Help Documents

The Blu-ray high definition disc formats not only provide great looking video, but they also provide higher quality audio possibilities as well.

The familiar DVD sound formats from Dolby and DTS are still available, and each have been enhanced with higher quality versions as well as lossless versions that provide bit-for-bit reproduction of the master audio source. Additionally, both formats have the ability to provide audio in PCM format, which is a multi-channel, uncompressed, lossless copy of the master audio source.

With these new capabilities comes the question of whether your existing receiver, or one that you are planning to purchase, is fully capable of accepting the audio these formats have to offer.

Will you have to buy a new receiver? Is the receiver you're looking at capable of making the most of the sound present on Blu-ray? Read on to find out!

For a run-down of the Dolby and DTS sound formats that can be found on HD DVD and Blu-ray, please see the following documents:

• Dolby Digital Sound on HD DVD and Blu-ray Explained
• DTS Digital Sound on HD DVD and Blu-ray Explained

Regardless of the audio format present on an HD DVD or Blu-ray disc, there are some fundamental differences in how the audio is handled on these new formats vs. what has been done in the past with DVD.

New interactivity and other features are available on HD DVD and Blu-ray, which necessitates that the movie's audio be mixed with other audio sources, such as secondary tracks (like from the Picture-in-picture commentary) and menu audio. This mixing makes it difficult to just send the Dolby Digital or DTS audio from the disc straight out through the player's audio outputs, since the players would need Dolby/DTS encoders to re-encode the data.

There is also the issue with the traditional coaxial and optical digital audio links that go from the player to the receiver. The data rates of some of these new audio formats exceed the capability of the optical/coaxial link, and most receivers do not have the ability to decode these new formats anyway.

So the simplest approach is to have the player decode the audio, mix in the extra audio needed, and send that audio out of the player in decoded multi-channel fashion through the HDMI and/or analog audio outputs.

How HD DVD and Blu-ray Players Output High Resolution Audio

To send the audio via HDMI, the receiver needs to be able to accept multi-channel PCM audio via HDMI. Most are able to do this, but not all, so check the documentation for your receiver, or one that you are planning to purchase.

Higher-end players have analog audio outputs, where the decoded sound is sent out of the player via traditional analog outputs, one per channel of audio, which you can connect to the multi-channel input of a receiver that has such input capability. Most advanced receivers have had this capability for many years, but home theater in a box systems and lower-end units may not.

Some higher-end HD DVD and Blu-ray players are introducing the ability to send the audio from the disc straight to the HDMI output, without any mixing, and still in the original format as on the disc. This requires your receiver to be able to decode the format provided, whether it be Dolby Digital Plus, Dolby TrueHD, DTS HD, or DTS HD Master Audio. As of November 2007, not very many receivers are capable of this decoding feature.

Which Approach is Preferable?

This simple question could launch hours of debate amongst enthusiasts, and it has been fodder for many threads of discussion on forums. There are pros and cons, future possibilities, and cold hard realities.

As of November 2007, we recommend that the best approach is to have the player output the mixed audio via HDMI to a receiver capable of taking multi-channel HDMI and delivering it to your speakers.

Most receivers will take the audio and send it through the same paths that audio coming from the coaxial and optical inputs. This means that if the receiver has DSP effects, equalization controls, level matching, or other features, the audio coming in via HDMI will be treated accordingly.

Often, multi-channel audio coming in from analog inputs is not processed, or may only have simple level adjustments made to it. In our case, our receiver does not process the level adjustments to all the channels in the same way our HD DVD player expects it to, so we have an issue with balancing the level of the subwoofer channel properly. This issue would be avoided if our receiver was equipped with an HDMI input (which was unavailable in most receivers in January of 2005, which now seems oh so long ago!).