[PD] Spectrum graphing amplitude problem
czhenry at gmail.com
Mon Oct 22 01:59:39 CEST 2007
> Any other ideas?
Another option is to use the 'plot as points' graph. You will get all
the points that way, even if the size is too small.
> 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?
exactly right. When you use rfft~ on a block-size of N, you will have
N/2+1 points in the real part, indexed from 0 to N/2. You will have
N/2-1 points in the imaginary part, indexed from 1 to N/2-1 (because
the imaginary part of the fft of a real-valued signal is zero at the 0
frequency and at the Nyquist frequency).
If you're using fft~, you will see the full spectrum from 0 to N-1,
where the second half of the spectrum is the conjugate of the first
half. For graphing purposes, you will probably just need the first
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