MATLAB: How to smooth this plot

Question

So i have a large data set. I just copied here one set, as an example. I tried to use filters to get rid of those small spikes, but i ended up with just a completely straight line.

I split this data in thre sectoins (720 length each) , because I want to kee that stepping characteristic of it.

I am using R2017b edition of matlab, so there are many functions i cannot use to do this.

Could anyone help me with this?

Answer 1

Try this:

[D,S] = xlsread('Book1.xlsx');
signal = D(:,1);
L = size(signal,1);
Fs = 1;                                                             % Sampling Frequency (Default, Time Vector Or Sampling Frequency Not Provided)
Fn = Fs/2;                                                          % Nyquist Frequency
msig = signal - mean(signal);
FTsig = fft(msig)/L;                                                % Subtract Mean (Makes FFT Easier To Interpret)
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                                 % Frequency Vector
Iv = 1:numel(Fv);                                                   % Index Vector
figure
plot(Fv, abs(FTsig(Iv))*2)
grid
xlim([0  0.05])
% Fs = 2250;                                                          % Sampling Frequency
% Fn = Fs/2;                                                          % Nyquist Frequency
Wp = 0.019*Fs/Fn;                                                   % Stopband Frequency (Normalised)
Ws = 1.2*Wp;                                                        % Passband Frequency (Normalised)
Rp =  1;                                                            % Passband Ripple
Rs = 60;                                                            % Passband Ripple (Attenuation)
[n,Wp] = ellipord(Wp,Ws,Rp,Rs);                                     % Elliptic Order Calculation
[z,p,k] = ellip(n,Rp,Rs,Wp,'low');                                  % Elliptic Filter Design: Zero-Pole-Gain 
[sos,g] = zp2sos(z,p,k);                                            % Second-Order Section For Stability
figure
freqz(sos, 2^18, Fs)                                                % Filter Bode Plot
set(subplot(2,1,1), 'XLim',[0 Fs/5])                                % Optional

set(subplot(2,1,2), 'XLim',[0 Fs/5])                                % Optional
signal_filt = filtfilt(sos, g, signal);                             % Filter Signal
t = linspace(0, 1, L)/Fs;                                           % Time Vector
figure
plot(t, signal, '-b')
hold on
plot(t, signal_filt, '-r', 'LineWidth',1.5)
hold off
grid
xlabel('Frequency')
ylabel('Amplitude')
legend('Original Signal', 'Filtered Signal', 'Location','SW')

It designs a lowpass filter that filters out most of the noise:

The stopband ‘Ws’ is set to be a specific multiplier of the passband frequency, so you only need to change ‘Wp’ to get different passband and stopband frequencies.

Experiment to get the result you want.