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the bins will go in the order of a non-shifted FFT: 0 to N/2-1 then -N/2 to -1 (i think)
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samples 0 ~ N/2-1 represent frequency range 0 ~ Fs/2 (0 ~ +.5)
samples N/2 ~ N-1 represent frequency range -Fs/2 ~ 0 (-.5 ~ 0)
if you put last half of vector to precede first half (fftshift) then:
samples 0 ~ N/2-1 => frequency range -Fs/2 ~ 0
samples N/2 ~ N-1 => frequency range 0 ~ Fs/2
i.e. dc centred.
each sample can be thought of as brick walled frequency band(bin) with own centre. thus the exact bin centres fall half band from each end of sides.
thus frequencies occur at points separated equally as follows:
f=linspace(0,1-1/N,N) *Fs
and the resolution = Fs/N Hz representing bin width.
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