unit of fft(DFT) x axis
dft, fft, matlab, signal-processing
Solution
The X axis is dimensionless. To get the correspondence between bin index and frequency you need to know (a) the sample rate (in Hz), `Fs`, and (b) the number of points in the FFT, `N`. The centre frequency for the bin is then:
f = i * Fs / N
where `f` is the bin frequency in Hz and `i` is the bin index.
See this answer for a more complete explanation.
Problem
Possible Duplicate: How to get Frequency from FFT result I am somehow confused with the x axis of fft(DFT) command in Matlab. When we do a fft command for a signal which has sampled in n point, we get a plot in which the x axis is 0 to n-1. Does it mean frequency in Hz? For example when I have a spike on n=2 is it mean that the signal frequency is 2Hz?