On Feb 5, 10:16 am, "quaste" <thomas.wald...@ctr.at> wrote:

> >quaste wrote:
> >> respectively
>
> >"1024 respectively 4096 samples"? Is English your mother tongue?
>
> >Jerry
> >--
> >Engineering is the art of making what you want from things you can get.
> >=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=

>
> no, my mother tounge is german - does it change anything about my
> problem?
> what's wrong about the formulation?
> ignore the 4096-version.
>
> quaste

It explains why I don't understand the way you use "respectively".
My computer died and this Google interface is the worst yet, so I'm
sorry for any errors of form. Steven Johnson's response is better than
any I could have made, so I apologize for having been a distraction.
Jerry

Reply by ●February 5, 20072007-02-05

On Feb 4, 3:02 pm, "quaste" <thomas.wald...@ctr.at> wrote:

> at the moment i'm just working with some test-data - 1024 resp. 4096
> samples. i'm trying to read a code from the spectrum, ie: at some
> well-defined frqs the can be a peak or not (will be 8-10 bins).
>
> doing this with the help of a full fft (dsp-powered) seems to be to slow
> for further applications. my research let me to the two algorithms:
> - goertzel
> - bluestein (chirp-z-transform, there should be also some interleaved
> version)
>
> which one would you suggest? speed is the critiria and some of the
> parameters can still be adjusted.

Let me make sure I understand you. The problem is that you want to
compute 8-10 bins of an DFT, and therefore the full FFT is somewhat
wasteful, and you want to know what will be better? Let me phrase it
more generally: you have data of length N and you want to compute K <<
N outputs of the DFT.
One option is to use either Goertzel or the DFT formula directly.
Both of these have O(N K) complexity, but Goertzel has a constant
factor better by several times, at the expense of sacrificing some
floating-point stability for frequencies near zero.
Another option is a "pruned" FFT algorithm, which is an FFT with the
unwanted operations thrown out. This has O(N log K) complexity.
Whether it is worthwhile in practice depends strongly on N and K and
which output bins you want, but I've observed it to be faster than
Goertzel for the K lowest-frequency bins for K as small as 10 if N is
large; see www.fftw.org/pruned.html for some example code and more
information. However, I'm guessing that this isn't worth it for
N=4096 and K=10.
I don't think Bluestein's algorithm is going to buy you any
performance if you want the same bins as the ordinary DFT, as opposed
to a finer interpolation of some portion of the spectrum. At best,
it would require you to implement a pruned convolution algorithm,
which is at least as hard as a pruned FFT and arguably harder. At
worst, the most common way to implement Bluestein is to use a *pair*
of FFTs of length > 2N-2, and this is obviously worse than doing the
full FFT.
Cordially,
Steven G. Johnson

Reply by quaste●February 5, 20072007-02-05

>quaste wrote:
>> respectively
>
>"1024 respectively 4096 samples"? Is English your mother tongue?
>
>Jerry
>--
>Engineering is the art of making what you want from things you can get.
>¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
>

no, my mother tounge is german - does it change anything about my
problem?
what's wrong about the formulation?
ignore the 4096-version.
quaste

Reply by Jerry Avins●February 5, 20072007-02-05

quaste wrote:

> respectively

"1024 respectively 4096 samples"? Is English your mother tongue?
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Reply by quaste●February 5, 20072007-02-05

me again - giving further info about my problem.
due to temperature and other influences the peak-position may vary and the
number of peaks will be around 8. all this information makes me kind of
sad, because the number of the bins to calculate exceeds 5/6*log2(N)
(Goertzel) and the chirp-z-trans seems to be even slower.
Does anyone have experience with Zoom-FFT or approximate FFTs?
Is there any chance to get quite proper phase-info on the approximate
FFTs?
I think I will have to increase my hardware-power, but maybe there is
somebody out there with a brilliant idea - keyword 'to grasp at straws'.
Thanks,
q

Reply by quaste●February 5, 20072007-02-05

respectively

Reply by Jerry Avins●February 4, 20072007-02-04

quaste wrote:

> Hi Guys!
>
> I'm quite a newby to all the stuff - but a motivated one - and have a
> question resp. a problem:
>
> at the moment i'm just working with some test-data - 1024 resp. 4096
> samples. i'm trying to read a code from the spectrum, ie: at some
> well-defined frqs the can be a peak or not (will be 8-10 bins).
>
> doing this with the help of a full fft (dsp-powered) seems to be to slow
> for further applications. my research let me to the two algorithms:
> - goertzel
> - bluestein (chirp-z-transform, there should be also some interleaved
> version)
>
> which one would you suggest? speed is the critiria and some of the
> parameters can still be adjusted.

What does resp. mean?
Do you know the frequency of the interesting peak in advance? Goertzel
is a spotlight you need to know where to point, not useful if you need a
floodlight.
Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Reply by quaste●February 4, 20072007-02-04

Hi Guys!
I'm quite a newby to all the stuff - but a motivated one - and have a
question resp. a problem:
at the moment i'm just working with some test-data - 1024 resp. 4096
samples. i'm trying to read a code from the spectrum, ie: at some
well-defined frqs the can be a peak or not (will be 8-10 bins).
doing this with the help of a full fft (dsp-powered) seems to be to slow
for further applications. my research let me to the two algorithms:
- goertzel
- bluestein (chirp-z-transform, there should be also some interleaved
version)
which one would you suggest? speed is the critiria and some of the
parameters can still be adjusted.
thanx in advance,
quaste