# ecg signal filtering

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m on 17 Sep 2011
Hello I am an undergraduate I am required to implement the following operations in MATLAB :
_First the ECGs were preprocessed (1.5–35 Hz band pass ﬁlter), then each 3.2 s segment of the ECG was Hamming windowed and its PSD was estimated as the square of the amplitude of the fast Fourier transform, zero padded to 4096 points_
the FS is 250hz
If not very hard please help me
thankU
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### Accepted Answer

Wayne King on 17 Sep 2011
Hi, You don't give enough information to fully specify your filter, but here is a filter with 40-dB of attenuation as a start. I'm assuming in my example that sig is your signal (vector). For 3.2 seconds sampled at 250 Hz, you have 800 samples. So just to get the code to run, let's create a white noise vector that is 800 samples in length.
sig = randn(800,1);
d = fdesign.bandpass('Fst1,Fp1,Fp2,Fst2,Ast1,Ap,Ast2',0.5,1.5,35,36,40,0.5,40,250);
Hd = design(d,'butter');
sig = filter(Hd,sig);
psdest = psd(spectrum.periodogram('Hamming'),sig,'NFFT',4096,'Fs',250);
plot(psdest)
You'll want to segment your data in 800 sample increments so that you have 3.2 seconds of data.
Wayne
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m on 18 Sep 2011
very thanks for your attention.
Is possible write codes step by step ?
for example:
1)First the ECGs were preprocessed (1.5–35 Hz band pass ﬁlter)
2)each 3.2 s segment of the ECG was Hamming windowed
3)its PSD was estimated as the square of the amplitude of the fast Fourier transform, zero padded to 4096 points

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