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Friday, 25 August, 2000, 10:34 GMT 11:34 UK
Q&A: Digital TV
BBC News Online answers key questions about digital TV and how it will affect you.

What is digital TV?

Digital broadcasting is a new system of transmitting TV, radio and the internet.

It turns pictures and sound into a string of binary digits (ones and noughts). This code is transmitted to your TV, which effectively becomes a computer that can convert this digital language back into pictures and sound.

The system also allows your TV to connect to the internet, take interactive programmes and carry many, many more channels.

Digital transmissions can be received in three ways - through your TV aerial, via a satellite dish and via cable. To receive digital TV you will need a set-top box to decode the digital signals - or a new digital TV set.

What is analogue TV?

Analogue TV is the old system of broadcasting that we have had since television began in the 1930s.

It converts sound and pictures into waves which are transmitted through the air and picked up by your rooftop or indoor aerial.

Is one better than the other?

Broadcasters and service providers say digital television not only means more programmes, but also a better quality pictures and sound. Viewers will also be able to get more channels, interactive television, the internet, home shopping and home banking.

But there are reports that Digital TV could have some drawbacks.

According to the consumer magazine Which? the main problem is compression, the process of squeezing transmission information so it travels faster and can be decoded quicker.

Compressing a picture means taking out any bit of the transmission that remains the same from one "frame" to another. For example, the static court in a tennis rally - all that moves are the players and the ball.

A detailed and complicated picture - such as a high-speed pan across a crowd could be troublesome as a huge amount of information is compressed. The result for the viewer can be jerky motion or a blocky picture.

Critics also say that most people are unlikely to notice any improvements in picture quality or sound, as they will not be apparent on most peoples' TVs.

When will analogue TV be switched off?

There is no set date, but Chris Smith, the Media Secretary, has said it could happen as quickly as between the years 2006 and 2010. This depends on two conditions.

One is that 99.4% of the population is within range of the new digital signals. The other is that 95% must have a digital receiver by that date or he won't switch analogue off.

Why does analogue TV have to be switched off and who benefits?

Analogue needs to be switched off because there is no point having analogue and digital TV together.

Digital will replace analogue just as colour TV replaced black and white. Once analogue is switched off, those frequencies can then be sold off for other uses, particularly mobile telephones.

Industry analysts estimate the government could make at least 10bn from the sale of analogue frequencies.

How much will a digital TV cost me?

It depends. You don't necessarily need a digital television set, though you can have one. At the moment they cost between 800 and 1,000, but that will come down.

You can, however, have a set-top box that turns your existing analogue set into a digital television, and at the moment several companies give these away for free, provided you subscribe to their channels.

The government may also introduce a cheap digital box which would allow viewers to see all the existing free stations.

Digital televisions are expected to allow viewers to receive all the free-to-air channels without subscribing to any company's multi-channel packages.

But it's doubtful whether people who choose not to pay would actually receive many of the services that are expected to be developed alongside digital television, such as banking, or video on demand.

How long will I be able to use my own television set?

Only for as long as they keep the analogue system going. As soon as the analogue system is switched off, the set on its own will not work, but it can be made to work for longer by having a digital set-top box, or by that stage, a very small adapter will probably be enough to help it receive the digital signals.

If I have got more than one TV will I need more than one set-top box?

Yes you will. This is one of the big problems. Many people now have three, four, or five sets because televisions don't break down like they used to. So when you get a new set you just put the old one in a bedroom say, and each of those will need some form of adapter to turn them digital.

But as well as buying digital TVs or set-top boxes, viewers will eventually need new video recorders as well.

Existing videos can record digital programmes, but not while another digital programme is being watched.

However, as newer video recorders are likely to include digital capability, this should only affect people with a machine that is several years old when the switch over occurs.

What are other countries doing about digital?

No other country is as advanced in terms of digital television as the UK particularly in terms of digital terrestrial television, which is the system that goes into an ordinary TV aerial.

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