Hitachi 31KX39K, 31GX31B, 31DX21B, 31DX11B Operating Manual page 35

-SOUND- FUNCTIONS
• SURROUND
OFF:
Use this for normal stereo/mono broadcasts.
ON:
Listener is surrounded by many sound sources such as a sporting event, etc.
NOTE: Some TV systems do not transmit optimum audio channel separation which can
reduce the effectiveness of the SURROUND function.