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