Severe High-Frequency Loss When Using External Plugin in Cubase 14.0.32 (Mac + RME)

Cubase
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I’m running into a pretty strange and serious issue with Cubase Pro 14.0.32 on a Mac Studio M2 Ultra (macOS Sequoia 15.1), using an RME Fireface 802 interface.
Whenever I use the External Plugin insert in Cubase to route audio through my outboard hardware (via the Fireface’s analog I/O), the return signal has a noticeable loss of high frequencies — specifically around 10kHz to 12kHz. The top end sounds dull, as if it’s being low-passed or something in the signal chain is degrading the highs.

  • The problem ONLY happens when using the External Plugin routing.
  • Playing back the same signal directly in Cubase (no External Plugin) sounds totally fine.
  • Running the same test in Ableton Live with the exact same routing works perfectly — no loss, full frequency spectrum.
  • Monitoring directly via TotalMix FX also sounds correct.
    f I power off and on the Fireface 802 while Cubase is open, the problem disappears — the high frequencies come back and everything sounds clean and open.
    But… if I restart the Mac, the problem comes back again as soon as I load Cubase and use the External Plugin.

This makes it pretty clear it’s not a hardware issue, not a driver issue, and not a TotalMix problem. Something’s clearly wrong with how Cubase is handling the External Plugin routing.

Let me know if you’ve seen anything similar or if there are tips to fix this! Thanks.

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Make sure you are not accidentally listening to your input twice, you may get a time delay between the 2 paths and this will change the summed sound.

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maybe there is something going on in Totalmix?

its a monster of a routing maze…

like maybe the Room Eq is on etc

4

Hi @PauloVilelaVeiga and welcome to the forum!

Based on this:

What happens if you don’t restart the Mac, only Cubase?

For example, try this, when the problem is present:

  1. Power off and on the Fireface 802 while Cubase is open (you say the problem goes away)
  2. Quit Cubase fully (do not restart the Mac)
  3. Start Cubase; is the problem now back?
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