DTV Audio Update 

From Dolby Laboratories | June 2008 | Vol. 9 No. 2

Over the last 18 months, various European industry groups—including DVB, the EBU, EICTA, and various national HDTV specification forums—have considered the selection of audio coding systems for next-generation HDTV broadcast applications using MPEG-4 video. Two standardized audio coding systems, Dolby Digital Plus (also known as E-AC-3) and HE-AAC (also known as aacPlus), have been highlighted as particularly suited to these next-generation transmissions. The EBU Project Group D/MAE, for example, concluded that the two coding formats are the best candidates for broadcasting HDTV audio services via satellite, cable, terrestrial, and IPTV networks.

Due to the diverse requirements of different broadcasters and operators, and the differing feature sets of these technologies, the industry groups have refrained from recommending a single audio system that suits all applications. For example, Dolby Digital Plus currently offers comprehensive support for 5.1-channel sound, as well as advanced metadata support. In the near future aacPlus by Dolby* will also offer this support, along with its already formidable coding efficiency, which today enables quality stereo services to be transmitted at extremely low data rates.

European HDTV Receiver Specifications
As DVB does not specify which audio codec should be used for next-generation broadcasts, various broadcast and manufacturer groups have recently worked collaboratively to gain consensus on the formats desired by broadcasters, formats that will then be included in new European receivers. In the table below, find the key outcomes for multichannel format requirements so far.

In addition, more than 200 European TV services already broadcast with conventional Dolby Digital audio, so next-generation receivers typically need to be compatible with this format.

New aacPlus by Dolby Broadcast Solutions
In November 2007, Dolby acquired Coding Technologies, the leading contributor to the HE-AAC standard. Dolby intends to bring to market enhanced solutions that will simplify and extend the use of this technology in all broadcast environments. In addition to enabling new professional encoding tools offering full compatibility with Dolby E and Dolby Digital metadata, we are also developing new multichannel decoder implementations—including a combined Dolby Digital Plus and aacPlus by Dolby decoder—that will make it easier and cheaper for receiver manufacturers to meet the requirements of European markets. Find out more about Dolby’s coding solutions. If you need additional information, please contact us.

* When released, aacPlus by Dolby will conform to the MPEG standard, and offer to broadcast and consumer equipment manufacturers optimized software solutions and metadata support.

Multichannel Format Requirements in European HDTV Specifications

Addressing DVB Audio Levels

Level differences between TV channels are an ongoing annoyance for television audiences. Dolby Laboratories is working in a number of areas to overcome this problem. Recently, we released Dolby® Technical Bulletin 11, an application note concerning a level issue specific to DVB services. The bulletin summarizes our findings in the area of loudness levels differences between MPEG-1 LII and Dolby Digital Plus audio.

For a number of years, Dolby has been working with the EBU as a member of the B/MCAT Project Group on improving the technical aspects of multichannel audio broadcasting. Until Dolby Digital was first introduced to digital television in Europe in the late 1990s, broadcast audio had been limited to stereo. At first, the only way to successfully transmit 5.1-channel Dolby Digital audio was to add the 5.1 bitstream to the existing program stream (which consisted of video and MPEG-1 LII audio). The Dolby stream benefits from dialogue normalization metadata, however; MPEG-1 LII audio coding does not.

European viewers with a set-top box connected to a home theater A/V receiver encountered a significant level difference between the two audio formats. The Dolby Digital bitstream (after having passed through the set-top box) was being decoded and attenuated in the A/V receiver, while the PCM audio from the MPEG-1 LII stream was output without any attenuation. [In DVB broadcast systems, the programming carries the MPEG-1 LII stereo audio track with a typical average loudness around –20 dBFS Leq(A), a level difference of almost 10 dB when compared to Dolby Digital at –31 dBFS.]

This issue became increasingly apparent during the significant uptake of Dolby Digital in DVB over the last ten years. Fortunately, though, the Dolby Digital or Dolby Digital Plus decoder implemented on every DVB HD and SD broadcast device can be exploited to provide a relatively simple solution to this issue.

On a given decoder, RF mode can be called, boosting the playback level of Dolby Digital to –20 dBFS (instead of –31 dBFS). In RF mode, the average level of Dolby Digital is much closer to that of MPEG-1 LII. For audio over S/PDIF and HDMI™ digital outputs, PCM audio can be cut by 11 dB, while passing the Dolby Digital bitstream unaltered. This approach ensures uniform levels on the outputs of the broadcast device, as well as when listening to the audio through a connected A/V receiver.

Technical Bulletin 11 provides specifics on how to implement these corrections, and is available to all Dolby licensees. The mode change in the decoder can be activated via an over-the-air update for devices and platforms already in use. Although these solutions do not completely resolve the issue, they offer an easy and effective fix, simply by calling an operating mode that is present in every Dolby Digital decoder around the world.

Euro 2008 Soccer Hits European Screens Live in HD and Dolby Digital 5.1

The UEFA Euro 2008™ soccer tournament is kicking off a summer of sport that will be a centerpiece for many of Europe’s new HDTV services. In common with other recent international sporting events—such as the soccer and rugby world cups—every match of Euro 2008 is being produced live in HD with 5.1-channel Dolby® Digital sound. New European channels offering fans the HD experience complete with Dolby Digital 5.1 include BBC HD in the UK, HD suisse in Switzerland, ORF in Austria, Sogecable in Spain, M6 and TF1 in France, and ARD in Germany, as well as the EBU.

To facilitate the coverage, a newly implemented surround microphone is being used to capture the ambience at each of the eight stadium venues across Austria and Switzerland. A rough audio mix is created using Dolby E and sent to the International Broadcast Centre in Vienna, where a dedicated 5.1 mixing studio is used to optimize the mix and ensure consistency across all venues. Finally, the mix is encoded in Dolby Digital, ready for distribution to rights-holder broadcasters via the EBU’s Eurovision satellite network.

To augment the live production sound, official Euro 2008 music has been created in 5.1 by acclaimed UK-based producer Rollo Armstrong of the band Faithless. According to Dan O'Toole, Brand Manager of the Union of European Football Associations, "As the filming and broadcast of the finals will be available in HD with 5.1 sound, the music has also been specially mixed with Dolby E surround sound to accompany the high-definition match action and fan imagery."

Find additional information on Euro 2008.

New Product Introductions and Tektronix Cerify Partnership Highlighted at NAB

At the 2008 NAB Show™, demonstrations at both the Dolby and Tektronix booths highlighted how the Dolby® DP600 Program Optimizer and Tektronix® Cerify® systems can be used together to provide a complete solution for analyzing file-based programming. In the automated quality-control demonstrations, top-level analysis of a multichannel soundtrack encoded in Dolby E was performed by Cerify; the programming was then automatically routed to a DP600 for detailed audio analysis and loudness correction.

Dolby has become a member of the Tektronix Cerify Developer Community, joining other member companies such as Omneon, Pro-Bel, Telestream, and Thomson. Learn more about Tektronix Cerify.

At NAB, we also demonstrated the new upmixing functionality for the Dolby DP600 Program Optimizer units. An optional software upgrade for the DP600 and DP600-C versions adds intelligent file-based upmixing functionality, allowing them to automatically create 5.1-channel programs from stereo or matrix-encoded Lt/Rt audio sources. The upmixing easily integrates into a DP600 work profile along with loudness correction, encoding, decoding, or transcoding functions.

Finally, we demonstrated Dolby Media Meter ($795 MSRP), our new loudness measurement software that can be integrated into Mac® and Windows® platforms. Well-suited to the needs of both broadcast and postproduction facilities, it is based upon technologies used in the Dolby DP600 Program Optimizer, including Dialogue Intelligence™ and the ITU-R BS.1770-1 algorithm. Dolby Media Meter can be used for loudness measurement in everyday applications such as program creation, postproduction, and quality control, and is perfect for optimizing broadcast, packaged media, VOD, and game media.

 Sound Bytes

The Window Channel Broadcasts in HD and Dolby Digital 5.1

The Window Channel has created a library of ambient programming produced in high definition with accompanying Dolby® Digital 5.1 surround. The content is currently offered to hotel operators for providing guests with soothing in-room entertainment. One scene follows a sunrise over Haleakala National Park on Maui. Hotels can also commission custom work that promotes the hotel property, amenities, services, and the brand. Learn more about the Window Channel.

China's BTV Olympics HD Channel Launches in Dolby Digital 5.1

On May 1, in anticipation of the upcoming 2008 Summer Games in August, China’s Beijing TV launched its new BTV Olympics HD Channel with 5.1-channel Dolby Digital.

Dolby at BroadcastAsia 2008 

At the BroadcastAsia 2008 conference, held June 17–20 in Singapore, Dolby showcased the DP600 Program Optimizer and LM100 Broadcast Loudness Meter products for broadcast audio loudness control.