Cubase mixing threads all keep failing and restarting

Hi all,

I’m part of a team that has developed a new commercial plug-in that runs in many formats on Mac and PC. We’ve tested it thoroughly in many DAWs, including Logic, Garageband, and Pro Tools on the Mac, and Ableton, Mixcraft, Cubase, Pro Tools, and other DAWs on Windows. Our plug-in runs great on every platform except for Cubase. Multiple customers reported that Cubase for Windows would suffer audio dropouts when moving the mouse over our plug-in’s interface, or when pushing buttons in the interface. This behavior is reproducible on every PC we’ve tested on.

We deactivated large parts of our plug-in and the behavior remained. We attached with a debugger and now we’re able to see what’s happening. The Cubase mixing threads - there can be 8 or more of them - keep all failing and then restarting. After discovering this, we turned off the “Activate Multi Processing” mixing feature, and our plug-in works perfectly. We’ve tested this with both VST2 and VST3 formats.

I’d be very interested to know, from the Cubase team or anyone else with similar experience, under what conditions Cubase will shut down and restart its mixing threads. Our plug-in is complex and uses some unusual technology, and if we knew what conditions could cause this behavior in Cubase, we could probably figure out a work-around. We’re using Cubase Elements 9.5 to reproduce the bug in our labs, but it doesn’t seem to matter what version our customers are using.

We contacted Steinberg’s phone support and they told us to send an email. We sent an email and they told us to post here. We appreciate any assistance at all. Thanks!


can you use the Windows tool : WPR “Windows Performance Recorder” which you could get from the Windows 10 SDK (Windows Performance Toolkit) ?
Start a session where you can reproduce these dropouts and send us the result…
If it does not work, maybe can you provide us a demo version of your plugin that we could check here.

Some others questions:

  • which SDK you are using (Juce,…)
  • which UI backend: openGL, VSTGUI,…
  • what do you mean by unusual technology ?
  • which audio block size are using ?
  • Which Windows version ?



I recorded 30 seconds of Cubase ending and restarting its audio threads, approximately once per second. The recording files are here:

We’d be happy to set you up with an NFR of our plugin, if that would be helpful. Please contact me privately for that.

<< - which SDK you are using (Juce,…)

  • which UI backend: openGL, VSTGUI,… >>

Our plugin is built using Juce. All the UI is our own custom code built around Juce.

<< - what do you mean by unusual technology ? >>

Our plugin interacts with a custom Java virtual machine. It’s likely that something about this interaction is causing the problem, though I don’t know what it could be. Java internally uses exceptions, though none of these exceptions reach the host program.

<< - which audio block size are using ? >>

I’m using an ASIO driver with a buffer size of 128, though that doesn’t seem to matter.

<< - Which Windows version ? >>

I’m using Windows 10 with all the latest updates.

I hope this recording helps! Thank you for your assistance.

All the best,

ok thanks, last question which Cubase version do you have 9.5.30 ?

<< which Cubase version do you have 9.5.30 ? >>

Yes, 9.5.30. It’s a trial - we could really use an NFR if that’s possible.


Hi friends,

Any update on this? We ran your tests and answered your questions, any information you can provide would be very helpful!


An update: we tested a Cubase demo on the Mac and this problem does not exist. It is only a Cubase Windows problem.