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Re: Harmonic distortion of a input signal

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On 5/19/2013 6:49 PM, Oscar Benjamin wrote:

>>>> import numpy as np
>
> Create a square wave signal:
>
>>>> x = np.zeros(50)
>>>> x[:25] = -1
>>>> x[25:] = +1
>>>> x
> array([-1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1.,
>         -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1., -1.,  1.,
>          1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,
>          1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.])
>
> Compute the magnitude spectrum:
>
>>>> spect = abs(np.fft.fft(x)[:25])
>>>> spect
> array([  0.        ,  31.85194222,   0.        ,  10.67342282,
>           0.        ,   6.47213595,   0.        ,   4.69726931,
>           0.        ,   3.73254943,   0.        ,   3.13762901,
>           0.        ,   2.7436023 ,   0.        ,   2.47213595,
>           0.        ,   2.28230601,   0.        ,   2.15105461,
>           0.        ,   2.06487174,   0.        ,   2.01589594,   0.        ])
>
> Find the index of the maximum element:
>
>>>> np.argmax(spect)
> 1
>
> So the peak is the lowest non-zero frequency component of the DFT. In
> Hz this corresponds to a frequency of 1/T where T is the duration of
> the signal.

While you were answering a specific question, I think the above is a 
nice tutorial example, because it is more meaningful than arbitrary 
operations applied to random data.

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Harmonic distortion of a input signal Anti Log <antilogeffects@gmail.com> - 2013-05-19 03:52 -0700
  Re: Harmonic distortion of a input signal Chris Angelico <rosuav@gmail.com> - 2013-05-20 01:34 +1000
    Re: Harmonic distortion of a input signal killybeard91@gmail.com - 2013-05-19 15:25 -0700
      Re: Harmonic distortion of a input signal Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-05-19 23:49 +0100
      Re: Harmonic distortion of a input signal Terry Jan Reedy <tjreedy@udel.edu> - 2013-05-19 19:19 -0400
  Re: Harmonic distortion of a input signal killybeard91@gmail.com - 2013-05-19 15:59 -0700
  Re: Harmonic distortion of a input signal killybeard91@gmail.com - 2013-05-19 16:03 -0700
  Re: Harmonic distortion of a input signal killybeard91@gmail.com - 2013-05-19 16:36 -0700
    Re: Harmonic distortion of a input signal Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-05-20 13:09 +1200
    Re: Harmonic distortion of a input signal Dave Angel <davea@davea.name> - 2013-05-19 21:11 -0400
      Re: Harmonic distortion of a input signal jmfauth <wxjmfauth@gmail.com> - 2013-05-20 10:23 -0700
        Re: Harmonic distortion of a input signal Christian Gollwitzer <auriocus@gmx.de> - 2013-05-20 19:50 +0200
          Re: Harmonic distortion of a input signal Christian Gollwitzer <auriocus@gmx.de> - 2013-05-20 19:56 +0200
            Re: Harmonic distortion of a input signal jmfauth <wxjmfauth@gmail.com> - 2013-05-23 04:44 -0700
        Re: Harmonic distortion of a input signal Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-05-21 15:58 +0100

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