Many viewers are irritated when changing channels or cutting to a commercial break leads to a significant variation in the audio levels accompanying the picture. Viewers generally adjust the sound to their liking when they settle down to watch their programme, only to find that changing channels or interrupting the programme for an advertising break requires them to adjust the volume control all over again.
ITU’s proposed new measuring technique will bring more uniformity to loudness in international programme exchange and make television viewing more pleasurable. Loudness variation has become more noticeable with the advent of digital broadcasting because of higher sound quality, so this development is expected to be eagerly received by industry and viewers alike.
Viewers often erroneously blame differences in loudness on careless sound technicians or deliberate policies on the part of broadcasters and advertisers. In fact, there are a number of technical reasons for differences in ‘loudness’ which are not currently easily controlled at the broadcast studio. When sound is measured on a technician’s VU meter, the equipment registers the strength of the electrical sound signal, which is not itself a direct measure of how loud the TV sound will be to viewers. Volume is also affected by other things such as the range (or degree of compression) of the sound.
To rectify the problem, broadcasters need a monitor or meter which displays ‘loudness’ (rather than electrical signal strength), and an agreement on a standard setting level for loudness, so that sound technicians everywhere can make the same adjustment. The draft new ITU-R Recommendation suggests how sound levels should be measured and set in international programme exchange to maintain more constant volume for viewers.
At its meeting in November 2009, Study Group 6 of ITU’s Radiocommunication Sector (ITU-R) agreed a draft new Recommendation for the standard audio setting in an internationally exchanged TV programme. This setting is termed the ‘target loudness’, and the new Recommendation establishes a numerical value.
Entitled ‘Operational practices for Loudness in the International Exchange of Digital Television programmes’, the draft Recommendation will now be submitted to national telecommunications administrations for approval.
The new standard complements existing Recommendation ITU-R BS.1770, which describes features of the ‘loudness meter’ that should be used by broadcasters to measure loudness. Work is underway to enhance BS.1770 with ‘gating functions’ in order to eliminate periods of silence or low-level signals that do not appreciably contribute to the perceived loudness of a programme, and this should be advanced at the next meeting of ITU-R Study Group 6 in April 2010.
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