Roland SuperNATURAL BRASS ARX-03 Owner's Manual page 19

Unison Mode
When you play a single key or multiple keys simultaneously with a
four-player ensemble setting, the various instruments will be assigned
as follows.
When you play single notes
All assigned instruments will sound at the same pitch. Each instrument
will sound in an octave that's appropriate for it.
When you play multiple notes simultaneously
Each instrument will automatically be assigned to a note you play.
Units of instruments automatically assigned to a note you play are
called a group.
Example: If you play two notes
Example: If you play four notes
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