second encoder means for binary encoding an output signal from said second means with a single threshold level proportional to a level of {HEAD ~ said signal} from {TAIL ~ said first means}; and 
second encoder means for binary encoding an output signal from said second means with a single threshold level proportional to a level of { HEAD ~ said signal } from { TAIL ~ said first means } ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH