The ultimate surround sound guide: Different formats explained

It was the summer of ’69. We’re not talking about the Bryan Adams song here; we’re actually referring to the first time surround sound became available in the home. It was called Quadraphonic sound and it first appeared on reel-to-reel tape. Unfortunately, Quadraphonic sound, which provided discrete sound from four speakers placed in each corner of a room, was confusing and shortlived — no thanks to companies battling over formats (sound familiar?).

Immersion in a three-dimensional audio sphere was not to be given up on, however. In 1982, Dolby Laboratories introduced Dolby Surround, a technology that piggybacked a surround sound signal onto a stereo source through a process called matrix encoding. Since then, Dolby, DTS, and others have helped advance the state of home surround sound with a variety of iterations. With so many options, though, the technology remains confusing for many. From basic 5.1 to Dolby Atmos setups with multiple overhead speakers, it’s a lot to wrap your head around. Our detailed guide aims to provide a little clarity to help you on your surround-sound quest.

Surround sound 101

The speakers

Surround sound, at its most basic, involves a set of stereo front speakers (left and right) and a set of surround speakers, which are usually placed just to the sides and just behind a central listening position. The next step up involves the addition of a center channel: A speaker placed between the front left and right speakers that is primarily responsible for reproducing dialogue in movies. Thus, we have five speakers involved. We’ll be adding more speakers later (lots more, actually), but for now, we can use this basic five-speaker arrangement as a springboard for getting into the different formats.

Matrix

For the purposes of this discussion, “matrix” has nothing to do with the iconic Keanu Reeves movies. In this case, matrix refers to the encoding of separate sound signals within a stereo source. This approach was the basis for early surround-sound formats like Dolby Surround and Dolby Pro Logic, and was motivated in part by the limited space for discrete information on early audio-video media, such as the VHS tape.

Pro Logic

Using the matrix process, Dolby’s Pro Logic surround was developed to encode separate signals within the main left and right channels. Dolby was able to allow home audio devices to decode two extra channels of sound from media like VHS tapes, which fed the center channel and surround speakers with audio. Because of the limited space, matrixed surround signals came with some limitations. The surround channels in basic Pro Logic were not in stereo and had a limited bandwidth. That means that each speaker played the same thing and the sound didn’t involve much bass or treble information.

5.1: Surround takes shape

Dolby Digital 5.1 / AC-3: The benchmark

Remember LaserDisc? Though the medium was first invented in 1978, it wasn’t until 1983, when Pioneer Electronics bought a majority interest in the technology, that it enjoyed any kind of success in North America. One of the advantages of LaserDisc (LD) is that it provided a lot more storage space than VHS tape. Dolby took advantage of this and created AC-3, now known better as Dolby Digital. This format improved on Pro-Logic in that it allowed for stereo surround speakers that could provide higher bandwidth sound. It also facilitated the addition of a low-frequency effects channel, adding the “.1” in 5.1, which is handled by a subwoofer. All of the information in Dolby Digital 5.1 is discrete for each channel — no matrixing necessary.

With the release of Clear and Present Danger on LaserDisc, the first Dolby Digital surround sound hit home theaters. Even when DVDs came out in 1997, Dolby Digital was the default surround format. To this day, Dolby Digital 5.1 is considered by many to be the surround sound standard, still included on most Blu-ray discs.

5-1-dolby-setupImage courtesy of Dolby

DTS: The rival

What’s a technology market without a little competition? Dolby more or less dominated the surround-sound landscape for years. Then, in 1993, DTS (Digital Theater Systems) came along, providing its own digital surround-sound mixing services for movie production, first hitting theaters with Jurassic Park. The technology eventually trickled down to LD and DVD, but was initially available on a very limited selection of discs. DTS utilizes a higher bit rate and, therefore, delivers more audio information. Think of it as similar to the difference between listening to a 256kbps and 320kbps MP3 file. The quality difference is noticeable, but according to some, negligible.

6.1: Kicking it up a notch

In an effort to enhance surround sound by expanding the “soundstage,” 6.1 added another sound channel. The sixth speaker was to be placed in the center of the back of a room and was subsequently referred to as a back surround or rear surround. This is where a lot of confusion began to swirl around surround sound. People were already used to thinking of and referring to surround speakers (incorrectly) as “rears,” because they were so often seen placed behind a seating area. Recommended speaker placement, however, has always called for surround speakers to be placed to the sides and just behind the listening position.

The point of the sixth speaker is to give the listener the impression that something is approaching from behind or disappearing to the rear. Calling the sixth speaker a “back surround” or “surround back” speaker, while technically an accurate description, ended up being just plain confusing.

To make things even more confusing, each company offered different versions of 6.1 surround. Dolby Digital and THX collaborated to create a version referred to as “EX” or “surround EX” in which information for the speaker is matrix encoded into the left and right surround speakers. DTS, on the other hand, offered two separate 6.1 versions. DTS-ES Discrete and DTS-ES Matrix performed as their names suggested. With ES Discrete, specific sound information has been programmed onto a DVD or Blu-ray disc, while DTS-ES Matrix extrapolated information from the surround channels.

7.1: The spawn of Blu-ray

Just when people started getting used to 6.1, 7.1 came along in conjunction with HD-DVD and Blu-ray discs as the new must-have surround format, essentially supplanting its predecessor. Like 6.1, there are several different versions of 7.1, all of which add in a second back-surround speaker. Those surround effects that once went to just one rear surround speaker could now go to two speakers in stereo. The information is discrete, which means that every speaker is getting its own specific information — we can thank the massive storage potential of Blu-ray for that.

Dolby offers two different 7.1 surround versions. Dolby Digital Plus is the “lossy” version, which still involves data compression and takes up less space on a Blu-ray disc. Dolby TrueHD, on the other hand, is lossless. Since no compression is involved, Dolby TrueHD is intended to be identical to the studio master.

7-1-dolby-setupImage courtesy of Dolby

DTS also has two 7.1 versions, which differ in the same manner as Dolby’s versions. DTS-HD is a lossy, compressed 7.1 surround format, whereas DTS-Master HD is lossless and meant to be identical to the studio master.

It’s important to note here that 7.1-channel surround mixes are not always included on Blu-ray discs. Movie studios have to opt to mix for 7.1, and don’t always do so. There are other factors involved, too. Storage space is chief among them. If a bunch of extras are placed on a disc, there may not be space for the additional surround information. In many cases, a 5.1 mix can be expanded to 7.1 by a matrix process in an A/V receiver. This way, those back surround speakers get used, even if they don’t get discrete information. This is becoming less common, however, especially when it comes to 4K Ultra HD Blu-ray discs, which often support multiple seven-channel mixes.

9.1: Pro Logic makes a comeback

If you’ve been shopping for a receiver, you may have noticed that many offer one or more different versions of Pro Logic processing. In the modern Pro Logic family, we now have Pro Logic II, Pro Logic IIx, and Pro Logic IIz. Let’s take a quick look at what each of them does.

Pro Logic II

Pro Logic II is most like its early Pro Logic predecessor in that it can make 5.1 surround sound out of a stereo source. The difference is Pro Logic II provides stereo surround information. This processing mode is commonly used when watching non-HD TV channels with a stereo-only audio mix.

Pro Logic IIx

Pro Logic IIx is one of those processing modes we mentioned that can take a 5.1 surround mix and expand it to 6.1 or 7.1. Pro Logic IIx is subdivided into a movie, music and game mode.

Pro Logic IIz

Pro Logic IIz allows the addition of two “front height” speakers that are placed above and between the main stereo speakers. This form of matrix processing aims to add more depth and space to a soundtrack by outputting sounds from a whole new location in the room. Since IIz processing can be engaged with a 7.1 soundtrack, the resulting format could be called 9.1.

What about 7.2, 9.2 or 11.2?

As we mentioned previously, the “.1” in 5.1, 7.1, and all the others refers to the LFE (low-frequency effects) channel in a surround soundtrack, which is handled by a subwoofer. Adding “.2” simply means that a receiver has two subwoofer outputs. Both connections put out the same information since, as far as Dolby and DTS are concerned, there is only one subwoofer track. Since A/V receiver manufacturers want to easily market the additional subwoofer output, the notion of using “.2” was adopted.

Audyssey DSX and DSX 2

Audyssey, a company best known for its auto-calibration software found in many of today’s A/V receivers, has its own surround solution called Audyssey DSX. DSX also allows for additional speakers beyond the core 5.1 and 7.1 surround formats, upmixing 5.1 and 7.1 signals to add more channels. With the addition of front width and front height channels on top of a 7.1 system, Audyssey allows for 11.1 channels of surround sound. There’s also Audyssey DSX 2, which adds upmixing of stereo signals to surround sound. With the advent of object-based formats like Dolby Atmos and DTS:X in recent years, however (see below), Audyssey has seen a decline.

3D/object-based surround sound

image courtesy Dolby Labs
image courtesy Dolby Labs

The latest and greatest development in surround sound offers not only discrete audio for height channels, but also a new way for sound engineers to mix audio for the most accurate, hemispheric immersion to date. The name “object-based” is employed because, with this discrete third dimension, the audio mixers working on a film can represent individual sound objects — say a buzzing bee or a helicopter —  in 3D space rather than being limited by a standard channel setup.

By adding discrete channels for ceiling-mounted or ceiling-facing speakers in A/V receivers at home, height channels are now represented as their own separate entities, leading to an extra number used to represent home surround channels. A 5.1.2 system, for example, would feature the traditional five channels and a subwoofer, but would also feature two additional speakers adding height information in stereo at the front. A 5.1.4 system would add four additional height channels to 5.1, including two at the front, two at the rear, and so on.

Dolby Atmos

Atmos in theaters

This shouldn’t come as a surprise after reading the rest of this article, but Dolby is the current leader in object-based surround sound technology. In a theater outfitted with Dolby Atmos, up to 128 distinct sound objects can be represented in a given scene (compared to, say, seven full channels for Dolby Digital 7.1), which can be routed to 64 different speakers. In the past, if there was an explosion on the right side of the screen, half of the theater would hear the same sound. With Atmos, the sounds in a theater will come from distinct locations based on where they’re placed by professional audio mixers.

Atmos in the home

Atmos began to be available in A/V receivers in 2015, in a much more limited capacity than the professional format. As mentioned above, the most common configurations are 5.1.2 or 5.1.4, which add two and four height speakers to a traditional 5.1 surround setup respectively, though Dolby supports much larger configurations. Atmos took off relatively quickly, as most A/V receivers above the low-end range of the spectrum now support the format. In fact, every receiver on the list of our favorite A/V receivers supports Atmos, even models priced at $500 or less.

In 2015, Yamaha introduced the first Atmos-capable soundbar, the YSP-5600, which uses up-firing drivers to bounce sound off the ceiling. Others soon followed, including our favorite to date, Samsung’s HK-950, which uses a total of four up-firing drivers and wireless surround speakers for a 5.1.4 Atmos configuration. There are even TVs like the LG W8 that support Dolby Atmos out of the box via an integrated soundbar. There are also other nimble speaker solutions that require a receiver, like Focal’s miniaturized Sib Evo system.

Meanwhile, the list of movies using Atmos continues to grow, offered via Blu-ray discs as well as streaming sites like Netflix and Vudu. The number of titles was small at first but has been steadily growing with each passing week. Atmos is even starting to appear in some live broadcasts, including the 2018 Winter Olympics.

DTS:X

Just as it does with other types of surround sound, DTS has its own version of object-based audio, DTS:X, unveiled in 2015. While Dolby Atmos limits objects to 128 per scene in theaters, DTS:X imposes no such limits (though whether film mixers are finding themselves bumping up against Atmos’ limitations is questionable). DTS:X also aims to be more flexible and accessible than Atmos, making use of pre-existing speaker layouts in theaters and supporting up to 32 different speaker configurations in the home.

While DTS:X was previously tacked on in updates for Atmos-enabled A/V receivers, it’s now available with newer A/V receivers right out of the box. Companies like Lionsgate and Paramount offer home releases in DTS:X, but for the time being, it remains less popular than Atmos. Still, that’s a relative thing: Every receiver on the aforementioned list of our favorite A/V receivers that supports Atmos also supports DTS:X, and you’ll find this to be consistent across the board.

DTS Virtual:X

DTS also recognizes that not all movie lovers have the space or time to put together an object-based sound system. Research gathered by DTS showed that less than 30 percent of customers actually connect height speakers to their systems, and less than 48 percent bother even connecting surround speakers.

To that end, the company developed DTS Virtual:X, which employs Digital Signal Processing (DSP) in an aim to provide the same spatial cues that a traditional DTS:X system could provide, but over a smaller number of speakers, even if you’ve only got two. This technology first rolled out in soundbars, which makes sense as they often only include a separate subwoofer and maybe a pair of satellite speakers at most. Since then, companies like Denon and Marantz have added support for DTS Virtual:X to their receivers, while Sony has its own virtual surround soundbar that reads DTS:X and Atmos mixes.

Auro-3D

It may not be as well known as Atmos or DTS:X, but Auro-3D has been around for much longer than either one of them. The technology was first announced in 2006 and has been used in theaters since, though it has only recently started to come to home theater systems with companies like Marantz and Denon offering it as a firmware upgrade — usually a paid upgrade.

Auro-3D doesn’t use the term “object-based” as its competitors do, but it does work in a similar way with similar results, adding to the overall immersion factor when watching a film. Auro-3D’s recent foray into living rooms isn’t likely to snatch away the 3D-surround crown from Dolby, but considering it’s already 12 years into its run, chances are it will continue to hang in there.

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