I hope I’m wrong but I don’t think event-list-to-midi-file let’s you use chords.

I can’t get the following to run:

(let ((events (list (make-event 'a4'e :start-time 0)
(make-event '(a4 b4 c5) 'e :start-time 0.1))))
(event-list-to-midi-file events :start-tempo 120
:auto-open nil))