The points of FFT transform

Hi, here

A basic problem of DSP make me confused. When we want to the spectrum
character of a signal sequence, we can use the function "fft( )" of
Matlab.

fft(X,n) returns the n-point DFT.
1) If the length of X is less than n, X is padded with trailing zeros
to length n.
2) If the length of X is greater than n, the sequence X is truncated.

If we want to do a DFT of a sequence of discrete signal X, with the
length of N.

What is the proper points for DFT? just "n=N" is enought, or the
bigger, the better?

If n>N, then padded zeros, it is equal to interpolation. While, if "n"
is infinite, it maybe equal to the fourier transform of continuous
signal. So, I am confused.

What is the proper points for DFT?

Thanks

.

Relevant Pages