Better, faster digital TV

By media correspondent Nick Higham

Attentive readers of this column may recall a throwaway remark a few weeks ago to the effect that the forthcoming £100 Pace digital terrestrial television (DTT) adapter "may not be that good at interactivity".

It was because the DTT receivers marketed by ITV Digital are notoriously slow when it comes to interactive services.

My colleagues at the BBC's research and development centre at Kingswood Warren, south of London, read that and realised I was talking through my hat.

Last week they invited me down for a day to learn more about digital television - and extremely useful it proved too.

My mistake in that earlier column had been to confuse DTT with ITV Digital.

Interactive

As Jeff Hunter and Richard Cartwright demonstrated at Kingswood Warren, ITV Digital receivers are indeed a good deal slower than Sky's digital satellite (or DSat) receivers, but that is because of the software inside them, not any inherent shortcomings with DTT.

Hunter and Cartwright have a number of other DTT receivers, not marketed by ITV Digital, which carry out interactive tasks very much faster even than Sky's.

Bob the Builder fans can build their own truck on CBeebies

They also showed me an example of one of the new uses for interactivity which they are developing, a Bob the Builder game in which CBeebies viewers can build their own truck: Sony Playstation it isn't, but your two-year-old may enjoy it.

If there is a problem with DTT and interactivity it is one of capacity.

Broadcasters are already trying to squeeze a quart into a pint pot on DTT, and the task is made more difficult by some of the legislative requirements.

Angry

The casualty in all this has been "multistreaming" - offering viewers video feeds of alternative camera angles or extra news feeds, for instance - which requires a lot of extra capacity.

Indeed ITV Digital was very angry last year when the BBC made its much-admired interactive coverage of Wimbledon available to Sky Digital's subscribers but not to digital terrestrial viewers - because, the BBC said, there was no room.

Engineers at Kingswood Warren are now working with ITV Digital and others on ways to increase DTT capacity and to reduce other sources of complaint - including poor reception and the fact that large parts of the country can't get the service.

ITV Digital was angry over BBC's interactive Wimbledon

Interference, often involving "blocking" or freezing of the picture, is mainly caused by what the experts call "impulsive noise events" - interference from thermostats and switches in the home.

Increasing the power of the DTT transmitters reduces that problem considerably - and the engineers have been relieved to discover it doesn't seem to create unacceptable interference to analogue TV receivers in the area.

But if DTT is ever to become the "default" way of getting digital, as the government hopes, and if analogue transmitters are to be turned off in 2010 there are still a good many problems to be overcome - a subject I will return to in future.

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A version of this column appears in the BBC magazine Ariel.