back to our original question concerning the behavior of OMNI mode in the transmitting keyboard. When we set our instrument to OMNI ON / MONO, it will transmit as we would expect, sending our single note down the assigned transmission channel. IF however, we set our instrument to OMNI OFF / MONO, we could be in for a shock. Some transmitters will separate our chords into single notes sending each note in the chord to the next numbered MIDI channel! Surprise! That's what the creators of MIDI intended. Now for another surprise: No one I know of has ever successfully implemented this! What's going on here?!?!

The MIDI standard says keyboard behavior when transmitting can be summed up as follows:

OMNI ON / POLY: All playing is sent to one channel.
OMNI OFF / POLY: All playing is sent to one channel.
OMNI ON / MONO: Each single note sent to one channel.
OMNI OFF / MONO: Chords are "broken" into single notes and sent to a separate MIDI channel each. The notes are assigned one after the other to the next ascending MIDI channel number. Pretty wild, huh?

Keyboard behavior when receiving can be summed up as follows:
OMNI ON / POLY: All channels received and played in POLY.
OMNI OFF / POLY: Normal operation. Receives on one channel only, and plays polyphonically (chords).
OMNI ON / MONO: All channels received, played one note at a time. (Imagine ALL channels trying to control one note!)

OMNI OFF / MONO: The assigned channel is received and sounded one note at a time.

It's VERY confusing at first to try to sort out what benefit could be derived from the implementation of the MIDI standard as it has been defined. I have YET to see chords broken into single notes and assigned to a separate channel each. It seems to be one of those weird anachronisms that no one attempts to implement, but it keeps showing up in owner's manuals and charts with confusing explanations.

Why in the world would the MIDI gods seek to make us so miserable with such a weird brew as this? The answer lies once again, in history. In the early days, when the MIDI standard was being conceived, MONO ONLY instruments were still common. Someone thought, "Let's set it up so a guy could have seven different MONO ONLY instruments in his chain, and then play chords!" Everyone thought this was a WONDERFUL idea, so it was added. No one realized that as the standard was released, MONO ONLY instruments were already joining the ranks of other notables such as brontosauruses, pterodactyls, and mammoths. So we have a standard that is just not useful in some ways.

Here's what most manufacturers seem to be doing now: Full implementation of the first three in each group, and implementation of the OMNI OFF / MONO mode to sound single notes at the LOCAL keyboard but send all notes to whatever channel is assigned for transmission. Receiver behavior likewise, simply responds to one channel with only one voice. This is certainly much more intuitive! MIDI is sometimes a prisoner of its primitive past, and in this case, most manufacturers just choose to abandon it for a more reasonable approach.

Having thoroughly destroyed any previous understanding you might have had about these matters, I'll try to find something a little less painful for next month. Perhaps that lower right molar...