Hello Heystek, This should have been part of your undergrad signal-processing course. Usually in an inverse FFT, they include a scaling factor of 1/sqrt(2) or something like that, I forget exactly. You might find some references here: https://www.dspguide.com/
The application is doing signal-processing in the frequency domain, which can often be computationally more efficient than in the time-domain. You'd multiply a window of frequency domain data with the frequency-domain representation of what your filter should look like, then IFFT to get a filtered time-domain signal. Just note that for a spectrometer we'd generally use a PFB, not just an FFT, so the same mathematical relation is NOT true for these cases. Regards, James On Thu, Apr 23, 2020 at 10:00 AM Heystek Grobler <[email protected]> wrote: > Hey James > > I thought of the “to workspace” sink. I am not to familiar to write from > Simulink to the workspace, but I will give it a go! Thanks for the help. > > Out of curiosity, if I have both halves of the symmetric FFT, what would > be an application do to another FFT? I have written an Matlab script to > play around with this idee. When I run the script, the the FFT of an FFT > gives me a time domain signal, but the result has a larges amplitude. When > I do a 3rd FFT I get the frequency domain again, and it is also amplified. > > It is just something that I picked up. > > Heystek > > On 23 Apr 2020, at 11:51, James Smith <[email protected]> wrote: > > Hello Heystek, > > You can probably use a "to workspace" sink, then you'll be able to display > the data however you want in some matlab code once the simulation is > finished running. > > Canonically, just applying an FFT to frequency-domain data will get you > back into the time domain, multiplied by some scaling factor. You need both > halves of the symmetric FFT though, so the output of e.g. the > fft_wideband_real wouldn't be meaningful to apply another FFT to it. > > Regards, > James > > > > > On Thu, Apr 23, 2020 at 9:40 AM Heystek Grobler <[email protected]> > wrote: > >> Good day Casperites >> >> I have an interesting question. I am using a FFT in simulink for the use >> in a spectrometer design. I want to test the output of the FFT by using >> some kind of scope. Simulink only has spectrum scope, that would be >> perfect, but the scope does a second FFT on the signal. The other option is >> a vector scope, but that does not give the result that I am looking for. >> >> Does anyone have a suggestion on how I can see the results of the FFT in >> simulink? >> >> Then I have another question. What would be expected if I do a FFT on a >> FFT? As far as I can figure out, the FFT of the FFT should just be time >> reversed? >> >> Thanks for the help! >> >> Heystek >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/62AFF5A0-0980-4FB7-8CB8-C053590F655E%40gmail.com >> . >> > > -- > You received this message because you are subscribed to the Google Groups " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG67D373fmnXJ7Os7jrBGJyTbvRA835okUMO%2B0x8hTT%3DGzyKrg%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG67D373fmnXJ7Os7jrBGJyTbvRA835okUMO%2B0x8hTT%3DGzyKrg%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > > -- > You received this message because you are subscribed to the Google Groups " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/8064F663-15CE-4C42-B13A-9AC9ABF82703%40gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/8064F663-15CE-4C42-B13A-9AC9ABF82703%40gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "[email protected]" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG67D37sAj_7sUdaJuAhRd95Ho8Xchdy0guhdLqhKO3e7YVGjw%40mail.gmail.com.
