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02-02-2005, 04:03 PM
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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! This message was sent using the Comp.DSP web interface on DSPRelated.com 
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02-02-2005, 04:22 PM
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Re: Zero Padding a DFT
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.
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02-02-2005, 05:29 PM
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Re: Zero Padding a DFT
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. ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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02-02-2005, 05:34 PM
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Re: Zero Padding a DFT
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. This message was sent using the Comp.DSP web interface on DSPRelated.com
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