(22 June 2007 8:40 pm)

SINGAPORE: IPTV services can now be operated at increasingly attractive data rates, thanks to recent advances in video and audio coding – but there are many other roadblocks on the way to providing successful audio in a new service.

Additional considerations have been discussed including flexibility to provide audio across the variety and quality range of today's home systems; benefits for the viewer at home; reasonable royalty; reliable performance in the home; interface with the upstream broadcast system equipment and people already in place; and plausible provision for the foreseeable future.

Addressing a session at BroadcastAsia, Dolby Laboratories' Thomas Spath said sound quality was largely the sole criteria in judging the technology or equipment that should be used to deliver audio. There were new demands on audio production and delivery as costs were squeezed and efficient programme production became imperative. Digital technology brought improvements in delivered quality and production techniques but this also mean a rise in expectations as far as the consumer was concerned – placing challenges before broadcasters to meet newer sets of requirements.

A significant consumer requirement at present was for digital surround sound which was broadly accepted as an essential ingredient of quality entertainment. In Europe, 32 per cent of homes have a digital surround system. Surround is also very popular in middle class homes in major cities in Asia, and broadcasters in both Beijing and Shanghai have been regularly transmitting programmes with 5.1 audio for almost a year.

"Surround has definitely arrived. With the roll-out of HD pictures and a new delivery pipeline in IPTV, we see the most significant opportunity to implement new technology since the start of digital TV in the 1990s. Such opportunities - to raise the standard in essential broadcast technologies without the concern of maintaining compatibility with set-top boxes (STBs) already in the field - do not come every day," he said.

Standards have already been set for next-generation audio in HD services and IPTV and operators now need to choose which audio offers them the best solution for new services.

Consumers want bandwidth efficiency and resulting audio quality, flexibility to provide good audio across the variety and quality range of today's home systems, benefits for the viewer at home, surround sound, additional audio features, consumer confidence in the new system, compatibility with products they already use, reasonable royalty cost, and consistent performance.

Experience has shown that following a specification is not an indication that products will always perform predictably. An end-to-end test of a representative selection of TV receivers and home audio systems is recommended, whatever audio technology is chosen for broadcast.

Over and above the surround sound experience, the viewer wants consistent loudness and easy connectivity. The ability to define at source the perceived loudness of a programme is essential, both for level matching between programmes, and to provide the reference point for good-sounding user-optional dynamics processing.

Audio enthusiasts will demand more audio channels, 7.1 being the next logical step. Although at present no mainstream content is produced in 7.1 or higher channel configurations, new disc formats can already carry this. Building this capability into an audio format for broadcast means it can be used when it is practically viable and makes business sense. New audio technologies, such as HeAAC and EAC-3, have recognised this and include the capability to do more than 5.1 channels.

But new features such as Hearing Impaired and Visually Impaired audio services are also in demand. In some applications these are legal requirements. AC-3 allows this feature through the use of two decoders, but this effectively doubles the audio royalty cost, making this feature unpalatable for broadcasters in vertically integrated markets and penalising those who benefit from such services.

AC-3 (Dolby Digital) is applicable today, but simply changing the encoder at the head-end will allow the use of another audio technology in future, provided that the metadata carried in Dolby E can be ported to the encoder in use as it is today with AC-3. This is the metadata used to ensure optimised replay of broadcast audio in the home and to match loudness of broadcast programmes.