Many non-percussion sounds have a sort-of inherent 'off' as well.

The problem is, all sounds are being generated by the various artificial component of the synth or tone module. None of this knows anything about the actual note, the components are merely responding to commands. I don't think any sounds have an actual inherent note off. So, the problem could be that if any note does not get an actual note off, then it will keep on playing. Even if there is no actual sound, because of other factors (i.e. envelope, filters, etc).

Most midi playing devices have a limit to their multi-timbrality. If it's, say, 32, and 32 sounds are still playing, even if they're not actually making any sound, then no new notes can play.

So, even if just to be tidy, any note on should be followed, in due course, with a note off. It may not make musical sense, but it does make sense to the tone module/synth.

If you're going to have an inherent note off, how do you set it? Every instrument could be different, and even a specific sound, say piano, may need a different setting at different times. OK, you were asking about percussion sounds, but the midi device cannot be certain which they are. To be honest, the midi mechanic of note on and note off gives YOU the freedom to do what YOU want, and I'd see that as a positive thing.

Interesting point, however.

Geoff

Hello. Actually, there is no technical difference between percussion instruments and keyboard instruments from a midi standpoint.
When you hit the pad of your percussion instrument, there are a few miliseconds in which your drumstick is in contact with its surface, and this is enough to trigger a midi note off event once the drumstick abandons the aforementioned surface of the pad. Plus, there are situations when the musician keeps the drumstick in touch with the pad for few seconds.
What you say about the ADSR of the instrument is true, Banibrata, as long as you are talking about the sound generator part of the instrument.
In percussion instruments, though, the most common way to set up this ADSR is a very short attack, if not zero, sustain zero and decay and release adjusted to the same value, being this a short one always.
Sustain zero makes the sound go even if you keep your drumstick in contact with the pad when you hit it, as percussion instruments do.
Decay is the time it will take for the sound to go in this scenario.
When you hit and release the pad immediately, which is the most common case, «release» is the time it will take for the sound to go, once the drumstick has left the pad. When you set both «decay» and «release» to the same value, being this a rather short one, this will give you the effect you are looking for.
Now, if you feel playful, you could set «decay» to an slightly shorter value than «release», so you can get a sort of «mute» effect that occur on drums when you leave your drumstick still touching the pad briefly, as opposed to the open sound that you get when you release the pad immediately.
Hope it helps. 🙂

What might be helpful here is to study the mid data generated. Does OP have the means to play the drum pads, less than a minute would be enough, and record the midi data and save the result into a midi file. If you could attach that midi file as a .zip, I can have a look at the innards of the midi data.

If there are in fact no midi note OFF events, that will be useful to know. If there are OFF events, where are they relative to the ON, and the overall beat, and the start of the next note?

If any OFF events are just coming too early, then the midi data can be edited to move the OFF so that the OFF does NOT interfere with the natural effect you aspire to achieve. The OFF could be moved right up to the next note, or even to just AFTER the next note.

Fiddly to do, yes, but it would tell you if all this is the real cause of your concerns? It might all be hardware dependent?

Geoff

Just to clarify, the MIDI NOTE ON and NOTE OFF messages are a fundamental part of how MIDI works, which means that they are not optional.
Now, if you use a DAW like Logic, for example, you will never find an explicit NOTE OFF message in the event list window, because the program «encodes» this as «duration», which is.the.calculated time between ON and OFF messages.
If you want to see this happening, you will have to record while this window is open. THEN you will see the NOTE ON and NOTE OFF messages arriving in their due time. Once you stop recording, the OFF messages will dissapear and you will see a «duration» parameter instead.
Also, there is the thing that some instruments use a NOTE ON message with velocity parameter «0», as NOTE OFF. This is very common, but is not to be confused with not having NOTE OFF at all. It's just a different implementation of it.
The main concept to remember here is: engineers who created MIDI were not musicians, and they interpreted things differently. For a musician, a note is PLAYED and has a certain duration. For an engineer, a note is ON and then OFF. Different concept, same result.
Just to explain why you cannot have NOTE ON without its corresponding NOTE OFF.
Greetings.