Home Theater: Surround Sound Formats

3d1Today’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.

Also part of this mini-series is Home Theater: Surround Sound Basics and Home Theater: More Surround Sound.

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Curt Robbins

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.

Two Dominant Formats: Dolby & DTS

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.)

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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.

DTS Neo:6

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:

You can follow him on Twitter at @CurtARobbins, read his AV-related blog posts at rAVe Publications, and view his photos on Flickr.

Home Theater: More Surround Sound

3d1Today’s blog post is another excerpt from my new Kindle book Home Theater for the Internet Age. It further explores home theater surround sound (also check out Home Theater: Surround Sound Basics), diving into discrete vs. matrixed audio and lossy vs. lossless compression—topics that continue to confuse both casual fans and enthusiasts alike.

Also check out Surround Sound Basics and Surround Sound Formats.

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Curt Robbins

Standardized System

Surround sound isn’t merely a speaker arrangement for your living room, but rather a standardized system by which content producers can compose, or “encode,” their content so that consumers, with the proper equipment, can decode it to simulate a more realistic, immersive audio environment. The intent of surround sound is to create audio that radiates from all around the seating positions of the viewers, while giving content producers the ability to specify from which of those speakers a particular sound or audio stream is projected.

While basic surround sound involves three speakers in front and two in back, more sophisticated systems employ between eight and 12 speakers. The more speakers involved, the more immersive and “surrounding” the sound becomes (and, relatively speaking, the more expensive the speaker system and receiver).

Discrete vs. Matrixed Surround

This book strives to avoid the overly technical and speak in plain English. However, it’s helpful to understand the difference between discrete and matrixed surround sound formats. Discrete surround involves sound information that’s specific, or dedicated to, particular channels and speaker positions (and fully independent of other channels). Thus, if a movie features a 5.1 soundtrack, it means the producers recorded and mixed six separate sound channels, each intended for a particular speaker position in your living room.

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Matrixed surround, on the other hand, involves your receiver producing sound information for six or more speakers that’s derived from a two-channel (stereo) signal. While not as good as discrete formats, matrixed surround can take standard stereo and make it pretty amazing—depending on the quality of your system. Assume you’re watching an old episode of Law & Order on cable TV and it’s encoded in stereo. If your AV receiver features a matrixed surround sound format, such as Dolby Pro Logic II or DTS Neo:6 (nearly all models for the past several years do), you can apply it to the stereo signal to direct sound to the other speakers in your home theater, not just the mains.

If a film or TV program features an audio mix that’s designed for surround sound, it will offer discrete channels. Dialog will be directed to the center channel, background noise like traffic, the din of a crowd, and sirens will come from the rear speakers, and the non-speech sounds and primary action will be directed to the main speakers. Because so much legacy content—be it music, TV episodes, or movies—features audio encoded in only stereo, you’ll find great benefit in applying matrixed surround filters to take advantage of those other speakers sitting in your living room. This is especially true for those who consume mostly TV content.

Lossy vs. Lossless Compression

When the audio portion of a video is created, it’s digitally compressed to make it smaller. Reducing the size of the data helps it stream smoothly from an internet video service (like Netflix) or fit on an optical disc (DVD or Blu-ray). However, there are different types of compression that impact the quality of the sound produced by any equipment, especially nicer systems.

Lossy Compression

Traditionally, data compression for audio has been lossy. This means that, during the compression of the audio, some information is lost—resulting in less data to play back. In a nutshell, less data equals lower sound fidelity. Different compression schemes produce distinct results in terms of sound quality. Overall, lossy compression is viewed as a bad thing. Music in MP3 (MPEG Audio Layer III) and AAC (Advanced Audio Coding) formats are good examples of lossy compression standards (and avoided by audiophiles). All music sold on standard compact discs (in CDDA format; see the Disc-Based Music chapter for more info) involves lossy compression (although of significantly higher fidelity than MP3 or AAC).

Lossless Compression

Lossless compression, on the other hand, is, well, lossless. It reproduces the original audio bit-for-bit, with no reduction in data or quality whatsoever (any decrease in fidelity reflects a deficiency in your equipment, not the audio itself). If you know an audio source is lossless, you don’t really need to learn anything else (except maybe the encoding standard employed to ensure that you can decode it on your particular Blu-ray player or AV receiver).

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The downside of lossless compression is that it results in significantly larger files than lossy schemes. This is why lossless audio is currently available only on high-capacity optical disc formats (like Blu-ray, which sports six times the storage of a DVD), but not in the form of internet streaming, where even the fastest broadband connections typically lack the bandwidth to support such high bit rates. Examples of lossless audio include Dolby TrueHD and DTS-HD Master Audio (both covered below). There are also internet-based download services that sell lossless music files in popular formats like FLAC and AIFF (higher quality than even regular music CDs, let alone MP3s).

Compression Levels / Bit Rate

Content compressed in a lossy format can be encoded at a variety of quality levels (measured in “bit rate” or bits per second, and sometimes called “compression levels”). For example, a 128 Kbps (kilobit per second) MP3 of Jessie’s Girl by Rick Springfield won’t sound as good as a 320 Kbps MP3 version. The 320 Kbps file contains nearly three times the data of the 128 Kbps version, enhancing the sound quality.

This is one reason that Blu-ray discs are so popular. While the video quality of Blu-ray (1080 lines of resolution) is certainly better than that of DVD, the audio improvement is even greater. Currently, there is no better sound that you can pump through your home theater than the lossless audio track of a Blu-ray movie or lossless music files like FLAC. (When it comes to audio only, there are also high-end music formats such as SACD, DVD-Audio, and Blu-ray Audio, which are covered in the Disc-Based Music chapter.)

Based on Standards

To clarify how this compression/decompression cycle works, it’s important to understand that content producers must encode their audio to a particular standard (like a United Nations interpreter choosing a language in which to speak). As you’ll learn below, for movies, this is typically a format from Dolby or DTS. Encoding makes files smaller for transport or distribution, regardless of whether it’s lossy or lossless. Your receiver or Blu-ray player incorporates a bunch of decoders. When you play a DVD or Blu-ray disc, the receiver applies the proper decoder, basically reassembling the audio data. In this respect, your AV receiver is just a specialized computer. (Some people will tell you that the audio on a Blu-ray movie is uncompressed, which isn’t necessarily true. Typically it’s compressed, but sometimes it isn’t. Even compressed, Blu-ray involves a lossless scheme.)

No Guarantees

It’s important to note that, simply because an audio source involves a lossless compression format, this doesn’t guarantee high-end fidelity. Technically, lossless compression simply means that the file reproduced by your playback equipment exactly matches the original, before it was compressed. If the original music file was of low quality to begin with (many movies and much music are poorly mastered or recorded in less-than-optimal live venues or studio environments), the best lossless format won’t make it sound good.

Curt Robbins is author of the following books from Amazon Kindle:

You can follow him on Twitter at @CurtARobbins, read his AV-related blog posts at rAVe Publications, and view his photos on Flickr.