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.
| chain | 
 an FFT chain  | 
| bufsize | 
 the size of the expected input FFT frames  | 
| binindex | 
 the integer index of the bin you want to query  | 
| whichmeasure | 
 0 for magnitude and 1 for phase. None of these arguments can be modulated.  |