If you want to trigger the Antares Harmony Engine plug-in with a MIDI keyboard in Studio One, make sure you have the keyboard setup as default MIDI device in Options > External Devices.
1. Start a new Song and add an Audio Track. Place a voice clip on that track.
2. Insert the Antares Harmony Engine plug-in to that same track as an insert, the Harmony Engine plug-in interface should open.
Select a preset.
3. Add a new track. Make this one an Instrument Track.
4. On the Instrument Output drop down of that Instrument Track, select the Antares Harmony Engine plug-in. This will route MIDI from your MIDI keyboard to the Harmony Engine plug-in track. Select your MIDI keyboard as the input.
5. Press start to start the track, you may not hear anything until you play your MIDI keyboard. You could also place MIDI data on this track and it will trigger the Harmony Engine plug-in.