Currently not possible.

Thanks for your reply Niles.

I wonder which focus the developers need to have to get some kind of audio routing feature like this, and to get a MIDI OMNI feature for instruments that use this one way or another. It's basic stufff, but off course features like this is about being able to use third party stuff in an optimal manor.

I agree.

On a somewhat related note: Is it possible to create audio feedback loops in Studio One 4?

I haven't tried this but I always defer to Niles on things like this as I'm not really that much of a guy who uses those kinds of tools. If Niles says no, I'd think that answer would be accurate. He's almost never (if ever) wrong about those types of things.

Having said that, I will create a quick VSTi to test this. Make a VSTi plugin with a sidechain input and see if that audio input is exposed on the sidechain send to the instrument from audio tracks. I'll post the results of that test later. This will be more of a "proof of concept", unrelated to whether or not a particular commercial instrument allows doing it another way perhaps not accessible to Studio One. The thing about side-chain inputs is that they are literal inputs, but what happens to that input signal after that is more dependent on what the plugin does with that signal, use it to trigger something or literally just maybe sum and pass it though the same channel.

Well... that didn't take long.

I created an empty VSTi plugin with sidechain inputs and they are not exposed for sending audio signals to from audio channels. However, I compiled that same VSTi as an audio effect and they are. In that non-typical case the instrument would reside on an audio track (a-la-Reaper) and would (if it had any actual generation functions) output it's audio to that same channel, and of course it also has a midi input for taking in source midi signals from any instrument track.

Interesting. As Niles suggested, it looks like Studio One just doesn't expose audio inputs for instrument class plugins. One possible caveat in this particular random test case is that test plugin being VST2, not VST3.

Thanks all.

Lawrence wroteI compiled that same VSTi as an audio effect and they are. .

What does this mean? How to compile a instrument plug-in as an effect, if it's not an effect plug-in?

I have no issues using a effect plugin on a track, were it also is possible to play it thru MIDI. That's why i specifically ask about instrument plug-ins that don't come as effect plug-ins.

LBH wroteThanks all.

What does this mean? How to compile a instrument plug-in as an effect, if it's not an effect plug-in?

Its not something mortals can do. Lawrence is a developer and wrote a skeleton VST as a test to see if S1 can access exposed audio inputs on instruments tracks. Sadly the initial test appears to be that no, they aren't accessible.

LBH wroteWhat does this mean? How to compile a instrument plug-in as an effect, if it's not an effect plug-in?

Flowstone. It compiles to either, or to an exe.

And (obviously as S1 4 is x64 only now) it will also compile 64-bit plugins now, thank god. It's still in beta though, the x64 version of it.