FabFilter User Forum

Pro-Q3 bug in Cubase

I think I have found a bug with the pro-q3 that was driving me nuts for an hour or so today until I figured it out.

When using the .vst version of the plugin, I was experiencing weird behaviour when applied on mono audio tracks. I was experiencing a volume boost amongst other things, and I also discovered I wasn't able to turn down the volume output knob - only turn it up. Example: I would turn the volume down to minus infinity, and I would still be hearing the dry signal at normal volume. My conclusion is that it seems like the plugin is adding the dry unprocessed signal to the dry.

This wasn't happening on stereo tracks, and I resolved it by switching to the vst3 version of the plugin which works normally on mono tracks.

Pretty weird bug. I hope this can be fixed to save some other users a lot of confusion. I'd also like to hear if other cubase users can replicate this behaviour on their systems. I'm running cubase 10 pro on osx.

Christian Ankerstjerne

Hi Christian, it sounds like you're simply using a multi-mono track, please note that multi-mono tracks are not the same as stereo tracks or mono tracks. If you change a mono track to a multi-mono track, it will copy the mono channel automatically and result in a volume boost of 3 dB because. You'll have separate controls over both the left and right instance with a separate mono instance of Pro-Q 3 for each channel. VST 3 automatically adapts to the channel layout, so it won't copy the track and result in the same volume boost.

Maarten (Fabfilter)

It is true it is an error that I saw a long time ago, since Pro-Q2 appeared and now also in Pro-Q3,I first noticed it in solo mode, it was not equal to Pro-Q1, I noticed that a lot of signal was passing that did not correspond to the soloed frequency, I discovered that there is a problem that only happens in Fabfilter VST2 inserted in a mono track in Cubase and Nuendo on windows or Mac. This does not happen with ProQ-1 or other VST2 from another brand. the strange thing is that it works well in Sonar and Studio One.

After several tests I solved it by opening the routing editor that in Nuendo 10 is in the upper right corner of the plugin, seeing that there was a dry signal passing directly and pressing reset fixed the whole problem.

The error is in:
Stereo Fabfilter VST2 inserted into mono tracks.
Mono Fabfilter VST2 inserted into stereo tracks.
I understand that the VST3 easily adapts to mono or stereo, but the question is why doesn't it happen in Pro Q1? And also because it doesn't happen with other VST2s from other companies?


Would love a normal solution to this problem! - I'm currently running Q3 in patchworks at the moment on mono channels in both Cubase and Nuendo to get around the issue.


@wariopaz your solution is sweet!

Just noticed the signal bridge you mentioned. Thanks for posting.


Hi, I'm having the same issues: Mono track or mono bus. I insert Q3 an get a 6db boost with no bands active. Even if I bypass the plugin I still have the boost. Only when I completely deactivate it does the signal return. Weird bug.


This is a routing issue with the mono VST2 version in Cubase. We have informed Steinberg about this, but they have not resolved it yet. Please use the VST3 version instead.


Ralph Verdult
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