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Symptom: Audio engine is peaked out red lined and no audio can be played back smoothly.
Fix: disable Asio Guard. Runs like a charm.
Why does this happen in Cubase 9.0.1 but Cubase 8 runs fine? Is this related to Nvidia card drivers?
Another problem I have: when Cubase is open, playing back audio through Chrome or another app will often be distorted and choppy. Closing Cubase solves this. Even if cubase has no session loaded, the fact that Cubase.exe is running seems to cause the issue.