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I have a discrete signal of length 98,000 samples and I am supposed to a FFT of the discrete signal with certain window size and FFT size. Can someone help me explain what is meant by the window and the FFT size here? Also, what would the size of the output of the signal post FFT?

Thanks in advance!

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  • $\begingroup$ This is something that is explained in every signal processing book. What have you read when researching this question? $\endgroup$ – MBaz Jun 8 '20 at 23:19
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There are lots and lots of related questions on this topic in this SE and also on many discrete signal processing books.

https://www.sjsu.edu/people/burford.furman/docs/me120/FFT_tutorial_NI.pdf https://holometer.fnal.gov/GH_FFT.pdf

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FFT is a fast algorithm that implements discrete Fourier transform (DFT). Because of the nature of FFT, The size of FFT is a power of 2; for instance: 4, 8, 16, 32, 64, 256 ... 1024 ... . For a long signal(or stream) like yours it's usual to divide the stream into a series of fixed packs like 256-sample packs (so window size = 256); then this fixed-size of samples are applied to the FFT process. The output's length of FFT is exactly the same as the input size. However, if the input signal is real then the half of the FFT output is useful because the other half is conjugate of the first half. Determining the window size depends on your signal's nature. The more detail-included and/or high-frequency your signal, the smaller the FFT window size and vise versa.

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