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