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, originally named Digital Theater Systems). But what’s the difference between the two?
What Are Dolby Digital and DTS?
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).
How They’re Different
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:
- Dolby Digital: 5.1 max channel sound at 640 kilobits per second (this is common on DVDs)
- Dolby Digital Plus: 7.1 max channel sound at 1.7 megabits per second (supported by some services like Netflix)
- Dolby TrueHD: 7.1 max channel sound at 18 megabits per second (“lossless” quality available on Blu-ray discs)
- DTS Digital Surround: 5.1 max channel sound at 1.5 megabits per second
- DTS-HD High Resolution: 7.1 max channel sound at 6 megabits per second
- DTS-HD Master Audio: 7.1 max channel sound at 24.5 megabits per second (“lossless”)
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.
Does It Even Matter?
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
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