MATLAB: Low pass filter that removes all the small ripples

hello
I would like a low pass filter that eliminates all the small ripples of this signal

Best Answer

I have no idea what signal you want to filter. I assume ‘E’, however ‘E’ does not look the signal you posted.
Try this: 
D = load('E.mat');
E = D.E;
N = numel(E);                                               % Vector Length
t = 0 : N-1;                                                % Time Vector (Not Supplied)
Ts = mean(diff(t));                                         % Sampling Interval
Fs = 1/Ts;                                                  % Sampling Frequency
Fn = Fs/2;                                                  % Nyquist Frequency
FT_E = fft(E-mean(E))/N;                                    % Fourier Transform
Fv = linspace(0, 1, fix(N/2)+1)*Fn;                         % Frequency Vector
Iv = 1 : numel(Fv);                                         % Index Vector
figure
plot(Fv, abs(FT_E(Iv))*2)
xlim([0 0.1])
title('Fourier Transform')
Fc = 0.03;
[E_Filt,df] = lowpass(E, Fc, Fs);
figure
plot(t, E_Filt)
title('Filtered Signal')
Look at the ‘Fourier Transform’ plot to decide where you want to put the cutoff frequency (or frequencies, if you decide on a bandpass design instead of a lowpass filter). This code will work with any time vector you want to create for it. You still will have to specify the filter type and cutoffs. If you use the ‘df’ (digitalFilter) output, use the filtfilt function with it to filter your signal.
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