Hi-def also means audio

Next-generation HD discs are here now. HDTV is at our doors, HD-ready displays are high street’s hot items. However, high-definition entertainment is about audio as well as video, reminds JASON POWER, Dolby Laboratories’ Director of Market Development.

With High Definition discs beginning to arrive in the shops, and HD players appearing in homes, it is clear that the next generation of disc media is beginning to take hold of the marketplace.

Dolby TrueHD is set to have a large impact on the next generation of discs, offering studio quality performance and delivering it to the home. Essentially, Dolby TrueHD will provide a ‘bit-for-bit’ copy of the master with up to 7.1 channels of sound on both HD formats.

However, bit-for-bit audio does not meet the requirements of all applications. Restrictions in bandwidth for broadcast may be an issue, or it might be necessary for multiple soundtracks to be carried on a disc more efficiently than using a lossless audio technology. This is where Dolby Digital Plus comes in, allowing high quality multichannel audio delivery at a low bit-rate. Dolby’s next generation audio codecs will be the centrepiece of audio technology as the industry moves into an exciting new phase.

Dolby TrueHD AND NEXT-GENERATION DISCS

Dolby TrueHD is all about delivering the highest quality audio to the end-user, but without inflicting the storage problems caused by conventional PCM. Dolby TrueHD is 100% lossless codec, which means that every bit of data on the studio master is delivered to the home. Essentially, the viewer’s experience will be true to the director’s intentions, bringing cinema-quality sound into the living-room in all its glory as never before.

Dolby True HD was developed from MLP Lossless, a codec that provided 24bit 96kHz 5.1 audio on DVD Audio discs. Dolby TrueHD is more efficient than MLP which means it takes up a lower percentage of the available space on a disc. TrueHD can deliver lossless 16bit 48kHz 5.1 audio with a smaller file size than that of some current generation lossy codecs. This, combined with the increase in capacity of the next-generation discs over DVD, means that there is more room for producers to add bonus content, additional language tracks, and audio descriptive tracks.

This commitment to quality and low storage demands allows the optical disc industry to differentiate itself from high definition TV services. Not only is the bitrate at which TrueHD operates unfeasible for broadcast, but it also supports the maximum 7.1 audio channels specified by both Blu-ray and HD DVD. This offers the ultimate audio experience possible at the moment, but the TrueHD decoder is actually capable of supporting up to 14 channels, which allows it to support most of the significant speaker placements as defined under SMPTE448 for future digital cinema layouts. Dolby TrueHD is not only cutting edge today, but will remain relevant into the future.

Dolby TrueHD has gained acceptance in the marketplace; it is included in both Blu-ray and HD DVD specifications; has been built into all of the current generation of HD DVD and Blu-ray players including Sony’s PS3; and is being included in the very latest AV equipment alongside its companion codec, Dolby Digital Plus.
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Dolby DIGITAL PLUS

Dolby Digital Plus is a development of Dolby Digital, the DVD audio standard. Dolby Digital Plus is an extremely versatile codec, capable of delivering 5.1 audio at bitrates as low as 200Kbps and as high as 6Mbps. This versatility has seen Dolby Digital Plus gain great interest in DTT, HDTV and IPTV markets.

Dolby Digital Plus raises the bar on audio quality for applications where bit-rate is an issue. Natively supporting 7.1 channels for HD discs, Dolby Digital Plus still offers full compatibility with the 50 million plus Dolby Digital 5.1 home theatre systems already sold thanks to a converter feature in the decoder.

Both Dolby TrueHD and Dolby Digital Plus are compatible with HDMI 1.3, and are prepared for the next generation of home theatres and A/V amplifiers. It is hoped that disc producers will use Dolby TrueHD to deliver a lossless main soundtrack, with a Dolby Digital/Dolby Digital Plus version of the main soundtrack (depending on the disc format) to maintain compatibility with existing home A/V equipment, and Dolby Digital/Dolby Digital Plus encoded alternate soundtracks for director’s commentaries and any extra features.

The flexibility offered by this solution is vital to the next generation of digital content as it will increase quality, maintain expected numbers of extras and still keep the storage demands realistic.

METADATA

Both new codecs carry metadata in the same way Dolby Digital does. Metadata, which is information and instructions controlling the audio data, is carried in each Dolby Digital, Dolby Digital Plus and Dolby TrueHD frame. It is used to optimise the audio to ensure the best possible playback on any type of audio equipment; be it mono, stereo, 5.1 or top end home cinema 7.1.

Primarily metadata offers three main controls: Dynamic Range Control, Dialogue Normalisation and Downmixing.

The Dialogue Normalisation (DialNorm) value aligns the average dialogue level of all programmes. Dynamic Range Control is then used to limit how much room the loud and soft parts of a programme have above and below the dialogue, which ensures that the programme will still sound good even on playback equipment with a small dynamic range. Downmixing is the presentation of a soundtrack in less channels than the original mix, and this metadata control allows the mixer to determine exactly how the multichannel audio will sound when played out through stereo or mono equipment.

Dolby MEDIA PRODUCER & CONTENT MASTERING

Having the ability to deliver multiple high-quality audio soundtracks, disc producers now face the problem of how to create the content. Dolby Media Producer is a software-based suite of tools that enables audio professionals to master productions for DVD, DVD-A, HD DVD and Blu-ray.

Dolby Media Producer is made up of three elements: Dolby Media Encoder, Dolby Media Decoder and Dolby Media Tools.

Dolby Media Encoder is now available in two versions: There is the server-based Media Encoder which allows three or more clients to submit jobs; and there is Media Encoder SE which has the same feature set, but has been optimised to run on a single computer.

Dolby Media Encoder simplifies the preparation of encoding jobs by limiting the choices of the user depending on which format and codec they have chosen, and offers full control of the encoding process via a simple GUI. It enables producers to import their audio files from a mixing programme set their metadata parameters, add a timecode and datastream information, and set their downmixing controls. Then, once the desired settings are achieved, which can be saved as a preset if required, the automatic encoding process begins at the touch of a button.

Completed files can be played back via Dolby Media Decoder, a professional reference decoder that can playback and monitor any Dolby Digital, Dolby Digital Plus, MLP Lossless or Dolby TrueHD file. Optimised for a single machine, Dolby Media Encoder, when used in conjunction with a professional 5.1 soundcard, can provide reference-quality playback and decoding for an individual audio room.

All consumer listening modes, including stereo, mono and 5.1 are supported, alongside other metadata variables such as dynamic range control. It can, in addition to the four digital formats, decode Dolby ProLogic II, Dolby ProLogic and Dolby Surround EX files.

Dolby Media Decoder provides transport control via standard 9-pin protocol for checking of A/V sync with video during QC of either source or encoded files.

Dolby Media Decoder also offers Dolby Headphone encoding so a realistic 5.1 listening environment can be created using a pair of quality headphones.

Dolby Media Tools can save time and money by allowing users to repair and update previously encoded files without having to re-encode them. Features include metadata editing, file trimming, time code striping and file concatenation. These features allow users to manipulate encoded files without the need to decode them to PCM first. Like Dolby Media Decoder, Media Tools is optimised to run on a single computer.

SUPPORT AND TRAINING

To assist audio professionals incorporate cutting edge Dolby technologies into their working practices, Dolby have developed an Approved Training programme. This is a wide range of courses that cover all aspects of Dolby technology including Dolby Surround ProLogic and ProLogic II, Dolby E, Dolby Digital, Dolby Digital Plus and Dolby TrueHD as well as implementation, installation and operational courses designed to educate users in how to get the best results from Dolby technologies.

The Dolby Approved Training courses are available from Dolby-trained instructors at many of our distributors around the world and, combined with Dolby Support, now allows production staff to get the training and back up they may need.

With High Definition, pictures are the initial attention-grabber, but it is high-quality audio that really completes the experience. Many broadcasters are adding 5.1 audio to their HD broadcasts and more and more HD games are being supplied with Dolby Digital soundtracks. HD discs are also proving popular as consumers actively seek out HD content to enjoy.

The toolkit of Dolby Digital, Dolby Digital Plus and Dolby TrueHD allows producers to choose a codec appropriate to their requirements; DVD, DVD-A, HD DVD or Blu-ray – all are supported by one or more Dolby technologies.

Dolby Digital Plus and Dolby TrueHD aim to deliver audio that complements the high-definition picture, but without excessive bandwidth and storage demands. Together they offer compatibility for both existing and future equipment, as well as ease of use for the consumer. The future of HD is bright, and now it sounds exciting as well....

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