Bandpass filter

I would like to filter out from my signal, what goes beyond the frequency range eg. 2-11 Hz. If someone could give me some advices on how to design such a filter?

Answer 1

[Wayne King]

Hi Magda, We need to know your sampling frequency to give some exact code, but I'll give you a general example and assume a sampling frequency.

I'll assume the data are sampled at 200 Hz. Again you need to use the correct sampling frequency. I'll simply choose to use 40 dB of attenuation in the stopband.

d = fdesign.bandpass('Fst1,Fp1,Fp2,Fst2,Ast1,Ap,Ast2',1,2,11,12,40,0.5,40,200);
Hd = design(d);
fvtool(Hd); % view the filter magnitude response
% filter data with filter()
output = filter(Hd,input);

Note that

    Hd = design(d,'butter');

gives a less expensive (computationally) IIR design. Depending on your sampling frequency and how much attenuation you need, your design can be very expensive.

[Magda]

Thanks a lot! This is what I need.