Many filmmakers say that what's on the screen is only half the movie, the other half is to be found in the soundtrack, carefully crafted by talented composers and musicians to elicit emotions of excitement, fear, sadness and joy in the viewer. Once of the major benefits of watching moves on DVD or hi-def formats is the availability of faithful reproductions of the multi-channel sound that can, when fed through a reasonable home system, sound even better than in many modern movie-theatres.

When most consumers go down to the store and pick up a big new flat screen plasma or LCD TV, they may think that they are all set and ready to go. In fact, the sound provided by even an expensive top-of-the-range TV is incredibly limited, providing little or no low-frequency response, producing only a flat, distorted version of the movies music, and generating little or no directionality. If they are good at anything, it is producing clear, audible dialogue, but that's pretty much it.

Modern movie soundtracks contain so much more information; they contain multiple channels so the viewer perceives the sound to be coming from a particular direction, such as a plane flying overhead, or dialogue coming from left or the right. They also contain low-frequency information, to reproduce deep bone-shaking sounds such as explosions or rumbling engines. To be able to access and hear all this extra information you need a dedicated home theatre audio system.

The basic home theatre audio system consists of an amplifier and multi-channel speaker set. The job of the amplifier is to decode and then amplify the multiple audio tracks present on the disc. To do this, it needs to be connected to the DVD or Blu-Ray player by a data-cable. A fiber-optic digital audio cable (also known as a TOS-link cable) will be needed for DVD's, but to decode next-generation hi-def audio will require a HDMI cable connection. The HDMI cable also carries the video stream, so most amplifiers will have a HDMI out socket, allowing the video information to continue on to the TV or projector.

In terms of power, a quality separate amplifier be marked somewhere in the 80-100 watt range, which is plenty for watching a movie in the average family home. Beware amplifiers that are built into DVD players, or into a speaker set, they are usually underpowered and will perform poorly. The most demanding audio signals to reproduce are the low-frequency type; so many speaker-sets will have “active” sub-woofers, which have small dedicated amplifiers built in.

Speakers for home-cinema can be purchased in packages of matched sets, or individually, allowing you to mix fronts from one manufacturer with rears from another. In general, purchasing a set of matched speakers is the best option for beginners and will produce a very good sound. Unlike regular stereo speakers, home cinema speaker-sets are generally split into dedicated low and mid/high frequency speakers, with the sub-woofer speaker handling the low-frequency sounds by itself. This works because it is very difficult to detect the direction of low-frequency sounds, so it does not matter where in the room the sub-woofer is placed. By contrast the direction of mid and high frequency sounds is easier to detect, so speaker-placement is key, with left/ right speakers best positioned level with the screen and widely spaced apart, the central speaker positioned directly beneath the screen, and the rear speakers positioned diagonally facing the viewer from behind. This setup is for a 5.1 speaker set, which is all that is really required for proper directionality, although 6.1 and 7.1 sets are available.