Dolby Laboratories Atmos User Manual

Dolby Atmos

October 2014

®

for the Home Theater

Dolby Atmos®, the revolutionary cinema sound technology, has come to home theaters.
With Dolby Atmos, content creators can precisely place and move sounds anywhere in your
living room, including overhead, to make entertainment incredibly immersive and lifelike.

This white paper is designed to explain how Dolby Atmos will work in home theaters and
how you can build a Dolby Atmos enabled system or upgrade your existing system to
support Dolby Atmos. This paper also explains the technological components of Dolby Atmos
in home theater and the tools that content creators and broadcasters will use to create and
deliver Dolby Atmos content to homes.

Why replace channel-based surround sound?

Dolby Atmos is a revolutionary technology that moves beyond the paradigm of channel­based audio, which has gone as far as it can in the home.

Dolby has led home theater technology since the late 1980s, when we introduced four-

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channel Dolby

Pro Logic®. We led the development of 5.1 and then introduced 7.1

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surround sound in the home and the cinema. But as home theater expanded to 9.1 and
even 11.1 systems, the problems of pursuing more and more channels became clear. Home
theater content often originates from theatrical content that is mixed, at best, in 7.1 sound
and many times in 5.1. That meant that 9.1 or 11.1 systems reached a point of diminishing
returns in parsing and upmixing that limited signal to serve more and more channels.

In addition, the ability to recreate reality using channel-based audio is inherently limited. In
real life, sounds move in specific and sometimes complicated ways—a hummingbird flies off
a tree branch, hovers in front of a pair of blossoms, and then dives down to a fountain for a
drink. Simply moving the hummingbird’s sound from the Left Height channel to the Right
Front channel can’t possibly recreate the detail of th at bird’s flight. And when you lose those
details, it detracts from the brain’s sense that what it’s watching is real.

A cinema solution

Dolby first started investigations into a solution to the problems of channel-based audio in
the cinema. Our goal was to free filmmakers from the limitations of audio channels by
developing a system that allowed them to determine exactly where a sound should be and
where it should move in three dimensions—that is, to fait hfully recreate that hummingbird’s
flight in all its complexity.

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Dolby Atmos in home theater

Dolby has now developed the technology required to translate the Dolby Atmos experience
in cinema to home theaters. In the case of the home theater, every sound in the mix is
represented as an audio object. What happens when you play a Dolby Atmos film, whether
from a Blu-ray Disc™ or a streaming video service, is quite remarkable. When you set up
your Dolby Atmos enabled A/V receiver (AVR), you’ll have informed your receiver how many
speakers you have, what type of speakers they are (large, small, overhead, and/or Dolby
Atmos enabled), and where they’re located. Your receiver will decide—in real time—exactly
which speakers it needs to use from moment to moment in order to reproduce the sounds
of the car careening across the screen and the child fleeing up the stairs. That detailed, very
specific movement of sound helps your brain suspend disbelief and feel as if what you’re
watching is real.

The flexibility of Dolby Atmos object-based sound makes it incredibly adaptable. A Dolby

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Atmos movie can be played back on nearly any speaker configuration in the home. You’ll be
able to hear the placement and movement of sound in a Dolby Atmos movie whether you
have a system with five speakers on the floor and two overhead, or 24 speakers on the floor
and 10 overhead (the current maximum for a Dolby Atmos supersystem). The more
speakers you have, the more precise the audio positioning becomes.

And you have lots of flexibility to upgrade your system. If you add more speakers, your AVR
can use them to provide you with even more detailed, richer sound.

Delivery of Dolby Atmos movies

Major Hollywood studios are partnering with Dolby to create Dolby Atmos home video
versions of current box office releases and previously released favorites. In addition to
global studio partnerships, Dolby is partnering with game, music, and broadcast content
creators to take advantage of Dolby Atmos technology for future home theater use.

We wanted to ensure that entertainment fans could get Dolby Atmos movies in the same
ways they get movies now, on Blu-ray Disc or through streaming video services.

We invented a new, scalable algorithm as well as new extensions for our existing
technologies, Dolby TrueHD, which is Dolby’s lossless Blu-ray™ format, and Dolby Digital
Plus™, which is used by leading streaming video providers or for secondary languages on

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Blu-ray Disc. Both formats now support Dolby Atmos sound, meaning that you’ll be able to
play Dolby Atmos movies from your Blu-ray player or streaming device.

A Blu-ray player that fully conforms to the Blu-ray specification can play a Dolby Atmos
movie without a firmware update. The player will need to be connected to an AVR capable
of supporting Dolby Atmos and set to audio bitstream out. Note that some Blu-ray players
default to secondary audio, a playback mode in which third-party content is mixed with the
primary soundtrack and output as a Dolby Digital signal; be sure to turn this feature off to
ensure decoding and playback of Dolby Atmos content by your AVR.

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There’s also no need to buy new HDMI
supports Dolby Atmos audio.

Dolby Atmos audio tracks (both Dolby TrueHD and Dolby Digital Plus) are backward
compatible. If you play a movie mixed in Dolby Atmos on a non Dolby Atmos system, you’ll
experience traditional 5.1 or 7.1 audio, depending on the layou t of your system. This means

cables. The current HDMI spec (v1.4 and later) fully

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content providers don’t need to maintain separate Dolby Atmos and non Dolby Atmos
mixes.

Setting up your Dolby Atmos home theater

Although Dolby Atmos is a revolutionary new home theater format, it doesn’t require that
you start from scratch. Although you will need a new AVR, in most cases, you’ll be able to
keep most, if not all, of your existing speakers.

Many people now have 5.1 or 7.1 systems with a subwoofer and either five or seven
speakers positioned at about ear level. Many of these speakers will work wit hout a problem
in a Dolby Atmos system.

The importance of overhead sound

In real life, sounds come from all around us, including overhead. Having the ability to
recreate overhead sounds is a key element in making Dolby Atmos sound so realistic. If we
see a helicopter take off onscreen and then hear its blades cutting through the air above our
heads, the experience makes us feel like we’re really in the scene, not just watching it.

Dolby Atmos cinemas recreate these overhead sounds with an array of overhead speakers
above the audience. Some home theater enthusiasts will also be able to install speakers in
or on their ceilings, but you don’t have to.

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But if you already have conventional speakers you like, you can simply buy Dolby Atmos
enabled add-on speaker modules. These include only the upward-firing elements. You can
place these add-on modules on top of your current speakers or on a nearby surface.

Figure 4: You can place Dolby Atmos enabled add-on speaker modules on top of or near your existing traditional
speakers.

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Dolby Atmos enabled speakers can produce an incredibly accurate Dolby Atmos experience
in many types of rooms. You’ll get the best sound if your ceiling is f lat (not vaulted or
angled) and made of an acoustically reflective material, such as drywall, plaster, concrete,
or wood. Testing by Dolby suggests that the user can achieve a high-quality overhead
experience from Dolby Atmos enabled speakers in environments where the ceiling height
ranges from 8 to 14 feet (2.4 to 4.26 meters).

In fact, the system is so robust that recessed lighting fixtures, chandeliers, crown molding,
and heating or air conditioning vents in your ceiling do not noticeably interfere with the
Dolby Atmos experience.

When to avoid overhead speakers

There are some rooms in which we don’t recommend using overhead speakers. If your
ceiling is low or you have to mount your loudspeakers on overhead trusses or brackets, the
overhead speakers will be closer to the listening position. The audio may be distracting
because you’ll hear exactly which speaker is producing the sound instead of feeling
immersed in an atmosphere in which sounds occur naturally overhead.

In this environment, Dolby Atmos enabled speakers may better reproduce the Dolby Atmos
sound you would hear in a movie theatre, where the overhead speakers are high in the

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auditorium, creating a more diffuse experience. Audio experts who have heard Dolby Atmos
enabled speakers agree that in certain rooms, the sound these speakers produce can be
preferable to the sound that overhead speakers produce.

Speaker recommendations

Dolby recommends that you use four Dolby Atmos enabled speakers when possible. Use of
four speakers will make the placement of overhead sounds more accurate, and you’ll get
more precise, realistic sounds as an object—such as a helicopter—passes overhead in a
video. Two of the speakers (whether they are integrated speakers or add-on modules)
should be in the front left and front right speaker locations of your system. The other two
should be positioned in the surround sound speaker locations, ideally the rear surround
speakers, if you have them.

If you opt to use only two Dolby Atmos enabled speakers, you’ll still g et a very immersive
experience, with sounds moving overhead. Simply place the Dolby Atmos enabled speakers

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at the front left and front right speaker locations.

For the best sound, place your speakers at or slightly above the height of your ears when
you’re seated. Avoid placing the Dolby Atmos enabled speakers higher than one-half the
height of your wall. Make sure the speakers are at least 3 feet (0.9 meter) away from you,
ideally 5 feet (1.5 meters) or more. If you’re using add-on modules, place them either on
top of your front and surround (ideally, rear surround) speakers or within 3 feet (0.9 meter)
of those speakers.

If you use overhead speakers, Dolby recommends that you use four or more speakers when
possible, though two speakers will still provide a great experience. If you use four overhead
speakers, you should place the front pair of overhead speakers in front of the position
where you’ll be listening and the second pair of overhead speakers behind you when you’re
seated. If you use two overhead speakers, mount them slightly in front of where you’ll be
listening. The ideal overhead speaker should be timbre matched to your primary speakers
and support equal power handling capabilities and full range performance.

Dolby recommends overhead speakers with wide dispersion patterns. If you use overhead
speakers with narrow dispersion (less than 90 degrees by 90 degrees) or those with aimable
drivers, angle the drivers slightly toward your listening position.

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The following figures show the most common speaker layouts in a Dolby Atmos system for
home theater.

Figure 6: A traditional 7.1 speaker layout with four Dolby Atmos enabled speaker s (7.1.4).

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Figure 7: A traditional 5.1 speaker layout with four Dolby Atmos enabled speaker s (5.1.4).

Figure 8: A traditional 5.1 speaker layout with two Dolby Atmos enabled speaker s (5.1 .2 ).

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There is one important consideration in expanding your system: new speakers must be
added to your Dolby Atmos system in pairs. A new speaker on the right side of the room
must be matched by a similar speaker on the left side of the room. This is true for speakers
located on the floor as well as overhead. This pairing ensures a balanced soundstage. The
exceptions to this rule are when you add speakers in the center or center back locations.

For high-end home theaters, a 7.1.4 system (a traditional 7.1-channel-based layout with
four overhead or Dolby Atmos enabled speakers) will provide a great listening experience. If
you’re ambitious, though, Dolby Atmos can support home theater systems with up to 34
speakers in a 24.1.10 configuration: 24 speakers on the floor and 10 overhead speakers.

Importantly, Dolby Atmos content is not tied to any specific playback conf iguration.
Whether you have a full 7.1.4 system, a 5.1.2 system, or an ultimate 24.1.10 Dolby Atmos
system, your receiver will get the same content and play it back in a way that takes full
advantage of your specific setup.

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As a starting point, Dolby recommends that any system include speakers in the positions
normally designated for a 5.1 system. This allows you to play legacy, channel-based content
as well as Dolby Atmos content.

Making the right connections

Once you have your speakers set up and you’ve purchased a new AVR, it’s time to hook up
your new Dolby Atmos system. Many AVRs that support Dolby Atmos have speaker
connections labeled HEIGHT. (Some AVRs do not use that label, but they allow you to
assign terminals for the height outputs.) Connect your Dolby Atmos enabled speakers or
overhead speakers to those outputs. If you’re using four Dolby Atmos enabled speakers or
overhead speakers (or think you might in the future), you need an AVR with four height
outputs.

Of course, not all the content you play on your home theater w ill be in Dolby Atmos. The
good news is that a Dolby Atmos home theater can play any channel-based content. You
can choose to have Dolby surround technology automatically adapt that channel-based
signal to use the full capabilities of your new system, including your overhead speakers,
thus ensuring that you hear realistic and immersive sound.

If you’re not able to upgrade your home theater to Dolby Atmos yet, we still recommend
that you purchase the Dolby Atmos version of content whenever that is available. The Dolby

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Atmos format was designed to be backward compatible, so it will play on both new and
existing hardware platforms. In the future, upgrading your equipment to products capable
of supporting Dolby Atmos will unlock the ultimate experience from Dolby Atmos content. In
the meantime, you will get a great surround experience from traditional channel-based
home theaters.

The technological building blocks of Dolby Atmos

Initially, you’ll be able to play Dolby Atmos content from a Blu-ray Disc or from a streaming
video service. Eventually, cable, terrestrial, and digital broadcast systems as well as video
game consoles will be capable of providing Dolby Atmos content.

To support the transport of Dolby Atmos content, we’ve updated and improved many of the
underlying Dolby technologies already in use today, including Dolby TrueHD, Dolby Digital
Plus, and Dolby Metadata-Enhanced Audio Transmission (MAT), while maintaining their full
compatibility with older content formats.

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The key to creating Dolby Atmos sound is the ability not only to recreate a movie’s sound—
such as the whine of an ambulance siren—but also to place that siren’s whine in a specific
place and recreate its movement through space as intended by the audio mixer. All Dolby
Atmos content includes both sounds and metadata that describe how those sounds move
through the multidimensional sound space.

The Dolby Atmos object audio renderer is the intelligence that directs the system. It
determines—on the fly—how to use your speakers to place and move sounds in exactly the
way the filmmaker intended.

The Dolby surround upmixer allows you, if you wish, to play channe l-based content while
making full use of your Dolby Atmos home theater, including overhead or Dolby Atmos
enabled speakers.

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Figure 9: This diagram represents the workflow for translating cinematic Dolby Atmos content to home theaters.

Dolby Atmos in Dolby TrueHD

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Dolby has expanded the Dolby TrueHD format, used in Blu-ray discs, to allow the format to
support Dolby Atmos content. Before Dolby Atmos, Dolby TrueHD provided lossless support
for channel-based audio, such as 5.1 and 7.1. We have added a fourth substream for Dolby
Atmos sound. This substream represents a losslessly encoded fully object-based mix.

Dolby Atmos in Dolby TrueHD is transmitted from a Blu-ray player to your AVR via an HDMI
connection. If your AVR supports Dolby Atmos, the Dolby TrueHD object-based audio and
related metadata will be decoded, processed, and rendered to your specific speaker
configuration.

Dolby Atmos audio can be encoded with Dolby TrueHD at multiple sampling rates (including
48 and 96 kHz) and bit depths (16- and 24-bit). Dolby Atmos enabled receivers will also
support legacy Dolby TrueHD bitstreams at multiple sampling rates ( including 48, 96, and
192 kHz) and bit depths (16-, 20-, and 24-bit) to provide full backward compatibility with
legacy Blu-ray Disc media and Dolby TrueHD music files.

Dolby Atmos in Dolby Digital Plus

The update to Dolby Digital Plus features a new decoder capable of processing content
encoded for Dolby Atmos. This module utilizes n ew bitstream metadata to extract Dolby
Atmos object audio and outputs this information for further processing. The sampling rate
for Dolby Atmos content is 48 kHz, the same sample rate for Dolby Digital Plus content.

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Both new audio decoders are designed to be fully backward compatible with legacy channel­based Dolby Digital Plus and Dolby TrueHD soundtracks

Dolby Atmos in Dolby MAT

In the past, the Dolby MAT encoder resided in a Blu-ray player to pack the variable bit-rate
Dolby TrueHD bitstreams for transmission over the fixed bit-rate HDMI. A MAT decoder is
subsequently used in an AVR to unpack the Dolby TrueHD bitstreams. With the introduction
of Dolby Atmos, we have expanded this technology to support encoding of Dolby Atmos
content as lossless pulse-code modulation (PCM) audio.

A key benefit of Dolby MAT 2.0 is that Dolby Atmos object audio can be live encoded and
transmitted from a source device with limited latency and processing complexity. Among
the possible sources are broadcast set-top boxes and game consoles. The Dolby MAT 2.0

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decoder in an AVR outputs the object-based audio and object audio metadata for further
processing. The Dolby MAT 2.0 container is scalable and leverages the full potential of the
HDMI audio pipeline.

Dolby Atmos object audio renderer

The Dolby Atmos object audio renderer is essentially the brain of a Dolby Atmos home
theater. Dolby Atmos content consists of both sound objects and metadata that includes
information about where those sounds should be placed and how they should move, along
with other data such as the type of object represented. The Dolby Atmos object audio
renderer knows the speakers available in your system (you’ll su pply this information by
following the setup instructions provided by your AVR manufacturer) and determines which
speakers to use from moment to moment to recreate the sound the filmmakers intended.

Depending on the receiver configurations, the Dolby Atmos object audio renderer can
support as many as 34 speakers—24 traditional floor-standing speakers and 10 overhead or
Dolby Atmos enabled speakers—along with one or more subwoofer(s). The renderer also
supports smaller configurations, making it fully scalable an d adaptable to a variety of home
theaters.

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Figure 10: Dolby Atmos for home theaters supports as many as 24 speakers on the floor and 10 speakers
producing overhead sound.

Dolby surround upmixer

If you invest in building a Dolby Atmos home theater, you want to get full use of it, ev en if
the content you’re playing isn’t mixed in Dolby Atmos. Th at’s where the Dolby surround
upmixer comes in.

If you choose to enable it, the Dolby surround upmixer expands the audio of legacy
channel-based content to take advantage of your entire system, including overhead or
Dolby Atmos enabled speakers. The Dolby surround upmixer employs th e original
soundtrack to create a highly accurate rendering of the environment in the movie while
simultaneously honoring and maintaining the artists’ intent for the mix.

Unlike previous wideband upmixing technologies, the Dolby surround upmixer operates on
multiple perceptually spaced frequency bands for a fine-grained analysis of the source
signal. The Dolby surround upmixer can individually steer frequency bands, producing
surround sound with precisely located audio elements and a spacious ambience. The Dolby
surround upmixer is included in the Dolby Atmos technology bundle and replaces the Dolby
Pro Logic II family of upmixers, offering greater flexibility and superior audio performance.

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To maintain the frontal spatial audio image, the upmixer will not send upmixed audio to
speakers that are located between the left, center, and right speakers or to the left and
right wide speakers. Additionally, the unmixed audio is not sent to the center surround
speaker. Spatial imaging is complemented through the use of overhead or Dolby Atmos
enabled speakers in these cases.

Translating cinematic Dolby Atmos content to the home

As we’ve noted, Dolby Atmos allows each sound in a movie scene to be represented as a
separate audio object. And each of these objects has its own metadata describing precisely
where it should originate and how it should move, among other data. This approach
produces incredibly lifelike sound, but for a scene with lots of action, it also produces a lot
of data. Getting all that data to your living room through th e limited bandwidth of a Blu-ray
Disc or streamed media pipeline is a challenge. We’ve met that challenge with a technology
called spatial audio coding.

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Spatial audio coding takes into account the spatial information , along with other
information, about the sound objects to efficiently encode them in Dolby TrueHD and Dolby
Digital Plus. Spatial coding is not a channel-based, matrix-en coding system like Dolby Pro
Logic II or Dolby Pro Logic IIz. Instead, it is a fundamentally new coding technique that
allows all of the original cinema audio objects to be sent to your home theater.

Filmmakers frequently remix a film to sound its best in h ome theaters (a process known as
creating a near-field mix). Spatial audio coding is a tool available to sound professionals in
the near-field mixing process. During playback, filmmakers can mon it or exactly how the film
will sound when it is encoded to Dolby Digital Plus for streaming or encoded losslessly in
Dolby TrueHD for Blu-ray.

Creating Dolby Atmos soundtracks

The first Dolby Atmos content for home theaters will be delivered via Blu-ray Disc and
streaming video via over-the-top (OTT) services. For Blu-ray, studios may employ lossless
Dolby TrueHD for the primary soundtrack and Dolby Digital Plus for secondary languages.
OTT services will be supported by Dolby Digital Plus. In the future, Dolby Atmos content will
be delivered via video on demand (VOD), broadcast (terrestrial and digital), and cable
services that use multichannel Dolby Digital Plus in their core architecture.

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Production houses that create Dolby Atmos content for home th eaters will use a tool called
Dolby Media Producer, along with its suite of professional encoding, decoding, and media­related tools.

Before using Dolby Media Producer, though, production houses have the option to perform
several preliminary steps, including a near-field remix and remastering of the cinematic
master file. In this stage of the process, audio mixers may make small adjustments to the
mix to ensure that it sounds as they inten ded in Dolby Atmos enabled home theaters.

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Figure 11: The content creation workflow for Dolby Atmos home content.

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Conclusion

Dolby has invested years of engineering and research work into accurately translating the
Dolby Atmos experience from the cinema to home theaters. Today we can bring a Dolby
Atmos experience to the home through established delivery methods while maintaining
backward compatibility with legacy playback systems. The result is nothing short of the
most realistic and immersive entertainment experience ever available for home theaters.

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Dolby, Dolby Atmos, Pro Logic, and the double-D symbol are registered trademarks of Dolby Laboratories.
Dolby Digital Plus is a trademark of Dolby Laboratories. All other trademarks remain the property of their
respective owners. © 2014 Dolby Laboratories, Inc. All rights reserved. S14/28273/28307

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