I experienced this problem before using Oxe FM Synth. This time very similar using U-He Repro 1 beta (you can download it here:https://www.kvraudio.com/forum/viewtopic.php?p=6603621.)).
If I reload my test song, at beginning the CPU usage is really “fucked up” to 99%, even though the song starts only with few instances. Suddenly at the second pattern, the cpu go to normal levels like 51% and also the start pattern plays normally…
After rendering, the first pattern will slow down again…
Since I had a similar experience using Oxe FM Synth, I would assume it’s maybe a Renoise problem?
Let me know if I should PM you the test song…
Made fancy video of this problem:
As you can see, it starts to play normally quite exactly at start of pattern 1… Isn’t this strange?
Is your Renoise set to deactivate vsts when they are not producing sound? If so, try leaving them on and retest. I have a suspicion it’s the vst initializing itself.
“Auto suspend” is disabled.Doesn’t matter, it only happens after loading or after rendering.
So here another observation:
The MORE instances are playing, the better the playback, until it reaches nearly full usage, song turns into fluent replay… After that, every place in the song plays back correctly.
EDIT: Maybe the synth is causing denormal exception if it did not play anything yet?
Also reported this to U-He, seems to be a bug/slowdown in the synth’s sequencer. So this topic can be deleted.