The state of play
Before the coronavirus pandemic upended life as we knew it, movie theaters were undergoing a renaissance of sorts. Not only were premium movie houses proliferating, offering luxury seating and restaurant-quality food, many venues were getting a major upgrade to their sound systems courtesy of Dolby’s revolutionary Atmos technology.
In the past, if there was an explosion on the right side of the screen, half of the speakers in the theater would play the same sound. With Atmos, the sounds in a theater could now come from distinct locations determined by the professional audio mixers that had arranged them. Known in the industry as “object-based” sound technology, Atmos allowed for up to 128 distinct sound objects to be represented in a given scene, which could be routed to up to 64 different speakers.
Competitors like Digital Theater Systems (DTS) soon followed suit, with the company boasting that its DTS:X technology could produce more individual audio feeds than Atmos, which was hard-capped at 64. This meant that, theoretically, theater operators were limited only by their appetite to add extra speakers and amplification.
With the development of compatible A/V receivers, the battlefield quickly shifted to the living room. Today, most quality A/V receivers support object-based surround sound, and the tech that helped revitalize movie theaters is now available in the home.
This being a top-to-bottom surround sound guide, however, we need to journey back before we can move forward. If you’re a layperson looking to understand how Atmos or DTS:X tech can revolutionize your home theater, you’ll need a quick surround sound primer and a brief history lesson before building your setup.
Surround sound 101
We’ll get to the history of surround sound and the specs of all the competing formats in just a minute — but first, let’s get the basics out of the way. Understanding a few core concepts will help orient you so that you can follow the conversation to come, so here’s what you should know before we get down to the nitty-gritty:
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), but for now, we can use this basic five-speaker arrangement as a springboard for getting into the different formats.
No, we’re not talking about the sci-fi franchise starring Keanu Reeves. 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 VHS tape.
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, 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 involve much bass or treble information.
Surround sound history
OK, so now that you know what surround sound is and what the current state-of-the-art tech is capable of, let’s talk about how we got here.
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 short-lived — 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 matrix encoding. Since then, Dolby, DTS, and others have helped advance the state of home surround sound with a variety of iterations. In the next section, we trace this evolution — from the standard 5.1 setup to state-of-the-art, object-based surround.
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 LaserDisc (LD) was that it provided a lot more storage space than VHS tape. Dolby took advantage of this and created AC-3, now known 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 — 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, 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.
Image 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 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 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 is 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 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 was also “discrete,” which means that every speaker got its own specific information. This developme