Apple TV (2nd generation) - Manual (Page 11)

Chapter 1 Connect. 11 Chapter 1 Connect.
Setting Up Apple TV
Apple TV connects to your TV through an HDMI port that delivers both audio
and video. Before you set up Apple TV, look at the ports on the back of your TV
to make sure you have the right cables.
You can connect Apple TV to a high-definition TV or home theater receiver that
has an HDMI port, using an HDMI cable for both video and audio.
You can also use an optical digital audio cable to connect Apple TV to a receiver
for audio.
Important: Before you connect Apple TV to a power outlet, carefully read
these installation instructions and the safety information in the included
Important Product Information Guide.