Apple TV (3rd 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:
 An HDMI cable: You can connect Apple TV to an HDTV or home theater receiver
that has an HDMI port, using an HDMI cable for both video and audio.
 An optical digital audio cable (optional): Use this cable if you want 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
Apple TV Important Product Information Guide.