Applying Two Filters Simultaneously

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Soeun Lee
Soeun Lee el 19 de Jul. de 2021
Comentada: Yazan el 20 de Jul. de 2021
I'm trying to apply notch (stop) filter and highpass filter simultaneously for my data. Below is the code that I have so far.
Fs=24414;
t=0:1/Fs:435.13;
X=RawData;
Wn=10; % high cutoff
[b,a]=butter(5,Wn/Fs,"high");
Wn_2=[60 60]; % notch filter
y=filter(b,a,X);
[b,a]=butter(5,Wn_2/Fs,"stop");
z=filter(b,a,y);
plot(z);
What I'm trying to do is first apply highpass filter to my RawData (X) to obtain filtered data y, and then apply notch filter to y to obtain z.
Below is the graph that I'm getting. Please let me know what is wrong with my code. Thank you in advance for your help!
  3 comentarios
Soeun Lee
Soeun Lee el 20 de Jul. de 2021
Here's the link to my data (the file itself is too large to upload) https://drive.google.com/file/d/1vmeak6nmDW5Z1v6IL0oVZc10I41K_thA/view?usp=sharing
Yazan
Yazan el 20 de Jul. de 2021
Provide what frequencies you are trying to filter. Do you realize that the cutoff frequency of your butter filter is specified as 10/Fs, which is 3.3554e-08 the Nyquist rate (Fs/2)?

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Respuestas (1)

Chunru
Chunru el 20 de Jul. de 2021
Fs=24414;
t=0:1/Fs:435.13;
X=rand(size(t))+2; % random noise + DC %RawData;
Wn=10; % high cutoff
[b,a]=butter(5,Wn/(Fs/2),"high");
% Filter response (Problem: very low cut off and very high Fs)
figure
freqz(b, a, 1024*64, Fs);
xlim([0 200]);
% DC will be filtered out by HPF
figure;
y=filter(b,a,X);
plot(y);
% Notch filter was not properly designed (againg Fs/F0 is very big)
% Wn_2=[60 60]; % notch filter
% [b,a]=butter(5,Wn_2/(Fs/2),"stop");
notchSpecs = fdesign.notch('N,F0,Q,Ap',6,60,10, 1, Fs);
notchFilt = design(notchSpecs,'SystemObject',false);
freqz(notchFilt, 1024*64, Fs);
Error using dfilt.basefilter/freqz (line 17)
This functionality is not available on remote platforms.
figure
z=filter(notchFilt,y);
plot(z);

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