In Calc, I’ve used the Data->Statistics->Fourier analysis facility to Fourier transform a time-series data set of 2 columns by N rows (as it happens, N is even). So far, so good - I have the output data. Unfortunately, I can’t tell which row of the output array relates to which frequency component. Please advise.
(I have a few clues - my input data are all real, so I know that, except for the DC components, the outputs should come in complex conjugate pairs with frequencies f and -f. I can see that row 1 and row N/2-4 of the output are not in any obvious complex conjugate pairs (and are almost perfectly real), so they must be DC components. I can also see that row N/2-4-1 and row N/2-4+1 form a complex conjugate pair, do they must relate to frequencies of equal size and opposite sign; and similiarly for row N/2-4-2 and row N/2-4+2, etc. - except that pattern doesn’t continue all the way, because row 2 and row N form a complex conjugate pair, as do row 3 and row N-1, etc…)