Every 120 samples, there is a temporal jump

PabloRocaPabloRoca España
edited June 2019 in Cyton
OPENbci Customer Service (or whoever is applicable),

By reviewing EEG records, we have found that time labeling is erroneous. We are taking 250 samples per second (250Hz) but the temporary labeling of them is not right. Time, instead of being linear, is stepped.

Every 120 samples, there is a temporal jump of 400-500ms approximately. And when there are no jumps the temporal labeling is also erroneous because each sample should be taken every 4 ms (1/250Hz) and the labeling shows that approximately 14 samples are needed to advance 1ms in the labeling (when 56ms=14samples*4ms should be advanced). It seems that this slowness is compensated by the temporary jumps that there are always every 120 samples.

Do you know this problem? It happens to me in all logs. Do you have a method to solve it?

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Pablo, hi.

    Currently the GUI labels the lines in the CSV text file, with the time of arrival at the GUI app. This can vary much due to OS loads and other apps running.

    You can be assured that the samples are actually recorded at the Cyton board at 250 Hz., every 4 ms.

    If you are seeing frequent 500ms jumps, this usually means that you have not adjusted the FTDI buffer settings, see:


    Regards,

    William

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