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I have a noisy signal with frequency between 1/3 and 1/5 of the sampling window.

DFT has a very low resolution for low frequency components, what is the best way to find the frequence?

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  • $\begingroup$ Do you mean you only get 1/3 to 1/5 of a period in the sampling window, or that you only get 3 to 5 periods in the sampling window? $\endgroup$ – Peter K. Apr 27 '13 at 1:30
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    $\begingroup$ I get 3-5 periods in the sampling window. I would like to find the frequency with a better precision then the FFT resolution. $\endgroup$ – user175348 Apr 27 '13 at 14:07
  • $\begingroup$ @user175348: Have you tried interpolating the FFT output? ccrma.stanford.edu/~jos/sasp/… gist.github.com/endolith/255291#file_parabolic.md $\endgroup$ – endolith May 1 '13 at 18:58
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Check out this article by Eric Jacobsen and Peter Kootsookos: http://www.ingelec.uns.edu.ar/pds2803/Materiales/Articulos/AnalisisFrecuencial/04205098.pdf

I had some success using this method for doing "sub-bin" frequency estimation when only one sinusoid is present.

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Have you tried just zero-padding?

Suppose I have:

SINE = sin(2*%pi*0.001923492369*[0:1023] + rand(1)2%pi);

enter image description here

And I zero-pad it:

SINE_ZERO_PADDED = [SINE zeros(1,10240)];

Then I can take the FFT of both:

enter image description here

where the blue plot is the absolute value of the FFT of the original, and the red (dashed) plot is the absolute value of the FFT of the zero-padded signal.

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