The basic building blocks of any entertainment system are sound, sources and displays. For most media rooms, the sound or audio system is a combination of an audio-video (AV) receiver plus five or more loudspeakers and a subwoofer.
The heart of the AV system is the receiver. Today's receivers perform many functions: They power the loudspeakers; the speaker wires are connected to the back of the receiver. All of the sources (cable box or satellite, DVD, game system, etc.) are connected to the receiver, which lets you select which source you want to hear.
The AV receiver lets you control the volume and adjust the balance between the loudspeakers. The receiver also sends the video signal to the television or monitor. The receiver processes the audio, including the information for surround-sound effects. On some newer receivers, it also performs video conversion.
Many better televisions also have audio amplifiers, connections for multiple sources and surround processing, but for most applications it is better to use a separate audio video receiver. The receiver will almost always have more power and flexibility.