# Forum: DSP What is the effect of reducing nfft less than the signal length

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Dear members,
I am analyzing a signal in matlab by taking its fft. The singal has 200
samples and I am currently taking nfft = 256. I understand that this
would result in zero padding. Now, I want to try to reduce the nfft to
128, 64 etc. I wanted to ask what should I expect to happen with the
fft.

Matlab says
for Y = fft(X,n)
If X is a vector and the length of X is greater than n, then X is
truncated to length n. What would this actually result in? Can anyone

Thanks in advance.

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You will get a reduced frequency resolution, and, depending on your
input vector, windowing artifacts (you can consider truncation as
equivalent to applying a rectangular window).

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You may also use Nfft = 200

I think in matlab you can use any number Nfft which is a factor of
2,3,5.
It is not neccesary to use Nfft = 2^n, You may also use
Nfft=200=2*2*2*5*5

Most fft librraries are able to use these numbers of Nfft (fftw, kissFFT
..)

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