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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