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From: Vivek Subramanian on 29 Jul 2010 07:25
Hi Everyone,

I'm having some issues using a Chebyshev filter for EEG data which I am extracting. For some reason, there is an unusual sinc function superimposed on my signal after I apply the filter. Here is the process I'm following:

1. Extract raw EEG data: http://uploading.com/files/5641c89e/RawData.fig/

2. Filter the data using a Chebyshev filter: http://uploading.com/files/1ed9emd7/AfterFiltering.fig/
Here is the code for initialization of the filter:
wp =[47 54]/(Fs/2);
ws =[48.5 52.5]/(Fs/2);
[n, wn]=cheb1ord(wp,ws,3,30);
[b, a] = cheby1(n,3,wn,'stop');

3. Continue signal processing and feature extraction.

Could someone please explain the reason for the unusual oscillations present at the beginning of the filtered EEG? Just FYI, my EEG signal is just noise because it takes time to prepare for an EEG, so I prefer to just have my machine acquire noise until I am ready to do an actual experiment.

Thank you so much for your help!!
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