H-Arp Manual

Overlapping MIDI Notes

Let me explain a scenario with MIDI and overlapping notes, which may cause unexpected behaviour.

MIDI is a simple protocol. It sends a Note On message to trigger a note, and a Note Off on the same channel to end it. The two notes have no relation other than a flag to put a note on and one later to put it off. When the same note overlaps, sometimes unexpected results can occur because different instruments (hardware and software plugins) dictate what happens on their own terms.

Take this piano roll example where we have a same note overlapping:

In a piano roll, this would usually be impossible, but the arp may cause this, as can a tracker sending MIDI because the grid allows a degree of note placement flexibility across columns. When a tracker uses samples, it is closely tied to the sampler that can resolve it as it can see how notes are tied,  but with MIDI instruments unexpected results can happen.

Above we see a note on (1) and corresponding note off (2). And below the same note overlaps with a note on (3) and its note off (4).

If this occurs, one of several things might happen:

1. For a polyphonic synth, the two overlapping notes may play exactly as expected (on top of each other). This is what you might call first in first out (FIFO) way of dealing with the MIDI note queue, both notes come on, then both end with 2 and 4 matching respectively.
2. The onset of the overlapping note (3) may cause the started note (1) to be cut, so the first note goes off abruptly. The device simply doesn't support any kind of overlapping note on the same MIDI channel (have seen this on older MIDI equipment).
3. The two notes might play, but the note off at (2) cuts the overlapping note (3), and (1) continues onto (4). This is what you might call last in first out (LIFO) way of dealing with the MIDI note queue.

Other scenarios may play out, but essentially different instruments can have different ways of dealing with overlapping incoming note on/note off queue on the same channel because notes are not tied together as such, so it picks a strategy to what note off might belong to what note on in this basic messaging system. This might not align to expectations!

The behaviour is very much device dependent. Most soft synths seem to do the first these days.

Often it is good to try to avoid overlapping the same note if you can, but often the results are negligible.

Another area that has similar behaviour is MIDI exporting/DAW importing. Usually DAWs try to avoid the same overlapping notes when importing MIDI, so you may see some notes cut off even if they were set to play longer by the arp, usually because the same note has occurred later but before the first‘s intended gate length, and so has been cut early. This occurs in the demo pattern “Investigation” played with the notes I used in the intro video when exported because a transposition resolves to the same note as one from the opening 4 step chord before that is complete, and so it cuts it when retriggered. But it is generally negligible since it is same note retriggered vs it just playing longer, but this is worth noting this is the reason if the MIDI you see isn’t exactly as how it might be portrayed by arp programming.

Also worth noting is some instruments don't like head-to-tail length MIDI notes (the note off is too near the next note on), so compensating slightly with the Gate Reduce % can solve this.