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Old 05-24-2024, 02:38 PM   #1
ShibuyaCyana
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Join Date: Jan 2020
Posts: 112
Default Laggy serum VST2, FL Studio Fast Idle, and CPU cost of high frame rate

This feels like half a bug report and half a feature request, so I'll just put it here. Feel free to move or delete it.

Serum VST2 runs in 30fps in REAPER. This includes knobs, visualized modulation display, ENV editor, but surprisingly the LFO editor runs in a smooth 120Hz. To make it more bizarre, the previous 30fps section all becomes 60Hz in VST3, while LFO editor section keeps at 120Hz.

To confirm these frame rate numbers, I set my cell phone camera shutter time to 0.1s, then take photos of my screen when quickly messing interface with mouse. Frame rate is calculated by counting the number of "ghost widgets" on the photo taken. Here are some examples to demonstrate:



The same technique can be used to determine the update rate of modulation visualization.

When searching this problem online, I found FL Studio is also suffering from this, and their devs added an compatibility option called "Fast Idle" back in 2021 or so. When enabled, you'll get a super smooth Serum interface (and super high CPU usage). But I didn't find any other VST plugin that can take the effect of this frame rate boost.

I also tested things from kHs because I thought they also run in 60fps - but I'm wrong, only 30-40 fps actually. I guess they somehow optimized input latency to make it feel responsive, while also limiting the interface update speed to reduce the CPU burden of updating GUI.

Here are all the frame rate and CPU usage data summarized into one table. I rounded the numbers to the closest common frame rate (except the modulation column), until later realized it shouldn't be done like that. CPU data is purely the total CPU usage shown in task manager. Idle means idle but with VST GUI opened. A number like 3.5% indicates it's jumping between 3% and 4%.


Windows 11, 120Hz monitor.

Last edited by ShibuyaCyana; 05-29-2024 at 10:00 AM.
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