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.
Just like music, surround sound platforms are available in multiple standards. The two big ones supported by most high-end home audio systems are Dolby Digital and DTS (short for the owner of the standard, Dedicated To Sound). But what’s the difference between the two?
Both Dolby and DTS offer surround sound codecs for 5.1, 6.1 (rare), and 7.1 setups, where the first number indicates the number of small surround speakers and the “.1” is a separate channel for a subwoofer. For the most common applications, playback of movies and TV shows via DVD, Blu-ray, and cable or satellite TV systems, both standards are used by the studio to compress the dense files necessary for multi-channel audio and decompress it by your receiver for playback.
In addition to 5.1 and 7.1 speaker playback in various formats, both standards have multiple extra technologies, like specific encoders for enhanced stereo, the older Pro Logic standards that simulate surround sound, converting up or down to match a non-standard number of speakers, enhanced surround for extra immersion, and so on. But for the purposes of a standard Blu-ray or satellite system with a high-end audio receiver, we’re going to focus on the surround sound playback.
A relatively inexpensive 5.1-speaker setup with an integrated Blu-ray player. It may not be compatible with the highest bitrate Dolby and DTS standards.
Both formats use compression to save space (either on the disc, in the case of DVD and Blu-ray, or streaming bandwidth, in the case of services like Netflix). Some forms of DTS and Dolby Digital are “lossy”, meaning it has a degree of audio degradation from the original source, while others get around this audio loss for “lossless” studio levels of performance while still offering some compression for space savings (see below).
Dolby Surround and DTS are proprietary formats, so a complete examination of the technology they use isn’t really possible (unless you happen to work for either company). But we can look at some of the specific specs available and make a rough determination.
First, each standard has its own “tiers” of quality, which you’ll find in different forms of media. Here are the options you’ll find for each:
As you can see, the propagation of two competing companies with evolving standards has resulted in roughly comparable levels of surround sound quality across three different tiers. There are some more technical differences between the codecs—for example, DTS-HD Master Audio can sacrifice the compression rates on some of its channels to boost encoding to a maximum of nine separate channels, and both DTS:X and Dolby Atmos are alternative “immersive” modes that offer even more distinct surround sound. But for most standard applications, you’ll be using one of the above.
At first glance, DTS seems to have the clear advantage on paper due to its higher bitrate encoding at all three tiers. But remember, we’re dealing with proprietary technology used in the original studio recording and in playback. Higher bitrate does not necessarily mean higher quality, because you aren’t comparing apples to apples…just like comparing MP3 bitrates to AAC bitrates isn’t exactly fair.
The difference between the lossless and lossy tiers is highly subjective as well, not to mention dependent upon the quality and setup of your specific home theater. The differences in bitrate between the lower and upper tiers will become more apparent with more expensive, higher-quality speakers…assuming that your hearing is actually good enough to discern the difference in the first place.
In addition, the values above represent the maximum optional channels and bitrates for each tier. Blu-ray discs have a ton of storage available, but they’re still limited to local files, and multiple audio channels take up a lot of space. Studios have to pick and choose which formats to support on each release, and at which maximum quality. For example, Blu-ray.com says that the Avengers Blu-ray release includes DTS-HD Master Audio in 7.1 channels for the English and French audio tracks, but only the lower-tier Dolby Digital 5.1 for the Spanish track. Avengers: Age of Ultron, from the same studio three years later, has DTS-HD Master Audio in 7.1 for English, but reverts back to Dolby Digital 5.1 for both French and Spanish. There’s a lot of variation here. Check out this Resident Evil anthology collection and click “More” under the Audio section; you’ll see that the specific codec and language combinations change with each movie.
Most surround sound systems support at least some flavor of both Dolby and DTS, and they’re smart enough to use the default standard for whatever source they have at the time, be it a DVD, Blu-Ray, web-based video, or live TV input. If you already have your home theater set up, and assuming you haven’t put a small fortune into audiophile-grade speakers, you’re probably fine with whatever the default setting happens to be.
Let’s say you’re planning on assembling a home theater from scratch, and you’re spending quite a lot of money on a high-performance receiver and speakers. Any new reciever will support both Dolby TrueHD and DTS HD Master Audio. The latest Blu-ray releases tend to stick to one or the other for their highest-resolution option, either TrueHD or Master Audio, then defaulting to a more compressed option like standard Dolby Digital 5.1 for alternate language audio tracks. If you want something extremely cutting edge, you might want to look into technologies like Dolby Atmos or DTS:X, and which specific receivers, speakers, and movies or services support them.
In the rare instance that you get to choose between an equivalent Dolby or DTS surround tier, and you don’t have a personal preference for one or the other, go with DTS for the higher bitrate. But again, I’d like to stress that the actual difference in audio quality is almost entirely subjective.
Image Credits: Blu-ray.com, Amazon