Bit Rates For HD DVD And Blu-ray Discs
Dear Gary:
I have a dedicated home theatre setup, and I’m seriously considering purchasing a second-generation Toshiba HD DVD player. I have a Lexicon® MC-8 surround processor that doesn’t have HDMI inputs, but it does have 5.1 analog bypass. However, if I use the analog inputs to play back high-resolution audio, I lose Lexicon’s wonderful 7.1 surround processing and bass management. I feel these 7.1 Lexicon features are very important in presenting an immersive and realistic audio experience to an entire home theatre audience, versus to a solitary listener sitting in the “sweet spot” of a 5.1 configuration.
It has been suggested that choosing to continue with a standard S/PDIF digital connection (rather than analog bypass) may be less of an audio quality compromise with Blu-ray Disc and HD DVD because I might be able to get Dolby® Digital and DTS® at full bit rates (640 kbps and 1.5 Mbps, respectively), which would be an improvement over standard DVDs. In addition, I was informed that Dolby TrueHD and uncompressed PCM tracks are currently truncated to 16 bits, while the Dolby Digital/DTS tracks come off the full 24-bit masters. So, for now, the audible differences between full bit rates over S/PDIF versus truncated Dolby TrueHD via analog bypass might be rather limited.
It would seem that, even without an HDMI connection or analog bypass, for now I might still benefit from both improved video and audio quality if I were to purchase an HD DVD player and if HD discs with 640 kbps and 1.5 Mbps bit rates were available.
Therefore, I decided to check Widescreen Review’s comprehensive database of DVDs to see if I could purchase any HD DVDs with improved bit rates. I was gratified to see that you had started to catalog new HD DVD and Blu-ray Disc releases, however, in reading the detailed information I see that although bit rates are planned for, they are not currently available. A review of the listings also prompted a few of questions that I hope you might clarify.
For example, on Lara Croft: Tomb Raider, it lists: Disc Soundtrack: Dolby Digital+ 5.1, 6.1, 7.1, DTS 5.1.
Does this mean that this HD DVD disc actually contains up to eight discrete channels of Dolby Digital Plus?
If so, do you know whether currently available HD DVD players can pass eight channels to suitably equipped receivers/preamps?
The listing only lists Dolby Digital Plus—in the interest of completeness should it also have listed standard Dolby Digital 5.1, or is it assumed if you have Dolby Digital Plus, you must also have standard Dolby Digital?
Is the absence of bit rates in your detailed listings due to the fact that the studios aren’t releasing this information?
Is it possible for your technical staff to request this information or measure the bit rates?
I noticed that you didn’t rate the sound quality for standard Dolby Digital tracks. Is it your plan to rate the sound quality of standard Dolby Digital tracks on HD DVD or Blu- ray Discs if they have bit rates in excess of the original standard DVD releases?
Lawrence Chanin
Managing Editor Danny Richelieu Comments:
That is one of the major problems with using the analog outputs from next-generation optical disc players—most processors do not touch the 5.1 (or 7.1) analog inputs, attempting to maintain signal accuracy by bypassing all internal converters and DSPs. I asked Andrew Clark, Vice President of Product Management at the Harman Specialty Group, if an update to the MC-8 would be available to include HDMI compatibility in the future, but it looks like it will not: “We will eventually have HDMI implemented across the board [for all Lexicon® products], but the MC-8 and MC-4 will not be modified to add HDMI I/O [input/output]. Doing so is a fundamental architectural change and is nearly as time consuming as designing a new product from the ground up. So rather than try to update the MC-8, we are pursuing other options that we are not yet ready to discuss publicly.”
It has been my conclusion, from listening to the advanced audio codecs compared to the legacy codecs, that, even at their full bit rates, Dolby Digital and DTS Digital Surround™ will not provide a listening experience like that which you can get from the advanced codecs. While the differences are relatively minute now, and in systems that do not have similar performance quality as our Reference Holosonic™ Spherical Surround™ Home Theatre Laboratory they may be difficult to hear at all, that does not mean future releases in TrueHD or PCM (or DTS-HD Master Audio for that matter) will be limited to the truncated 16 bits. And, in the case of some Blu-ray Disc releases (Buena Vista’s Glory Road and Touchstone’s Gone In Sixty Seconds are examples), there have been titles that have been released with 24-bit, 48 kHz PCM encodings on the disc, which provide noticeably improved dynamic range over the Dolby Digital encodings.
We do intend to include the bit rate information in our comprehensive online database, once we have players, or a processor, that will give us this data. Our only option now is to contact the studios directly, and getting that information from them is not an option that is consistently available.
Thanks for pointing that out, Lawrence. Our database now has separate fields for Dolby Digital Plus 5.1, 6.1, and 7.1, as well as separate fields for DTS-HD and Dolby TrueHD for all three-channel configurations. Lara Croft: Tomb Raider (as well as most of the titles released in HD to date) only has six (5.1) discrete channels encoded in the soundtrack, and is now listed that way in the database. All titles have been corrected in the database to accurately represent how many channels are available.
As of this time, there have not been any HD DVD or Blu-ray Disc players released that include analog outputs for 6.1- or 7.1-channel encodings, but all of the players (to my knowledge) will deliver the 6.1- or 7.1-channel information through their HDMI outputs digitally.
Unlike DTS-HD High Resolution Audio and DTS-HD Master Audio, Dolby Digital Plus does not also include a core encoding of the legacy codec (in the case of Dolby Digital Plus, Dolby Digital; in the case of DTS-HD, DTS Digital Surround). So, yes, in the interest of completeness we should have listed the standard Dolby Digital encoding, if it is included on the disc. We have also made this change in the database, and will continue listing this for future releases. Thanks for finding these problems in our database.
It has been our policy to not rate the Dolby Digital encoding found on newly released HD DVD or Blu-ray Disc releases if a more advanced codec is used on the disc as well, as it is a given that the encoding will sound at least marginally better than the DVD’s encoding, assuming a higher bit rate was, in fact, used.
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