CJ Flynn explains why an Atmos DCP label will soon just say "IAB"

WHERE’S MY ATMOS?

Spoiler alert: IAB is the SMPTE standard; Dolby Atmos is a system that can playback that standard.

AND WHAT’S AN IAB?

CJ Flynn, Detailer, CinemaTestTools.com

Does your cinema have a Dolby Atmos immersive audio rendering system? Are you playing DCPs labeled “Atmos”? Then your cinema can also play a DCP labeled with “IAB”... … and that labeling is what you will see on DCP file names - instead of Atmos - moving forward.

The purpose of this article is to inform movie theatre operators that a change is coming which will cause people who examine the TMS (theatre management system) for keys and correct DCPs to wonder where their Atmos DCP has gone, and also to help train those who only know, robotically, what to look for. If you are confused by any of these three letter acronyms, have no fear, they will all be explained momentarily.

The Short Explanation

Immersive audio is a technology defined by a set of SMPTE standards that all immersive audiocompliant media players follow. This includes integrated media blocks (IMBs) inside the projector, and separate external systems (SMS).

The SMPTE ST 2098 standards for immersive audio were originally published in 2018 and are now finally being adopted by the cinema industry. Thus, content owners (i.e. studios) and content service providers (i.e. motion picture labs) will start distributing movies with the IAB label meaning:

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All movies that use the standardized method for immersive audio will use the term “IAB compliant”.

IAB compliant soundtracks will be labeled “IAB” in their content play list (CPL) and via the DCP Naming Convention.

A cinema’s media player, TMS or library management system (LMS) will begin displaying the term “IAB,” not Atmos. Cinema operators may be more familiar with seeing Atmos on the movie designation. In future, only IAB will be used.

This will not change the DCP content – Dolby has been shipping SMPTE Compliant “IAB” DCPs for many years.

Soon, your TMS and SMS will only display “IAB”. They will not display the word “Atmos”.

When will this happen?

Sometime in the near future. The

studios need to make certain the equipment is ready and the cinemas need to make certain their equipment is updated.

Studios also wish to make

certain that everyone is aware and comfortable with the name change so that there is no confusion and / or 11th hour panic calls.

The Long Explanation: A Detailed Background

In the Digital Cinema Book of Abbreviations, most entries are created by combining the first letter of each word.

These are called acronyms – IAB is one more three letter acronym (TLA) in the cinema technology pool, standing for immersive audio bitstream. Bitstream is a computer term that we should explain first. Simply put, in a standard audio system the audio starts from the media server, then goes to an audio processor, then is played directly into the sound system... read on for more details.

Inside the Magic Box

In a sound system that can play immersive audio, the audio system includes a magic processor chip that delivers a second stream of information to the sound system. The chip may be magic, but the information it is sending – called a data stream – is not. The stream of data follows a standard that was agreed upon by a group of engineers, who designed an immersive audio standard so that every magic “IAB” system will receive the same immersive audio information, then do its magic to present it to the immersive audio speaker system. That stream uses ‘bits’ of information, so it is called a ‘bitstream’. Since it is a computer, the word ‘bits’ has a special (crazy computer-style) definition.

Computers only understand two choices. Everything in the memory, the processors, and in the back and forth communication, is described as a one or a zero (or a combination of both). Every unit of information is one of these “binary” choices. Binary means exactly that: two choices. In computers, each binary digit is called a “bit.” When those bits are put together in a particular order, and sent in a stream from the magic box, that stream is called… a bitstream.

A UDIO SYSTEM FROM SERVERS TO SPEAKERS

SOUND & VISION ACCESSIBILITY EMITTER

CLOSED CAPTION EMITTER RJ45 SWITCH

NON DCI PROJECTOR

2K / 4K DCI PROJECTOR

MEDIA SERVER

ATMOS

D/A CONV EQS AND AMPS

Before Dolby Atmos

Before the release of the Dolby Atmos sound system at CinemaCon in April 2012, there were mainly 5.1 and 7.1 surround sound systems. The 11.1 and 13.1 Auro systems from Barco were released a few years prior in 2010. These systems are called “channel-based”. Typically, these systems include three front channels (left, center and right) and two surround channels (left surround and right surround). They also include the “point 1” of the 5.1 channel-based system – the low frequency effects (LFE) channel. The 7.1 system added two rear surround channels. The Auro system added upper channels to include a height element.

Just to be clear, even though the LFE channel might have several cabinets of speakers, it is only one channel. This is the same for the side surround channels – every speaker on one wall gets the same channel of sound. Together they are called an “array” or “speaker array”.

For example, you might hear a tech say, “The amplifier for the left surround array is fried.” And the tech would be talking about all of the speakers on the left wall of the auditorium. Each of the front speaker cabinets also usually has more than one speaker. Inside, there is usually a high frequency speaker and perhaps a mid-frequency speaker and one or two low frequency speakers. But each set is still just one channel.

And just to emphasize the point: usually, if you look at the back of the amplifier rack, one set of wires goes from one amplifier channel to one channel of speakers.

What Did Atmos Add?

The Dolby Atmos system introduced a new concept to the auditorium, called the “object”. The Atmos system still includes the 5.1 or 7.1 channels and it calls these the bed channels. The word “bed” is used in the music business. For example, you will hear a band say, “Let’s lay down the bed tracks.” Those are the basic tracks for the rhythm and harmony with the main melody elements of a song. So, bed tracks in a DCP are the basic 5.1 or 7.1 channels of the movie’s audio. But the object is different. It is a sound, but it has no particular channel to play out of. There is no particular cable for it to travel on. The object has a position in space to go to. It needs an IAB system to tell the sound object, “Go to four meters in front of the screen, three meters from the left side and one meter from the ceiling. Be very narrow, but very loud. Then take five seconds to move somewhere else in 3D space and be very wide.” However, those positions in space probably don’t have a speaker, right? Because if they did, the speakers would be blocking the picture on the screen.

In fact, with Atmos and the other systems, AuroMax and DTS:X, there are a lot of extra speakers. The problem is that a smaller auditorium might only have eight additional speakers

Additional speakers for the object to use are circled in red

The Evolution of Cinema Sound

This is simple magic. After a lot of practise, several engineers in different parts of the world noticed that you can trick the hearing system if you could play sound from a combination of speakers.

To explain this, we will go back before all these extra channels, to the time when there was just one speaker, the mono speaker. Then we will proceed to the left and right. Then, the magic of stereo.

Because, for a long time, there was only one speaker behind the cinema screen. After a while, some people put in multiple speakers, but all playing the same sound. That was just the level of the technology of the time. You need more volume, you need more speakers. But the signal was mono – one channel. Since there was nothing else to compare it to, they probably just called it “the speaker,” not the mono speaker. That is similar to the acoustic guitar. Before the electric guitar was developed, no one called it the acoustic guitar. It was just the guitar.

Mono to Immersive

So when two separate channels are available for sound, the audio mixer has some decisions to make. Everything can be mixed to one channel or to the other, or to both.

For example, the sound mixer might put all the sound from one voice, or one instrument of the music, into one channel. That would be fine if two people are standing on the left side of the screen and the sound is all coming from the left speaker. The reverse is true if people are on the right side of the screen. But it would certainly be confusing the other way around. So, many mixers might put all the sound into both speakers.

There is a trick that can be played on the ear, though. If the same sound comes from two speakers into the ears at the same time, the sound will seem like it is coming from the center speaker – even if there is no speaker there! This is called a phantom center. If you are sitting in the center seat you can hear this most clearly. People on either side can partly hear it, but not as perfectly. And the further from the center, the less the phantom center effect is created.

plus the bed channels, but in another auditorium there might be 20 additional speakers, in different positions. In fact, the total combination of speakers can be up to 64. So, maybe there is a speaker in that position… but there probably isn’t.

And it requires computer magic - and sound magic - to do this. This magic tricks the Human Hearing System (HHS).

Immersion Mimics Real World Sound

The immersive audio standard uses the phantom center trick. If the mixer wants the sound of an eagle to be over your head in a certain position, they move a position pointer to that place and the computer creates a magic set of numbers for that sound to be in that place at that time. It might use some of the side speakers, and some of the front speakers to get that sound to “appear” to where they want it.

Remember that bitstream stuff from earlier? Those position and time values, with the values for the level of that

But, fortunately, in cinema auditoriums, there is a center speaker. So when a person is walking from the left to the right side of the room, the mixer doesn’t have to play tricks to get the sound to seem like it is going from one side of the screen to the other. Using the surround speakers lets the mixer take the sound further right and left around you. sound, and how wide or narrow? What the mixers place into space are all converted into bits, which all flow into a larger number of bits; the bitstream.

Try drawing a picture of all these elements happening for one sound. Draw three speakers making a sound of an explosion that starts as a small point then expands to a large space. Draw a picture of another then another. Write down some numbers under each speaker to represent the percentage of the sound from each, and another number for the volume from each. Use paper clips or whatever is on the desk to help. Now, move all of this work across the desk and prove that gravity works. That waterfall of paper, pencils or batteries and cables or whatever you used is showing how an immersive audio bitstream works. Yell out, IAB! A stream of bits representing audio that is immersive.

Imagination | Engineering | Artist Intent

So, that’s it. Easy, right? A bunch of engineers figured out how to convince computers to do magic, creating phantom sounds that can appear anywhere... and the magic boxes can make the same phantom sound appear using eight speakers or using 20, 32 or 64 speakers.

The engineers at Dolby put rows of additional speakers on the ceiling. The Barco engineers put the Auro speakers above the surround speakers, at the edge of the ceiling, and one or more speakers on the ceiling, using a concept of layers.

The Xperi engineers also have a formula for their DTS:X Cinema System which defines the speaker placement depending on the room.

In an Atmos system, each speaker of a surround array now gets its own amplifier for an Atmos mix for an immersive audio mix. When playing a 5.1 or 7.1 movie, they get treated as an array, but when a movie is in “immersive mode” the mixer can also use them to precisely plan an object in space. DTS:X and Auro keep these as arrays in immersive mode.

THE PHANTOM CENTRE

Will it all work together?

That was the question and task for the ISDCF – the InterSociety Digital Cinema Forum.

This global group of industry professionals took on the task of coordinating the creation of test materials and gathering engineers and equipment from different companies for this practical application. In what’s called a “plugfest,” a list of tests and processes are performed individually and randomly until there is some certainty how the equipment will perform when applying the SMPTE standards. Sometimes, the only certainty is>

EQUAL SIGNALS

PHANTOM CENTRE

EQUAL SIGNALS EQUAL DISTANCE

The layered speaker concept in an auditorium

Auro 3D Panner puts objects into 3D space

Today, Dolby Atmos content is being mixed and mastered in dubbing stages on Dolby Atmos authoring tools and being provided to Dolby Atmos-equipped auditoriums for a unique Dolby Atmos experience.

Back to the Reality of Making Magic

After all the engineering work, each company spent millions to make the chips and new variations of those chips, and then the final verification of those chips, not to mention all the development work that makes certain features of their products possible. But the movie studios said, “We only want to distribute one version of the immersive audio movie, not one for every company who makes a different bitstream.”

And the cinema exhibitors said, “We are not going to buy something like this unless it will work with all the different bitstreams. No matter what, we have to buy a lot of new amplifiers and a lot of new speakers and hang them and wire them. Just the cost of the scaffolding will be $100,000. The magic boxes must be compatible.”

One Bitstream To Rule Them All

SMPTE helped assemble technical volunteers from many manufacturers, many studios, and many system integrators, and even a few techs from cinemas. Countless weekly meetings occurred for several years to make certain that the various immersive audio “magic” systems would all understand the same language and the same definitions of space and time. (Seriously, there would be days of discussion about how to describe space – from the center of the screen? From the edge of the screen? From a viewer’s position in the center of the auditorium?)

Each system had to incorporate the same agreed upon functions, using the same terms, while also leaving space for specialty features that are not shared or which might be developed in the future. In other words, each system follows the same instructions - IAB - and plays them back for their own distinctive immersive sound.

SMPTE Immersive Audio Standards

ST 2098-1 – Immersive Audio Metadata ST 2098-2 – Immersive Audio Bitstream (IAB) ST 2098-5 – Digital cinema immersive audio channels and soundfield groups Which work in conjunction with the following: ST 429-18 – D-Cinema Packaging – Immersive Audio Track File

ST 429-19 – D-Cinema Packaging — DCP Operational Constraints for Immersive Audio

ST 430-1 Addendum 2019 – Immersive Audio KDM [Key Delivery Message] ST 430-14 – Digital Sync Signal and Aux Data Transfer Protocol

ST 430-17 - SMS-OMB Communications Protocol

Specification EG 2098-3 - Immersive Audio Renderer Expectations and Testing Recommendations

Will it all work together?

that there’s more work to do, that some “obvious” understanding of the standards was a not-so-obvious misunderstanding – but these sessions are useful because the engineers actually get to see their equipment in action under circumstances unique to a plugfest. And that is the long explanation of “Why IAB is the SMPTE standard; Dolby Atmos is a system that can playback that standard.” So, now sound mixers have an elegant tool for fulfilling the director’s intent. We’ve all experienced the wonderful sound of the river splashing on boots in “The Revenant,” and the effects giving us the point of view of “The Batman,” while its music was placed around the screen so it didn’t interfere with the dialog. If that had been done 10 years ago, people would have freaked out! So remember: soon, every Atmos movie that is released to over 6,000 Dolby Atmos auditoriums will have IAB on the label of the DCP file name... and the TMS... and the external media server... instead of Atmos.