Diatonic MIDI Harmonizer

In my latest project, I'm building a MIDI harmonizer that does more than stack intervals. It understands musical context – harmonizing based on key and scale, not just fixed distances. You play a single note on your MIDI controller (like an EWI), and the harmonizer adds harmonies that make sense within your chosen key.

How It Works:

At the core is a configurable key system. You define a tonic note, choose between major or minor, and optionally specify accidentals. From there, you can select up to three harmony intervals – like a 3rd, 5th, or 7th. These intervals aren't blindly applied: they're diatonically derived, which means they adjust based on the actual scale. For example, if you play an A in C major and ask for a "3rd," you'll get a C – not C# – because that's what fits the key.

Who's It For?

This tool is aimed at expressive MIDI performers, especially those using wind controllers, keyboards, or experimental interfaces. It's also a great fit for producers who want to generate intelligent harmonies without diving deep into music theory – or who want fast inspiration in the DAW.