Another iOptigan tip, until we finish the user manual: there are three triggering modes for the chord buttons, selectable in the settings.
“MIDI G#0-E2 for Chords” lays out all the chord buttons in a chromatic mapping. Priority was placed on fitting everything with the keyboard scale on a standard 61-note keyboard, so the layout isn’t very intuitive, but it gets the job done. Chords are at the lower end of the keyboard, SFX tabs at the upper end.
“MIDI Chord Detection I” is a more intuitive mode, which allows the user to simply finger the desired chord in the low octave of the keyboard. Playing a C maj triad produces the C maj chord. Playing a C min triad produces the C min chord. etc.
“MIDI Chord Detection II” allows for more extended chords to be played using the time-honored Optigan technique of playing two chord buttons at once to approximate more complicated chords. There’s alot of trial-and-error involved with this, and results vary depending on the disc, but if you finger, say, a Cmaj7 chord on the keyboard (again, in the low octave), iOptigan will play the C maj and E min chords simultaneously. Try fingering other extended chords to see what you get, and you’ll likely stumble upon some unexpectedly pleasing combinations!