MATLAB: FFT and smoothing of signal

Question

Hi, I have the attached signal (TENS_LOW). I would like to obtained the smoothed FFT of the signal. How can I smooth the spectrum?

Thanks

Answer 1

Now I understand what you want to do. This is most easily done with the Signal Processing Toolbox sgolayfilt function to create the Savitzky-Golay filtered spectrum.

The Code —

D = load('Isma_gp TENS_LOW.mat');  
sig = D.TENS_LOW_42;
sig = sig - mean(sig);                                      % Remove d-c Offset
L = length(sig);
Fs = 1/0.0117;                                              % Sampling Frequency
Fn = Fs/2;                                                  % Nyquist Frequency
FTsig = fft(sig)/L;
Fv = linspace(0, 1, fix(length(FTsig)/2)+1)*Fn;             % Frequency Vector
Iv = 1:length(Fv);                                          % Index Vector
FTsiga = double(abs(FTsig(Iv))*2);                          % Truncate, Magnitude, Convert To Double
sgf_sm = sgolayfilt(FTsiga, 5, 501);                        % Create ‘sgolayfilt’ Filtered FFT
figure(1)
plot(Fv, FTsiga)
hold on
plot(Fv, sgf_sm, '-r', 'LineWidth',2)
hold off
axis([0  1    ylim])
grid
xlabel('Frequency')
ylabel('Amplitude')
legend('Original Spectrum', 'Savitzky-Golay Filtered Spectrum')

Experiment with the sgolayfilt parameters to get the result you want.