JUCE 7.0.8 - AudioProcessorParameterChange repeated notifications

We have migrated to JUCE 7.0.8 for our plugin host and we are having some strange behavior with Fabfilter plugins. The issue was not occurring with JUCE 7.0.7

Specifically, we get an AudioProcessorParameterChange notification every time the process block is getting called.


To replicate the issue, open the example J7.0.8 AudioHost and add the Fabfilter Pro-C 2 VST3 and you can see the notification being constantly called.

We have validated that this behavior does not occur when using JUCE 7.0.7

I’ve encountered a similar issue with Fabfilter plugins in JUCE 7.0.8. It’s causing repeated AudioProcessorParameterChange notifications during the process block. Any solutions or workarounds?

I’ve taken a little look at this, the behaviour was introduced in June with this commit, following another issue reported on the forums regarding Korg plugins.

If I’m not mistaken this means that FabFilter are setting the parameters on each process callback, regardless of if they’ve changed or not. I’ve put an internal MR together that prevents listeners being notified if the value hasn’t changed. I’ll keep you posted.

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Sorry for not getting back to this sooner but this should be fixed on the develop branch now. Please let me know if you experience any more issues with this.

Any reason why Fabfilter might be doing that?

I can’t speak for FabFilter but I can see sense in the approach.

  1. I can see sense in only updating parameters in the process block in terms of managing thread safety (I haven’t confirmed however that they only update parameters from here)
  2. I can see sense in always performing these updates so not having to branch in the process block

I think given the callback we have suggests the parameter has changed it’s fair that we only call this in that scenario that the parameter has actually changed, I think it’s fair to say this was a bug in our implementation that warranted a fix.


We confirm the issue has been resolved.

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