A home cinema is any collection of equipment you can use for watching films at home. At a very basic level, this can be as simple as a normal TV and a mono VCR (video cassette recorder). This will allow you to watch the pictures and hear the sound, but that's about it.
A true home cinema will usually feature a widescreen TV. The only important feature of the TV is the picture quality - the sound will be coming from somewhere else. The source of the pictures may be a VCR, but will more usually be a DVD player. The sound will come from the source via an amplifier to some speakers. Speakers vary in number according to the sound standards available, of which there is a bewildering variety.
This entry is an attempt to explain the standards available, according to the number of speakers they require. It will make no attempt to explain obscure technical differences between the standards, as these are irrelevant to the general listener.
Connecting a source (eg a VCR or DVD player) with an amp is usually done with phono leads. These are available from any electrical retailer. Most DVD players also have a digital optical out port, which can be connected to the optical in socket on some amplifiers.
Stereo. Two different sound signals are produced, one designed to be heard from the left, one from the right. Many TV programmes are broadcast in NICAM stereo, and most VCRs sold today have a NICAM decoder built in. The VCR can thus be connected to the AUX (auxiliary) input of almost any amplifier, no matter how old, using phono leads. This will usually lead to a noticeable improvement in the quality of the sound compared to hearing it from the TV speakers.
Dolby Prologic is an analogue sound standard which produces four sound channels - front left and right, as for stereo effects, a centre channel usually used for dialogue, and a single rear effects channel. Many Dolby Prologic systems come with five speakers - two at the back - but the sound from the two rear speakers is the same. This is therefore not a true 'surrounding' effect. Dolby Prologic effects can be encoded on video tape, and a Prologic decoder is required in the amplifier to send them to the appropriate speakers.
Six Speakers - Dolby 5.1
Dolby 5.1 (sometimes simply called Dolby Digital) is, as the latter name suggests, a digital sound standard. Like the other well-known digital sound standard, MP3, the sound is compressed in order to fit as much as possible onto the disc. It is thus only available on digital media such as DVD. It uses five separate sound channels for a true surround effect - front left and right, centre dialogue, and separate rear left and right.
The 'point one' in Dolby 5.1 refers to another separate channel specifically for low frequency sounds. A lot of the impact of cinema sound effects is felt in low frequency sounds - the crashing of the ocean waves, the 'thrup' of helicopter blades, the boom of the footstep of a Tyrannosaurus Rex. Humans cannot distinguish which direction low frequency sounds come from, so the speaker for these can go anywhere - for instance behind the sofa. It is usually big and box-shaped, and can make much lower frequency sounds than even the 'woofer' part of a normal speaker. It is therefore called a subwoofer.
Dolby 5.1 is the most widespread sound format on new films on DVD. Some DVD players have a Dolby Digital decoder built in and can output sound directly to a set of speakers. Others must be connected to an amplifier with a decoder built in, and the amplifier directs the sound to the speakers. Most 'home cinema' amplifiers feature a Dolby Digital decoder. Do not assume simply because a DVD player has 'Dolby Digital' on the front that it has a decoder built in. It may mean only that it is able to send a digital signal to an amplifier which can then be decoded. All DVD players can do that.
Six Speakers - DTS
DTS is another Dolby Labs sound standard. The initials stand for Digital Theatre System, and the system also features five sound channels plus a subwoofer channel. However, the sound is much less compressed than in Dolby 5.1. For this reason, a high-end home cinema system allows the listener to hear the difference between a film soundtrack encoded in 5.1, and one encoded in DTS. In particular, high frequency sounds are said to be noticeably clearer in DTS.
However, this system has a number of disadvantages. Firstly, it is more expensive to buy even basic DTS equipment. Secondly, unless your listening environment is acoustically favourable, you are unlikely to notice the difference from 5.1. Thirdly, and possibly most importantly for the film buff, because DTS is a much less compact format, it takes up much more space on the disc. This drastically limits the space available for all the good stuff you normally get on a DVD such as director's commentaries and 'making of' documentaries. Possibly for this reason, DTS remains a relatively rare format.
Again, beware of DVD players with the DTS logo on the front. This merely means that they can play DTS discs - like every other DVD player in the world. They do not necessarily have a DTS decoder built in, and you will almost certainly need to buy a separate amplifier to get the DTS effect.
Dolby Digital EX, or THX surround, adds yet another pair of speakers to the mix. The listener now has left and right front, rear and middle speakers for a totally surrounded effect, a centre dialogue speaker and the good old subwoofer. The equipment to play this is still relatively rare and expensive, and at the time of writing only one disc exists with sound encoded in this format - Star Wars - The Phantom Menace. More discs will follow in time.
Which to Choose?
If you have a VCR and a HiFi with an AUX input, a cheap phono lead can transform your listening and viewing experience. If you have a DVD player and a HiFi with an AUX input, this goes double or more! If you are considering actually buying a home cinema sound system, look for an amplifier* with, as a minimum, Dolby Digital (also called AC3 or 5.1). Prologic is an analogue format and is pretty much obsolete. DTS and EX may be the future, but then they said that about WAP.