These instruments process external MIDI telling the synth which chord is currently sounding. This MIDI can come from pre-recorded MIDI tracks in the VST host application or can be played in real time by the musician with the left hand. The Chord Detector looks for 4-note 6th and 7th chords in root position (Root-3-5-7 or Root-3-5-6). It assumes that the bottom note is the root and looks for other chord tones above it to decide what kind of chord it is. For example, on this screen a Cmajor7 (aka CM7) chord in root position (C-E-G-B) is being played in by me on the left side of the keyboard. The detector sees that the bottom note is C and that above it are a major 3rd (E), perfect 5th (G) and major 7th (B) represented by the LEDs labelled "M3", "p5" and "M7" above the root. So the detector uses internal logic to conclude it's a major 7th chord. For each type of chord it can detect, you can select which scale you want that chord to trigger. The harmony tables are classified by the scale they come from, because that was the best way I could think of to do it. Currently it uses all modes of the major and jazz melodic minor scales plus the half-whole and whole-half diminished scales.
