How to view the filter coefficients from thebandpass fitler desinged

Hello,

I designed a bandpass filter as below

d = fdesign.bandpass('N,F3dB1,F3dB2',40,500,1500,6000);
Hd = design(d,'butter');
fvtool(Hd)

But how to get(or see) these filter coefficients. Thanks.

Answer 1

[Wayne King]

The following will get you very close:

 Hd = fdesign.bandpass('N,Fc1,Fc2',40,500,1500,6000);
 B = design(Hd);

Compare

fvtool(B,1);
fvtool(BPF_coefficients,1)

Answer 2

[Wayne King]

Hi Stefan, the filter design here uses second-order sections a matrix of quadratic polynomials in z^{-1}. Each row of Hd.sosMatrix is a polynomial of the form

b_0+b_1z^{-1}+b_2z^{-2}+1+a_1z^{-1}+a_2z^{-2}

This results in a robust IIR design. You can obtain the filter coefficients in the form of B and A vectors by using:

[B,A] = sos2tf(Hd.sosMatrix,Hd.ScaleValues);

However (big however), you should realize that second-order sections are used for a reason and you may find that the resulting B and A design is not as well-behaved as the original SOS design

fvtool(Hd); figure;
  fvtool(B,A);

[Stefan]

Actually have a set of coefficients as in the attached file and the designer says the band pass filter coefficients are generated by using

Sampling frequency = 6000 Hz, Lower cut-off frequency = 500 Hz, Upper cut-off frequency = 1500 Hz, Filter type = FIR, order=40.

But I am not sure of how to get (I mean the code to be used to get) the filter coefficients from the above data (filter parameters). Can I know how to make this. Thanks.

[thanh nguyen]

Hi, i have an issue with this filter desig too. When i designed a filter as below:

d = fdesign.bandpass('N,F3dB1,F3dB2',40,500,15000,60000);

Hd = design(d,'butter');

fvtool(Hd);

i received the resull as below:

So how can i get the coefficient as in the equatation:

y[n] = b0*x[n] + b1*x[n-1] +...+ bN*x[n-N] - a1*y[n-1] - ... - aM*y[n-M]

Answer 3

[Stefan]

Hi,

Can you please suggest a good way of designing a bandpass filter of order 11(to get 12 fitler coefficeints) with sampling frequency of 100Hz (as signal is being sampled at 100Hz)and also to save the filter coefficients in a variable.

I guess I need the bandpass lower cutoff=3Hz and higher cutoff=0.8Hz because when I checked the frequencies in my data I mostly have 1Hz frequency components and some lying below 3Hz.

The two data sets are attached here. thanks.