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