Unpack1FFT(chain, bufsize, binindex, whichmeasure=0)
Takes an FFT chain and extracts a single scalar value as a demand-rate stream. To call it, a "demander" is needed, which fires whenever the FFT chain fires - this is normally achieved using PackFFT but can also be done using Demand.
an FFT chain
the size of the expected input FFT frames
the integer index of the bin you want to query
0 for magnitude and 1 for phase. None of these arguments can be modulated.