Surround sound is akin to a symphony of audio, enveloping you from all directions, all perspectives, and now, even from above. We are embarking on a profound exploration of the inner workings and technological marvels that have brought us to the pinnacle of audio excellence today. This includes an in-depth look at surround sound technologies, the advent of 3D audio formats like Dolby Atmos, and a comprehensive guide to achieving exceptional surround sound — complete with links to our detailed guides on specific topics.
But before we delve into the annals of technology, let us first glance at the current state of the art: Dolby Atmos, a cornerstone standard in creating an immersive home theater experience.
### Objectively superior sound
Before the emergence of Dolby Atmos, soundscapes could traverse from left to right, or front to back, within a horizontal plane. While this delivered a certain level of immersion through routing sound to up to six distinct locations (plus a low-frequency channel), it was confined to a single plane — the horizontal domain. It also posed challenges for sound engineers in maneuvering specific sounds while keeping others fixed spatially.
However, Atmos revolutionized this landscape by introducing a myriad of discrete sound source locations, including those positioned overhead. This advancement allowed for a total of 64 diverse sound source locations, enabling engineers to treat individual sounds as “objects” that could be freely moved within a sphere of sound, without impacting other elements of the soundtrack. A Dolby Atmos soundtrack could feature up to 128 such sound objects concurrently.
From the audience’s perspective, the transformation is striking — particularly evident in action-packed films replete with explosions, vehicles, weaponry, and dynamic sound sources that characterize a typical Hollywood blockbuster.
Dolby Atmos has experienced a meteoric rise in popularity in recent years. The format is now prevalent in the majority of commercial cinemas, and leading streaming services like Netflix, Disney+, and Apple TV+ offer an array of movies and shows with Dolby Atmos soundtracks. Even budget-friendly AV receivers and soundbars incorporate Dolby Atmos technology, ensuring its widespread adoption.
Dolby Atmos has also made a mark in the music realm. Dolby Atmos Music champions a new era of spatial audio, offering an immersive listening experience that can be savored on nearly any smartphone with a good pair of headphones.
We shall revisit Dolby Atmos later, along with its competitors. Before that, let’s meander through the historical evolution of surround formats that paved the path to our current juncture.
### Recorded sound 101: the symphony of speakers and channels
Before we embark on this journey, it is imperative to grasp the foundational elements of all sound systems and recordings, be it in surround sound or any other form.
Sound recordings are structured on channels, distinct sets of recorded sounds. While playing a single channel of sound simultaneously on two speakers may enhance volume or ensure uniform room coverage, it remains akin to traditional “mono” sound.
To transition to stereo sound, two channels of recorded sound (each with unique audio content) along with a minimum of two speakers are essential. The greater the number of channels (and speakers), the more extensive control sound engineers wield over the depth and realism of the audio ambiance.
Generally, home theaters feature one speaker for each sound channel (barring a few exceptions we’ll touch upon shortly). However, this is not a stringent rule. In larger spaces like concert halls or auditoriums, the number of speakers for a single channel may need to be doubled or even tripled to achieve the desired power and precision.
At its core, surround sound entails three channels and four speakers, encompassing a set of stereo front speakers (left and right) and a set of surround speakers typically positioned to the sides and slightly behind a central listening position. The subsequent evolution involves adding a fourth channel and a fifth speaker, positioned between the front left and right speakers, primarily dedicated to dialogue.
We shall introduce further speakers later on (a plethora of them), but for now, this basic five-speaker arrangement provides a platform for exploring diverse surround sound formats.
### The evolution journey from two to four channels
It was in the summer of 1969 that surround sound ventured into the realms of home entertainment. The inception of Quadraphonic sound marked a revolutionary stride, offering four discrete sound channels channeled to four speakers situated in each corner of a room. Initially appearing on reel-to-reel tape, this innovation eventually extended to vinyl records.
Despite its ingenious concept, Quadraphonic sound encountered commercial struggles. Owing to the complexity and cost involved in creating and reproducing Quadraphonic sound amidst the pre-digital era, its evolution was marred by challenges.
The surmounting issues with Quadraphonic sound stemmed from various companies attempting to resolve technical impediments by introducing disparate four-channel formats that ultimately led to compatibility concerns, mirroring subsequent challenges faced in the home AV realm. Regrettably, this predicament heralded the demise of the inaugural true surround sound format.
### Dolby Surround: The gateway to success
Thirteen years later, in 1982, Dolby Laboratories introduced Dolby Surround for domestic usage, marking the inception of a triumphantly successful surround sound format. Departing from focusing solely on music recordings, Dolby directed its endeavors toward the burgeoning home video industry catalyzed by Sony’s Betamax and later bolstered by JVC’s VHS tape format.
Dolby Surround incorporated a surround sound signal into a stereo source through a technique called matrix encoding.
### Pro Logic: A new dawn
Upon playing a VHS tape featuring Dolby Surround on a conventional Hi-Fi (stereo) VHS player, one could experience stereo sound. However, individuals equipped with additional gear featuring Dolby’s Pro Logic circuitry could decode the two supplementary channels from Dolby Surround, enriching the center channel and surround speakers with audio content.
Despite its innovative approach, matrixed surround signals in the rudimentary Pro Logic format possessed certain limitations. For instance, the surround channels in basic Pro Logic lacked stereo rendering and had restricted bandwidth. This design implied that each speaker relayed the same audio content without intricate detail.
### Embracing contemporary surround sound expressions
### Dolby Digital 5.1/AC-3: Setting the benchmark
Possibly recalling LaserDisc’s inception in 1978, it wasn’t until 1983 when Pioneer Electronics acquired a majority stake in the technology, subsequently propelling it to success in North America. LaserDisc boasted a superior storage capacity compared to VHS tape, prompting Dolby to seize this opportunity to craft AC-3, more commonly recognized as Dolby Digital. This format outshone Pro Logic by encompassing more detailed stereo surround channels and introducing a dedicated low-frequency effects channel — denoted as the “subwoofer.” All sound components in Dolby Digital 5.1 are discrete for each channel, eliminating the need for matrixing. An ode to analog technology, certainly.
With the debut of “Clear and Present Danger” on LaserDisc in 1995, the first Dolby Digital surround sound experience graced home theaters. By the time DVDs emerged in 1997, Dolby Digital had solidified its position as the quintessential surround sound format. To this day, Dolby Digital 5.1 remains a paragon in surround sound standards, retained on the majority of Blu-ray discs and a plethora of streamed films.
### DTS: The challenger
Elevating the technology realm, DTS emerged in 1993 to rival Dolby in the surround sound arena, providing digital surround sound mixing services for film production and making its theatrical debut in “Jurassic Park.” This technology subsequently filtered down to LaserDisc and DVD platforms. DTS boasted a higher bit rate, delivering an enhanced audio experience akin to differentiating between a 256kbps and 320kbps MP3 file. This quality disparity was perceptible, although not unanimously embraced across all audio enthusiasts.
### Kicking it up a notch: 6.1
In an endeavor to amplify surround sound efficacy by broadening the acoustic landscape, home theater enterprises introduced 6.1, augmenting an additional sound channel. The sixth speaker, positioned at the center of the room’s rear, earned the moniker “back surround” or “rear surround.” Alas, confusion ensued.
Traditionally, individuals associated surround speakers (erroneously) as “rears” due to their widespread placement behind a seating arrangement. However, recommended speaker arrangements underscored the importance of situating surround speakers to the sides and slightly behind the listening locale.
The rationale behind introducing a sixth speaker was to evoke a sensation of sounds approaching from or receding into the rear. While the nomenclature of “back surround” or “surround back” depicted an accurate description, it inadvertently initiated perplexity.
Moreover, each company presented distinct versions of 6.1 surround sound. Dolby Digital and THX collaborated to forge a version called “EX” or “surround EX,” employing the trusted matrix encoding method to incorporate the sixth channel within the left and right surround signals.
Conversely, DTS advanced two separate 6.1 iterations. DTS-ES Discrete saw specific sound data ingeniously embedded onto DVDs or Blu-ray discs, while DTS-ES Matrix adopted a similar technique akin to Dolby Digital EX to derive information from the surround channels.
### The spawn of Blu-ray: 7.1
Just as 6.1 gained acceptance, the realm of 7.1 surfaced in conjunction with HD DVD and Blu-ray discs becoming the coveted medium for surround formats, subsequently eclipsing their predecessors. Much like 6.1, several 7.1 deviations welled up, encompassing a supplementary back surround speaker.
This fortuitous evolution meant that surround effects, originally directed to a solitary rear surround speaker, were now dispersed across two speakers in a stereo configuration. The discrete nature of information allocation to each speaker was facilitated by the capacious storage potential of Blu-ray.
Those who previously acquired a designated back surround speaker during the transition to 6.1 unexpectedly found themselves scouting for a fresh pair of back surrounds, typically from an identical model used for the left and right surrounds.
Dolby rolled out two distinct 7.1 surround sound versions. Dolby Digital Plus, the “lossy” rendition, streamlined lossy compression throughout all discrete audio channels, optimizing space utilization. Hence, Dolby Digital Plus assumed precedence as the preferred surround format for streaming video services. Dolby TrueHD emerged as the gold standard on platforms like Blu-ray discs, boasting lossless characteristics where no sound information incurred loss during compression, preserving the sonic integrity of the studio master.
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