# WaitBlanking missing frames **URL:** \ **Category:** Uncategorized\ **Created:** [September 5, 2006, 9:49pm UTC](https://psychtoolbox.discourse.group/t/waitblanking-missing-frames/1252 "2006-09-05T21:49:12Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![mpqrowe](https://avatars.discourse-cdn.com/v4/letter/m/df788c/32.png) [@mpqrowe](https://psychtoolbox.discourse.group/u/mpqrowe)\ **Post date:** [September 5, 2006, 9:49pm UTC](https://psychtoolbox.discourse.group/t/waitblanking-missing-frames/1252/1 "2006-09-05T21:49:12Z")
Can anyone suggest a reason why Screen(windowPtr,'WaitBlanking') might miss vertical blanking intervals \*besides\* the BlankingDuration set in PrepareScreen? My hardware: A 300 MHz Macintosh G3, a Radeon ATI 9200 graphics card, and a ViewSonic P95f+ monitor. My software: MacOS 9.2.2, Matlab 5.2.1.1421, PsychToolbox 2.55. I have a web page describing one of my tests: [http://www.lifesci.ucsb.edu/~mrowe/MonitorIssuesII.html](http://www.lifesci.ucsb.edu/~mrowe/MonitorIssuesII.html) including the code I used to test it. I've also just tried: > \>\> [PeekFrame, PeekTime] = Screen(windowPtr,'PeekBlanking'); ... Screen(windowPtr,'WaitBlanking',120); ... [PeekFrame2, PeekTime2] = Screen(windowPtr,'PeekBlanking'); With the monitor refreshing at 120 Hz, that should take 1 second each time I run it. However, if I run it in a loop 100 times, I will almost invariably get one run or more where PeekTime2-PeekTime is one frame time longer than a second. This despite the fact that PeekFrame2-PeekFrame is always 120. I have tried setting BlankingDuration both by editing PrepareScreen and by calling: Screen(windowPtr,'Preference','BlankingDuration',NewDuration); No duration I've tried (from 10 microseconds to 30 milliseconds) has caused any change in this behavior. If I lower the framerate to 85 Hz, WaitBlanking may not miss any frames (my tests at that frame rate have not been as extensive, but I've yet to see a dropped frame at that setting). At 90 Hz I also don't seem to drop frames, but at 100 Hz I do. I'm using the setup for physiological experiments in non-human animals, so higher frame rates are extremely desirable... If anybody can suggest anything I might not have tried in order to ensure that all vertical blank signals are caught, I'd appreciate it. Thanks! -- Mickey P. Rowe ([mrowe@...](mailto:mrowe@...))