Page 19 of the Voyager Manual:
FINE TUNE:
Fine tune control can be used to tune the Voyager’s oscillators + or - 2 semitones for matching an external reference pitch.
Where is this control?
?? Well, look at the pictures 
Silly me.. I thought it was in the menus.. 
That’s OK - I always thought you turn that knob to come up with a good song. 