High-pass Butterworth filter and filtfilt

Question

Guglielmo Giambartolomei 2017-2-15

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/325172-high-pass-butterworth-filter-and-filtfilt

评论： Star Strider 2017-2-16

Hello everyone, I'm trying to high-filter a signal beacause when I perform a fft of the original signal I find a contribution at very low frequency even if I take the fft of detrend(signal). I want to cut out that contribution. I wrote this simple script:

Fcp=3;  %cutoff frequency
[z,p,k]=butter(8,Fcp/(Fsp/2),'high');
sos=zp2sos(z,p,k);
%fvtool(sos,'Analysis','freq')
x101filtfilt=filtfilt(z,p,x101);
figure;
plot(t101,x101,t101,x101filtfilt);
grid on
title('PE101 (pressure signal)')
xlabel('t (s)')
ylabel('Pressure (kPa)')
legend({'Original PE101 Signal','Actual PE101 Signal (filtered and realigned signal)'});

The sampling frequency is 600 Hz and the signal x101 is about 180 s long. I receive the error: "Warning: Imaginary parts of complex X and/or Y arguments ignored". As a matter of fact the new signal x101filtfilt contains imaginary numbers. Where am I wrong? Thank you very much.