Shown here is mixing down audio for tennis at the Athens 2004 Summer Olympics Games in the BBC’s OB vehicle 10.
5.1 surround sound
High-definition television services already are on-air in the USA, Japan and Australia. And with HD display sales gaining momentum, the inevitable question is: What is the future for HD in Europe? In the transition to digital broadcasting, the European industry took a somewhat different route than other regions, opting to offer a vast selection of standard-definition channels. It is only recently that launch plans have been made for HD services.
Fortunately, European viewers can already benefit from part of the “HD experience.” HDTV is not just about increased picture resolution; the overall experience is created by combining this with a more cinematic widescreen aspect ratio and immersive 5.1-channel surround sound. On some broadcast services in the UK and across Europe, viewers already can benefit from widescreen programming and full Dolby Digital 5.1 surround sound, even though the picture resolution is SD. This is the combination that has proved so successful on DVD in recent years.
For years, conventional broadcasts and video recordings have offered surround sound using a “matrix technology” called Dolby Surround. However, the advent of digital media enabled the creation of Dolby Digital, a digital soundtrack format designed to deliver an even more realistic and dynamic surround sound experience. Compared with matrix technology, it offers increased accuracy as sounds can be placed precisely around the listener. It also offers increased impact thanks to a dedicated low-frequency channel for effects that can literally be felt rather than just heard. Originally introduced into the cinema, Dolby Digital soundtracks can now also be enjoyed in the home by listeners with a digital home cinema system.
Creating 5.1 surround programming
The term “5.1” refers to the speaker channels used in the surround sound system: three front channels (left and right, plus a centre near the screen) to give a realistic sound that reflects the on-screen image; two surround channels (behind or to the side of the listeners) to immerse the viewers in the action; and the “.1” low-frequency channel for effects.
Dolby Digital is the standard audio format for DVD, and most major movie DVDs feature a 5.1 soundtrack. It is also the standard audio format for HDTV in the USA and Australia, as well as an option for digital broadcasts elsewhere. When used for broadcasts, it allows viewers to enjoy the cinema experience in their own homes when watching films, and to feel as if they have the best seat in the house for sporting events and concerts. In the UK, Dolby Digital 5.1 sound is offered by Sky on around 130 movies per month and can be received by any subscriber with a Sky+ box. Elsewhere in Europe, broadcasters as varied as Premiere, ORF, Sat.1, TVN, Pro7, Swedish Television, ZDF and Polish Television are all offering Dolby Digital 5.1 programming.
The need for metadata
The widespread adoption of digital audio workstations and mixing consoles has meant that the increased number of tracks and channels needed for surround sound production are now affordable and practical. Principles of recording and mixing soundtracks in 5.1 surround sound for post-produced genres such as drama are quickly becoming established, as techniques and tools can be borrowed from the film world and adapted to meet the timescales and budgets of television. In fact, many large-scale productions are already mixed in matrix surround for the television market, or even in 5.1 ready for subsequent release on DVD.
Similarly, some live events, including sports broadcasts, have been produced in matrix surround for some time. However, techniques for creating live content in 5.1 are now also starting to develop, as broadcasters begin producing sports and large events such as award shows and concerts with full 5.1 sound. In Europe, key innovators in live 5.1 programming have included Sat.1 in Germany, with its live coverage of UEFA Champions League football, as well as ORF, with its fantastic production of the famous “New Year Concert” from Vienna.
Whenever a 5.1 mix is created, it is important that the appropriate metadata be created to accompany it. The primary purpose of this metadata is to optimize replay of the soundtrack in each and every home receiver, in line with the wishes of the original soundtrack creator. In some situations, including on most DVD discs and in digital broadcasts in the USA, the 5.1 stream is the only audio that is included. The 5.1 stream is then down-mixed in any home receivers where a stereo or mono output is required, under the control of metadata. Metadata also enables the dynamics of the soundtrack to be tailored for playback on a small speaker system or late at night, again according to the wishes of the original production team.
Practical tools already exist to enable creation of metadata and auditioning of the effects in real time. Usually, metadata presets can be stored for particular genres of programming. So, in practice, only minimal adjustments are required whilst mixing.
As few professional videotape recorders are capable of supporting six audio channels, completed 5.1 mixes can be recorded on separate 8-track Hi-8 tapes. Alternatively, the Dolby E system can be used to record up to eight channels plus metadata in the space of a stereo track on a conventional videotape or server. Unlike Dolby Digital, which is designed for delivery to the home, Dolby E is a professional format that broadcasters use internally for contribution and distribution of 5.1 program using an existing stereo infrastructure. Many European broadcasters already are transmitting SD services with surround audio using Dolby E internally to simplify the internal routing, storage and processing of the audio.
Begin planning today
New HDTV services can be expected to take advantage of new codec technology to make the most efficient use of bandwidth. In addition to offering superb quality surround sound at an attractive data rate, broadcasters also need flexibility from their audio system. For example, they need to be able to add alternative languages or to provide new services for the visually impaired.
To meet these requirements, the DVB recently added Dolby Digital Plus, also known as E-AC-3, to its broadcast specifications. When partnered with next-generation video codecs such as AVC (also known as H.264 or MPEG-4 Part 10), an even more spectrum efficient stream can be created.
With new HD broadcasts on the way in Europe, many pundits are claiming that next year looks set to be an exciting year for HD. However, in the meantime, digital broadcasting is giving us at least some of the benefits associated with HD — widescreen and superior sound, a combination that has proved such a winner on DVD.
With European broadcasters now gaining experience in providing thrilling 5.1 surround soundtracks with their SD programming, there's every sign that 5.1 sound will be as important a part of HD here as it already has elsewhere in the world.
Jason Power is market development manager for Dolby Laboratories.