Low pass filter that removes all the small ripples

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.