A subtracting unit subtracts {HEAD ~ the input signal} from {TAIL ~ the first delayed signal} to generate a difference signal 
from
A subtracting unit subtracts { HEAD ~ the input signal } from { TAIL ~ the first delayed signal } to generate a difference signal
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH