I copy and paste these 2 in.. one is the left piano, the other right.

In the Layers panel, editing layer 1 for example, select 'note edit' then 'volume' - then right-click and paste this into the pane:

Volume = [-23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -4, +1, 0, 0, -1, -1, 0, -1, +1, +1, +2, 0, +1, +2, +2, 0, -2, -1, +2, -2, -2, +2, +2, +1, 0, -3, +1, +2, +1, 0, +1, +1, 0, -1, 0, 0, 0, 0, 0, +1, -1, -2, 0, 0, +1, 0, 0, +2, +1]

and repeat the process for layer 2 but with this to paste in..

Volume = [0, -1, -2, +1, 0, +1, +1, 0, -1, 0, +1, 0, +1, +2, +1, +1, 0, 0, 0, +1, -1, 0, 0, 0, 0, -1, -1, +1, +2, 0, -1, -1, -2, -1, -3, +1, 0, +4, +1, +1, +2, +1, -2, 0, 0, +2, +1, +2, +2, +3, 0, -4, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23, -23]

I like the way this hard split melds - plenty of times, trying to get a fine gradated sloping mix (hand drawn or from some mathematical basis) can get me into more work than I want - but it's nice that, for me, this really simple split still seems to have given me my best results so far. Hope that helps and maybe saves a lot of time for people trying this out. Cheers!

Nice! We can reduce things like sympathetic resonance in the note editor - but a kind of nicely designed meta control that zero's out a bunch of those types of things to result in no resonant audio (beyond like you say just volume) - could be good for details or other designs! Cool idea.

@Antonio M - not sure what glitch you had trying to upload the FXP but give another try - I sometimes pick the wrong box (audio instead of FXP) - a bunch of things have tripped me up when I didn't keep an eye on the "upload successful" messages.. or could just have been a small web server glitch without an error msg too - but yeah, give another go following the prompts and hopefully it'll work out next time.

@Antonio: are you able to post your fxp? In which octave did you make the transition?

well, I don't know what I'm doing but that didn't prevented me from trying.
I tried to upload to the FXP corner but nothing happened... what goes?... I can't find it.

transition is from C2 to B2, I cannot notice when it starts on the left but C3 does sound different when playing note by note...
transition dB from -3 to -13 and -11 to -3 (hand drawn)
and the "silent" notes to -96 dB (that's as low as I could get them).

Also I started from a heavily edit NY and HB versions as my keyboard black keys have lower volume than the white ones.
does the FXP include the velocity curve? also heavily edited to start with low slope and increase rapidly from 50 to 127.

So - if you can find it - just take it as an example and build your own - hopefully someone more familiar with all this can post a better version if there is interest.

After all, if we just silence by volume we still have the sympathetic ressonance being transmited on both pianos (layers).

I was able to layer the HB Steinway on the right and the NY on the left.
This gives the clarity on the bass from the NY and the sweetness of the HB on the right.
The transition is made in one octave.

The results and necessity of this will of course depends on the sound system.