Issue: Audio export consumes extraordinarily much CPU with sample rate conversion

Discovered in 12.0.30, reproducible in 12.0.40; might have been there before, hasn’t been like that in Cubase 11.

Steps to reproduce:

  1. Create empty project
  2. Mark some region of about 3 minutes and export with output sample rate different from project sample rate

Effects: CPU usage on Threadripper 3960X stays at 100% for about 10s (this does take far longer for real projects, even with no plugins running). Target is on very fast SSD. Without sample rate conversion this is twice as fast and only consumes around 20% CPU. Sample rate conversion on import is practically instantaneous for the result file, so this doesn’t add up.

Problem becomes more serious for actual projects which can take up to 10 times as long to export than in Cubase 11, but behavior is similar there (CPU usage goes down to reasonable values and export is sped up considerably when output sample rate matches project sample rate). It also makes real-time export impossible with sample rate conversion engaged (stops at some rather soon point with a timeout), even for rather simple projects.

From the looks of it (but this is just based on outside observation) the worker threads allocated to the cores get spuriously woken with nothing to do all the time, with required synchronization taking away CPU from actual work.