Listen with headphones to hear the lower bass content...
The OC-5 is a totally upgraded version of the OC-3 with a lot of nice tweaks.
Vintage mode is a spot on recreation of the vintage BOSS OC-2 (so totally monophonic)
POLY Mode – Is the updated OC-3 which included better tracking, sound engine and improved range mode control.
Range mode control now has a LOWEST note mode. This means that only the lowest note will sound the octave effect
New Octave up setting. This is both Poly and Vintage modes