That's going to be tough because the speed of the fall-off is sampled. It's not like a modeled/intelligent thing that can be easily manipulated.

In keeping with those fall-offs the way you would do this is take those fall-off samples and edit them in some audio software to stretch time and keep the pitch the same. Create a waveform for import on your MODX or manually import the .WAV files one-by-one and generate your custom waveform inside MODX. Then replace the stock fall-off elements with your custom slower ones.

I can't remember the exact performance name, but basically if you strike the keys a little harder than normal, the trumpet sound "falls off".

Waveform 1369 is just one of the preset waveforms with 'fall' in the name and it is a trumpet.

You can modify pitch/filter/amplitude envelopes to create your own fall offs.

Post the specifics of what you are trying to do and/or a link to a video that has the sound you are trying to get and someone may be able to provide help with an envelope approach.

A fall off is à trumpet playing notes at some rate to gliss down. Anything you do to pitch is going to make the real fall-off sound artificial and uncharacteristic.

There's not a way to tell the sample to play slower and keep the pitch the same. That's essentially what is asked for.

You have to get or create a sample that does this. Could you take a whistle sample and make it gliss down using PEG to simulate what the fall-off does (using the raw sample, not PEG)? Yes, but it wouldn't sound right. Just about anything you try to synthesize using built in features is going to sound that kind of wrong.

This is where modeling would be beneficial.

The only other idea I would have would be to use an arpeggios that fakes a fall off and you can program it to play a descending legato line. The bad of this is that arpeggios are difficult to place just anywhere (in time) reliably and really wouldn't be a good tool for the job unless maybe you just did this once in a tune and do not need tight accuracy of when it fires off. You'd use a 2nd Part for this with the arp and could tell it to play using XA Control (Assign switches on/off functions that let elements play or ignores elements).

If there's a built in downward gliss arpeggio already as a preset then this would save you a lot of time. Can't help you find it right now. Still, I don't think this is the best way.

There's not a way to tell the sample to play slower and keep the pitch the same

Just to be clear - that isn't what I was suggesting. I just mentioned waveform #1369 as the possible waveform OP was using.

A fall off is à trumpet playing notes at some rate to gliss down

That is more what I meant to implement by using portamento as Bad Mister explained here:
https://yamahasynth.com/forum/stepped-glissando#reply-103987

He also describes how to create your own 'glissando' waveform and then use that in your element.

OP doesn't seem to care about the 'stepping' mentioned in that article so portamento should do the job.

I recently stretch it using up to three layered fall-offs starting with a delay, each having a different lower velocity to match the entire sequence, so that at some point of the first wave the second trumpet starts but with a lower velocity to simulate continuity, etc...

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Thank you, Andrew.

MIDI and the likes are so tricky, and so inspiring...

My next song wil be named MIDI-tricky MIDI-tricky tricky-tricky tricky-tón.

And then comes the choirs, very many, saying : MIDI-tricky, MIDI-tón.

But it will have to wait for M8X...

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