how to start with FFT

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Eva
Eva 2020년 3월 29일
댓글: David Wilson 2020년 3월 29일
HI every one ,
I had data for 3 sensors with time ,the data = 33034 cell
so Now I need to change from time domain to freqancy domian
I don't know exactly how to start . first calcute the time interval / sampling freqancy
  댓글 수: 1
David Wilson
David Wilson 2020년 3월 29일
Try the following:
(1) First subtract the mean from each of the 3 trends. They look reasonably stationary, so that should be OK.
(2) Take the fft, (using the fft command) of each of the 3 columns individually. You can actually do that in one go if you want.
(3) Plot the abs(fft(x)) for each of the 3 signals. This will be the correct shape, but the units will be normalised. You should also note the mirror line in the middle. I'm assuming you are most interested in the power within each frequency band as opposed to the phase.
Now since you have neglected to both give us the data, and the sampling time, we can only roughly guess from the plot what the sampling rate, and hence Nyquist frequency will be.

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