MATLAB: How to filter a signal

filteringfrequencyMATLABreconstruction

I have a signal and I filtered the signal using a cheby1 filter. the frequencies of the signal range from 0.058 to 349Hz. I had to remove frequencies above 0.7Hz. after filtering the signal again when I find the frequencies I'm getting frequencies above 0.7Hz.

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I showed you how to correctly design a filter here. If you want to design a filter to remove all frequencies above 0.7 Hz, design a lowpass filter, specify the passband frequency as 0.7/Fn and the stopband at 0.72/Fn. Use a Chebyshev Type II filter for this, instead of a Type I, since you now want a relatively flat passband.

Related Solutions

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

Déjà vu

how to design IIR highpass filter with cutoff frequency of 20Hz and FIR bandpass filter with cutoff frequency of 10Hz and 15Hz?

Make the appropriate changes to get the cascaded filter you want.

MATLAB: Removing outliers in data

Although picture may be worth a thousand words, having your data to work with is worth a thousand pictures.

I would begin with a Fourier transform of your data (the fft (link) function) to determine what part of your data are your signal and what part are noise.

Once you have the frequency information, and you know you can filter out the high-frequency noise, a prototype lowpass filter design for you to experiment with is:

Fs = 1000;                                                  % Sampling Frequency (Hz)
Fn = Fs/2;                                                  % Nyquist Frequency (Hz)
Wp = 100/Fn;                                                % Passband Frequency (Normalised)
Ws = 105/Fn;                                                % Stopband Frequency (Normalised)
Rp =   1;                                                   % Passband Ripple (dB)
Rs = 150;                                                   % Stopband Ripple (dB)
[n,Ws] = cheb2ord(Wp,Ws,Rp,Rs);                             % Filter Order
[z,p,k] = cheby2(n,Rs,Ws);                                  % Filter Design
[soslp,glp] = zp2sos(z,p,k);                                % Convert To Second-Order-Section For Stability
figure(3)
freqz(soslp, 2^16, Fs)                                      % Filter Bode Plot
filtered_signal = filtfilt(soslp, glp, original_signal);    % Filter Signal

This design has a much steeper transition region than your Butterworth design, so it may have less effect on the part of your signal you want to retain. Make the appropriate changes in the parameters for your signal.

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Related Solutions

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

MATLAB: Removing outliers in data

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