FFT SIZE DETECTION

Dear members,
                      I am encountering a peculiar problem, wherein i
have to dynamically detect size of the FFT of the signal taken.

for example a signal is taken and fft of it is taken, it may be 128 or
256 or any size. utimately i dont have any iota of knowledge of the
signal nor length of the fft taken.

i have to dynamically detect the size of fft taken.

please do help me in this .

thanks in advance
particle

PARTICLEREDDY wrote:
> Dear members,
>                       I am encountering a peculiar problem, wherein i
> have to dynamically detect size of the FFT of the signal taken.
> 
> for example a signal is taken and fft of it is taken, it may be 128 or
> 256 or any size. utimately i dont have any iota of knowledge of the
> signal nor length of the fft taken.
> 
> i have to dynamically detect the size of fft taken.
> 
> please do help me in this .

Who does the FFT that you don't know what happened?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

hi jerry,
           thanks for your interest. the question is like that.
again reiterating i need to dynamically detect size of fft taken on the
signal..

i dont have any knowledge of signal nor length of fft taken..

this is my question. no who's and no what's

regards
particle

PARTICLEREDDY wrote:

> hi jerry,
>            thanks for your interest. the question is like that.
> again reiterating i need to dynamically detect size of fft taken on the
> signal..
> 
> i dont have any knowledge of signal nor length of fft taken..
> 
> this is my question. no who's and no what's
> 
> regards
> particle
> 

If you have 2N complex FFT outputs for 2N real input points then you can 
just look for symmetry. If it's complex input data or a more compact 
output representation then you're probably out of luck.

Paul

PARTICLEREDDY wrote:
> hi jerry,
>            thanks for your interest. the question is like that.
> again reiterating i need to dynamically detect size of fft taken on the
> signal..
>
> i dont have any knowledge of signal nor length of fft taken..
>
> this is my question. no who's and no what's

That's a funny question.

The output of an FFT is usually stored in an array. If you don't know
the length of the array (and with it the length of the FFT), how do you
know when the array stops and other data begins?

ok andor,
             before saying it as a funny question, try to put your
brain into new technologies then you will know, where exactly this
question has arised. i am sorry, but your idiotic answer is provoking
me to say this..have brain and think and then only answer..

and further behave has an engineering professional before giving
USELESS and WORTHLESS ANSWERS.

particlereddy

PARTICLEREDDY wrote:
> ok andor,
>              before saying it as a funny question, try to put your
> brain into new technologies then you will know, where exactly this
> question has arised.

Enlighten me about those new technologies, please.

> i am sorry, but your idiotic answer is provoking
> me to say this..have brain and think and then only answer..
>
> and further behave has an engineering professional before giving
> USELESS and WORTHLESS ANSWERS.

It does seem odd that you have data, but don't know how much of it you
have.


> 
> particlereddy

PARTICLEREDDY wrote:
> 
> hi jerry,
>            thanks for your interest. the question is like that.
> again reiterating i need to dynamically detect size of fft taken on the
> signal..
> 
> i dont have any knowledge of signal nor length of fft taken..
> 
> this is my question. no who's and no what's

No who or what's? wow! You have no idea who generated the signal or who
performed the FFT or what hardware was used, what operating system, what
numerical format or what memory structure was used to encode the data.
All you know is that it is digital data and some how you got it into
your head that it contains FFT blocks and you wish to identify them.
Tough problem. 

	Somebody else already mentioned symmetry. That seems like your only
hope. 

-jim

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jim wrote:

> 	Somebody else already mentioned symmetry. That seems like your only
> hope. 
> 

I suppose if it were a stream of FFTs then you could look for 
periodicity (assuming that successive FFTs were reasonably correlated).

Paul

PARTICLEREDDY wrote:
> hi jerry,
>            thanks for your interest. the question is like that.
> again reiterating i need to dynamically detect size of fft taken on the
> signal..
> 
> i dont have any knowledge of signal nor length of fft taken..
> 
> this is my question. no who's and no what's

I'll try to put it differently. How does it happen than an FFT is 
performed? What agency does that? First, there are the data; can they be 
counted at that point? Then an FFT is run on them, and the results are 
presumably a list or array; can that list (or array) be counted?

What is it that you know, and what do you need to know? What relates one 
to the other?
Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������