Articles and whitepapers

IPTV: The Advantges of Dolby Digital Plus (1/12/2006)

By Jason Power, Dolby Laboratories

Internet Protocol Television (IPTV) is expected to grow at a staggering rate, with an anticipated increase of more than 200% in the UK by 2010. Although much has been spoken of next-generation video coders like H.264 and Windows Media, consideration of the appropriate audio technology is vital, both in terms of attracting viewers and building strong technology that can deliver the right audio features now and in the future.

A Sound Experience

Consumers are increasingly expecting quality surround sound from all of their entertainment experiences. Over 7,500 movies and almost all Hollywood titles and major domestic releases are now created in Dolby Digital 5.1, as are entertainment series such as Lost, ER and 24, and premium programming like natural history and documentaries. Broadcasters are also starting to add the excitement of surround sound to their premium sports coverage. Events as varied as the Superbowl and German Bundesliga soccer have been produced and broadcast live in 5.1, transporting the viewer at home right into the middle of the action.

Having grown accustomed to being immersed in the action, whether it be a film with bullets whizzing past your head, a game where you can hear your enemies creeping up behind you, or a concert where you feel as if you are part of the audience, consumers are increasingly expecting the cinematic entertainment experience offered by digital 5.1-channel surround sound in all of their media environments.

IPTV Services beginning to launch across Europe are recognising this. French services Free and Neuf, and Fastweb in Italy have all incorporated Dolby Digital 5.1 surround sound as a valuable added feature to their services.

So with the expectations of viewers set so high, can IPTV operators really afford to ignore the audio?

Specific issues for IPTV

For IPTV applications, bitrate and bandwidth preservation are key issues to be resolved. IPTV services need to make difficult decisions about what quality levels and features will be appreciated most by their customers. Any audio solution for IPTV needs to deliver high quality sound, not Internet-quality sound, but given these bandwidth limitations, it will need to achieve this at a low data rate of around 200kb/s.

To deal with this, Dolby has developed Dolby Digital Plus, which enables the same 5.1 channels of surround sound to be transmitted at an IPTV-friendly data rate, leaving space for other elements such as video, telephony and the Internet. This is significantly lower than the data rate used to transmit 5.1 surround sound with conventional digital broadcasts.

Having said that, adding 5.1 audio doesn not always require as much bandwidth as people seem to think. To start with, it is not necessary to deliver separate 5.1 and stereo audio streams. Using Dolby Digital Plus, a single data-efficient 5.1 audio stream is delivered to each set-top box. This is then downmixed inside the box to output soundtracks in 5.1, stereo and mono to suit viewers with different equipment.

Secondly, next-generation audio coders like Dolby Digital Plus have been designed specifically to partner with new video coders like H.264, offering even more attractive data rates for audio to match the savings for video. This means that home cinema audio can be delivered using data rates practical for IPTV.

However, it is vital that the right audio technology is included in IPTV set-top boxes from the beginning of deployment. If it is not, operators who subsequently decide that they need to offer 5.1 might end up having to 'simulcast' separate stereo and 5.1 audio streams to ensure that all viewers can receive audio, exacerbating the date rate constraint problems.

It is also critical that good connectivity is provided to output the encoded 5.1 audio stream to viewers' existing home cinema systems. As many home cinemas only have inputs for encoded digital audio, rather than decoded multichannel audio, it is important that the connection format is supported by the maximum number of systems to maximise the audience that can enjoy full surround sound.

Audio possibilities

Audio is already perhaps more important in the marketing of TV services than it has ever been before. But the future brings further possibilities - delivery of soundtracks with 7.1 or even more channels, multiple language versions, streamed director commentaries to be overlaid over the main soundtrack and improved audio for the visually- and hearing-impaired, to name but a few.

But for today, it is critical to note that the audience already has an expectation for home cinema audio with their TV entertainment, not Internet-quality audio. Fortunately, if the audio solution used by their IPTV supplier has been chosen carefully, they won't be disappointed.

Jason Power is the Market Development Manager for Dolby Laboratories. Dolby Laboratories develops and delivers products and technologies that make the entertainment experience more realistic and immersive. For four decades Dolby has been at the forefront of defining high-quality audio and surround sound in cinema, broadcast, home audio systems, cars, DVDs, headphones, games, televisions, and personal computers.

www.dolby.com