Sony KDS-55A2000 Operating Instructions Manual page 29

Dual Sound
Tip
Sound menu options other than "Dual Sound" cannot be used for headphones and audio output sockets.
Selects the sound from the speaker for a stereo or bilingual broadcast.
"Stereo", "Mono": For a stereo broadcast.
"A"/"B"/"Mono": For a bilingual broadcast, select "A" for sound channel 1, "B" for
sound channel 2, or "Mono" for a mono channel, if available.
Tip
If you select other equipment connected to the TV, set "Dual Sound" to "Stereo", "A" or "B".
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