I'm practising my new MD WALKMAN SONY MZ-NH700. I've put a MD 74mns in to test the microphone recording and the MZ didn't recognize it as a MD but as a HI-MD which it is definitely not and once out of the MZ all my other machines ( Sony MZ R30 and Sony MDS JE520 could read the MD identifying it as a HI-MD ! Any clue?