Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook