Franco
I have owned (and sold or traded-in) many different arranger keyboards through the years, but I have always kept my original RA-50 Real Time Arranger and still use it often - mainly for adding the arranger function to my XP-80 workstation. The only pitch shifting function available on the RA-50 (other than setting its response to incoming pitch bend wheel commands) is the master or global tune function that affects the pitch of all tones simultaneously. It does not provide an "Octave Offset" function for any of the "parts". I strongly suspect that your RA-90 is the same, in this respect.
B U T . . . . .
for the past several years I have used three Casio keyboards, of the new CTK/WK workstation model lines, as well as my trusty old XP-80 work-horse, working into my Roland JV-2080 sound module. Whenever I would use the "Octave Offset" feature of any of the keyboards, the keyboard would send MIDI notes whose pitches were an octave higher or lower, in accordance with the chosen "Octave Offset", and the affected JV-2080 part/sound would respond accordingly. That is, "Octave Offset" is a function of the transmitting keyboard, and not the sound module. You do not say what type of keyboard you are using to drive your RA-90, but check its manual to see if it provides for "Octave Offset" individually on its various parts: full keyboard, upper shift, lower shift, layer. If so, your RA-90 should respond accordingly.
Good luck !
Ted
