MIDI control over KEY & SCALE (my preference) is the most versatile way If you have enough switches (that can send a MIDI CC value, or toggle between two static values), you can dynamically change intervals within each harmony voice. Here’s the overall process: https://www.eventideaudio.com/comment/7167#comment-7167 … But MIDI isn’t for everyone. You can cover much of the same ground with 2 or 3 Aux switches. (An expression pedal will also work, but it doesn’t ‘snap’ between two discrete values – see [F]actory presets).
For example, in the Diatonic algo through H9 Control, you’d want to Set Parameter 3 and Set Parameter 4 both to the same Aux switch. Define a range of about ’60’ for a 3rd, and ’62’ for a 4th. Step on the switch (latching or momentary), and the harmony intervals shift. A similar method uses ‘Set expression pedal (aka HotKnob value)’ in H9 Control, to create a ‘HotSwitch’-style mapping. The advantages here are easier range mappings, and saved pre-preset, (unlike the global Aux switch settings).
I haven’t run through the theory in the link above, but let’s assume it’s correct. Dial in the Heel value of the expression pedal to B min (Aeolian). The Toe value goes to B Hmin (or F# PHRG). Map an Aux switch to the expression pedal action. Momentary or latching, that 2nd Aux switch now toggles between two preset keys & modes. With a third Aux switch, you can bring up B MAJ (Ionian), E MLYD , or B DOR, …
