Serum knob turning has visual lag at <30 FPS in FL Studio, but runs fine at 60 FPS in Ableton

Started by sdrzn

Here's a thread on Image-Line for more info:
And here's a video showing Serum knob turning in FL Studio v.s. Ableton:

Serum has noticeable visual lag in FL Studio (Windows), despite it being the only VST in my project and my PC being spec'd out (1080 TI + i7-8700k). The ^ thread shows that this doesn't happen in Ableton. Also this lag doesn't exist in your OTT plugin when I use that in my project. Another thing is you can notice the low FPS when moving around the Envelope curve (30 FPS) v.s. the LFO curve (60 FPS). The only difference between moving the two curves is that when moving around the Envelope curve it also turns a couple of knobs (ADSR). So maybe its only the knob turning that's causing the framerate drop, and it may be tied to how FL Studio is constantly keeping track of knob amounts (e.g. it shows the knob amount in the hint bar in the menu bar).

If there's any advice for fixing this I would greatly appreciate it! And if it's a bug, I suggest looking at OTT's code when adjusting knob amount and seeing how it differs from Serum's knobs.



Make sure you're using the latest Serum version. Please use the contact form if I can help you locate your registration.

Hey Steve, I am using build 1.305 and FL Studio on Windows. Also I updated my email here to match the one I use on Splice to pay for Serum. If you have discord I can screenshare and help you debug this if you'd like.
In any case, thank you so much for all your great work, you are a godsend.


Cheers, I don't think this is my issue to fix, as I do nothing specific for FL in terms of draw operations - they could take a look at the idlerate they are passing to VST2 plugins and try raising it. A lot of plugins force repaint but I try to adhere to the VST spec - in Serum as the draw operations can be intensive and I'd prefer to let the DAW throttle it. Also your audiobuffer size can be a factor for some redrawing.

I already tried adjusting my audiobuffer size, audio device, and various other settings to no avail :(
I was playing around with Serum today and noticed that moving the sliders on the MATRIX page is perfectly smooth with no lag. But then moving around the VELO or NOTE curves look laggy.
I will contact Image-Line devs about raising the idlerate for VST2 plugins, thank you so much for looking into this :^)
Edit: I just submitted a ticket on their support forum, I'll post it here it's solved