Sony hdw-730 Operation Manual page 39

qg EARPHONE jacks (minijack)
You can monitor the E-E sound during recording and playback sound
during playback. Plugging an earphone into the jack automatically cuts
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off the built-in speaker, and you hear the alarms about the camcorder's
operation and status through the earphone.
The signals output from these jacks are the same. You can connect two
earphones to these jacks at the same time.
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Chapter 2 Locations and Functions of Parts and Controls