Zero Padding a DFT

What I meant to ask about crosscorrelation:

Suppose I have 2 signals r[n] and y[n] each of length N, and zero pad them
to double their lengths and compute Y[k]R[k]* using FFTs in matlab.  And
then I zero pad that product with 8N zeros BEFORE taking the 10N-IFFT to
get the crosscorrelation.  

It seems my correlation results are worse, but I cant understand exactly
why.

any help is appreciated!
		
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quick one wrote:
> What I meant to ask about crosscorrelation:
> 
> Suppose I have 2 signals r[n] and y[n] each of length N, and zero pad them
> to double their lengths and compute Y[k]R[k]* using FFTs in matlab.  And
> then I zero pad that product with 8N zeros BEFORE taking the 10N-IFFT to
> get the crosscorrelation.  
> 
> It seems my correlation results are worse, but I cant understand exactly
> why.
> 
> any help is appreciated!
> 		
> 		This message was sent using the Comp.DSP web interface on DSPRelated.com


The usual technical verbal shorthand (jargon) hides a lot of details.

Zero padding of a time sequence before taking its Fourier transform
is fairly straightforward to describe and understand.

BUT what is zero padding of a sequence of Fourier coefficients? When
done slowly and in full detail the Fourier transformed operation of
zero padding transforms into an interpolation operation which takes
a moderately complicated explanation. Perhaps you need more that
about 1/3 of a jargon filled sentence to say what you intended and
what you did.

Homework season strikes again.... second posting of EXACTLY the same
question. Hmmmmmm.....

Sorry it was to help understand some results from a lab i did.  But I have
already since figured it out on my own!  Thanks :)
		
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me again wrote:

> Sorry it was to help understand some results from a lab i did.  But I have
> already since figured it out on my own!  Thanks :)
> 		
> 		This message was sent using the Comp.DSP web interface on DSPRelated.com

Please don't keep us in suspense; explain a little.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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yes, this was a last resort to help me understand results of a lab, after
trying to figure this out over the period of a week with no avail.  i have
since figured out what was happening!  thanks.

		
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