FFT-subdivide the frequency range

I work on FFT. My frequency range varies from (0-60 Hz). For my study, after FFT, i have to subdivide the frequency range into the following frequency range :0.5-4; 4-8; 8-12; 12-30; 30-60. How to subdivide the required frequency range after performing FFT???

Answer 1

[Guru]

Without knowing anything about the signal/data you are taking the FFT of, this is impossible. If you think your frequency range should vary completely between 0-60 Hz, then you can create a frequency vector that spans this range and say there is a 1:1 correlation between this frequency vector and the FFT, suppose your FFT variable is X:

% X = fft(...)
f = linspace(0,60,length(X));

I wish someday users would actually look at some other example questions and realize the best questions contain some MATLAB code that clearly describes what they are doing and supplement that with what they want to do, rather than rather cryptic text that describes what they want but no idea of what they are doing or dealing with (or a related example - we need not know the specifics of what you are doing but needs more context)

Answer 2

[Matt J]

 YourSpectrum=fftshift(YourSpectrum);

     N=length(YourSpectrum);

     dF=... %frequency sampling interval

     frequencyAxis = ((0:N-1) -ceil((N-1)/2))*dF;

 interval= frequencyAxis>=0.5 & frequencyAxis<=4; %One of the intervals

 plot(frequencyAxis(interval), YourSpectrum(interval));