OpenViBE forum

Dear all,

I have to buy a new graphic card and a new screen. I would like to know if somebody knows about specific problem with the following graphic card using Ogre (I didn't see anything on the Ogre forum):
http://www.nvidia.fr/object/product-gef ... 5m-fr.html

Furthermore, I would like to know whether the strong hardware limitation of a 60 Hz refresh rate will be removed in the future. By the way, what is the reason for this limitation ?

Best regards,

Duvi

Hello Duvi,

any graphic card should be able to use vsync to enforce the refresh frequency to the one of the monitor.

This limitation is fundamental. In order for the SSVEP to work, the application must work at exactly the same frequency as your monitor. This is not necessarily 60Hz, many monitors actually work on different frequencies for different resolutions. If you want to use a different frequency for your monitor you have to change the flickering frequencies of the targets as well.

And this is where the problems come, you can only use frequencies which are entire divisions of your fundamental frequency. For example on a 60Hz screen you will use three frames for each flash of a 20Hz target. If you choose 15Hz then you will use four frames. This also means that on a 60Hz screen you can not reproduce any frequency between 15 and 20Hz. 60 as a number is quite useful as it is divisible by quite a lot of interesting numbers (2, 3, 4, 5, 6 ...)

Cheers
Jozef

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Ok, thank you for your answer. I tried Openvibe 12 with my new computer and everything is working well except for non integer frequencies. Actually, if I use 60/9=6.666 or 60/7=8.5714 as frequencies (with a refreshing rate of 60 Hz), the flickering is not regular. I mean that for a while, the flickering is regular (2 or 3 seconds) then, there is a kind of hiccup before beging again regular. I had the same behavior on three different computers/screens. Do you also have this phenomenon ? Do you know was is the cause and how to correct that ?

Thanks a lot !

duvi

Hello duvi,

this is indeed a bug (due to the fact that I reset the counter every 60 frames). It will be fixed in openvibe 0.13.0 which will come out very soon.

Thank you for the report
Jozef

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