I want to get FFT from my .mat data that have been saved in workspace. I have a timeseries data.>> t.mat (time) & data.mat (magnitude). I want to have a continuous plot for FFT .what must I do? can anyone help me? Thank you very much.

get fft from discrete data>> time and magnitude that have been saved as .mat file in workspace. How can I do that???

Answer 1

[Rick Rosson]

doc load
doc fft
doc fftshift
doc abs
doc plot

[vahid torabi]

Thank you for answering,could you please expand your answer in more details sir?

[Rick Rosson]

What have you tried so far?

[vahid torabi]

I added a JPG file that might help you.Thank you.

[Image Analyst]

Rick knows what an FT is - he doesn't need an image like that to explain it. He was wondering if you attempted anything like

mySpectrum = fft(mysignal);
plot(real(mySpectrum), 'b-');

or anything like that. (Sounds like you have not attempted anything yet.) Have you tried to adapt the demo/example code in the help for fft() to your signal yet???

[vahid torabi]

I didn't want to make Rick sad,I just wanted to clarify what I'm gonna do.Sorry anyway. I've tried very codes to reach that FFT plot but I didn't. So now I'm very eager to know what is yours.Thank you very much.

[Image Analyst]

I gave you code, as did the help documentation. Did you see his comment "What have you tried so far?" We can't see it unless you copy it from your MATLAB script and paste it here, or else attach your m-file with the paper clip icon. Also supply data in addition to the code so we have something to run it on.

[Rick Rosson]

Image Analyst is right. Please post your MATLAB code here so we can see what you have tried and then we can possibly help you.

[vahid torabi]

these are my files. I've attached them. my code:

n = length(magnitude);

Ts = t(2)-t(1); % sample time

Fs = 1/Ts; % sampling frequency

NFFT = 2^nextpow2(n); % Next power of 2 from length of magnitude

Y = fft(magnitude,NFFT)/n;

f = Fs/2*linspace(0,1,NFFT/2+1);

% Plot single-sided amplitude spectrum.

plot(f,2*abs(Y(1:NFFT/2+1)))

title('Single-Sided Amplitude Spectrum of y(t)')

xlabel('Frequency (Hz)')

ylabel('|Y(f)|')

[Rick Rosson]

Your code looks pretty good. Do you have any specific questions? Does your code work as expected? Are you getting any errors?

[vahid torabi]

I don't get any error.but the plot is not the thing I wanted to be! have you tried plotting with my files that I attached for you?

[Rick Rosson]

Please add the following line of code at the very end of the script:

   xlim([0 200e3]);

Also, try replacing the plot statement with:

   plot(f,20*log10(abs(Y(1:NFFT/2+1))));

Label the y axis as:

   ylabel('|Y(f)| (dB)')

Finally, in the line that computes the fft, instead of dividing by n, please divide by NFFT.

Does that help?

[vahid torabi]

It worked.My special thanks goes to you sir.I really appreciate your help.I admire you for your tips.Wish you luck.

[vahid torabi]

Hi back Mr.Rick. I attached a zip file that has the results. my plot starts at -80 but in article it starts at almost 0.why??? could you please help me sir??? thank you very much.

[vahid torabi]

this pdf has my results.