[PD] Spectrum graphing amplitude problem
Jason Plumb
jason at noisybox.net
Mon Oct 22 01:37:40 CEST 2007
Ed Kelly wrote:
> It is really just the pixel-resolution of the graph. The graph size is
> 252, but the FFT size is 4096 ( giving 2049 points within the Nyquist
> frequency ).
Hmmm....I think I follow...but if that reason holds, if I expand the
graph to 256 and use a block size of 512, it should be pixel perfect eh?
I tried that earlier today, but saw the same behavior...
> So you will see magnitude peaks between the pixels as lower amplitude
> because the screen doesn't display pixels between pixels.
> I hope this makes sense,
That *does* make sense. It's for display reasons that I ultimately want
to build a little scaling control into the abstraction...but I gotta get
the basics going first.
Any other ideas?
I'm a bit new to FFT in the pd context, but I think I grok Nyquist --
Sampling at S can, at best, yield the S/2 frequency (where S is the
sampling rate). But how does this relate to block size in the DFT?
Your original statement sounds like the max frequency out of the fft is
(block size)/2...but that can't be right, eh?
Thanks,
-jason
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