Do you know about LabVIEW Waveforms? This is basically a cluster whose main component is an array of numbers representing data sampled at a fixed delta-t (time interval), along with the delta-t and the starting time (t0) of the sample. The FFT routines like using such a data structure, as it contains both the amplitude array and the sampling interval, but they can also work with just the data array, alone.
Just to reiterate, the data array, itself, represents the amplitudes you need. The "frequency" information is simply 1/delta-t, which the routines figure out for themselves if you give them the data as a Waveform, or you can provide the (fixed) frequency, or they will use a default value and you can adjust things after the FFT is finished.
Bob Schor
