Assuming that {TAIL ~ no tone signals} have been applied to the decoder 14, the output signal from comparator 56 is at {HEAD ~ a low logic level} 
Assuming that { TAIL ~ no tone signals } have been applied to the decoder 14 , the output signal from comparator 56 is at { HEAD ~ a low logic level }
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD