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

von Usman A. (Company: LUMS) (usmanashraf678)

Rate this post
not useful
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 

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 
explain, please?

Thanks in advance.

von Andreas S. (andreas) (Admin) Flattr this

Rate this post
not useful
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).

von Martin B. (Guest)

Rate this post
not useful
You may also use Nfft = 200

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

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


Entering an e-mail address is optional. If you want to receive reply notifications by e-mail, please log in.

Rules — please read before posting

  • Post long source code as attachment, not in the text
  • Posting advertisements is forbidden.

Formatting options

  • [c]C code[/c]
  • [code]code in other languages, ASCII drawings[/code]
  • [math]formula (LaTeX syntax)[/math]

Bild automatisch verkleinern, falls nötig
Note: the original post is older than 6 months. Please don't ask any new questions in this thread, but start a new one.