An improved decoder 17, wherein said {HEAD ~ reference frequency} is in the range of 250 Hz to {TAIL ~ 6 kHz} 
An improved decoder 17 , wherein said { HEAD ~ reference frequency } is in the range of 250 Hz to { TAIL ~ 6 kHz }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL