Dolby Digital Plus Surround Sound - dummies

By Danny Briere, Pat Hurley

Dolby Digital Plus surround sound is an improvement on the super-popular Dolby Digital/Dolby Digital EX system. Dolby Digital Plus improves on Dolby Digital and EX by

  • Increasing the bit rate: Dolby Digital Plus can be encoded with up to 6144 Kbps (kilobits per second) of data, where Dolby Digital tops out at 640 Kbps. (448 Kbps is the maximum from current formats, however.) All else being equal, higher bit rates mean better sound quality because the audio signals need to be compressed less.

  • Improving the encoding: Dolby Digital Plus does a better job of encoding (or digitizing and compressing) sound. Therefore, at a given bit rate, you get better sound quality. Combine this with the vastly increased bit rate of Dolby Digital Plus, and you get great sound!

  • Adding more channels: Dolby Digital Plus can provide up to 13.1 discrete channels of sound (14 total speakers, including the subwoofer). You can really envelop yourself in the action with 14 speakers!

  • Providing backward compatibility: Dolby Digital Plus decoders can automatically downconvert your sound to the older Dolby Digital formats. So you can play Dolby Digital Plus programs on your older system without having to buy new hardware. And when you do upgrade, you gain all the advantages just mentioned.

One drawback of Dolby Digital Plus is that the very high bit rates it supports overwhelm the digital audio connections that are traditionally used to connect DVD players or set-top boxes to your receiver. If all you have on your receiver is coaxial or optical digital connections, you’ll still be able to listen to Dolby Digital Plus, but you’ll have to get by with using analog audio connections or by letting your DVD player downconvert to 640 Kbps Dolby Digital.

If you have a newer receiver with an HDMI 1.3 connection, you won’t have this restriction and will get the full Dolby Digital Plus experience because the decoded signals can be carried as multichannel PCM over these high-bandwidth interfaces without sonic compromise.

Some receivers have HDMI connections but still can’t handle Dolby Digital Plus — you’ll need a receiver with HDMI 1.3 capabilities and an internal Dolby Digital Plus decoding capability. If your receiver doesn’t have these capabilities, it won’t keep you from enjoying the benefits of Dolby Digital Plus, but you’ll need to use a set of analog connections or configure your receiver to send the Dolby Digital Plus signal as linear PCM instead of as a bitstream.

Dolby Digital Plus is an optional format for Blu-ray discs, so any Blu-ray disc player should support Dolby Digital Plus, though not all discs will use the format. Dolby Digital Plus may also be used for other HDTV content — and may end up being encoded in a lot of the HDTV shows you get from your cable, satellite, or other TV service provider.