you're right, and as I said :
Not that I'm against such a feature
I'm totally for it, if done right !
So, to ellaborate on this feature :
Theoretically FE1 = note-frequency*2^(1/768) which is +1/64 semi-tone
That's why I was thinking, FE1 is far from coarse, but actually the frequency of the chorus-like effect is dependent on the note you play :
note-frequency * (2^(1/768)-1)
So for a A4 at 440 Hz, you will have a chorus with a frequency of 440*9.029426*10^-4 = 0.39729...Hz, so a period around 2.517 seconds
(not very fast).
It will be twice as slow on A3 but twice as fast on A5, etc.
So you're probably right, on higher notes even FE1 might be too coarse, meaning that the chorus will go too fast.
So if you aim for a consistent chorus/detune effect accross all notes of the keyboard, and if I'm not mistaken, then the random variation applied should be an addition
to the frequency, from 0 to + 5Hz max for example , so that your slider would directly reflect the range of the chorus frequency (from 0 to + 5Hz).
Now, how are we gonna use this random variation ?
Obviously to make it work you still have to play two notes at a time : one with the variation, one without. But then doesn't it mean that you will need 2 versions of the same instrument (one with random pitch checked, and one without) ?
It's definitely not as simple as the other random variations that are instantly useful and hearable. To get a real instant detune effect, then this option could also automatically trigger 2 voices of the same instrument (but is it even possible ?)