# single sided amplitude fourier spectrum

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Muhsin on 12 Oct 2017
Commented: Star Strider on 18 Oct 2017
Hello all, I am new user that trying to learn coding. I have an acceleration-time history with a time-step of 0.01 sec. The total duration is 14 sec. I would like to get a single-sided fourier spectrum of it. Is there any packed code for it? Any kind of help is appreciated. The attached file contains the data. Thank you.
Muhsin

Star Strider on 12 Oct 2017
Edited: Star Strider on 12 Oct 2017
See the documentation for fft (link).
The Code
D = dlmread('Muhsin A00.txt', '\t', 1,0);
t = D(:,1); % Time (s)
a = D(:,2); % Acceleration (g)
L = length(t);
Ts = t(2)-t(1); % Sampling Interval (sec)
Fs = 1/Ts; % Sampling Frequency (Hz)
Fn = Fs/2; % Nyquist Frequency (Hz)
FTa = fft(a)/L; % Fourier Transform (Scaled)
Fv = linspace(0, 1, fix(L/2)+1)*Fn; % Frequency Vector
Iv = 1:length(Fv); % Index Vector
figure(1)
plot(Fv, abs(FTa(Iv))*2) % One-Sided Amplitude Plot
xlabel('Frequency (Hz)')
ylabel('Amplitude (g)')
grid
EDIT Changed ‘Ts’ calculation to accommodate ‘t(1)=0.01’ and ‘t(end)=0’.
Star Strider on 18 Oct 2017
The smoothdata function would likely work. (It was introduced in R2017a, and since I do not know what version you have, I did not suggest it.)
You would use it on the absolute value of your single-sided Fourier transformed data.

### More Answers (1)

Image Analyst on 12 Oct 2017
Isn't that what pwelch() does? (Signal Processing Toolbox required for pwelch).
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Image Analyst on 12 Oct 2017
You might also like spectrogram() function.
Or the Signal Analyzer app on the Apps tab of the tool ribbon.