New feature needs testing: VST 3 Audio Bus Configuration

Hey All,

For the last month or so I’ve been working on the ability to configure audio busses on VST 3 plugins - and I think it’s nearly ready

It’s mostly straightforward, but there’s a couple of quirks so I made a video showing what’s new and how it works.

As mentioned in the video, I’ve tested with quite a few plugins but I can’t possibly test them all and I’d like to get some feedback before putting it in the experimental release feed. If you’ve got time, and can deal with possible issues, please watch the video and try it out with any VST 3 plugins you have.

Build 4172 - Get It!

Build 4173 - Get It!

Keen for feedback :slight_smile:



In the middle of changing my setup here, but I watched the video and that is going to be an awesome feature to add to all the other awesome features of Cantabile. You sir are the Energizer bunny of programmers. I picture you hunched over the keyboard, with a rubbish can littered with Red Bull and Monster cans. I can’t wait to try this out as I’m just finishing up a home studio and things are a bit chaotic at the moment. The video explains it perfectly if you were accepting feedback on that. .



Looks pretty easy to get the grey matter around. :+1:

@Brad, I’m getting an “audio engine timeout” that never resolves when loading my default setlist with the 4172 build. I did not experience this issue with build 4171. Nothing in my setlist or USB audio interface configuration has changed, and 4171 still works fine. Log file is attached. (914.5 KB)

Hi Bruce,

Thanks for reporting this - as best I can from the log it looks like a plugin hanging on setting the speaker arrangement for one of it’s busses. I’ll need to reproduce this here but it’d be best if you can narrow it down a little first:

  1. If you’ve got set list pre-loading turned on for that set list, turn it off, and see if you can narrow this down to a particular song.
  2. Once you’ve narrowed it down to a song, send me that song file and I’ll see if I can reproduce it.
  3. Even better… it’d be good to try and narrow it down to a particular plugin by unloaded (right click plugin → Unloaded) a half of them and then divide and conquer to isolate a particular plugin.
  4. You should be able to prevent the hang (in order to enable/disable plugins) by using the “Don’t Start Audio Engine” option in the recovery dialog that appears when you start Cantabile after crash/force kill.

TL;DR: anything you can do to help me reproduce this here will be very helpful.


@Brad, with pre-loading turned off and the “don’t start audio engine” startup option enabled, the setlist loads and I can open every song with no problem. I can then turn on pre-loading with the audio engine off and all songs load and I can switch between songs with no issues. As soon as I turn the audio engine on, it hangs.

BTW, this behavior occurs when I am using my Steinberg UR22C USB interface or when I am disconnected from the UR22C and routing Realtek audio through my laptop speakers. So the ASIO driver vs. the WASAPI driver appears not to matter. I can also replicate this issue on multiple setlists that were created at different points in time.

Back on 4171 and everything is working normal again.

Hi Bruce,

I’ll need to narrow this down to reproduce it. Please try this:

  1. Turn set list pre-loading off
  2. Turn audio engine
  3. Step through your set list and see if you can narrow this down to a particular song or plugin that’s triggering this.

If you can narrow it down, please send me the problematic song and any referenced racks and I’ll look into it.



I identified the VST3 plugin that is hanging. It is Waves Audio - CLA MixHub Lite Stereo. I use this plugin extensively as a channel strips in my main mixer rack.

The VST2 version of this plugin opens with no issue in 4172, so the problem is specific to the VST3 variant.

Hope this helps. Again, the CLA MixHub Lite Stereo VST3 plugin loads fine in build 4171 and all previous builds.


Hi @bpeterson1123

Excellent. Thanks narrowing it down. I’m out all day tomorrow but will look into this asap.


Hi @bpeterson1123,

New build 4173 should fix this. Please let me know how it goes.

Download 4173


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Works like a champ, Brad. Thank you for addressing this issue so quickly.

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Hi Bruce,

Great… thanks for letting me know.


Hi Brad,

In Wiring View I see this with Kontakt7. It’s a bit annoying to see 54 unassigned busses.


Also, in Properties → Audio Busses, when I select multiple objects (shift-click or drag), deselecting a single bus doesn’t deselect all the ‘blue’ ones, as expected, but only the one I clicked on.


I don’t know if this is by design or if it needs some improvement. Or just that is. My bad, the space bar!


This is all by design…

  • All those ports are shown is because the plugin is reporting that those busses should be activated by default.
  • To check/uncheck multiple items, select them and press the space key.


Since upgrading from 4171 to 4176 (Performer 4 x64 Win 11), I’ve been experiencing an intermittent bus config problem with the FabFilter Pro-Q VST3. Cantabile will often only get audio on the Right side of its Stereo output, even though the plugin is sending audio on both Left and Right (according to the gain meter inside the plugin’s GUI).

To temporarily fix it, I can disable and re-enable the VST a few times, or randomly unselect and re-select bus assignments on the “Audio Busses” tab until the problem disappears. (But if I disable and re-enable the VST again, such as during song switches, the problem usually returns until I fix it again.)

Here are screen shots of the plugin’s Info, Busses, and Ports screens:

Thanks for reporting this.

I just did some pretty extensive testing here with Pro-Q 3 and couldn’t reproduce any issues.

  • Are you able to reduce this to a simple song file with an instrument → ProQ and nothing else loaded?
  • Does this only happen with instances of the plugin loaded from an older song file, or does it also happen with new instances in a new song?


Here’s a rack that exhibits the problem with only one instrument plus Pro-Q 3:

ProQError-MWE.cantabileRack (63.0 KB)

I’ve only seen it in racks that originate from pre-4176 versions, but the above rack was resaved in 4176 and still exhibits the problem. I only just switched to 4176 yesterday though, so I’m not sure whether that’s a general pattern. I tried creating a fresh rack in 4176 and couldn’t get it to happen, but the problem is intermittent so I’m not sure whether I tested enough. Sometimes it doesn’t occur for hours, and then other times it’s every time I load the rack.

Hi @Hamlen,

I tried your rack and couldn’t reproduce any issues. What exactly should I be doing to try and provoke this?

I tried enabling/disabling the plugin, enabling/disabling the rack, switching between songs. Probably tried each of the above 30-40 times and it always seems to come back just fine.

One difference I noticed: I’m running a slightly newer version of the plugin 3.2.5 vs 3.2.2. Could you update to the latest just to be sure I’m not chasing something that’s been fixed in the plugin (unlikely, but still…)


I retried and can confirm that it’s much harder to reproduce using the MWE. It seems like simplifying the rack made a difference. Here’s the original rack, which isn’t minimal but hopefully not too complex (two instruments, a few irrelevant bindings, and ProQ):

Rock Organ.cantabileRack (356.7 KB)

Here are my steps:

  1. Load the rack into a blank song, wire any midi source (e.g., the onscreen keyboard) to its midi-in, and wire its audio-out to any audio sink. (Ignore the rack’s midi-out port.)
  2. Play a few notes. Usually it sounds correct (left and right channels both audible).
  3. Disable the rack by clicking on the green box, then enable it again.
  4. Play a few notes. Usually I only get sound out of the right channel.
  5. Repeating steps 3-4 yields no left-channel sound about 90% of the time for me.

Note: I’m still on ProQ v3.2.2 since I wanted to avoid changing too many things at once. If these steps don’t reproduce it on your side, I’ll try upgrading and see whether that changes anything on my side.