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Surround sound is one of the most exciting parts of a home cinema system, and today it's possible to use exactly the same digital soundtracks as leading cinemas.

To enjoy the full experience, you'll need a processor box to decode the sound from your DVD player or set-top box, and five or more loudspeakers placed around your room.

Most surround sound systems employ five main channels of sound, and require five loudspeakers. Ideally you'll have one in each corner of your room, and one above or below your screen, naturally called the centre speaker.

A sixth channel of sound is used to drive a special loudspeaker called a subwoofer, which generates very deep bass and rumbling sounds. They're optional, but make a massive difference when watching action movies. Subwoofers may be relatively large boxes but, since it can be hard to identify where deep bass sound is coming from, the actual position of this speaker is not as important as the main five.

The surround sound processor or AV receiver does the hard work of decoding an audio signal and working out what should go to each speaker. There are several different types of audio signals that can decode into surround sound.

The simplest is analogue stereo, which can be turned into surround using Dolby Pro Logic or Pro Logic II decoding. Pro Logic will produce surround sound from any stereo signal, although it does the best job when the material was meant to be heard in surround; movies shown on TV, for example, will work better than CD albums.

Delivering far better quality are the digital surround sound formats. These take the original surround sound signals from the Hollywood studios and encode them into a single digital signal. This is decoded by your processor or AV receiver at home and fed to the relevant speakers.

Since most movies use five main channels and one for the subwoofer, they're said to have 5.1 soundtracks. There are different ways to encode a 5.1 soundtrack, though. The most common are Dolby Digital and DTS, the former delivered as standard on virtually every DVD movie, and even on some Sky TV broadcasts using Sky+.

DTS uses less compression and sounds a little better; you'll find it as an optional soundtrack on some DVDs. Most processor and AV receivers can decode both Dolby Digital and DTS soundtracks.

If five speakers aren't enough, how about seven around your room? So-called 7.1 systems use the same three speakers at the front, but swap the pair in your rear corners for two at the side and a further two on your back wall. This can sound great in large rooms.

Dolby's version of 7.1 is called Surround EX, and DTS' is called DTS-ES. Again, these can be found on some DVD movies, and you'll need a compatible processor or AV receiver to decode the extra channels; luckily these discs are also compatible with 5.1 systems.

AV receivers
AV receivers look like hi-fi amplifiers, but with one big difference: they'll take the audio signals from your DVD player, set-top box and other devices, decode them into surround sound, then power a number of loudspeakers placed around your room.

The price of AV receivers ranges hugely from models costing less than £200, to monsters weighing in at more than £2,000. Spending more on an AV receiver will get you better quality sound, support for more surround sound formats (with the possibility of upgrades in the future), greater device connectivity and switching, and most obviously, more powerful amplification. Some models also feature THX, which is a certification of quality from George Lucas's audio company.

We would recommend spending at least £500 on an AV receiver, and ensuring that it has support for both Dolby Digital and DTS, along with identical power amplification for each channel for consistent sound; note that subwoofers normally have built-in amplifiers.

If you want a 7.1 channel system, make sure that the AV receiver you purchase is also capable of decoding Surround EX and DTS-EX soundtracks, and has seven channels of amplification.

Speakers
Some companies claim to simulate surround sound with two speakers, but to experience it properly, you really have to install five or more boxes around your room. A subwoofer is optional, but makes a huge difference to action movies.

Obviously the more you spend on loudspeakers the better the sound quality, but crucially, try to ensure that they're as similar as possible so that when the sound goes from left to right or back to front, it doesn't change tone.

Ideally go for identical speakers and ensure that any placed close to your TV (such as the centre speaker) are magnetically shielded so as not to interfere with the picture.

Hi-fi separates
Hi-fi enthusiasts, or audiophiles, enjoy better-quality sound by using separate components for each job, rather than all-in-one hi-fi systems. For starters, it lets you cherry-pick the best individual components - CD player, amplifier, MiniDisc player, digital tuner - to build the ultimate system that's tailored to your own needs, and which can be added to or upgraded as time goes by.

This logic can be applied to home cinema audio, i.e. using a separate DVD player and AV receiver rather than an all-in-one home cinema system. True audiophiles tend to get a bit carried away here. Rather than use a single AV receiver, for example, a dedicated audiophile might go as far as buying a separate surround sound processor and power amplifier.

This probably isn't necessary for most users, but a hi-fi or home-cinema system built on separates is going to give you more flexibility, and often better quality, than the all-in-one systems.

Connecting your sound system
To enjoy digital surround sound, you'll need a digital audio connection between your DVD player and the AV receiver or processor. There are two types: optical and electrical/coaxial, each using a single plug. The choice is ultimately made by which you have on your DVD player and receiver. If you have both, an electrical connection normally gives slightly better quality.

If your set-top box, PVR or games console also has a digital audio output, connect it to your surround receiver for better quality or digital surround sound. Connect any analogue devices such as set-top boxes without digital outputs using standard stereo cables.

Finally, we'd recommend dumping the cables supplied with audio and video devices and upgrading to better quality ones from specialist hi-fi stores. Spend £20 to £50 for each cable and you'll notice a big difference in sound and picture quality.

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