Today’s blog post is another excerpt from Chapter 7: Surround Sound in Home Theater for the Internet Age. It will help you understand Dolby, DTS, and the multitude of surround sound encoding/decoding standards used for so many TV shows and movies and available in most modern AV receivers.
Surround Sound Formats
There’s a small handful of popular surround sound formats. The only reason you really need to understand them is so you can apply the most appropriate decoding standard to a particular TV episode or movie. Most modern receivers decode all surround formats that have been in popular use for the past twenty years.
As you’ve learned, Dolby and DTS are the two dominant audio surround standards in use today. Both companies are based in the United States and work closely with both Hollywood studios and home theater equipment manufacturers to ensure that the encoding/decoding cycle works the way it should.
You’ve probably heard of Dolby. Many remember it from the old days when most cassette players featured Dolby A and Dolby B noise reduction. Today, both Dolby and DTS represent a competing collection of encoding technologies designed to enhance the audio of all forms of entertainment. Thankfully, these two vendors aren’t offered on an either/or basis; both are available on receivers of all price ranges. (SRS, which has marketed software and hardware designed to create a “3D” immersive sound field using only two speakers, was purchased by DTS in 2012.)
The following surround formats are in popular use today, from the oldest (and most primitive) to the newest (and most advanced).
Dolby Pro Logic II
The oldest standard currently built into receivers, Pro Logic II turns a stereo soundtrack into “fake” 5.1 surround. As you learned, this matrixed sound is created on-the-fly by your receiver based on sound information pulled from the two-channel stereo signal. Just like the plot of the popular movie The Matrix, the additional channels in the mix aren’t really there (at least not in the original content). Dolby Pro Logic II works well at taking standard stereo signals and making them sound like legitimate surround sound on your system.
The Dolby Pro Logic (DPL) standard has been revised slightly to Dolby Pro Logic IIx, a format that is nearly identical to DPL II, except in 7.1 channels. There’s also a DPL IIz, with the “z” denoting the addition of the front height channels in a 9.1 setup.
Similar to Dolby Pro Logic IIx, DTS Neo:6 takes two-channel stereo content and creates a matrixed 6.1 sound environment. It’s nearly identical to Dolby Pro Logic IIx in function. If your receiver supports both standards, try comparing DTS Neo:6 with Dolby Pro Logic II the next time you have a stereo signal that you wish to hear in matrixed surround. Standardize on whatever sounds best to your ears, in your particular environment and with your equipment.
Dolby Digital & DTS Digital Surround
Both Dolby Digital and DTS Digital Surround are 5.1 channel discrete lossy formats. Dolby Digital is currently the most common standard for surround sound encoding (although most new release films on Blu-ray embrace newer lossless formats). Most receivers manufactured for the past several years, at all price ranges, include both Dolby Digital and DTS Digital Surround decoding capabilities. Many movies are encoded in Dolby Digital (including a big chunk of the Netflix catalog), some in DTS, and a few are released in both, allowing you to choose one from a disc’s setup menu.
Why are Dolby Digital and DTS Digital Surround better than Dolby Pro Logic II and DTS Neo:6? Because your receiver doesn’t have to play a game of creating matrixed sound channels from the basic left and right channels of stereo. Instead, Dolby Digital and DTS Digital Surround simply decompress and decode the six channels provided in the content and route them to your speakers, plain and simple. You hear the surround in the exact way that the content producers intended. From a surround sound perspective, this is perfect. From a fidelity perspective, however, it still involves lossy compression (it just happens to be pretty good lossy compression).
Unfortunately, Hollywood and media outlets aren’t always on the ball in terms of providing the best surround sound format possible, and are sometimes inconsistent. For example, if you check out the popular TV series Dexter on Netflix, you’ll find that the first two seasons are encoded in Dolby Digital (providing six separate and discrete sound channels). Season 3, however, is delivered only in stereo—meaning you’ll have to employ Dolby Pro Logic II or DTS Neo:6 if you want to experience “fake” surround. Season 4 of Dexter? Encoded in Dolby Digital again. Unfortunately, this lack of consistency and concern for the audio quality of content is all too common. Audio is typically a small percentage of the production budget for TV shows and films.
Dolby Digital Plus
Dolby Digital Plus, decodable on any hardware that features Dolby Digital, is a slightly enhanced version of Dolby Digital that’s designed for mobile devices and streaming boxes where bandwidth might be limited or fluctuate. It enhances audio somewhat by making vocals easier to discern in muddy soundtracks. Dolby Digital Plus is fairly new and beginning to appear in devices that stream media, like receivers and Amazon’s Fire TV streaming box. It’s also common on many Netflix movies and TV episodes.
Dolby Digital EX
Dolby Digital EX is a small bump up from Dolby Digital, adding an additional rear surround channel (for 6.1 and 7.1 systems). It’s still a lossy compression scheme, and, in all other respects, very similar to Dolby Digital. This format, co-developed with THX (and sometimes identified as THX Surround EX), involves discrete channels, meaning your equipment reproduces the sound in exactly the manner intended by the content producer.
DTS-ES (for “Extended Sound”) is the DTS answer to Dolby Digital EX, providing an additional rear center channel to achieve a 6.1 surround sound audio stream. It’s available in two variants, matrixed and discrete. Conveniently for consumers, video encoded in either type is backward compatible and interpretable by nearly all devices (AV receivers or Blu-ray players) that include basic DTS decoding but lack DTS-ES. This encoding format is also sometimes used to produce disc-based high-resolution music (Sheryl Crow’s The Globe Sessions, T. Rex’s The Slider, and Bjork’s Volta are examples).
This unique format takes stereo, 5.1, 6.1, or 7.1 content and creates a matrixed 11.1 surround sound mix. DTS Neo:X goes largely unused because there are so few 11.1 home systems in existence. Until you save enough money and are able to convince your spouse to install a slew of additional speakers to achieve your dream 12-channel setup, this format will be happily waiting for you. When you make the jump to home theater hyper-hobbyist, ensure that the receiver you’re considering includes this format and 12 speaker terminals.
Dolby TrueHD & DTS-HD Master Audio
Dolby TrueHD and DTS-HD Master Audio are both lossless 7.1 channel formats currently found only on Blu-ray discs (afforded by the higher storage capacity of the format). These compression schemes are presently the best available, producing the richest sound possible from movies.
What makes Dolby TrueHD and DTS-HD Master Audio unique is their lossless compression quality. They are the first mass-market movie audio encoding standards to feature lossless audio. The sound produced by films with these formats is truly impressive. The difference can be heard on home theaters of all price ranges and sophistication, but it really shines on better systems that are capable of reproducing high-fidelity audio with both wide dynamic range and an expansive soundstage.
Eventually, video streamed from the internet will also be encoded in TrueHD and DTS-HD (or similar lossless formats). Currently, however, most people’s internet bandwidth—even “broadband”—is simply too limited to pull this off. These high-end surround sound formats are supported only by Blu-ray players and AV receivers manufactured within the past few years.
Curt Robbins is author of the following books from Amazon Kindle:
- Home Theater for the Internet Age ($9.95)
- Understanding Personal Data Security ($4.99)
- Understanding Home Theater ($4.99)
- Understanding Cutting the Cord ($4.99)
- Understanding Digital Music ($4.99)