Matlab FFT command for sinusoids

Asked Feb 19 '16 at 02:42

Active Feb 19 '16 at 02:52

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I am trying to test a set of data to see how close it is to a perfect sinusoid. I want to do this by using the fft command in Matlab. Essentially when I plot the magnitude of the fft I am suppose to get a spike around w=0.3. The data I am trying to analyze is essentially just about 200000 data points.

If you simply plot t VS data you will get a sinusoidal graph with some noise.

Basically, my question is how do I plot the magnitude of the fft of a set of data so that I can see the behavior of the spike?

What I have so far for my code:

t = data.time; %Putting the time measurements in t
data = data.values; %Just putting all the sinusoid data in data

freq = 0:0.1:2;

Y = fft(data);

magY = abs(Y);

plot(freq, magY);

asked Feb 19 '16 at 02:42

Kira

How is the code you posted not showing the behavior you'd like to see? – SleuthEye Feb 19 '16 at 02:51
1

`abs` is the command to find the magnitude of complex-valued data, or essentially whatever the FFT gives you. What is wrong with your code? – rayryeng Feb 19 '16 at 02:56
I believe there is something wrong with my frequency, I do not think my frequency scale is correct. – Kira Feb 19 '16 at 04:55
Consult the duplicate. In your case, `N` is the size of your array. – rayryeng Feb 19 '16 at 05:48

Matlab FFT command for sinusoids

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