Sony BRAVIA KDL-46BX421 Operating Instructions Manual page 32

Alternate Audio
Select among the available options to switch among the alternate audio streams. The
Digital chan_els o_I3, program you are tuned to may be broadcasted in a different language in the alternate
audio streams.
Speakers TV Speakers
Select to use the TV speakers.
Audio System Select to use an external audio system for the TV sound. By
selecting this option you are disabling the TV speakers.
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