Refresh rate problem

[Theo Desbordes]

Hi and thank you very much for distributing this nice package !

I am experiencing a problem of refresh rate on my laptop : the test suite gives me an anormaly high result, between 500 and 1200Hz when I only have a 60Hz monitor.
I tried with different settings for open_gl, but this doesn't seem to affect the result of the test suite.

What's more, when  I run my task and measure the timing of presentation with a photodiode it seems that  expyriment doesn't block the execution of the code until the frame is presented : the trigger code I send right after the presentation of the stimuli arrives about 40ms before the signal measured by photodiode...

Do you have any advice that could help with this ?

Thanks in advance !
Théo

[Florian Krause]

Hi Theo,

what your are describing sounds as if your video card is not synching to the vertical retrace. What video card are you using (and which driver, on which OS)? There is usually an option for it in the video driver settings. While you are in there, make also sure that no power saving is going on (Nvidia for instance calls this "Adpaptive Performance"; this should be changed to "Maximum Performance").

Once you are sure the video card is doing the right thing, you can experiment with the settings in Expyriment. If the default setting does not allow for accurate presentation reports, try setting control.defaults.open_gl=3 (alternative blocking), before starting the test suite.

Best,

Florian

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[Theo Desbordes]

Thank you for a fast answer ! I changed the video card settings and the vertical sync is now happening properly.

Surprisingly (to me), on my Intel HD(R) Graphics 4400 the vertical sync parameter needs to be set on "Driver settings" instead of "Application settings'" (the only 2 possible choices).

Anyways, thank you again.
Théo

Le dimanche 12 mars 2017 17:17:18 UTC+1, Florian Krause a écrit :

Hi Theo,

what your are describing sounds as if your video card is not synching to the vertical retrace. What video card are you using (and which driver, on which OS)? There is usually an option for it in the video driver settings. While you are in there, make also sure that no power saving is going on (Nvidia for instance calls this "Adpaptive Performance"; this should be changed to "Maximum Performance").

Once you are sure the video card is doing the right thing, you can experiment with the settings in Expyriment. If the default setting does not allow for accurate presentation reports, try setting control.defaults.open_gl=3 (alternative blocking), before starting the test suite.

Best,

Florian

On Sun, Mar 12, 2017 at 10:40 AM, Theo Desbordes <desbord...@gmail.com> wrote:

Hi and thank you very much for distributing this nice package !

I am experiencing a problem of refresh rate on my laptop : the test suite gives me an anormaly high result, between 500 and 1200Hz when I only have a 60Hz monitor.
I tried with different settings for open_gl, but this doesn't seem to affect the result of the test suite.

What's more, when  I run my task and measure the timing of presentation with a photodiode it seems that  expyriment doesn't block the execution of the code until the frame is presented : the trigger code I send right after the presentation of the stimuli arrives about 40ms before the signal measured by photodiode...

Do you have any advice that could help with this ?

Thanks in advance !
Théo

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[Theo Desbordes]

Hi again,

After some time of testing I still can't get the vertical synchronization to behave properly and hope you can give me a hand.
In the Intel HD Graphics Control Panel there are 2 options for vertical synchronization : "Application Settings" and "Driver Settings". When I select the first one, I get a very high refresh rate estimation but no delay in presentation time on the expyriment test suite; whereas when I select the second option it is the opposite : the refresh rate is at 60hz but I have a delay of a few ms in more than half of the trials.
All other settings have been tweaked without any result, and of course no 'power saving' option is activated.
in both case changing the opengl setting in expyriment doesn' alter the result.

Here is a little more about my specs : Windows 10, Intel(R) HD Graphics 4400 with driver version 20.19.15.4549 and graphics outout protocol version 5.0.1037, OpenGL version 4.3.
The problem happens in both expyriment 0.8 in python 2.7 and with expyriment 0.9 in python 3.4.

Best,
Théo

[Florian Krause]

Hi there,

what exactly do you mean, when you say "I have a delay of a few ms in more than half of the trials"?

Could you send a screenshot of the results of the test suite?

Best,

Florian

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[Theo Desbordes]

Hey,

Sorry for the lack of clarity. Here's the results with the vertsync setting on 'Applications settings'  :




And with vertsync on 'Driver settings'  :

[Florian Krause]

Mmh, your video card does not support blocking on the vertical retrace apparently. If setting "control.defaults.open_gl=3" does not improve things, then I am afraid that there is nothing you can do. I personally have similar experiences with Intel graphic cards. I have good experiences with Nvidia cards.

Some background: We use the OpenGL GL_FINISH call to achieve the blocking. It seems that video card drivers have some freedom in implementing this routine. At least this is how I understand the situation.

Oh wait, just looked at your screenshots again. One last thing to try: Is there a setting in the Intel driver settings to use a double buffer (instead of a single one, as it does right now)? If so, try setting it to use a double buffer.

Best,

Florian

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[Theo Desbordes]

Hey,

I also tried but with a double buffer but this doesn't improve the behavior. Thank you very much anyway for your help and advices; I think that in the end I will use another computer with a more permissible graphic card.

Cheers,
Théo

Le mercredi 15 mars 2017 21:32:35 UTC+1, Florian Krause a écrit :

Mmh, your video card does not support blocking on the vertical retrace apparently. If setting "control.defaults.open_gl=3" does not improve things, then I am afraid that there is nothing you can do. I personally have similar experiences with Intel graphic cards. I have good experiences with Nvidia cards.

Some background: We use the OpenGL GL_FINISH call to achieve the blocking. It seems that video card drivers have some freedom in implementing this routine. At least this is how I understand the situation.

Oh wait, just looked at your screenshots again. One last thing to try: Is there a setting in the Intel driver settings to use a double buffer (instead of a single one, as it does right now)? If so, try setting it to use a double buffer.

Best,

Florian

On Wed, Mar 15, 2017 at 8:14 PM, Theo Desbordes <desbord...@gmail.com> wrote:

Hey,

Sorry for the lack of clarity. Here's the results with the vertsync setting on 'Applications settings'  :




And with vertsync on 'Driver settings'  :

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