Sync problems at high Hz

I am running an experiment at 100Hz on CRT screens and ran into some problems with the timeByFrame and the reported Hz by windows at 100Hz. Windows says it can run at 100Hz, but whenever I try to run a timeByFrame it shows 85Hz. This phenomenon only happens at 100Hz and all other Hz works fine.


What OS, graphics card, and display model are you using, is it VGA?

I’ve encountered this issue with Windows in the past with ViewSonic displays. You can set the refresh rate higher than what your graphics card can supply for a given resolution in the control panel; not all resolutions can take advantage of the max refresh rate. There should exist a resolution x refresh rate combination that can give you true 100 Hz. On my system it was 1152x864.

Hi mdc, thanks for the interest.
It is a windows 7 with an internal Intel® HD Graphics card and Yes it is VGA at 800 x 600, I cannot come to the screens since we are using them for running the experiment right now (on some other computers). The weird thing is that it used to be able to show at 100Hz.


internal Intel® HD Graphics card

Is this a laptop or a multi-monitor setup (with different resolutions)? It is possible the refresh rate of the secondary is locked to the primary display’s by the driver.

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It is a multi-monitor display with the screen at the laptop is turned off. But I think it might not be that, since the MAX refresh rate on the laptop screen is 60Hz, and the Hz on the external monitor is caped at 85.