Filtering ECG raw data
giuseppetx1
Italy
in Cyton
Dear all, thi message for a comparison with you regarding ECG data filtering. By applying a 5 -50 Hz passband (as seen in the OpenBCI GUI) to ECG raw data saved by Cyton, the corresponding plots do not correspond with those seen during acquisition in the GUI. Maybe I am missing something, just as detial, I am plotting using IGOR and applying a low pass filter at 5Hz e and an high pass filter at 50 Hz. Does anybody experienced something like this? Thank you.
Comments
Giuseppe, hi.
You have the filter sense inverted. You want high pass at 5 and low pass at 50. Alternately, and preferable, just use a simple BANDPASS from 5 to 50.
Regards, William
Dear William, thank you ! I solved, just a mistake in setting the filter on Igor....now I was able to plot the ECG correctly, they seem very similar to what I see on the OpenBCI GUI. Lastly, the unit of mesaure on the Y axis, do I need to convert them? or do they represent Vrms dirctly? Best, Giuseppe
The sample units are microvolts. The GUI shows uVrms as just an indication of average amplitude. Samples have no RMS averaging / smoothing.
https://en.wikipedia.org/wiki/Root_mean_square
@giuseppetx1
Pls, can you help me with the code for the filters?
Thanks in advance
https://brainflow.readthedocs.io/en/stable/Examples.html#matlab-signal-filtering
Dear, I use a software for plotting and data analysis, IgorPro, it provides a user interface for the filters setting, showing the resulting pass band, the important this is you set the sampling 250 Hz, just to explain see the screenshot in attachment. I know that other software like Origin Pro can provide the same functionalities. Sorry but I am not programming by coding ....
Giuseppe
@giuseppetx1
Thanks for the response.
@giuseppetx1
Pls, how did you insert raw ECG data into the IGOR since it is in a text file? Was it a direct plot or there is a menu for uploading? Thank you for your time
Igor can in general read .txt file, but with the openbci raw data I found many problems in importing settings, so the fastest way I am finally using is to organize the columns in a file excel and import that file .xls with Igor, so that the columns are already ordered with the openbci channels, ready to be filtered and plotted.
@giuseppetx1
That's awesome. Thanks for the tips