Steps

1. Press the HOME button, then select [Settings].

2. Select [Sound] → [HDMI/DVI Audio Source] → the desired option.
   

Available Options

[Auto]

Automatically sets the audio signal source based on the video signal.

[HDMI Audio]

Sets the HDMI input as the audio signal source.

[PC Audio]

Sets the PC/HDMI audio input as the audio signal source.
Available options vary depending on your model.