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I find that the Reg does not save the split detail.
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It is not true, registration keep Split Point. You have to uncheck the chekbox from Utililty -> Parameter Lock.
According to
Data List, page 88 "Split&Fingering" the Split will save in Registration as
Split&Fingering
Split Point(Left) in Style Group
Split Point(Style) in Style Group
Split Point(Right3) in Voice Group
so you need to check Style and Voice when save the registration.
On the Next Page, 89, you have Part Octave, and it will save in registration as All right parts under the Voice Group and Left under the Style Group.
So also, you need Voice and Style groups checked!
Be attention to Parameter Lock in Utility for Split, to be unchecked!!!
Edited:
If you select another voice by using Part Select (or touch screen) it is normal to load the default octave for that voice. You want a voice with already down 2 octaves, save as a user voice (I did not test).
But I think you have to select what voice you like to change on R3 (it will reset octave) go and press octave - two times to get a -2 octave value, and save to another registration. You only have to switch between registrations!
Regards,
Vali