Dynamic surround sound for DVB
Customers worldwide are demanding a higher quality of sound for digital television. Market figures for home entertainment systems clearly show that they like 5.1-channel surround sound, as illustrated by the rapid acceptance of Dolby Digital 5.1 sound on DVD. Since the launch of DVD-Video in 1997, more than 50 million DVD-Video playback units with Dolby Digital have been sold. So with DVD as a benchmark for the consumer, television services will be expected to deliver 5.1 digital surround sound as well.
Potential listening environments for a Dolby Digital bitstream.
Various steps already have been taken to achieve this. Early developments were driven by the United States, where Dolby Digital has been the audio standard for the ATSC HDTV system for a number of years. Then in July 1999, at the request of broadcasters and under pressure from consumers wanting 5.1 sound through their TV sets, the Digital Video Broadcasting (DVB) Project incorporated Dolby Digital technology into the DVB digital television standard.
A better viewing experience
5.1 audio offers the listener an all-encompassing entertainment experience. The term 5.1 refers to the five discrete channels of high-quality full bandwidth sound, plus a sixth ‘.1’ channel for powerful low-frequency effects that are felt more than heard. The five main speakers are typically positioned Left, Center, Right, Left surround, and Right surround. The multiple discrete channels enable more sharply-delineated spatial effects, and the “.1” LFE track makes it possible to reproduce low bass effects with stunning impact.
The significant adoption of 5.1 sound in the home has been fueled by the popularity of DVD. Dolby Digital 5.1 sound is available on the majority of DVD titles and all consumer DVD players contain a Dolby Digital decoder as standard. With a vast array of consumer hardware already in the market place that can decode Dolby Digital, the expectation of the 5.1 surround experience has been well set in the mind of the consumer.
For broadcasting digital television with 5.1 audio, DVB- and ATSC-based systems also use the Dolby Digital audio delivery system. In addition to encoding high-quality audio into a datastream at a bit rate suitable for broadcast, this system employs a unique and novel approach that enables better audio to be delivered to all receivers: from the largest 5.1 home theatre to the smallest mono and stereo TV sets.
When a conventional audio coding system like MPEG is used for DTV audio delivery, the audio dynamic range must be broadcast pre-processed for the lowest common denominator so that it can be passed to a mono TV set via the RF interface. Because no further adjustments are possible in the decoder, this same signal will be used in all other audio applications, such as hi-fi or home cinema systems, with the same limited dynamics. As a result, in the TV application, it offers no improvement in quality over FM and is arguably not as good as NICAM.
Dolby Digital employs metadata carried with the audio bitstream so that it can be optimized locally for a mono TV, the hi-fi or the home cinema system, as required. One transmitted Dolby Digital stream can therefore yield both an exciting dynamic 5.1 mix for the home cinema in the living room and a compressed mono or stereo version for the TV in the kitchen. Metadata also provides a solution for the longstanding problem of loudness differences between programs and channels, enabling all content to be normalized toward the same average loudness level without additional compression.
Currently on air
Since the addition of Dolby Digital to the DVB specification in 1999, broadcasters around the world have chosen to add 5.1 capability to their terrestrial, satellite and cable systems. The German satellite services ProSieben and PREMIERE WORLD were the first in Europe to offer 5.1 audio. ProSieben broadcasts with Dolby Digital audio 24 hours a day and shows feature films twice a week in Dolby Digital 5.1. In April 2001, PREMIERE WORLD launched Cinedom Deluxe, a direct-to-home pay TV service with Dolby Digital 5.1 audio, and more recently equipped its main service, PREMIERE One, with the ability to use Dolby Digital 5.1 for special events and feature film highlights.
In December 2001, the UK’s British Sky Broadcasting (BSkyB) became the latest satellite broadcaster to start transmissions in Dolby Digital. They already are screening 30 new movies with 5.1 soundtracks every month.
5.1 audio also is becoming an important feature in the promotion of terrestrial services. Australia was one of the first supporters of Dolby Digital, originally insisting in 1998 that Dolby audio should be included as part of the DVB standard. Three Australian networks already are on-air with Dolby Digital.
Several European terrestrial platforms also have chosen to adopt 5.1 sound. The French towerCast trial in late 2001 featured Dolby Digital as a key feature of its ‘value-added’ terrestrial DTV service. The Scandinavian Nordig receiver standard also mandates Dolby Digital, and Finnish broadcaster YLE was the first Scandinivian operator to broadcast a Dolby Digital terrestrial service back in August 2001.
Several more European broadcasters are expected to announce the addition of 5.1 audio to their services over the coming months. Dolby Digital also features in many of the standards being set for DTV broadcast in Asia including, for example, the terrestrial standard for Singapore.
More than 100 set-top boxes
Receiving 5.1 surround sound via DVB has become easier and cheaper over the last year. The number of set-top boxes available with Dolby Digital capability in Germany alone has rocketed to 100 different models from more than 20 different manufacturers. The cost of including the Dolby Digital decoding circuitry in consumer electronics products is lower than one might expect, as continued integration has led to the inclusion of the Dolby Digital audio decoder on the same chip as the MPEG video decoder, demultiplexer and control systems.
A great opportunity
Audiences worldwide are regularly experiencing 5.1 audio, not just in the cinema, but also in the home. The success of DVD in particular means that 5.1 audio is becoming the expected norm for digital entertainment media.
DVB digital TV services with Dolby Digital 5.1 surround sound already are on-air in several European countries, and are being planned as part of Asian standards. European broadcasters are already using the Dolby Digital logo as a key part of the marketing of their services. Including Dolby Digital decoding in a DVB set-top box or IDTV adds minimal extra cost, yet has a big impact in the mind of the consumer.
Digital TV presents a great opportunity to deliver better audio to the viewing audience. It is not only a chance to offer more involving, better defined digital surround sound, but also to move away from the heavily compressed sound that we have come to expect of broadcast television. This is only possible if we change the way we think about broadcasting audio and start delivering sound that is optimized for each and every listener rather than compromising audio for the lowest common denominator. With the success of Dolby Digital on DVD and now on DTV, the signs are that this change in thinking is already well under way.
Jason Power is market development manager for Dolby Laboratories.
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