HOME CINEMA -- YOUR TOP TEN QUESTIONS

1. WHAT IS HOME CINEMA?

Basically it is an attempt to recreate the experience of  watching a movie at the cinema, in your own home. In the USA, where the idea originated they go all the way, with huge projection TV screens and powerful audio systems, but their houses are normally a lot larger than ours. Over here, in the UK, the emphasis is on cinema-style surround sound, though in the last couple of years there has been a trend towards buying larger-screen TVs of 25-inches and above. However, the size of British TVs are limited by the size of British living rooms, and it's unlikely sales of  true 'cinema' TVs, -- screens of 40-inches plus -- will ever take off in this country.

2. WHAT IS DOLBY SURROUND?

There's a lot of confusion over the terminology so we'll start at the beginning. Dolby Stereo is a four-channel audio system (yes you can have four-channel stereo...) that has been used on over four thousand movie soundtracks made since the mid seventies. Two of the four channels are used for normal right and left stereo sound. The third carries mostly dialogue, and is heard from speakers placed close to the centre or behind the screen, this helps to fix the audience's attention to the screen, especially for those seated away from the centre of the auditorium. The fourth channel is mainly used for sound effects and is piped through speakers along the sides and at the back of the auditorium; together they bathe the audience in a sea of sound. In the encoding process the four audio channels are electronically mixed into the normal two channel stereo optical soundtrack on movie film, this means films with Dolby Stereo soundtracks can be played in older, non Dolby-equipped cinemas.

Now we come to Dolby Surround; when movies with Dolby Stereo soundtracks are transferred to video, or shown on TV, it becomes known as Dolby Surround. The same term is used for material originated for TV. Dolby Stereo information is quite robust and normally survives intact on any reasonably good quality stereo transmission or recording medium.

In the cinema, and latterly in the home, the four audio channels are separated from the stereo soundtrack using a Dolby Surround decoder; in home systems they're normally built into other devices, like audio-visual (AV) amplifiers, VCRs or TVs. Currently there are two main types of domestic decoder, the simplest ones, now almost obsolete, are known as 'passive matrix' decoders can only resolve the two stereo channels, and the rear effects channel. Today most decoders use an  'active matrix' system, this is also known as Dolby Pro Logic, they can resolve all four channels and do a much better job of recreating the original cinema sound. There is a third family of decoders, called THX, it's a sort of turbo-charged Dolby, but at the moment equipment for home use is scarce in the UK and very expensive, a half-decent system would cost several thousand pounds to install.

3. HOW DO I CONNECT IT ALL UP?

The first thing you will need is a stereo source, i.e. a means of receiving or replaying Dolby encoded stereo material, we'll look at the various options in more detail in a moment but for now let's assume you have a reasonably modern stereo hi-fi VCR. The stereo line audio output from the VCR is connected to the audio input of the device containing the Dolby decoder, the simplest option is an AV amplifier, most of them have the necessary four or five channels of amplification, to drive all of the speakers directly. In effect you are integrating your video system (VCR and TV) with your hi-fi system, that, in a nutshell is the essence of home cinema.

4. HOW MANY, AND WHAT TYPES OF SPEAKERS WILL I NEED?

That all depends on what sort of TV you have, and what type of decoder you are using. If you've already got a stereo TV, or are using your hi-fi system speakers then you will only need two extra speakers, to place behind or to the side of your viewing position. If you have a Pro Logic decoder you will need to site another speaker above or below your TV screen; it's advisable to used a magnetically screened speaker, one specially designed for AV use, otherwise if it is too close to the screen it could cause colour 'staining'. The side or rear-effects speakers can be almost any size or type (providing they match the amplifier), and  they needn't be expensive top-performers either, as the sounds coming from the effects channel have a fairly limited frequency range.

5. IS IT BETTER TO HAVE THE DOLBY DECODER IN THE TV, VCR OR AMPLIFIER?

There's no simple answer to that one, it all depends on how much money you want to spend, and what, if any, items of home entertainment equipment you are planning to buy or renew. From the economic and performance points of view the best option is to have the decoder in a good quality AV amplifier, however, this is the least flexible method, if you want to be able to use the rest of your hi-fi system at the same time; moreover, your main stereo speakers may have to be re-positioned for audio listening. AV amplifiers start from around £300, rising to well over £1,000. At the moment there are only two makes of Dolby-equipped TV, from Toshiba and Hitachi, and these are by far the simplest routes into home cinema as they come with all the necessary speakers and cables. The downside is that these TVs are quite expensive, in the region of £800 to £1500, and the sound systems are not going to blow your socks off, if you're into that kind of thing. You will still need a stereo VCR if you're going to watch films on video. Dolby-equipped VCRs are rather thin on the ground and at the moment, in fact only Akai are making them for the UK market. You will still need extra speakers and a stereo TV, or integrate the VCR with your hi-fi system, so it's not much more convenient than a AV amplifier, though it is more flexible, and a little cheaper (around £600) than having the decoder built into the TV.

At least one satellite receiver now has a Dolby Surround decoder built-in, but it only works on satellite broadcasts, which isn't much use if you want to watch a Dolby-encoded movie on a terrestrial channel, or on tape.

6. IS DOLBY SURROUND BROADCAST ON TV?

Yes, but... The Dolby Stereo soundtracks on recent movies, broadcast in areas with NICAM sound, and from satellite channels should be recoverable on any Dolby decoder; the but is there's no way of knowing whether or not the movie in question has a stereo or indeed a Dolby Stereo soundtrack (many prints made for TV transmission are in mono), or not. The situation is a little better on made for TV programmes and  series, and there's more of them these days, though few if any of them are 'flagged' at the beginning, or listed in published TV schedules; sometimes the first and only indication that a programme has a Dolby Surround soundtrack is in the end credits.... There are some honourable exceptions, including the Simpson's cartoon, shown on Sky One, where the Dolby Surround logo is shown at the start.

7. WHAT OTHER SOURCES OF DOLBY SURROUND ARE THERE?

In theory Dolby Surround signals can be carried by any good quality stereo recording or transmission system, and in the UK that means  VHS hi-fi VCRs, and the NICAM and Panda II/Wegner stereo systems used by terrestrial and satellite broadcasters. Other AV sources, such as Laser Disc also support Dolby Surround, and it is very popular in the USA and parts of Europe. Sales of discs and players in the UK have been very slow, mainly due to the limited availability of titles (compared with tape), though there are plenty of enthusiasts who appreciate the high-quality sound and pictures.

8. SO WHAT PRECISELY IS LASER DISC

The Laser Disc system was originally developed in the early 1970's by Philips, and it has spawned a number of related optical disc technologies, including CD and CD-I. The discs, which are the same size as a 12-inch vinyl LP, is a sandwich of transparent plastic, with a thin metallic film in the middle. The film is made up of  a spiral track of microscopic mirrors and pits. Inside a Laser Disc player the spinning disc is scanned by a laser and the resultant reflections are processed and turned into a video signal, which can be displayed on a normal TV. 

Laser Disc has gone through a number of changes since its inception and on the current generation of discs the video signal is in an analogue format, whilst the stereo sound signal is processed digitally, in a similar manner to audio CD. Sound and picture quality are both very good, as good as broadcast TV in fact, and unlike tape it is possible to quickly move from one part of the recording to another.

The next generation of Laser Discs are likely to be wholly digital and use the CD-sized discs. The most promising technology is an extension of the CD-I (the I stands for interactive) system, called full motion video or FMV, which allows up to 70 minutes of VHS-quality video to be compressed onto a 5-inch disc. It will be a while before it poses any threat to VHS tape but the signs are good and this could become the main carrier for pre-recorded movies within the next ten years.

9. WHAT IS DIGITAL SIGNAL PROCESSING

Digital signal processing or DSP is a facility found on some of the more upmarket AV amplifiers and it is used to simulate the acoustic properties of a variety of listening environments. In plain English that means DSP can fool you into thinking that you're sitting in a concert hall, theatre, open-air stadium, jazz club, cathedral or any number of large-scale venues with a distinctive 'sound'. Purists are naturally scornful but if you can set aside your prejudices, and close your eyes, some of the effects can be quite convincing.

DSP works by reproducing the multiple sound paths, reflections and reverberations that are created in large spaces, which give the impression of 'size'. Like Dolby Surround it requires a second set of speakers, placed to the side or behind the listening position. The digital processor circuitry inside the amplifier feeds small and carefully controlled amounts of the original sound to the front and rear speakers, delaying some sounds by a few milliseconds (reverberation and echo) and selectively filtering others, to mimic the absorptive and reflective properties of walls, ceiling and furnishings. On some of the more expensive DSP systems the 'environments' are based on actual measurements taken by sound engineers at internationally renowned concert halls and theatres; some of them even allow you to choose your seating position. In the end, though, DSP is a clever con, and it only works on a limited range of material (live rock concerts are one example). Most digitally-generated venues sound empty and hollow; generally speaking recordings on tape, LP and CD sound as the artists, producers and engineers wanted them to sound, and need no further coloration.

10. WILL ANY TV DO FOR HOME CINEMA USE?

Not really, you would have a hard time convincing yourself you were at the movies watching a 14-inch portable with surround sound, for instance. The first criteria is size, the bigger the better, and if you're really keen, not to say well-off, then you should be thinking about a widescreen set with a 16:9 aspect ratio screen. They're just the job for watching movies in all their widescreen glory, and you can even blow up normal TV-shaped (4:3 aspect ratio) pictures to widescreen size. 

However, any TV with a screen more than 26-inches across is a good starting point; conventional TV screens go up to 33-inches, but you really need a bigger room (and strong floorboards) for one of those monsters. If you've got a large enough room, and even deeper pockets, then a projection TV or video projector is just what you need. Screen sizes go from around 36-inches, for a back-projection display, up to 200-inches for a front-projection system.

SIDEBAR 1  -- INTEGRATED PACKAGES

The simplest way to acquire a home cinema system is to buy an integrated AV package, or Dolby-equipped stereo TV. An increasing number of electronics manufacturers now put together complete mini and midi stack systems which include an AV amplifier with a built-in Dolby Surround decoder, CD player, tuner, tape deck and a set of matching speakers, all you need to add is the TV and video source component, and that usually means a stereo hi-fi VCR, preferably one that also has an on-board NICAM decoder. Prices start as low as £350, though be prepared to spend in excess of £600 if you want a system with half-decent speakers and a reasonably capable CD player.

One-box systems, like the Toshiba and Hitachi Dolby-equipped TVs are the most convenient of all, and even though they have built-in NICAM decoders as well, you will still need external source components, like a stereo VCR and stereo satellite receiver.

SIDEBAR 2 -- UPGRADING TO HOME CINEMA

If you already have a stereo system, which you're prepared to integrate with your video equipment the obvious solution is to buy a stand-alone Dolby Surround decoder, though there's only one or two still on the market these days. More realistically you're going to need an AV amplifier, to replace your existing hi-fi amp. Go for a model with plenty of power, especially if you're into action blockbusters (and have tolerant neighbours). It's a good idea to choose one which can act as the control centre for the rest of your system, and that means plenty of extra inputs, for the CD player, tuner, tape deck and turntable, as well as extra AV inputs for the VCR, satellite receiver Laser Disc player, and so on. Some have tuners built-in, they're a good bet if you're trying to cut down on the number of boxes in your system. Make sure it has remote control too, unless you're an exercise freak... . Thus far most AV amplifiers are aimed at the middle of the market, so if you're a serious audiophile be prepared to compromise, or wait until THX systems come down in price. 

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R.Maybury 1993 0308