contact wrote:

> I want to fully understand the process and the code linked below
> (which appears in a previous 'comp.dsp' chirp-Z thread) has a
> multi-dimensional input, is that previously FFT'ed sample data?
> Java Chirp-Z thread:
> http://www.dsprelated.com/showmessage/13193/1.php 

No, the input of czt() is complex-valued but in the time domain 
(transform duality aside). To treat real input, provide an array of 
pairs a[n] = [x[n],0].


Martin

-- 
Quidquid latine scriptum est, altum videtur.

"Dale Dalrymple" <dbd@ieee.org> wrote in message 
news:5798666f-f323-444e-b644-b76c02659b0d@x5g2000prf.googlegroups.com...
> On Sep 15, 2:22 pm, "contact" <cont...@invalid.com> wrote:
>> Hello, can someone clear up some confusion for me?
>>
>> This article on the Chirp Z transform (using FFT) appears to show the
>> algorithm creating better precision by zooming in on a narrow band of
>> frequencies. For example,  the two peaks being separated in the diagrams.
>> Link to 
>> article:http://www.embedded.com/columns/technicalinsights/17301593?_requestid...
>>
>> I read other posts on here and elsewhere stating that the chirp-Z does 
>> not
>> create extra precision, but simply acts the same as zero-padding (only
>> cheaper for big pads) - or perhaps the 'zoom-FFT'.
>>
>> Can someone verify that this actually gives better precision, rather than
>> simply interpolate the standard FFT?
>> Thanks.
>> ...
>
> Participants in comp.dsp have already remarked on this issue. See the
> reader comments at the end of the linked article.
>
> Dale B. Dalrymple

I didn't see those, thanks Dale.  I guess the Uncertainty Principle can't be 
cheated. The article is highly rated as well - typical.

Can anyone answer my second question:
I want to fully understand the process and the code linked below (which 
appears in a previous 'comp.dsp' chirp-Z thread) has a multi-dimensional 
input, is that previously FFT'ed sample data?
Java Chirp-Z thread: http://www.dsprelated.com/showmessage/13193/1.php

Thanks,
Dave

On Sep 15, 2:22 pm, "contact" <cont...@invalid.com> wrote:
> Hello, can someone clear up some confusion for me?
>
> This article on the Chirp Z transform (using FFT) appears to show the
> algorithm creating better precision by zooming in on a narrow band of
> frequencies. For example,  the two peaks being separated in the diagrams.
> Link to article:http://www.embedded.com/columns/technicalinsights/17301593?_requestid...
>
> I read other posts on here and elsewhere stating that the chirp-Z does not
> create extra precision, but simply acts the same as zero-padding (only
> cheaper for big pads) - or perhaps the 'zoom-FFT'.
>
> Can someone verify that this actually gives better precision, rather than
> simply interpolate the standard FFT?
> Thanks.
> ...

Participants in comp.dsp have already remarked on this issue. See the
reader comments at the end of the linked article.

Dale B. Dalrymple

Hello, can someone clear up some confusion for me?

This article on the Chirp Z transform (using FFT) appears to show the 
algorithm creating better precision by zooming in on a narrow band of 
frequencies. For example,  the two peaks being separated in the diagrams.
Link to article:
http://www.embedded.com/columns/technicalinsights/17301593?_requestid=286320

I read other posts on here and elsewhere stating that the chirp-Z does not 
create extra precision, but simply acts the same as zero-padding (only 
cheaper for big pads) - or perhaps the 'zoom-FFT'.

Can someone verify that this actually gives better precision, rather than 
simply interpolate the standard FFT?
Thanks.

Also, I see some Java code here:
http://www.dsprelated.com/showmessage/13193/1.php
(C version: 
http://www.mat.ucsb.edu/projects/allosphere/browser/AlloBrain/AlloBrainSource/lp.quadmap/dsp/src/ChirpZ.h?rev=194 )
This has a two dimensional array as input and doesn't appear to relate to 
the article, is the input also real/imaginary?

Cheers,
Dave.