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Is there a way to tell if my oscilloscope's FFT is HW or SW?
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jonpaul:
bonjour
check définition of " real time" signal processing the FFT

a moment please for a historic note....

Joseph Fourier invented the Fourier Series in 1807.  Then the Fourier Transform.  In 1960 Cooley and Tukey at BTL created the fast Fourier Transform, computation time was proportional to # points,rather than to # points squared.


At work, 1968..1971, we had a Nova 800 and custom boards that could render 103024 points FFT in 1mS

Enjoy

Jon
switchabl:
To avoid confusion, time complexity for N points:
- "Naive" discrete Fourier transform (DFT) is indeed quadratic O(N^2).
- Fast Fourier transforms (FFT) like Cooley/Tukey are actually O(log(N) * N). For example going from a 1024 point FFT to 1 Mpt may take ~10000 as many operations (still a 100 times improvement!). This is what most oscilloscopes will use (either in software or FPGA/ASIC accelerated). More sophisticated forms of FFT may be used for "spectrum analyzer" apps that allow you set the span independently (Bluestein's algorithm allows "zooming-in" on an area of interest) but they are broadly in the same category.
- Sliding DFT can actually be linear O(N) for the update step (shifting the window). But you need to compute one full FFT first to get you started. And applying window functions in the usual way doesn't work. May be used for "real-time" spectrum analysis on higher-end models.
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