# FFT of High Frequency and Low Frequency?

When we plot FFT in a matlab it doesn't ask for Frequency , all we need to input the sequence and it simply shows the output using stem command. If i want to compute two different signal using FFT, one with High and the other with Low frequency what should i suppose to do ? and what will be the difference between the two of them ?

Here is simple code for the FFT calculation ,

x=[1 2 1 0]
n=0:3
y=fft(x)
subplot(2,2,1)
stem(n,y)


• As you noted, for an input signal of length $N$, taking its DFT will yield $N$ frequency-domain samples. For a real signal, only half of those contain any information, because the spectrum of a real signal is conjugate-symmetric. However, for a complex time-domain signal, all $N$ values may be distinct and contain usable information. Your note about half of the samples being imaginary is not true; DFT outputs are complex values in general; there is no split between real and imaginary components, except in some rare cases where certain types of symmetry occur in the time domain. – Jason R Aug 30 '12 at 3:54
FFT is just the implementation of the mathematical formula of DFT, if you want to know something like frequency, try periodogram or see here