Simulating Non-Integer Flicker Timing on LCD (e.g. 39 Hz at 480 Hz)

[Ceomod7]

I'm working on a vision science project replicating older psychophysics experiments that involved precise flicker stimulation, originally performed using oscilloscope or CRT monitors with fast phosphor (P4).

I'm currently working with an AOC Agon AG246FK, a 240Hz TN panel (480Hz via frame-doubling or low-persistance strobing), and I'm using Psychtoolbox (MATLAB) for stimulus presentation.

I understand that LCDs generally have locked frame durations, however....

I'm wondering:

• has anyone found a workarounds to simulate or approcimate fractional-frame flicker?
• are there specific display technologies (e.g. OLED, VRR panels, strobing backlights) that allow for sub-frame cycle tuning or timing tricks?
• can G-Sync, FreeSync, or driver-level overrides be used to "stretch" frame intervals in ways that would approximate partial-frame cycles?

I am mostly prototyping and not expecting true CRT precision but any help and advice would be very much appreciated!

[RealNC]

Sounds like you want VRR. It will cause the display to only refresh when you present a frame. If you present every 12.82ms, that's 78Hz, so you can flicker at 39Hz. This assumes you're using a 3D API for your software, that is. OpenGL, DirectX, Vulkan.

Unless I misunderstood something.

[Ceomod7]

Thanks for your helpful response.

So I’m working on a Dell OptiPlex 5000, and the system is currently running integrated graphics only (no dedicated GPU installed). The monitor supports Adaptive Sync via DisplayPort.

Given this setup, do you think there’s any way I could still make use of VRR to present flicker at exact frame intervals? Or would I need to install a discrete GPU to realistically get that level of control?

Would appreciate any recommendations—ideally something low-power that would work in this kind of office PC if a GPU is necessary.

Thanks again!

[RealNC]

Given this setup, do you think there’s any way I could still make use of VRR to present flicker at exact frame intervals? Or would I need to install a discrete GPU to realistically get that level of control?

If VRR works, sure. You can use it. I'm not familiar with laptops in general though.

[Ceomod7]

Thanks again

Just clarifying:

I’m not using a laptop—this is actually a Dell OptiPlex 5000 desktop running on integrated Intel graphics at the moment (no dedicated GPU installed). My monitor (AOC AGON AG246FK) supports Adaptive Sync via DisplayPort.

Given that setup, do you think there's any way VRR could still be usable, or would I definitely need to add a discrete GPU to enable frame-accurate timing (e.g. for flicker at 39 Hz)?

Just want to confirm whether there's a path forward with this machine, or if upgrading is my only option.

Thanks again for the guidance

[RealNC]

Well, have you tried enabling VRR? What kind of integrated graphics is it? Is there a VRR option in the driver control panel?