Timing problem with 2 monitor

1
hi everyone

We are using WinXP, i5-3470 with graphic card NVIDIA GTX550Ti (dualhead), and 2 CRT monitor.
We need to generate 100Hz stimulus (1 frame flip twice at 100Hz) and to avoid unexpected stimulation by MATLAB window or something else, so we are using 2 monitor in the same time, one for us and one for subjects, the stimulus only play on the screen of subjects.
But the timing problem is always bothering us. I have attached the timing record (every 2 flip, so it is 0.02s) of the stimulus. Sometimes it's like the right part of the figure, stable timing; sometimes it's like the left part of the figure, with a 4ms shorter or longer.If everything goes well, it should be a smooth horizontal line. I know if we using a mirror mode everything will goes fine. But I wonder if there is any way to solve this problem.
Btw, at the start of PTB, the warning says that the beamposition queries have some problem. Is it the possible cause of my problem? I already install the latest version of the driver.
Thank you for reading this.

Fishburger
2
Strange. Have you tried the PTB demos which test flip timing vs VBL to see if the same thing occurs there?


On Thu, Dec 26, 2013 at 1:26 AM, <fishburger921@...> wrote:

hi everyone


We are using WinXP, i5-3470 with graphic card NVIDIA GTX550Ti (dualhead), and 2 CRT monitor.
We need to generate 100Hz stimulus (1 frame flip twice at 100Hz) and to avoid unexpected stimulation by MATLAB window or something else, so we are using 2 monitor in the same time, one for us and one for subjects, the stimulus only play on the screen of subjects.
But the timing problem is always bothering us. I have attached the timing record (every 2 flip, so it is 0.02s) of the stimulus. Sometimes it's like the right part of the figure, stable timing; sometimes it's like the left part of the figure, with a 4ms shorter or longer.If everything goes well, it should be a smooth horizontal line. I know if we using a mirror mode everything will goes fine. But I wonder if there is any way to solve this problem.
Btw, at the start of PTB, the warning says that the beamposition queries have some problem. Is it the possible cause of my problem? I already install the latest version of the driver.
Thank you for reading this.

Fishburger


3

weird. it seems the file was failed to upload.

4
Ok, i think i don't understand the description of your problem?

Is the following correct?

a) You are only using one of your CRT monitors to display stimuli in a PTB onscreen window. The other one shows the normal Windows/Matlab GUI.


b) You run your monitor at a refresh rate of 100 Hz to show some animation that updates 100 times per second, at each monitor refresh cycle.


c) The timestamps you plotted are only from every 2nd Screen('Flip') and should show a horizontal line at 0.020 secs, but instead show some triangular pattern?


d) You said PTB warns about problems with beamposition query? If so, please post the actual output of PTB, i can't guess what it says. But if high precision timestamping doesn't work, you would expect funny abberations from the expected horizontal line due to timing variability of your machine, although that pattern is pretty weird.


e) What graphics card? Did your follow all troubleshooting tips in "help SyncTrouble"?


-mario


5

Hi everyone


The timing problem was solved after we use the graphic card NVS300 in stead of GTX550Ti, except the beamposition query problem is still there.


Fishburger