Tuesday, May 7, 2013

Zero Padding Examples

First, a 190 second window, sampled at 100 Hz, 1.9Hz and 5.2Hz sine.  Note the near-zero values in the spectrum

Now a ONE second zero padding addition to the same.  Note the sinc convultion in spectrum.  This is clearly not due to change in freq-domain granularity increasing from 1/190 sec to 1/191 sec.

 Now lets remove that one second pad by filling in the second w/ real data.  Poof, the sinc convolution is gone, yet we are at the same (1/191sec) granularity as the zero-padded.  I think that this spectrum differs qualitative from the first b/c we are no longer at exact multiples of the fundamental freq

Now the 191 sec window w/ a one second zero pad:  

Here's the same as above, w/ noise added.  Note the persistence of the sinc convolution.

Finally, let's add a bunch more padding and zoom in around one of the fundamentals.

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