first summing {TAIL ~ amplifier means} for generating a left right summing output signal which is a function of the sum of said {HEAD ~ left and right output pulses} 
first summing { TAIL ~ amplifier means } for generating a left right summing output signal which is a function of the sum of said { HEAD ~ left and right output pulses }
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD