View Full Version : Technology Dolby Digital Plus

14th March 2007, 15:44
Has anyone heard of Dolby Digital Plus?

I expect you have all heard of Dolby Digital as it is used on pretty much every DVD Video release, with less also including DTS which is slightly higher quality. Both formats generally use a 5.1 soundspace with 5 main speakers (front, left, right, left rear, right rear) and a sub woofer for the sub bass frequency fill in.

More recent additions to the standard has pushed the ability to add more speakers to a Dolby Digital setup with 6.1 adding a rear centre speaker to the setup, and 7.1 adding an additional speaker to each side of the setup.

Well Dolby Digital Plus is based on the older Dolby Digital standard, but has been developed to take advantage og High Definition having more bandwidth and larger capacity storage on video disc media. Thankfully this new format is fully backwardly compatible with all existing Dolby Digital receivers which is good news.

What this new standard introduces is much higher quality audio encoded at up to 6 Mbits, which is actually higher than most DVD video was ever encoded on commercial releases! It also supports 7.1 channel audio, plus has additional support for further channels, but both Blu-Ray and HD-DVD standards currently restrict it to 7.1. It also has direct support for HDMI.

Dolby Digital Plus also gives a strong argument towards buying HD-DVD discs instead of Blu-Ray, especially if you are an audiophile. Why? Blu-Ray Discs support a bit rate performance of up to 1.7Mbps, whereas HD-DVD supports a bit rate performance of at least 3Mbps! So almost twice the audio bit rate of Blu-Ray. But it is a lot more complicated than just those facts and reading a complete breakdown of the two formats audio abilities Blu-Ray ends up also having some positive benefits over HD-DVD.

HD-DVD audio is restricted to the same sized audio packet sizes of 0.5Mbps, the same as DVD, whereas Blu-Ray isn't, so can use larger packet sizes of say 640Kbps. This is higher than Digital Broadcast format audio used by TV!

But there is also another difference in the two formats just to confuse the choice of one format or the other. With HD-DVD discs, the audio will be provided in Dolby Digital Plus format and the player will have the ability to downmix the audio to either 7.1, 5.1 or 2.1 depending on the audio receiver. With Blu-Ray this isn't the case. The standard will remain the same as DVD with all discs only required to have Dolby Digital 5.1 as standard, and Dolby Digital Plus will be an extra audio track on the discs if it is included. This means that unless the production house decided to incluude the newer higher quality format, all Blu-Ray discs may end up just having 5.1 audio identical to the DVD releases.

This could actually attract many production houses to go for Blu-Ray over HD-DVD as they would not need to re-encode their audio to the new Dolby Digital Plus format required by HD-DVD, but instead could just use the same audio they already have encoded for the DVD release of the same films.

You can read more about Dolby Digital Plus at http://www.dolby.com/consumer/technology/dolby_digital_plus.html

14th March 2007, 16:02
Update. I just did a check on the audio formats being used and I can confirm that for PAL releases all Blu-Ray discs I just looked at are using the old 5.1 Dolby Digital audio standard and HD-DVD are using the new Dolby Digital Plus or they do not have the standard listed.

So for audio it does look like HD-DVD is currently the better option. Another reason to wait longer to find which of the two formats will win the battle and if Blu-Ray releases will eventually start to support the better Dolby Digital Plus format.