Where Is My Atmos, and What Is An IAB?

By C J Flynn | June 13, 2022 12:05 am PDT
Where Is My Atmos and What Is An IAB?

SPOILER ALERT: IAB is the SMPTE standard; Dolby Atmos is a system that can playback that standard.

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, IAB, is the 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 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 Audio Compliant 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:

  1. All movies that use the standardized method for Immersive Audio will use the term “IAB Compliant“
  2. IAB Compliant soundtracks will be labeled “IAB” in their Content Play List (CPL) and via the DCP Naming Convention
  3. A cinema’s Media Player, Theater Management System (TMS) or Library Management System (LMS) will begin displaying the term “IAB,” not Atmos
  4. Cinema operators may be more familiar with seeing Atmos on the designation for a movie. In the future, only IAB will be used.
  5. This will not change the content in DCPs – Dolby has been shipping SMPTE Compliant “IAB” DCPs for many years.

Soon, your TMS and SMS will only display “IAB”. The 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 change in naming so that there is no confusion and 11th hour panic calls.

The Long Explanation – A Detailed A 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. If you want to talk to techs, you have to be familiar with these TLAs, just so you can nod your head wisely – then look them up later.

IAB stands 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.

The Auditorium Audio System from the library system to the speakers. The IAB – Immersive Audio Bitstream – device is shown in green. Like the Media Server and the Audio Processor, these might be inside the projector, or they might be separate units.

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 magic. The stream of data follows a standard that was agreed upon by a lot of engineers who do understand magic.

They 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 of information uses bits of information, so it is called a ‘bitstream’. Since it is a computer, the word “bits” has a special definition. And, of course, it is a crazy computer-style abbreviation.

Computers – in their deep dark places – only understand two choices. Everything in the memory, everything in the processors, and everything in the back and forth communication, is described as a one or a zero – or combinations of ones or zeros. We say that every unit of information is one of these “binary” choices. Binary means exactly that: Two Choices. In computers, each Binary Digit are called a “Bit.” When those bits are put together in a particular order, and sent in a stream from the magic box, that stream of bits is called…all together now – it is called a Bitstream… really, it is a kind of magic.

Theater Management Systems (TMS) and SMS units pull their movie titles from the Content Play List (CPL), a text file in the Digital Cinema Package (DCP) – the portion that they show is the ContentTitleText (CTT). These screenshots show part of the CPL for the same movie, demonstrating how the small change in the CTT will appear – and therefore, what the TMS and SMS will show when Atmos movies are listed as IAB movies.

Before Dolby Atmos
Before the release of the Dolby Atmos sound system at CinemaCon in April of 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 the three front channels (Left, Center and Right) and the 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 2 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.” The tech actually would be talking about all of the speakers on the left wall of the auditorium.

Each of the front speaker cabinets usually have more than one speaker also. Inside there is usually a high frequency speaker and perhaps 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 go from one amplifier channel to one channel of speakers.

What Did Atmos Add?
The Dolby Atmos system introduced a new concept to the auditorium. The name of this new development is called the “Object”.

The Atmos system still includes the 5.1 or 7.1 channels. It calls these the Bed Channels.

The word “bed” has a tradition in the music business. For example, if you hang around a band you will hear them 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.

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 5 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 8 additional speakers plus the bed channels, but in another auditorium there might be 20 additional speakers – and they are placed in different places in the auditorium. In fact, the total combination of speakers can be 64. So, maybe there is a speaker in that position, …but there probably isn’t.

And it requires magic to do this. Computer magic. And sound magic. That kind of magic that tricks the Human Hearing System (HHS).

The additional speakers for the objects to use are circled in red – the magic is that there could be more, or less. The IAB unit guides the sounds to the proper speakers to help duplicate the sound that the mix engineer and director want us to hear.

The Evolution of Cinema Sound
This is simple magic. After a long time of practice, 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 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
When two separate channels became available for sound, the audio mixer has some decisions to make. They can mix everything 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 might be perfect, for example, if two people are standing on the left side of the screen, it is logical that this sound is all coming from the left speaker. The same is true if people are on the right side of the screen, to put their sound into the right speaker. It would certainly be confusing the other way around.

But, if you are sitting on the left side of the screen, you might not hear the sound from the right side. 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 center, the less the phantom center effect is created.

Fortunately, in cinema auditoriums, there is a center speaker. When a person is walking from the left to 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.

Immersion Mimics Real World Sound
The Immersive Audio standard uses this phantom trick. If the mixer wants the sound of an eagle to be over your head at 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 speaker to get that sound to “appear” to be where they want it.

This is an example of an audio mixing tool used to make an Immersive Mix – which puts objects into 3D space. They are typically plug-ins or are already incorporated into programs – such as the Dolby tools built into Logic Pro, Final Cut Pro, and DaVinci systems.

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

Imagine, or even take some time to draw a picture of all these elements happening for one sound. Go ahead. Take a minute and 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 erasers 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 and pencils or batteries and cables or whatever else you have on your desk is showing how an Immersive Audio Bitstream works. Yell out, IAB! A stream of bits representing audio that is immersive.

These are examples of The Sony and Arts Alliance Theatre Management Systems, both displaying “IAB” where Atmos used to be.

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 or 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.

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 company’s 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.”

The Final Stages – One Bitstream To Rule Them All
SMPTE helped assemble technical volunteers from many manufacturers, and 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 viewers 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.

But Will it All Work Together?
That was the question and task for the group known as the ISDCF – the InterSociety Digital Cinema Forum. This group of professionals from all over the world and all segments of the industry took on the task of coordinating the creation of test material and gathering together the engineers and equipment from different companies into many auditoriums for this practical application. In an adventure called a “plugfest,” a great 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 that there is 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 that are unique to a plugfest.

…and that is the end of the long explanation of: Why “Why “Immersive Audio Bitstream – IAB – is the SMPTE standard; Dolby Atmos is a system that can playback that standard.”

Now sound mixers have a rather elegant tool for placing sounds in space and fulfilling the Director’s Intent. We have all experienced the evolution of that Immersive Audio, from the wonderful sound of the river splashing on the roots and boots in “Revenant,” and the way the effects gave 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 someone had done that 10 years ago, people would have freaked out!

Now cinemas have a new tool to differentiate their offerings from the home experience. Certainly, there are home DTS:X, Dolby Atmos and Auro products, but they don’t play sustained high impact audio like in a movie theatre. To begin with, the laws of physics demand a large room to get the super low-end sound going.

But that is a different lesson for another time.

Now we only have to remember: Beginning 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 Theater Management System… and the External Media Server… instead of Atmos.

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 interfacing standards,

  • 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
C J Flynn