Borrar filtros
Borrar filtros

FFT and smoothing of signal

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Isma_gp
Isma_gp el 16 de En. de 2017
Comentada: Star Strider el 2 de Dic. de 2022
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
  5 comentarios
Adam
Adam el 16 de En. de 2017
How to smooth the spectrum depends what you want to do with it really. There are plenty of ways to do it, depending how aggressive you want to be. A simple mean filter would do if you just want aggressive smoothing, but not if you want to retain certain information in peaks etc
Isma_gp
Isma_gp el 16 de En. de 2017
sampling frequency is 0.0117

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Respuesta aceptada

Star Strider
Star Strider el 16 de En. de 2017
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.
  12 comentarios
SYML2nd
SYML2nd el 1 de Dic. de 2022
Hi @Star Strider, I think this is a brilliant solution to smooth the fft for which there are not so much other oprions to smooth it, such as for the PSD where we can use pwelch and a windowing. Are there any reference (literature) where this method of smoothing is used?
Star Strider
Star Strider el 2 de Dic. de 2022
@SYML2nd — Not to my knowledge, although I did not do a literature search. My approach here is essentially empirical.

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