One thing you have to be careful about when programming string sounds with the ability to sustain is, how does the sustain behavior work..?
If you lift the sustain pedal but then immediately afterwards re-press it, does the sustain pedal ‘catch’ the release of the string sound and continue to hold whatever sound is left, or does it let the string sound die no matter how fast you re-engage the sustain?
Now, this type of ‘catching the release’ behavior is actually very good for acoustic piano sounds, it’s what a piano does, and it used to be the ROM behavior of quite a lot of string and pad sounds with longer releases in the G/E series Roland’s (they fixed it for the BK series, though, thank God!).
Trouble is, while you want this behavior for the piano sound, you DON’T want it for the strings or pad! Or you will get this wash of notes you no longer want quietly going on under the new chord, using extra polyphony and adding a faint dissonance to your playing.
I don’t have a Yamaha to test, but perhaps if the ‘catching the release’ behavior is default on their sound engine, this is why they program strings to not sustain?
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An arranger is just a tool. What matters is what you build with it..!