Please follow these instructions to control Harmony Engine with a MIDI track in Logic Pro X:
1. If you intend to use a MIDI keyboard, connect it to your computer, start Logic Pro, and make a new session.
2. Create an audio track and software instrument track. Record or import an audio recording onto the audio track.
3. Set the output of the audio track to "No Output."
4. Load Harmony Engine as the "Instrument" input on the software instrument track. (It's available under: AU MIDI-controlled Effects)
5. In the Harmony Engine plug-in window, click on the "Side Chain" drop-down menu in the upper right corner and select the audio track you created in step 2 (for example, "Audio 1").
6. Set the "Harmony Source” control to “MIDI omni.” (There are two other specialized MIDI modes as well. For a more detailed explanation about how each of these work, please see the Harmony Engine user guide).
7. Select the software instrument track and click on the red "R" button to record enable it.
8. Start playback (or recording) and perform on your MIDI controller to harmonize your audio input. Alternatively, you can import a MIDI file onto your software instrument track and use this instead.