VCV Host-FX: unsaved parameters


I’ve noticed than some VST plugins (most probably not very well coded) revert to their parameters default values whenever I close / reopen my patch or VCV.

For instance with Ambient Reverb or Dead Duck Software effects bundle

Checking their JSON, it seems that pluginState is empty for them.

  "plugin": "VCV-Host",
  "version": "0.6.2",
  "model": "Host-FX",
  "params": [],
  "data": {
    "parameterIds": [
    "pluginName": "AmbientReverb",
    "pluginState": "",
    "blockSize": 128,
    "bypass": false

I’m not sure if this can be fixed or not.

As a workwaround, I assign the parameters to one of Host FX’s 16 slots and simply send a CV to set them. It works.

Thank you!


Do other DAWs have this issue with these plugins?

@Vortico Thanks Andrew, these plugins work fine with FL Studio 20.

Host-FX assumes that plugins support the effGetChunk opcode, which is how a VST host asks a plugin to save its state. Ambient Reverb ignores that opcode.

Most DAWs will then fall back to iterating through all of the plugin’s parameters, and will save and restore all the values separately. Host-FX doesn’t currently do that.

Thank you Richie, that makes sense.
Such fallback would be great to have in a future update for better compatibility (same thing applies to Host for instruments btw)

it is the same for Fabfilter Pro-q2, windows 10 64bit

I’ve fixed this by implementing the fallback I mentioned above, and the fix will be in the next release of Host.

Tested with Ambient Reverb, Dead Duck Software effects, and Fabfilter Pro-q2.

Thanks to @jsmonzani and @VCVRackIdeas for your help!


Great news, thanks a lot for your help, @Richie !

I had the same problem with VCV Host few weeks ago, and i also thought the same, but after a short dialog with Andrew i checked it more thoroughly.

So i detected that VCV-Host DO SAVE the parameter values, and that the only thing it don’t save is the position of the current preset, i.e.: once the patch is reopened the preset list shows “default” as the current preset, BUT if you look carefully the knobs, sliders, and the rest are as you left them when you saved the patch … I detected also that it only happens with free VST and VSTi, i had no problems with comercial ones, although i see now that VCV Rack Ideas seem to have had problems with a comercial one.

My system: Mac OS X 10.10.5

Anyway the problem source has been detected already, so surely it will be solved in the next release (thanks @Richie!)

@Josep: That sounds like a different problem. Which plugin were you using?

'Morning @Richie, here is how i explained the problem to @Vortico:

Let me put an example: let’s say that i load a VSTi or VSTe and i select a preset that i like (#07, for example), and i tweak some knobs, switches, and sliders to my own taste … When the patch is saved, the current VST state is saved correctly (both in Mac as well as in Windows), but when the patch is reopened every knob, switch and slider on the VST are as they where when it was saved, but the preset number is preset #00 (i.e.: the default VST preset) … So if you browse to the preset of the example (#07) and then you get back to preset #00, you find out that you have the the same sound (i.e.: same tweaked knobs, switches and sliders) in both presets

And here the plugins i used to check it, again as i explained to @Vortico :

I use only free VSTs, but i have installed a couple of commercial VSTs for checking also …



  • Arturia Buchla Easel V (ok)
  • Korg Legacy M1 (ok)
  • Xils Lab PolyKB III (ok)

From all these, only Oril River have this behavior also in the DAW (Reaper)
All the rest preserve presets across saves.

My system:

  • VCV Rack version: 0.6.2c
  • VCV Host/Fx version: 0.6.2
  • System: Mac OS X 10.10.5 (mainly) + Windows 10 Pro 1604 (ocasionally)

ADDITIONAL NOTE (Checked on Mac): Today i made a further verification, and detected that if after the first save, you reopen the patch (as i have said in the example above, you’ll have preset #7 in preset #0), and you tweak some knobs, etc. and then you save the patch and reopen it, the new tweaks are saved also … So i verified that as long as you don’t move from preset #0 (which in fact is preset #7 in the example) you can save further tweakings you make in the VST (original preset #7 is not modified at all) … Once you reopen the patch the tweaks will be there in the same way you left them before saving the patch (no mather how many saves you can do), even if you close VCV Rack with the patch and reopen it … :thinking:.

If you need me to do some more verifications, just tell me and I will do it with pleasure.

Having the same problem with different Soundtoys and some other plugins, they are working without problems in other DAWs.

Sorry @Josep, I missed your reply. What you’re describing is not the same problem that I’ve fixed, I’m afraid. I’ll take a look when I can - thanks for all the information!

Hi @Josep,

The problem of VCV-Host not restoring the preset number will be fixed in the next release.


Great news, @Richie looking forward to this release! Do you have by chance a rough idea of its date?

Thank you!

@jsmonzani: I don’t know when the next Host release might be - that’s up to @Vortico.

No problem, we’ll wait! Thank you for your answer :grin:

I’ll get to it soon, after I test on the 3 OS’s.

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My cat ate my Macbook charger, but a new one is ordered for delivery Friday so I can test and make a Mac build and release an update.

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If you need someone for a Betatest let me know… Found more and more plugins were this is the case.