John,
You must go into the midi area of the keyboard and select song for the harmonizer to trigger from the a midi file. Though it is somewhat difficult, you can have the vocal processor turn on and off at various segments of the song as well. It may be easier just to turn the harmonizer on and off with a foot switch while the song is playing.
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)