butterworth band pass filter

can you tell me how to apply a butterworth bandwith filter which only allows frequency of 0.5-25hz where sampling frequency is 1000 samples per second to a signal .

[Mehmed Saad]

see here

Answer 1

[Star Strider]

Try this:

Fs = 1000;                                                  % Sampling Frequency (Hz)
Fn = Fs/2;                                                  % Nyquist Frequency (Hz)
Wp = [1   25]/Fn;                                           % Normalised Passband (Passband = 1 Hz To 25 Hz)
Ws = [0.5 35]/Fn;                                           % Normalised Stopband (Passband = ½ Hz To 35 Hz)
Rp =  1;                                                    % Passband Ripple/Attenuation
Rs = 60;                                                    % Stopband Ripple/Attenuation
[n,Wn] = buttord(Wp, Ws, Rp, Rs);                           % Calculate Filter Optimum Order
[z,p,k] = butter(n, Wn,'bandpass');                         % Create Filter
[sos,g] = zp2sos(z,p,k);                                    % Second-Order-Section For Stability

figure
freqz(sos, 2^26, Fs)

That is a (reasonably) complete way to design filters using the individual function syntax.

[Udit Narayan]

can you tell me how to apply this filter to my signal ????

[Star Strider]

filtfilt

[Udit Narayan]

should i directly use [sos,g] in place of (b,a )in filtfilt( b , a , x ) or there is another way

??

[Star Strider]

Yes.

Use ‘sos’ and ‘g’ as:

y_filt = filtfilt(sos, g, y);

.