Surround sound is exactly what it sounds like: a category of products and technologies designed to immerse you in audio from all sides, all angles, and, increasingly, from all heights too.
We’re going to take a very deep dive into exactly how it works and the technologies that brought us to today’s state of the art. That includes surround sound technologies, 3D audio formats like Dolby Atmos, and everything you need to know about getting great surround sound — including links to our guides on more specific topics.
But before we delve into the technology’s history, let’s start with a quick look at the current state of the art: Dolby Atmos, currently one of the most important standards to look for when putting together a home theater.
Objectively better sound
Before the advent of Dolby Atmos, soundtracks could be mixed in such a way that sounds moved from side to side, or forward or backward, but that was the extent of it. Granted, with the ability to route sound to as many as six discrete locations (plus a low-frequency channel), it was pretty immersive. But it was limited to one plane — the horizontal. It was also a tricky business for soundtrack engineers to move some sounds arounds while keeping others fixed in space.
With Atmos, these limitations were fundamentally changed. Because Atmos introduced far more discrete sound source locations, including those that are positioned above the audience’s heads, a total of 64 became possible. Engineers were also given the ability to manage individual sounds as “objects” that can be moved freely anywhere within a hemisphere of sound, without affecting music, dialogue, or any other non-object parts of the soundtrack. Up to 128 of these sound objects can exist simultaneously in a Dolby Atmos soundtrack.
From the audience’s perspective, the difference is palpable — especially in fast, action-filled movies where the story taking place on-screen involves a wide variety of explosions, vehicles, weapons, or other moving sources of sound. In other words, a typical Hollywood blockbuster.
Dolby Atmos’ popularity has exploded in recent years. The surround sound format is used in the majority of commercial cinemas; major streaming services like Netflix, Disney+, and Apple TV+ offer tons of movies and shows with Dolby Atmos soundtracks; and even the most affordable AV receivers and soundbars have Dolby Atmos technology built-in.
Dolby Atmos has also found a home in the music business. Dolby Atmos Music is now at the forefront of a new wave of spatial audio that you can experience on almost any smartphone as long as you have a set of headphones.
We’ll come back to Dolby Atmos later — along with some of its competitors — but first, let’s take a step back and talk about all of the surround formats that came before and brought us to this point.
Recorded sound 101: speakers (and channels)
Before we begin, it’s helpful to understand the principle building blocks of all sound systems and recordings, regardless of whether they’re surround sound or not.
All sound recordings are based on channels. A channel is a unique set of recorded sounds. If you played a single channel of sound on two speakers simultaneously, it might sound louder, or it might do a better job of filling the room evenly, but it would still be what we think of as “mono” sound.
To get to stereo sound, we need two channels of recorded sound (each with its own unique audio) and at least two speakers. The more channels (and thus the more speakers), the more control sound engineers have over the level of immersion and realism they can deliver.
Generally speaking, home theaters have one speaker for each channel of sound (with a few exceptions we’ll cover in a moment), but this isn’t a rule. If you had a really large auditorium or ballroom, you might need to double or even triple the number of speakers dedicated to a single channel of sound — it’s all about how much power and control you need for your given space.
Surround sound, at its most basic, involves three channels and four speakers: 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 fourth channel and a fifth speaker, placed between the front left and right speakers, that is primarily responsible for dialogue.
We’ll be adding more speakers later (lots more), but for now, we can use this basic five-speaker arrangement as a springboard for getting into the different formats.
Surround sound history
From two to four channels
It was the summer of 1969 when surround sound first became available in the home. It was called Quadraphonic sound, and as the name suggests, it provided four channels of discrete sound routed to four speakers placed in each corner of a room. It first appeared on reel-to-reel tape, but eventually became available on vinyl too.
It was a genius idea that proved to be a commercial failure. Quadrophonic sound was difficult to create and even harder to play at home due to the expense and complexity of the equipment needed. Keep in mind, this was in the pre-digital era.
Quadrophonic sound’s troubles only increased as a variety of companies tried to solve the technical hurdles by introducing a number of incompatible four-channel formats — something that has since played out over and over in the home AV space. This eventually led to the demise of the first true surround sound format.
Dolby Surround
The first truly successful surround sound format appeared 13 years later when, in 1982, Dolby Laboratories introduced Dolby Surround for home use. Instead of focusing on music recordings, Dolby’s efforts were centered on the rapidly growing home video industry kicked off by Sony’s Betamax and then massively expanded by JVC’s VHS tape format.
Dolby Surround piggybacked a surround sound signal onto a stereo source through a technique known as matrix encoding.
Pro Logic
Playing a VHS tape with Dolby Surround on a conventional Hi-Fi (stereo) VHS player would let you hear stereo sound, but if you owned additional equipment with Dolby’s Pro Logic circuitry, you could decode Dolby Surround’s two extra channels, which fed the center channel and surround speakers with audio.
Because of the limited space, however, matrixed surround signals came with some limitations. For instance, the surround channels in basic Pro Logic were not in stereo and had limited bandwidth. That means that each speaker played the same thing and the sound didn’t have a lot of detail.
Modern surround sound 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 the LaserDisc (LD) was that it provided a lot more storage space than VHS tape. Dolby took advantage of this and created AC-3, more commonly known as Dolby Digital. This format improved on Pro Logic in that it allowed for more detailed, stereo surround channels. It also introduced a low-frequency effects channel — the “.1” in 5.1 — handled by a subwoofer. All the information in Dolby Digital 5.1 is discrete for each channel — no matrixing necessary. Sorry, Keanu.
With the release of the film Clear and Present Danger on LaserDisc in 1995, the first Dolby Digital surround sound hit home theaters. By the time DVDs came out in 1997, Dolby Digital had become the default surround sound format. To this day, Dolby Digital 5.1 is considered by many to be the surround sound standard and is still included on most Blu-ray discs and tons of streamed movies.
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 came along, providing its own digital surround sound mixing services for movie production and first hitting theaters with Jurassic Park. The technology eventually trickled down to LaserDisc and DVD, but was initially available on a very limited selection of discs. DTS uses 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 as with so many audio-related comparisons, not everyone was sold on it.
6.1: Kicking it up a notch
In an effort to enhance surround sound by expanding the “soundstage,” home theater companies created 6.1, which 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 some confusion began to swirl.
People were already used to thinking of and referring to surround speakers (incorrectly) as “rears” because they were so often 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.” It uses the tried-and-true matrix encoding method to embed the sixth channel inside the left and right surround signals.
DTS, on the other hand, offered two separate 6.1 versions. DTS-ES Discrete and DTS-ES Matrix perform as their names suggest. With ES Discrete, specific sound information is programmed onto a DVD or Blu-ray disc, while DTS-ES Matrix uses the same technique as Dolby Digital EX to extrapolate information from the surround channels.
7.1: The spawn of Blu-ray
Just when people started getting used to 6.1, along came 7.1 in conjunction with HD DVD and Blu-ray discs becoming the new must-have surround format and 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 was also “discrete,” which means that every speaker got its own specific information. This development was enabled, in part, by the massive storage potential of Blu-ray.
Those who bought a dedicated back surround speaker during the shift to 6.1 now found themselves shopping for a new, matched pair of back surrounds — typically the exact same model they had bought for the left and right surrounds.
Dolby offers two different 7.1 surround versions. Dolby Digital Plus is the “lossy” version. Instead of using matrixing, it applies lossy compression to all of the discrete audio channels, which helps to take up less space. This is why Dolby Digital Plus is the preferred surround format for streaming video services. When space is at less of a premium, like on a Blu-ray disc, Dolby TrueHD is the gold standard. As a lossless format, no sound information has been removed during compression, and it’s as close to the studio master as you can get.
DTS also has two 7.1 versions, which differ in the same manner as Dolby’s versions. DTS-HD is a lossy 7.1 surround format, whereas DTS-Master HD is lossless.
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 they don’t always do so. There are other factors involved, too, with storage space being chief among them. If a bunch of extras are placed on a disc, there may not be space for additional surround information. In many cases, a 5.1 mix can be expanded to 7.1 by a matrix process in an AV 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. Before we continue, let’s take a quick look at what each of them does.
Pro Logic II
Using the same matrixed four-channel sound as the original Pro Logic, Pro Logic II can create a 5.1 surround sound mix from a stereo source. Pro Logic II also has another trick up its sleeve: It can separate the surround signal into stereo left and right channels instead of the original Pro Logic’s dual-mono presentation. This processing mode is commonly used when watching non-HD TV channels with a stereo-only audio mix.
Pro Logic IIx
If your video source is presented in 5.1 surround — and your home theater system supports additional speakers — Pro Logic IIx can take that mix and expand it to 6.1 or 7.1. Pro Logic IIx is subdivided into movie, music, and game modes.
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.
Despite the addition of these height channels, Pro Logic IIz does not enable a true 3D placement of sounds. To enable that, you’ll need Dolby Atmos or DTS:X, which we describe below.
What about 7.2, 9.2, or 11.2?
As we mentioned previously, the “.1” in 5.1, 7.1, etc., 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 instead of one. Both connections output the same information since, as far as Dolby and DTS are concerned, there is only one subwoofer track. Since AV receiver manufacturers wanted to market the additional subwoofer output, the notion of using “.2” was adopted.
You may even see some wild new soundbar systems like the Nakamichi Dragon touting a “.4” in the place of the normal .1 or .2. That’s right, it ships with four wireless subwoofers.
For most people, a single subwoofer will provide ample low-end bass and rumble. However, adding a second sub can enhance this effect, especially in larger media rooms. Check out our subwoofer placement guide to learn why a second sub might be right for you.
Audyssey DSX and DSX 2
Audyssey, a company best known for its auto-calibration software found in many of today’s AV receivers, has its own surround solution called Audyssey DSX, which allows for additional speakers beyond the core 5.1 and 7.1 surround formats by 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 3D formats like Dolby Atmos and DTS:X in recent years, however, Audyssey has seen a decline.
3D/object-based surround sound
As we mentioned earlier, the latest and greatest development in surround sound is known as “object-based” or “3D” surround. For viewers, “3D” offers the best description of this technology because of its ability to make sounds feel as though they are moving through space. For instance, you might hear a helicopter take off from in front of you, hover over your head, and then disappear into the distance behind you.
“Object-based,” on the other hand, is the moniker preferred by the sound professionals who create these 3D soundtracks because it describes their ability to move a single sound-producing object (like a helicopter) anywhere in 3D space.
This immersive hemisphere of sound is made possible by adding discrete channels for ceiling-mounted or ceiling-facing speakers in home theater systems and soundbars.
Because these channels no longer need to extrapolate their signals from audio running to other speakers as they did with Pro Logic IIz 7.1, they get their own number. A 5.1.2 system, for example, would feature the traditional five channels and a subwoofer, but it 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 and two at the rear.
Dolby Atmos
This shouldn’t come as a surprise after reading this article to this point, but Dolby is the current leader in object-based surround sound technology. We’ve been over Atmos’ bid to revolutionize the movie theater experience, but what about home theaters?
Atmos in the home
Atmos debuted on compatible AV receivers in 2015, but 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, and most AV receivers above the low-end range of the spectrum now support the format. In fact, every receiver on the list of our favorite AV 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. Since then, soundbar manufacturers have fully embraced Dolby Atmos. Some achieve the Atmos effect by using dedicated wireless surround speakers with up-firing drivers to complement the front speakers in the bar. Others use a technique known as virtualized Dolby Atmos to convincingly simulate the Atmos effect using fewer speakers.
Some TVs, like LG’s line of superb OLED TVs, claim Dolby Atmos support through the TV’s built-in speakers. Because Dolby Atmos can be calibrated for as few as two channels, we suppose this is technically accurate. However, buyers should be aware that two-channel Atmos will never sound as good as discrete 5.1.2 or better Atmos.
Movies with Dolby Atmos soundtracks are now very common on Blu-ray and Ultra HD Blu-ray discs. And streaming sites like Netflix, Amazon Prime Video, Disney+, and Apple TV+ all offer a selection of Atmos movies and shows. Atmos is even starting to appear in some live broadcasts.
One thing to keep in mind with Dolby Atmos is that it’s a finicky beast. In order to hear Dolby Atmos sound, every part of your home theater system — from the source to the speakers — needs to support it. Here’s our full guide to getting great Dolby Atmos sound.
Dolby Atmos Music
Dolby Atmos Music uses all the same object-oriented 3D audio tools as the movie soundtrack version, but puts them in the hands of professional music producers.
The result is immersive music that goes well beyond what traditional two-channel stereo or even quadraphonic sound can achieve. There are several ways you can experience Dolby Atmos Music:
- Using a smartphone, if your streaming music service support Dolby Atmos Music, you can hear a special version that has been created specifically for headphones or earbuds. Any headphones will do, and you can be connected by a wire or wirelessly.
- Using a dedicated Dolby Atmos Music speaker like the Sonos Era 300, Amazon’s Echo Studio, or Apple HomePod, you can once again use your smartphone to stream Dolby Atmos Music tracks directly to the speaker.
- Most streaming services that have Dolby Atmos Music collections have apps for platforms like Apple TV, Roku, Google TV, and Amazon Fire TV. If your TV is connected to a Dolby Atmos sound system, these apps will let you stream Dolby Atmos Music through your TV.
In a few select clubs, Dolby Atmos Music is being used by DJs and other live performers to produce an immersive music environment for dance floors.
It’s worth noting that Sony also has a 3D immersive music format known as Sony 360 Reality Audio that competes with Dolby Atmos Music. It too can be found on some streaming services, and on a limited number of devices.
DTS:X
Just like with other types of surround sound, DTS has its own version of object-based audio, DTS:X, which was unveiled in 2015. DTS:X aims to be more flexible and accessible than Atmos, making use of preexisting 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 AV receivers, it’s now available with newer AV receivers right out of the box. Companies like Lionsgate and Paramount offer home releases in DTS:X, but its lack of widespread adoption on disc-based media — and (currently) zero adoption among streaming services — is its biggest limiting factor.
Still, hope is on the horizon. In January 2023, Disney+ said it plans to bring DTS:X to its catalog of IMAX Enhanced movies. Technically speaking, the DTS:X codec is baked into IMAX Enhanced, but streaming companies have the option of only using IMAX Enhanced’s picture benefits, like its full-screen aspect ratio. For now, that’s how all IMAX Enhanced content is presented.
Once services like Disney+ start streaming the format with DTS:X, it will help home theaters imitate IMAX Signature Sound in an IMAX theater, including the deep bass.
DTS Virtual:X
DTS also recognizes that not all movie lovers have the space or the time to put together an object-based sound system. Research gathered by DTS showed that less than 30% of customers actually connect height speakers to their systems, and less than 50% even bother connecting surround speakers.
To that end, the company developed DTS Virtual:X, which employs digital signal processing (DSP) in an effort to provide the same spatial cues that a traditional DTS:X system would 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. Today, if a soundbar doesn’t support Dolby Atmos or DTS:X, it almost certainly offers DTS Virtual:X. Companies like Denon and Marantz have also added support for DTS Virtual:X to their receivers.
Technically speaking, “virtualized” Dolby Atmos and DTS Virtual:X are very similar, however, Dolby prefers not to distinguish between Dolby Atmos implementations. As far as it’s concerned, Atmos is Atmos, whether it’s virtualized through two, three, or five channels, or fully baked using a discrete 5.1.2 or better speaker system.
Auro-3D
Though you may not have heard of Auro-3D until now, it was on the scene well before DTS:X or Atmos appeared. The technology was announced in 2006 for use in theaters, but wasn’t available for home theater systems. Thanks to Denon and Marantz pushing it through as a firmware upgrade, you can now use it with your home speakers — though you have to pay for it.
Despite its apparent likeness to Dolby Atmos, Auro-3D creates a surround sound experience through a three-tiered sound system. Multiple speakers really showcase this kind of layered sound. We recommend 11 speakers to get the most out of the sound, making Auro-3D the most expensive setup you can recreate at home. Because Auro-3D usually uses a single overhead channel, its speaker configurations aren’t optimal when used with Dolby Atmos sound.
We haven’t seen a growth in popularity for Auro-3D in the U.S., but considering its pervasive usage in Europe and Japan, it’s only a matter of time.
MPEG-H
MPEG-H refers to a whole family of audio and video standards, but for surround sound, we’re interested in a specific part of it: the support for 3D Audio. In this regard, MPEG-H is very similar to Dolby Atmos and allows developers to set an incredible amount of audio objects in a 3D space. It’s also an extremely versatile standard, allowing developers to give users the option to control specific parts of the sound like dialogue or choosing where specific sounds come from. Check out our in-depth guide to MPEG-H for all the details.
While MPEG-H isn’t as common in North America, you can find it on Brazilian and South Korean broadcasts, as well as a variety of home theater products from brands like Denon and Marantz. As the standard becomes more popular, especially for broadcasts, it could become a sought-after way to watch live TV in 3D audio.
In summary …
While it may seem like things are getting more complicated, studio-quality home theater sound is more accessible than ever. Innovations in “object-based” or “3D” surround sound, combined with the addition of dedicated speakers to the standard 5.1 setup have upped the ante, sure — but you don’t need to be a sound engineer or audiophile to create an immersive experience at home. A little bit of research goes a long way, so keep this guide handy as you build your setup and you should have no trouble figuring out what’s right for you. Happy viewing/listening!
