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ChrisVeigl / BrainBay

Open Source Biofeedback Software
http://brainbay.lo-res.org
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Patches without filter before magnitude give massive power values #45

Closed pellet closed 2 months ago

pellet commented 2 months ago

I'm currently using an openbci cyton via brainflow as the source. When I plug a line directly into magnitude, it is giving a very large power value, the power also steadily increases over time. I managed to fix it by popping a butterworth bandpass filter before the magnitude component, as shown in the screenshot: filter required I was under the impression that a filter was not required after reading the documentation. Thought I'd just let you know of this behaviour in case it is not expected.

wjcroft commented 2 months ago

Cyton is a "DC coupled" amplifier and all sample values contain this "DC offset" in the range of millivolts. This is a feature not a bug.

https://openbci.com/forum/index.php?p=/discussion/201/large-millivolt-data-values-fbeeg-full-band-eeg

pellet commented 2 months ago

Thanks @wjcroft this makes a lot of sense now. I'm glad that brainbay supports this ILF/SCP range since I was trying ILF protocols earlier but was not completely sure how well it was working. Applying a high pass butterworth filter at 0.5hz looks to have done the trick. Thanks again.