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Extracting periodicity with Fast Fourier Transform

  1. Mar 31, 2012 #1
    Hello all,

    I want to extract the period out of a complex discrete signal.

    Currently I have the Matlabscript of the attachement.

    However, the values I get out of this script are not correct. There is some kind of systematic bias in it.

    I think it has something to do with index * samplefrequency.

    Anyone an idea what could be wrong?

    Thanks in advance!
     

    Attached Files:

  2. jcsd
  3. Mar 31, 2012 #2
    Right, you should divide by sample frequency. Period and frequency have inverse relation.
     
  4. Apr 1, 2012 #3
    Thanks, I tried it, but now the values are extremly big. Maybe I am using the y-axis value of the frequency domain graph, instead of the x-axis value (which says something about thefrequency of the original signal, right?)?

    Getting confused now :confused:
     
  5. Apr 1, 2012 #4
    What are the values of index and Samplefreq?

    I think you should use this:

    Period=(Length of the sequence)*dt/index
     
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