The centre channel's primary duty is the reproduction of dialogue and general background audio ('foley') effects, while the two surround speakers manage the film's ambient (background or 'atmosphere') effects, such as wind, raindrops or echoes, and are responsible for literally 'surrounding' the viewer with sound. When combined, these five speakers totally immerse the viewer in sound; no longer will you merely observe films from a distance, you will feel as though you are actually in the film, participating in the action.

The heart of any home theatre is the AV (audio/video) amplifier or receiver. Although similar to a conventional amplifier, an AV amplifier includes five or more channels of amplification; that's at least three more than a conventional stereo amplifier. These miltiple channels of amplification are needed to power a home theatre's five or more audio channels. The processing system that allows an AV amplifier to reproduce the sound heard in theatres is called 'Dolby Pro Logic'.

Dolby Pro Logic 'unfolds' four separate audio channels from conventional stereo recordings. Any stereo recording is capable of including surround-sound information, and nearly all of the videos at your local video store include surround-encoded stereo soundtracks. All you need to hear this extra information is an amplifier or receiver with Pro Logic processing and a hi-fi video. Many TV programmes are also recorded in surround-sound and with the same amplifier and video you can listen to your favourite shows in full surround-sound.

In addition to Dolby Pro Logic, two audio systems that have become increasingly common on AV amplifiers are 'Dolby Digital' and 'DTS Digital Surround'; both generically known as '5.1' systems (as both commonly have five independent full-range audio channels and one limited-frequency bass channel). Both Dolby Digital and DTS offer significant improvements over Dolby Pro Logic, including increased channel-separation and considerably greater dynamic range (the difference between the loudest and quietest sounds that can be reproduced).

Unlike Dolby Pro Logic, both Dolby Digital and DTS Digital Surround include completely discrete full-range surround channels, allowing 'split-surround' audio effects (that is, stereo surround audio effects). Split-surrounds allow much more precise sound localisation, placing sounds precisely behind the listener, not just vaguely "behind… somewhere". Both systems also include an optional dedicated 'LFE' or bass channel, which significantly enhances bass reproduction. Dolby Digital and DTS Digital Surround are currently restricted to the newer DVD videodisc and D-VHS formats and the latest DSS, DTV and HDTV digital television systems.

Even though a home theatre uses three more speakers than a conventional stereo system, these speakers needn't be large and can be discreetly placed, allowing them to seamlessly integrate with a home's decor. For those who wish to avoid the hassle of choosing an AV amplifier and extra speakers, complete home theatre packages are readily available. Although much more convenient than individually selected 'separates' based systems, you should bear in mind that these systems will not offer the performance levels component-based systems are capable of.

Many reputable manufacturers, such as Sony, Pioneer and Denon, offer all-in-one home theatre packages that include five speakers, Pro Logic and Dolby Digital/DTS processing, and five or more channels of amplification in a single convenient package. These systems are usually small enough to be tucked away out of sight, and are controlled by a single remote control. As an added bonus, these systems cost considerably less than systems that use separate components.

Whether you want an entry-level or a top-of-the-line system, your first port of call for advice and information should be your local specialist audio dealer (ie. not your local Big Al's 'Lectronic Superstore). Your local home theatre dealer can advise you which systems best suit your needs, and answer any questions you might have about home theatre technology and features.

To get the most from your new purchase, I suggest calibrating your new surround-sound system with a specialised calibration disc (DVD) such as 'Digital Video Essentials' or the 'Avia Guide to Home Theater'. These discs can also be used to calibrate your television, allowing the films you watch on TV to look as good as their makers intended. Good luck and happy hunting!