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Large number of points FFT

Andrew Costa
Prodigy 30 points

Hi everybody,
I need your help in order to solve a problem.
I have a signal to process with the following  fixed parameters :
- Fs (sampling frequency) = 25K Hz
- Delta_f (Frequency resolution) = 0.25 Hz
Starting from these parameters the total FFT’s points is Nfft = Fs / Delfa_f = 100 K points.
I analyzed CMSIS DSP Lib for MSP432XX . It computes up to 4096  FFT points only.
My question is : How can I compute this very large FFT using MSP432XX family ? Or is there some other family TI’s DSP / microcontroller ?
NOTE: I compute sampling operations once per hour so  I don’t need real time processing.
Thanks for reply
Andrea

  • 0
    TI__Guru 73441 points
    Andrew,
    This would require a very large amount of RAM. I will ask for some recommendations.

    Chris
  • 0 in reply to Chris Sterzik
    Prodigy 30 points

    Thanks Chris.

    I'm waiting for your feedback.

    Thanks a lot

  • 0 in reply to Andrew Costa
    TI__Guru 73441 points
    Andrew,
    To your original questions.
    (1) You cannot compute the large fft with the MSP432. The RAM size if limited to 256K across all members of the family.
    (2) I am not aware of any solutions which support such a large FFT computation.

    I am going to move this to the Processors/DSP group to see if they can comment.

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    TI__Intellectual 1930 points

    Andrew,

    Can you share more details about what you're trying to use the FFT for? While it's not really feasible to run a 100k point FFT on an MCU depending on what you're trying to do there might be other ways about it. For example you could actually run 2 FFT's at different sampling rates to cover both requirements, one 4096-point FFT at 25kHz with ~6Hz resolution covering the full 0-12.5kHz spectrum and a second 4096-point FFT at 1kHz (by saving every 25th sample at 25kHz) with ~0.25Hz resolution for the low frequency 0-500Hz range (if that's where you need the finer resolution).

    Regards,

    Brent Peterson

  • 0 in reply to Brent Peterson
    Prodigy 30 points
    Hi Brent,
    I 'm tring to explain you better my work enviroment.
    I should analyze in frequency domain a signal with 5KHz bandwidth.
    To do this I'm sampling the signal with Fs = 25KHz (five times bandwidth to prevent aliasing problems. For my application, several scientific articles suggest to sample signal from 5 to 10 times bandwidth).
    In whole range 0-5KHz I need a resolution of 0.25Hz.
    My work isn't restricted to use MCU, but I could move to DSP (e.g. C55XX family or others).
    Thanks a lot for reply
    Best regards
    Andrea
  • 0 in reply to Andrew Costa
    Guru 43635 points

    If you really want to do this, you will need to look at "in-place" fft algorithms:

    You will probably need 131072 points (a power of 2)

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