[Numpy-discussion] zoom FFT with numpy? (Nadav Horesh)

Ray S subscriber100@rjs....
Thu Mar 15 13:30:40 CDT 2007


Hi Nadev,
 >A long time ago I translated a free code of chirp z transform (zoom 
fft)
 >into python.

Thanks, I'll try it out.

I did, however read before on the differences:
 From Numerix http://www.numerix-dsp.com/zoomfft.html:
"One common question is : Is the zoom FFT the same as the chirp 
z-transform.

The answer is : Absolutely not. The FFT calculates the FFT at N 
equally spaced points around the unit circle in the z-plane, the 
chirp z-transform modifies the locations of these points along a 
contour that can lie anywhere on the z-plane. In contrast, the 
zoom-FFT uses digital down conversion techniques to localise the 
standard FFT to a narrow band of frequencies that are centered on a 
higher frequency. The chirp z-transform is often used to analyze 
signals such as speech, that have certain frequency domain 
charactgeristics. The zoom-FFT is used to reduce the sample rate 
required when analysing narrowband signals - E.G. in HF 
communications."

http://www-gatago.com/comp/dsp/34830442.html I just saw was good 
reading too.

It will be interesting, and the code is appreciated!
Also, czt.c might be particularly fast if compiled with the Intel FFT 
lib and weave.blitz().
Again, the goal is increased f resolution within a known small band 
for the ~same CPU cycles...

Ray



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