Can I hear footsteps behind me?: Surround sound can bring villains right into your living-room, says Steve Homer

WHEN Helen Mirren appears on our television screens tomorrow in Prime Suspect 2, some viewers will hear a little extra. The series is one of a handful of programmes made for British television recorded in Dolby Surround Sound, a system designed for the cinema that is increasingly finding its way into people's homes.

According to Dolby, this is only the fourth British-made Surround Sound television production. All have been produced by Granada. Dolby developed Surround Sound for cinemas in the Seventies. It consists of a left, right and centre speaker at the front and at least 10 speakers behind the audience.

What is so clever about the Dolby system is that the information for the additional speakers is carried in the normal stereo

recording.

This has had one unexpected benefit: any film recorded in Dolby Stereo, which includes the Surround Sound encoding, will decode when the soundtrack is received in stereo. That means that all the 'Dolby Stereo' videos in your local video shop and - if you live in an area served by stereo television - all stereo films broadcast to your home, can be decoded into Surround Sound.

What difference does this make in your living-room? The most obvious type of effects can be heard at the beginning of the first episode of Prime Suspect 2. The rain is falling, a body has been discovered, police cars are arriving from all directions.

With Dolby Surround Sound, you hear the rain falling around you, cars pass behind you and people shout from all directions. But the real beauty is that the system restores some of the film's 'depth'. When the hero or heroine walks through the woods, you can hear the leaves rustling almost imperceptibly. When they walks along a dark and dangerous alleyway, you hear the echo of their footfalls from all directions. Even in the quietest of scenes, small, atmospheric noises are picked up.

So far, home surround sound systems have been slow to take off. Dolby says about 8 million systems have been sold worldwide, about half in North America. Sales of equipment have reached 2 million a year, and with decoder chips costing about dollars 5, it is a cost- effective addition for television, video and hi-fi manufacturers.

The problem has been a traditional chicken and egg situation - broadcasters do not want to make surround sound broadcasts because there are too few viewers with surround sound equipment and the consumer electronics companies do not want to market the equipment because there is no programming. But in the United Kingdom, VHS Hollywood movie videos and stereo transmission of movies on television have helped make the UK the fastest growing market for surround sound in Europe. Even so, television production is still a rarity.

'It's amazing that other companies have been so slow off the mark,' says Craig McNeil, the production executive who was in control of Prime Suspect 2. 'People go out and hire films in Dolby Surround Sound, why shouldn't they get the same off terrestrial television?

'If you go into any hi-fi shop, you will see they are all selling surround-sound hi-fi systems. Toshiba even does a television with surround sound speakers. They wouldn't do that unless there was a market.'

But Mr McNeil says Granada is also looking to the future. High- budget, quality programmes such as Prime Suspect, have a long shelf life. He believes that surround- sound is likely to become commonplace within a few years.

Creating a surround sound version added less than pounds 5,000 to the overall budget of about pounds 1.8m, so it was a good investment.

Other broadcasters are interested in surround sound, but none has yet committed themselves. As the Dolby Surround Sound broadcaster's hardware only costs pounds 1,300, that is surprising. For the BBC, surround-sound presents a particularly difficult problem. With Nicam stereo, the system now used for stereo television transmission, only officially launched in August 1991, it is loath to confuse the market.

Is it worth spending your money on surround sound? For me, at least, the answer is yes. I have been using a Kenwood mini system for the past month and am hooked. With competition growing, prices are bound to fall. Many quite basic midi and mini hi-fi systems now come with surround sound as standard. Or you can buy a separate decoder for between pounds 200 and pounds 300 and use it with your existing hi-fi system. The biggest expense is the additional speakers.

'We've been talking about video, television and hi-fi coming together for years. At last people can see and hear movies in their homes as producers and directors expected them to,' says Bob Tomalski, technical editor of What Video? magazine. 'It adds another dimension to watching movies.'

A centre speaker to sit on top of the television will cost at least pounds 90, and two smaller surround speakers to position behind the viewers will cost at least pounds 100, Mr Tomalski says.

Given its popularity in the United States, surround sound is bound to grow in the next few years. Already some compact discs are being produced in surround sound, and the first computer game using the system has been released.

But Dolby Surround Sound is certainly not the end of the story. The company has developed a way of putting digital sound on to cinema films. Batman Returns was the first movie to use the system, but only a handful of cinemas worldwide, including the Empire Leicester Square, in London, were equipped to make use of it. Already another 12 films have been released using the system. The problem for Dolby is to find a way to add the digital quality signal on to VHS tapes and broadcast programmes.

'Prime Suspect 2' is on ITV tomorrow and Wednesday at 9pm.

(Photograph omitted)