Sound in the Round
Up til now, this introduction has focused almost exclusively on video, but audio plays a critical role in any home theater system. At the most basic level, in fact, simply adding a surround sound system turns your TV and entertainment equipment (DVD, VCR, etc.) into a home theater. The impact that a high-quality sound system can have on any home entertainment setup cannot be overstated. In fact, it's not at all uncommon for people to think that the quality of their display improves purely by making a jump in the quality of their audio components.
The most dramatic change to sound is switching from stereo to a surround sound system, which often includes five separate speakers and a subwoofer, a configuration known as 5.1 sound. (Note that it is possible to have surround sound without a subwoofer.) The speakers are configured as a left, center and right across the front of your viewing area, two speakers behind you (one rear right, one rear left) and then a subwoofer, which can be placed anywhere in the room. Other configurations, such as 6.1 and 7.1, both of which add additional rear speakers and reposition the "original" rears more to the rear side, are also possible, although not all systems will support these additional speakers. In all of these configurations, the speakers need to all be connected to and are driven by your system's audio receiver/amplifier. And for many new home theater owners, therein lies the rub. Trying to figure out how to position and run the speaker wires to the surround speakers can be a real challenge—and even a deal killer for some. Some vendors have begun to experiment with wireless rear speakers (although they require a power cable—unlike traditional speakers) and I expect to see more of these systems over time.
In terms of connections, audio is much simpler than video. Traditional analog stereo audio signals are made with the common red and white RCA connectors between your source components, such as your DVD and VCR, and your receiver. (If you have an "all-in-one" home theater system, you may not have any separate audio cables at all.) Then all the speakers are connected to the receiver or, if you have one, dedicated power amplifier.
In order to get surround sound, you have to use a digital audio connection—traditionally either optical or coax—between your source devices and your receiver. Both optical and coax deliver the same compressed, multichannel audio signal that comes from sources such as DVDs, digital cable and satellite boxes, etc., but simply use a different type of connection and cable. Optical uses a special fiber-optic cable that uses light to transfer the sound signals, while coax, which features a regular, single (often black) RCA connector, can use a regular audio cable (but carries the signal digitally). In either case, the audio signal, which is typically compressed in the Dolby Digital and sometimes also the DTS (Dynamic Theater Sound) format, is then decompressed by the receiver and converted into separate signals that are sent to your system's speakers.
But compressed multichannel audio is not the only option for music enthusiasts with home theater surround speaker systems. Super Audio CD (SACD) and DVD-Audio are two competing standards that offer higher stereo audio quality than traditional CDs as well as the possibility of uncompressed, multi-channel digital audio. In the case of SACD or DVD-Audio players you can use six separate analog RCA audio connectors (one for each of the five channels and the subwoofer) or, increasingly, either 1394 or HDMI digital connections. HDMI is also capable of carrying compressed digital audio (such as Dolby Digital or DTS), eliminating the need for separate digital audio cables (in most cases).