FFT of Downsampled Signal

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Oliviawilliams02 - 2021-01-19T14:00:26+00:00
Question: FFT of Downsampled Signal

I have an aperoidic signal that is being sampled at a very high frequency, 3.125 MHz. The signal is sampled for 8 minutes, leaving me with a very large dataset to process (1.3E9 samples). Moreover, I am confident that the data is being oversampled by a large factor so I believe that I can downsample it by a factor of ten. I am chosing to downsample primarily because of computational limits.   Would I best use downsample() or decimate()?   And the real question: How would downsampling/decimating the data by an order of 10 affect the FFT? I would like to have a meaningful frequency axis in the power-spectrum-density plot. Would I just treat my sample frequency as fs/10, 312.5 KHz?

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    • Expert Answer

    Profile picture of Neeta Dsouza Neeta Dsouza answered . 2025-11-20

    If you have significant noise on the signal, then decimate(x,10) or resample(x,1,10) would be preferable. Your resulting sample rate is as you have indicated (312.5 kHz).
    I would take a spectrogram on the resulting signal to see how the frequency content changes over time.


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