How to change the sample rate in openBCI GUI?

lettiemdmlettiemdm United States
edited April 2019 in OpenBCI_GUI
Hello!

I'm trying to reduce the amount of data I have, and for the purposes of my experiment, I don't need to record data every 0.005 seconds (I suppose that that is the default?!). 
Is there a way I can change that to record data every 1/30 second instead? 

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited April 2019
    Lettie, normally this kind of signal processing is done in your EEG data analysis program. In such a programming environment it is easy to just use every x samples, dropping those in between. This is called down-sampling. Alternately you could say average the sample values in a given set, to derive the value that you use.

    But no, the GUI does not let you select a lower sample rate. Higher rates can be used with the Wifi Shield.

    A disadvantage to down sampling at the rates you suggest, is that you will lose most of the higher brain wave frequencies. Due to the Nyquist limit. Practically, you want four or so samples per EEG waveform. At 200 Hz sample rate / 4, that gives about 50 Hz max EEG brainwaves can be recorded and utilized. At a 30 Hz sample rate, dividing by 4 gives 7.5 Hz. So you are throwing away all of the EEG except delta and theta bands.

    More typical use of downsampling is when the EEG system is running at say 1000 Hz sample rate, and is downsampled to 500 Hz, with averaging.

    Regards,

    William

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