Noise repeats at 5 second intervals

AndreBCIAndreBCI San Diego
edited May 2017 in Cyton
I have a 16 Channel Mark IV and I am using OpenVibe to record and analyze the signals. Periodically, I observe the noise shown below.Typically in most of the channels, but often in only some of them. The high amplitude ripples can take a regular pattern and appear about every 5 seconds. I have turned off cell phone, WiFi, WiFi router and while this has helped a bit with noise in general, it has not eliminated the problem. Any suggestion?
image

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Andre, hi.

    Is it possible your location might be in some kind of beam path of a cell tower base station or other EMF noise source? Can you try repositioning your setup to another room or floor or building? Also be sure your headset is not near power bricks, AC power lines, or AC power conduits running through walls or floors. A few feet from the AC power sources should be sufficient.

    One other test you can conduct is to connect all three (channel, reference, Bias) leads together with a short circuit. This should produce close to 0 microvolts with no noise.

    So it sounds like the noise is only present some small percentage of the time you are using the Cyton? But when it does happen, it repeats at 5 second intervals. I assume you have a notch filter at 60 Hz, and that you might even want to bandpass filter say from .5 Hz to 50 Hz.

    William

  • AndreBCIAndreBCI San Diego
    William,
    thank you for your input. With regards to your suggestion that my location might be in some kind of beam path of a cell tower base station or other EMF noise source, if the (very poor) reception I have on my cell is any indication, I would conclude that I am not close to any cell phone tower or a cell phone tower beam. I also have no near power lines or other obvious EMF source.
    I have tried connecting one of the channels in the 3-way you suggested, with SRB and BIAS on the same board (Cyton). I connected  ch9 (red circle in the figure) to SRB and BIAS and here is what I see now on all channels from the same board. Clearly not a flat line at 0 uV. Not sure what this means. All recordings are with WiFi off on the computer, and  with cell phone completely turned off. 
    image
  • wjcroftwjcroft Mount Shasta, CA
    Did you try moving your laptop and headset to another location as I suggested? The cell towers differ for each cellular wireless carrier. And poor reception on one carrier may have no correlation with other carrier facilities in the same region. Did you also check that no power bricks or AC power conduits are directly near you location? Conduits run inside floors and walls and so are otherwise invisible. If your headset is within a few feet of a power brick or conduit, it could result in noise pickup.

    The fact that you are getting noise above (in OpenViBE?) on all channels, including ch9 is quite unusual. With the Reference and Bias connected to ch9, it should be markedly different than the other channels. And close to zero uV. What is the scale on the graph above. Can you rerun new tests with the GUI please instead of OpenViBE. And make note of the scale factor button.

    This might mean some bad connection problems you are having with your Reference or Bias leads, wires, connectors. Can you try swapping some of your cables around to eliminate connection issues? Do you have gold cup electrodes and paste, can you try a test with those three cups together? Then with the cups on your head.

  • wjcroftwjcroft Mount Shasta, CA
    The pulses on these graphs appear at approximately 5 TIME PER SECOND, not EVERY FIVE seconds?

  • rosannezrosannez
    edited May 2017
    Im also capturing data using OpenVibe and finding similar noise every 5-10s. This is repeated all through the data. One example shown in this image (after bandpass filtering 1-100Hz and notch filtering at 50Hz)
    image


  • AndreBCIAndreBCI San Diego
    William,
    when I connect anyone of the channels with SRB and BIAS and use the OpenBCI GUI, I indeed see a flat line with 0.1-0.7uVrms (slightly different values depending on the channel tested). In addition, when away from cell phones, with WiFi off etc, I can record normal-looking signal in OpenBCI GUI . Somehow the problem seem to be related to OpenVibe. Not sure if it is a software setting issue or a bug, but in OpeBCI GUI the noise present in OpenVibe recordings is gone.
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