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Media experts have warned that measuring television audiences will

become more expensive and complicated for advertisers and agencies when

digital TV arrives.

The current system, where the number of homes tuning in is gauged by

measuring the signal carried by each channel’s own frequency, will

eventually become obsolete, as digital channels will share

frequencies.

Lynne Robinson, director of research at the Institute of Practitioners

in Advertising, warned that the changes will cost millions and are

unlikely to be in place for the launch of digital TV this autumn.

A number of different systems for measuring audiences are currently

being tested. These include a digital probe which identifies different

broadcast signals; a station identity broadcast by each station, which

is inaudible and invisible; and ’picture matching’.

The latter system involves recording a sample of the TV picture in each

panel household to work out which channel is being watched at any

particular time.

Robinson said that in order to obtain an accurate audience measure, a

mixture of all three systems is likely to be used. Information will then

be aggregated in an attempt to provide an accurate measure.

In addition, the Broadcasters’ Audience Research Board will have to

start building up information about the number of digital homes on the

current panel or increase its size, as happened with satellite TV.