Re: Harmonic distortion of a input signal

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From	Oscar Benjamin <oscar.j.benjamin@gmail.com>
Date	Tue, 21 May 2013 15:58:15 +0100
Subject	Re: Harmonic distortion of a input signal
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On 20 May 2013 18:23, jmfauth <wxjmfauth@gmail.com> wrote:
> Non sense.
>
> The discrete fft algorithm is valid only if the number of data
> points you transform does correspond to a power of 2 (2**n).

As with many of your comments about Python's unicode implementation
you are confusing performance with validity. The DFT is defined and is
a valid invertible map (barring roundoff) for complex vectors of any
integer length. It is also a valid method for understanding the
frequency content of periodic signals. The fastest FFT algorithms are
for vectors whose length is a power of 2 but the other algorithms
produce equally *valid* DFT results.

In the example I posted the computation of the DFT using numpy.fft.fft
was (as far as I could tell) instantaneous. I could use timeit to
discover exactly how many microseconds it took but why when I already
have the results I wanted?

> Keywords to the problem: apodization, zero filling, convolution
> product, ...
>
> eg. http://en.wikipedia.org/wiki/Convolution

These points are not relevant to the example given.

Oscar

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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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