I've just noticed, Cthulhu (

) and realized that there ARE VST plugins that can generate MIDI data (eg. loop sequencers, arpegiators) which can be sent to other tracks within a DAW like Ableton or FL Studio.

I want to write one of these myself, to algorithmically generate musical tracks that are sent to other instruments within my DAW. But I can't find any tutorials or examples of how to do this.

All the VST tutorials and examples I'm seeing seem to be of VSTs as instruments or effects.

Can anyone give me some pointers to where I can find out more about programming a VST that sends MIDI?

3 Answers 3


While Cthulhu is great for comming up with new and creative patterns, you could very well just us the in-build chord tracks in Cubase (or the similar chorder in Studio One) for simple harmonies and circle of fifths stuff.

It's acctualy a time saver when working with fixed harmonies music - like those in folk or indie genres.

Tutorial video on this chord feature:

  • 1
    That does not seem to be related to the question. Sep 19, 2021 at 22:37

One interesting possibility I've discovered is ReaJS which is a free VST plugin from Cockos that you can get as part of the free ReaPlugs VST suite : https://www.reaper.fm/reaplugs/

You seem to write scripts for the plugin in something called "js" (that doesn't seem anything to do with Javascript).

There's a manual here : https://www.reaper.fm/sdk/js/js.php

  • 1
    That looks interesting! Unfortunately I was unable to understand how to route MIDI in and out of this plugin in my DAW (Cubase) as it seems to be available only as an audio insert. So the audio manipulations works but how do I make MIDI manipulation work? Usually with other plugins it's regular VST instruments that just outputting MIDI so you can route the output MIDI to another instrument. Any help? Sep 20, 2021 at 7:59
  • I'm afraid I don't know Cubase. Since I wrote that answer I've been exploring Protoplug which is a great Lua scriptable VST : osar.fr/protoplug Here's a video tutorial I did of how to write a MIDI processing plugin (a simple arpeggiator) using it, which I run in FL Studio. youtube.com/watch?v=MHo1FXyRvrA Unfortunately, each DAW seems to handle internal MIDI routing differently. I suspect it must be possible in Cubase, but you'd have to look somewhere else for instructions on that.
    – interstar
    Sep 21, 2021 at 5:18
  • Thanks! At first site that looks like a better option considering that the programming language here looks more friendly to people who are used to scripting language like python or javascript. I hope I'll manage to route MIDI properly. Sep 21, 2021 at 17:26

I had some success writing a MIDI-generating VST plugin using the JUCE framework. Besides audio and MIDI support for standalones and VST & AU plugins, it also gives you a pretty good UI framework and the tutorials seem thorough.

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