Filter Design

Hi, I am a recent graduate, intermediate user of MATLAB. I want to design a filter that can say chop down the harmonics of 20Hz but not 20Hz itself. I have been trying using comb notch filter but it chops down my 20Hz frequency as well.

Thanks.

Answer 1

[Wayne King]

Hi Deep, I'm assuming that you want to try and only remove the content around the harmonics of 20 Hz, so that a general lowpass filter won't do. I'll assume a sampling frequency of 1 kHz.

 Fs = 1000; 

 d1  = fdesign.notch('N,F0,Q,Ap',6,40,10,1,Fs);
 d2  = fdesign.notch('N,F0,Q,Ap',6,60,10,1,Fs);
 d3  = fdesign.notch('N,F0,Q,Ap',6,80,10,1,Fs);
 Hd1 = design(d1);
 Hd2 = design(d2);
 Hd3 = design(d3);
 Hcas = dfilt.cascade(Hd1,Hd2,Hd3);
 fvtool(Hcas,'Fs',Fs);

[Deep]

Hey thanks.

I need some more help if you dont mind. I am trying to design a filter that filters out all the harmonics of 5 Hz and itself with an order of 1500. Fs=5Khz.

Thanks.