Dry/Wet is a parameter that one can target as a destination in the modulation matrix ("Mod Control" -> "Control Assign" ) within each Part. You need a source controller that relates to velocity. You can setup envelope follower to do this. The "problem" with the approach is how source controllers do not follow notes -- and the dry/wet parameter doesn't follow a note. So say you hold down a pad with your left hand and use a very slow velocity. Inversely proportional - the pad will start with a high Dry/Wet setting. However, say you start playing in your right hand with a high velocity. Your left hand pad will now see the inversely proportional Dry/Wet setting of a low value now.

With this caveat - here's the general rundown:

1) Burn a Part in slots (1-8) so you get keyboard control ON
2) For this burned Part - set it to FM-X. It allows for infinite hold.
3) Set the Part to mono so multiple notes don't make this Part louder. Set to sine with no modulators so it's fairly simple. Set to a fixed frequency so all keys play the same note. Set the AEG so the release is infinite. I also setup so there is no shape to the AEG (constant volume).
4) Setup the velocity response so the slower you press a key - the quieter this burned part is. The harder you.press the louder it is. Try to achieve as much range as possible.
5) Set the Burned FM-X Part's output to OFF. It will only be used as a source for the envelope follower
6) Any Part(s) you want inversely proportional to "velocity" - setup their Mod/Control->Control Assign source to Envelope Follower #X where X is the Burned Part. Set the curve ratio to negative so the "louder" the burned FM-X part gets - the more you subtract from Dry/Wet. And set Dry/Wet to the maximum so you are subtracting from it.

You may need to fiddle with the envelope follower gain, hysteresis, etc. And you may need to fiddle with the Dry/Wet programmed value which is the initial offset which will be biased by the envelope follower subtracting.

This all works reasonably well for notes that happen in proximity to the FM-X volume differences due to the caveat shown above. Due to the "following" nature - you may run into lag. The only compensation here is the hysteresis. Depending on how tight you need this loop - the lag may still not be ideal.

That's about the only tool you have in the box to change dry/wet with "velocity".

I think we went to a similar school of "problem solving". I'd thought through this approach, when I couldn't find a direct way to use velocity as a controller, and come to the exact same conclusion, that the lag would make it useless (for this particularly fast/responsive need/desire for it).

DOH!!

I was hoping I simply didn't know where I could find/use/read velocity as a controller.

DOH. DOH. DOH!!!

And, thank you, very much, for confirming my suspicions, that it can't be done. Knowing that is better than being uncertain.

DOH!

Yeah, It's been brought up before in 2017 ...

https://www.yamahasynth.com/ask-a-question/note-number-as-mod-source

and, for different reasons, I wanted velocity as a destination

https://www.yamahasynth.com/ask-a-question/can-control-destinations-affect-velocity

Velocity is an interesting parameter because it comes before the note starts. Making it a fairly powerful item for manipulation.

The envelope follower idea I do use for certain things. It really depends on if your application can deal with the caveat(s).

THANKS FOR THE LINKS. Agreed, on all fronts!

Velocity is an interesting parameter because it comes before the note starts. Making it a fairly powerful item for manipulation.

Have you seen the specs for the new ASM Hydrasynth Deluxe and (little) Explorer? Both have added release velocity!