HD FOCUS

During the last year or so there has been tremendous excitement surrounding the introduction of two High-Definition media formats, Blu-ray and HD DVD. The advent of a new visual experience has sparked media and consumer imaginations, which has somewhat overshadowed another revolution in the world of audio technology.

Increased capacity afforded by the two new HD formats has allowed the two main players in the audio arena, Dolby and DTS to offer not only four new audio formats but to increase the number of audio channels.

Part 1 of our introduction to High Definition Audio examines the formats available and which ones you are likely to find on your Blu-ray or HD DVD disc and why. Part 2 looks at the practical implications and guidelines for getting the most out of the new formats.

What are the benefits?

The highest quality audio formats, Dolby TrueHD and DTS HD Master Audio offer acoustic quality that is on a par with the original movie soundtrack. Measured in Mega Bits Per Second (MBps). The higher the rate, the better the quality.

5.1 surround sound on DVDs refers to a multichannel soundtrack that is split into five discrete channels of digital sound information. A sixth channel is reserved for the subwoofer, and is referred to as the .1 in a 5.1 soundtrack. The new audio formats offer more discrete channels, with the potential for a vastly improved surround sound experience.

Dolby Sound

To most people who have had anything whatsoever to do with DVD's or movie going in general the name 'Dolby Digital' is synonymous with sound. Virtually any widely available acoustically enabled device on the planet has the ability to decode Dolby Digital. Surprisingly, many audio enthusiasts believe that Dolby's rival DTS has a sound format that is superior to Dolby's at least within the confines of normal DVDs.

But things have moved on, and the new battleground is the High Definition arena, where the competing formats can potentially fulfil the promise of there respective technologies unrestricted by the confines of limited capacity.

Dolby Digital

So why are we beginning a discussion on new High Definition sound formats with Dolby Digital? The reason is that depending on what film or format you are watching, the soundtrack could potentially be Dolby Digital. The multi-channel sound technology used on most DVDs and capable of delivering 5.1 channels of sound is mandatory on Blu-ray discs while Dolby Digital Plus is optional.

With HD DVD, Dolby Digital, Dolby Digital Plus, or Dolby TrueHD can be used as the only soundtrack on the disc, as every player will have a decoder capable of processing any of those three formats (remember, HD DVD players have to be able to play any of the three formats above, but the HD DVD disc only need to provide one or more of the compatible soundtracks).

Dolby Digital Plus

The first of Dolby's new digital formats 'Dolby Digital Plus' (DDP) builds upon the company's established 'Dolby Digital' DVD format with potential bitrates of up to 6Mbps. The technology is a mandatory feature of the HD DVD format and an optional one on Blu-ray. Although there is potential for 6Mbps, HD DVD currently supports a 3Mbps rate with Blu-ray offering 1.7Mbps.

The most interesting aspect of DDP is that it can support up to 13.1 channels of discrete audio. HD DVD and Blu-ray currently support up to eight channels making DDPs extra capacity somewhat arbitrary, but Blu-ray and HD DVD technology does have the potential for expansion which could take advantage of 13.1 channels at some future point in time.

Dolby TrueHD

Dolby's other new high-definition format is a lossless one which bit for bit is identical to the original studio master. Based on MLP lossless technology, TrueHD offers bitrates of up to 18Mbps. Dolby TrueHD is downward compatible with Dolby Digital, giving existing kit with Dolby Digital a TrueHD compatibility.

A mandatory feature of the HD DVD format and optional for Blu-Ray, Dolby TrueHD has already appeared on some High Definition discs - notably Harry Potter and the Goblet of Fire and Constantine.

DTS HD

DTS is a 'lossy' format which has the potential to deliver 7.1 channels of sound at bitrates of up to 6.0Mbps on Blu-ray and 3Mbps on HD DVD with a resolution of 96Hz/24bit.

The DTS-HD High Resolution Audio bit stream is equipped with the DTS 1.5 Mbps core for compatibility with existing DTS-enabled home theatre systems, facilitating delivery of 5.1 channels of sound at more than twice the resolution found on most standard DVDs.

DTS-HD High Resolution Audio is optional on both the HD DVD and Blu-ray formats

DTS HD Master Audio

Bit-for bit, DTS-HD Master Audio delivers sound that is identical to the studio master. Delivering audio at very high variable bit rates which are much greater than standard DVDs. DTS-HD Master Audio has the potential to provide up to 7.1 audio channels at 96k sampling frequency / 24-bit depths which is identical to the original.

The DTS-HD Master Audio bit stream is packaged along with the DTS 1.5 Mbps core for compatibility with existing DTS-enabled home theatre systems, facilitating the delivery of 5.1 channels of sound at more than twice the resolution found on standard DVDs.

DTS-HD Master Audio is optional for both the HD DVD and Blu-ray formats.

What does all this mean?

As we can see, the new High Definition sound formats are full of potential, but are already generating a fair amount of confusion in their implementation and availability.

Although very unlikely, consumers may find many of their HD discs sporting a 'Dolby Digital' soundtrack and nothing else.

In reality, lots of high quality soundtracks in various formats will become available, and this is bound to generate a huge amount of confusion surrounding the hardware consumers should think about buying to support the new audio formats.

To give you some idea of potential conflicts, Panasonic's DMP-BD10 currently supports Dolby Digital Plus and TrueHD while the Samsung BD-P1000 supports none of the new formats.

So how can you make sure that the kit you own or are thinking of buying is compatible with or can be adapted to use with your preferred audio format?

Part 2 of our guide to High-Definition Audio Technology next month will guide you through all you need to know to make the most of the new audio formats ...