# fast fourier transform frequency limit [closed]

I'm a french student in engineering and I'm given a kind of mandatory technical project to work out on until February.

I must investigate the following article : https://www.osapublishing.org/DirectPDFAccess/C41EF419-AD7D-EDF3-A173E8B93A0B610C_350066/oe-24-19-22110.pdf?da=1&id=350066&seq=0&mobile=no and implement the same kind of iterative algorithm on MATLAB.

Actually I'm not good at signal processing either that much, only have the basics, however I don't understand why they say "the inherent frequency interval limit (of fFT) can be overcome using discrete Fourier transform". In my opinion that is non-sense because fFT is basically just the same as dFT, you just have to sum the sampled values an other way with their odd and even indexes. Therefore I don't really understand what do they apply dFT for...

If someone could help me please he would be more than welcome !

Thank you

## closed as unclear what you're asking by jojek♦Nov 22 '17 at 12:01

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• can't load that link. – Marcus Müller Nov 21 '17 at 23:04
• Cannot open the file either. DFT and FFT sre different in the basic thing is that FFT requires the length of discrete data to be multiple of 2, thus the frequency resolution must also be multiple of 2. I guess that is what they mean "inherent freq interval limit". DFT is not limited by this length constraint. I cannot say anything further without the paper. – AlexTP Nov 21 '17 at 23:29
• Hi, I am closing the question since the link is dead and you didn't provide any details about it. – jojek Nov 22 '17 at 12:02