The Fundamentals of Atmos (3 Viewers)

[JohnRice]

Understood. So what about my two rear speakers Dolby EX, each on separate channels? (this is my last question, I promise!!)

Those are essentially the same as the rear surrounds in a 7.1 DTS HD or Dolby HD soundtrack.

So, like I said, you basically have a 7.1 system, you just duplicated the two side surround channels into two duplicate pairs of speakers. If the room is deep and you have multiple rows of seating, it makes sense to do that.

 

[JohnRice]

What is the actual crux here? That setting up a home "ATMOS" system is just a waste of money because the overhead speakers are improperly or not used at all?

Not even remotely. My point is that, due to the limitations of the current HOME Atmos system, it's probably not worth going beyond the standard four surround and four overhead channels.

 

[Edwin-S]

Not even remotely. My point is that, due to the limitations of the current HOME Atmos system, it's probably not worth going beyond the standard four surround and four overhead channels.

Okay. That makes sense, since it looks like you are saying that Home Atmos only support a maximum of 12 channels.

 

[DFurr]

Those are essentially the same as the rear surrounds in a 7.1 DTS HD or Dolby HD soundtrack.

So, like I said, you basically have a 7.1 system, you just duplicated the two side surround channels into two duplicate pairs of speakers. If the room is deep and you have multiple rows of seating, it makes sense to do that.

I was thinking a 7.1 but you've confirmed that now.
Thanks

 

[JohnRice]

Okay. That makes sense, since it looks like you are saying that Home Atmos only support a maximum of 12 channels.

It's actually 16, but I don't want to go that road of semantics again regarding what channels and objects are. A channel is pretty much a defined thing, but "Objects" can have multiple meanings.

 

[Edwin-S]

Would most home theater setups in a typical home theatre even need more than 12 channels, supposing that Home ATMOS supported it?

I suppose that would be the case if a person was one of the 0.1% that lived in a cavernous mansion, but the typical middle class home?

 

[JohnRice]

Would most home theater setups in a typical home theatre even need more than 12 channels, supposing that Home ATMOS supported it?

I suppose that would be the case if a person was one of the 0.1% that lived in a cavernous mansion, but the typical middle class home?

That's basically my point. How many HTs would get any benefit from a system larger than 7.x.4 anyway? Home Atmos processors can theoretically produce many more channels than that. The problem is, home Atmos systems work a certain way up to 7.x.4, but things change once you go beyond that.

My basic impression is that if someone wanted more than four surround or overhead speakers, the way things currently work, they'd actually be better off configuring them the way Don did his second pair of side surrounds. By duplicating one pair of speakers, rather than adding another pair of processed ones.

 

[DFurr]

I've been retired from the theatre business since the year 2000, long before Dolby brought in Atmos. Do most commercial theatres put their Atmos speakers in the ceiling or on the side walls?

 

[JohnRice]

I've been retired from the theatre business since the year 2000, long before Dolby brought in Atmos. Do most commercial theatres put their Atmos speakers in the ceiling or on the side walls?

Well, the question is a little off. Atmos is a much more elaborate surround system that allows cinema theaters to have as many as 128 sound "Objects". Objects can be an single sound, or a collection of related sounds. As in, a helicopter flying overhead actually contains several sounds. At some point in the mastering process, every one of those sounds might have been a separate object, but in most cases, they'll be combined into a collection of related sounds, which can still be referred to as an "Object". That's where some of the confusion is coming from.

So, cinema Atmos has that vastly expanded channel/object capability, but it also includes overhead speakers. Atmos overall is the entire system, but the most obvious feature is the overhead sound capability.

 

[JohnRice]

I've been retired from the theatre business since the year 2000, long before Dolby brought in Atmos. Do most commercial theatres put their Atmos speakers in the ceiling or on the side walls?

To clarify, the overhead speakers are in the ceiling, not just high on the side walls. They are supposed to be over the audience’s heads. Not just elevated to the sides.

 

[Carlo_M]

This is one of the better videos I've seen explaining Atmos, beds vs. objects, and some good Q&A from an industry professional who does Atmos soundtracks (John Traunwieser) and some of the Audioholics guys and home theater installers. It's 2 hours but I had it going on in the background while doing chores and found it insightful and helpful.

 

[JohnRice]

This is one of the better videos I've seen explaining Atmos, beds vs. objects, and some good Q&A from an industry professional who does Atmos soundtracks (John Traunwieser) and some of the Audioholics guys and home theater installers. It's 2 hours but I had it going on in the background while doing chores and found it insightful and helpful.

They really got right to and confirmed a few of my issues withg the marketing of Atmos in the first ten minutes. He does confirm that going beyond 7.1.2 doesn't result in what most people tend to expect. He emphasizes 7.1.2 bed channels several times, though I thought the most common "bed" configuration was 7.1.4. Another bit of info that I suspected was his comment that excessive object use doesn't tend to mix down very well for more common home configurations, so it's generally not done.

I'll have to come back and watch at least all of the comments from the studio mixer.

 

[JohnRice]

...aaah. A second thing he confirms around 16:00 is that he believes the official Dolby guidelines for overhead speakers in a home setup is too far off axis from the viewing position.

 

[Carlo_M]

They really got right to and confirmed a few of my issues withg the marketing of Atmos in the first ten minutes. He does confirm that going beyond 7.1.2 doesn't result in what most people tend to expect

At the 10:30'ish mark he talks about if you're going to move a sound using the "bed" channels, it will skip speakers going from front to back, whereas if you're using objects, it will scale it like a vector and move it from front to back sending it through every speaker (this was in response to the question "can you comment on the claims that objects can't be placed between top front and LCR and top rears and surround rear. Basically there's large gaps where objects can't be placed").

Later in the video he says how movie soundtracks (music/orchestra) are almost never recorded in full Atmos, usually only in 5.1 surround at most, and so the movie soundtrack tends to live only in the bed layer and will never be in Atmos height speakers.

So what I took from it (layman that I admittedly am) is that if something is put into the bed channels, then it's confined in the 7.1.2 which is the limit of the Atmos bed channels. But if it's coded as an object, it can use the full 7.1.4. Now the question is: does every mixing engineer for the home (nearfield) mix go through this effort when converting from the theatrical mix (which can have many more overhead channels)? Or more likely, there is a workflow built into the renderer to automatically downmix the theatrical mix to a 7.1.4 speaker setup for home (if Dolby programmers are worth anything their renderer has presets/algorithms to do this so that an audio mixer doesn't have to re-create from scratch a separate home/nearfield mix). He indicates that he does (by his comments later in the video) but who knows what the industry standard practice is.

More importantly, if something is "upconverted" from a former 5.1 or 7.1 mix, how much time/effort does the person who creates the Atmos mix put in creating objects that use all four of the possible overhead Atmos speakers? I think that's an open question and likely varies from "hardly any effort" to "a lot" depending on the project and the care of the person(s) working on the new soundtrack.

Side note: what's funny is how unsettled the debate is even on 5.1 rear/surround speaker placement even among industry professionals who author the mixes (it's later in the video).

Next post will be a compilation of some definitions of Bed Channels, Objects, and Stems, as well as Dolby's implementation/explanation of them. I think I'm starting to get a little bit of an understanding now on the terms.

 

[Carlo_M]

Some helpful links, quotes and definitions:

Dolby's marketing spiel

Freeing sound from channels — the Dolby Atmos concept​

Dolby Atmos® creates powerful, moving audio by introducing two important concepts to cinema sound: audio objects and overhead speakers. Together, these completely change how soundtracks are created and heard.

Traditional surround soundtracks confine all sounds to a small set of channels that can deliver sound to you from only a few perceived angles. They cannot put sound above you. Further, sounds exist only as part of a channel mix. If one sound is emphasized in a traditional mix, another must be diminished.

In Dolby Atmos, by contrast, sound can be freed from channels. It enables artists to treat specific sounds as individual entities, called audio objects. These can be precisely placed and moved by the soundtrack creator anywhere in the cinema's three-dimensional space, though the artist can continue to use channel capabilities as desired. The Dolby Atmos cinema processor then determines which of a cinema's huge array of front, back, side, and overhead speakers it will use to recreate this lifelike movement.

As a result, a Dolby Atmos soundtrack brings alive the onscreen story as never before possible. The movie's sounds flow all around you to completely immerse you in the action, heightening the impact of the story and creating a powerfully moving cinema experience.

What is a bed?

A bed is a channel-based premix or stem that includes multichannel panning, and does not need dedicated panning via Dolby Atmos metadata. Use a bed for stereo or surround panning. A bed can be thought of as a traditional channel-based stem with the rules and expectations of stem configurations (such as 2.0, 5.1, and 7.1). These are fixed locations in space that are tightly constrained to traditional speaker environments, including theatrical environments where a speaker array might be used.

In Dolby Atmos, the largest bed configuration that exists is 7.1.2. This configuration allows for Low-Frequency Effects (LFE), with left and right side walls, and an additional overhead stereo pair. Dolby Atmos supports the use of multiple beds.

What is an object?

An object is a discrete audio element that can be placed anywhere in the three-dimensional soundfield. Objects can consist of mono or stereo content and are positioned via dedicated Dolby Atmos panning. Use objects for precision positioning of your content. An audio object can utilize as few, or as many, speakers as defined by the positional and size metadata for that object. Objects can be static or moving and are not constrained to the outside edges of the Dolby Atmos soundfield.

What is a stem?

In audio production, a stem is a discrete or grouped collection of audio sources mixed together, usually by one person, to be dealt with downstream as one unit. A single stem may be delivered in mono, stereo, or in multiple tracks for surround sound.

For the following this post will get too long if I paste each one here, but going to each page and reading it gave me a bit of a better understanding of Atmos.

What’s the difference between beds and objects?

What do I need in terms of source material to do a Dolby Atmos mix? (this one covers considerations of a mixer who is working off of older non-Atmos sources)

A nice little summary of the differences between beds and objects:

Dolby Atmos supports both object-based audio (objects) and channel-based audio (beds). An object will have its audio (mono audio clip) and the corresponding metadata, but Dolby Atmos also supports channel-based audio, by using 7.1.2 beds (7.1 + 2 height channels)

So what I'm reading there is a bit different than some of the posts on Page 1 and 2.

Object-based audio is from what I can tell, something that is new to Atmos, and contains both the sound and positional metadata. But you can't just have an Atmos soundtrack/program that only supports object based audio because that's not how most other audio (like the aforementioned movie's orchestral soundtrack) is recorded. Those are done in the more traditional channel-based audio, and those live in the bed layer. These don't have positional metadata like objects, but rather are assigned to channels (in stereo, left and right, in 5.1 L/C/R/SL/SR/LFE).

The one thing I keep reading in the earlier pages, but I haven't been able to confirm anywhere are the following statements:

Current home Atmos is limited to 16 channels, which in the lingo of Atmos are also called "Objects". Nothing is false in that statement.

Yes. The setup for a commercial theater is completely different, and much more complicated. No automation involved. Everything is mapped, if it's done correctly. Also, commercial Atmos has the capability for (as I recall) 168 objects, vs 16 for home.

So, as Josh also dug into, home Atmos soundtracks have 12 "bed" channels. That is the basic 7.1.4 configuration. Those channels (objects) are not object oriented.

This seems to be conflating what "beds" and "channels" and "objects" are (and are in conflict with the white papers from Dolby) and also assigning a 16 vs. 168 object maximum for home which I can't find confirmation of anywhere on the web other than these posts. That last part about Atmos having 12 "bed" channels contradicts Dolby's own admission that it only supports 7.1.2 bed channels. Anything that requires more precise positional location requires that the sound be coded as an object (with positional metadata) and not as part of the bed channel (because again, bed channels are for audio recorded in the more traditional channel-based methods).

I agree that there has to be, by definition, some downconversion from a fully discrete "maxed out" Atmos theatrical mix. In a fully decked out Dolby Atmos Theater there can be many more discrete overhead channels than the x.y.4 we have at home. So an object can be panned going from front to overhead to back in, say, discrete 15° increments (I'm making that number up but let's just say for the sake of argument there are 10 distinct overhead channels at about 15° intervals) and so when that sound's motion is "translated" to home Atmos, it has to be downconverted to the 2 front height and 2 rear height speakers to "approximate" the travel from front to overhead to back that was handled in a much more discrete fashion in the theaters. To my mind, it's just like a well-handled left-to-right pan on a stereo speaker setup. Could you have 9 front speakers with 9 discrete channels, 10° apart and would it make for a "smoother" left-to-right pan across 90°? Sure. But that left-to-right pan can still be successfully achieved with one L and one R speaker.

Again, one would hope that Dolby's automation tools within their renderer in the DAW would have the ability to do this conversion automatically without the mixer having to re-do all that work.

Now if as I mentioned in the previous post, the assertion is that most movies (whether new, or upconverted old soundtracks) don't make use of the overhead channels much, well that's something I can't speak to as I've not done a deep dive on it. But you know what? It didn't stop me from creating a 5.1 system when most movies were still stereo or Dolby ProLogic Surround. Because when you encountered that great 5.1 soundtrack, it made it worth it. So even if most movies don't activate my 4 overhead channels much, when they do, I'm glad they are there.

 

[JohnRice]

That last part about Atmos having 12 "bed" channels contradicts Dolby's own admission that it only supports 7.1.2 bed channels.

When I typed that I was going from memory about a conversation I'd had a year or two earlier. My mistake was thinking the maximum bed channel configuration was 7.1.4 (12) instead of 7.1.2 (10). I fail to see how that's a "contradiction" rather than just remembering the specific numbers incorrectly.

I also incorrectly remembered that theatrical Atmos can have up to 168 objects rather than what it actually can, which is 128. I believe I pointed this mistake out later. I even admitted I wasn't certain of 168, since I prefaced it with "as I recall".

At the time I was researching this, I did find sources discussing the 16 channel (or whatever you want to call it) limit of home Atmos, which includes the bed channels. I admit, it was difficult to find. But then it was personally confirmed by a resource I definitely trust. That conversation went on to include his wish that the home Atmos system would be expanded to 32 in the future.

My ultimate point remains, and the first minutes of the video linked earlier confirm, if you listen to it, that it's quite debatable how much benefit is gained by installing a home Atmos system larger than 7.1.4, or now it seems it might actually be 7.1.2, since the additional speakers will only reproduce dynamic objects (or stems...) so will reproduce little to no sound most of the time. That is what has been lost in all the hoopla.

I know this is difficult for people these days to understand. I genuinely am not interested in "right fighting". I'm trying to find out how it actually works, rather than trying to win an argument. Nothing I saw in the video contradicts what I've come to understand, other than my apparent mistake that the maximum bed channels is 7.1.2 rather than 7.1.4. I'm more than willing to admit to remembering that incorrectly.

 

[JohnRice]

There's a very interesting bit of info there in the Dolby links...

• Bed channels map differently to different overhead speaker configurations. Overheads in an x.y.4 configuration will create a phantom center of the x.y.2 component, whereas in an x.y.6 overhead configuration, it will use the point source speakers. If you have a concern about a source in the overhead beds, try switching it to an object so you can have more control over how it renders.

It seems to state that even though there are a maximum of two overhead bed channels, when the system has four overhead speakers, it will "phantom" the two channels to come from all four speakers, but when the system has six overhead speakers, the two overhead bed channels will only come from the center pair. That's a useful bit of info.

I wonder if it's common for an engineer who's tasked with remastering home Atmos soundtracks in previously released movies to just do some sort of Auto remaster to the 7.1.2 bed channels and call it a day.

 

[Carlo_M]

I'm not interested in "right fighting" either but I am interested in spreading correct(ed) information. I don't purport to have the answers up front and my stance can (and will) change if new, updated, factually corroborated information emerges.

My current understanding, based on both that video and the official Dolby documentation (from the professionalsupport.dolby site, not their pretty aimed-at-consumers site) are that bed channels and objects are two distinctly different things. Bed channels are for audio tracks and stems that are recorded in the traditional channel oriented fashion. For stereo this would be Left and Right, for 5.1 it would be L/C/R/SL/SL/SW, etc. These have zero Atmos positional metadata. This support needs to happen as every soundtrack and audio track not encoded as an object is/was recorded in this fashion.

Objects comprise both the audio and positional metadata which tells the Atmos renderer where in the 3D space it goes. This has some inherent weaknesses mentioned in both the video and in Dolby's own documents. It does not have native access to the LFE channel. It can (but not always, this is dependent on the mixer's decision on how important the sound's fidelity is, and how "busy" the mix is) be encoded at a lower bit rate so it may not have the full fidelity of the overall soundtrack. The difference between the Professional and Home implementation is that the theatrical can have many discrete overheads (and this number isn't universal to all theatrical Atmos installations, it varies from theater to theater) and that's why they use object based positional metadata vs channels, so that the metadata tells the decoder what the object sound should do (e.g. move from left, to upper left, to directly overhead, to upper rear right, to back rear right) and the decoder knows "in Theater X install I have 12 overhead channels I can discretely accomplish this with, in Theater Y install I only have 6 overhead channels, etc." and for home theater it's either .2, .4 (or in some cases .6).

In Dolby's own documentation they mention the home version can recreate all the objects of the theatrical mix. There's no mention of the "dark secret" limit you and your source say exist (and again, you seem to not separate audio that is within a bed channel and audio that is an object). If you can provide a trusted third party link with that information I'll be happy to read up on it and, if it checks out, change my stance, or at the very least enhance my understanding.

I understand if there is a "dark secret" that Dolby wouldn't be keen to announce it, but the way web tech journalism works, that secret wouldn't stay dark for so long.

I did watch the whole 2+ hour video and John Traunwieser is not shy about criticizing many aspects of mixing, soundtracks, his own and his colleagues techniques, and Atmos channel usage. He's not acting as a Dolby surrogate. But at no point does he mention anything remotely resembling the "dark secret" limit you mention. And in fact he agrees with the overall assessment of the panel (summarized towards the end of the video) that for effective home Atmos you need at least 7.1.4, to "not bother with just a .2" system.

I wonder if it's common for an engineer who's tasked with remastering home Atmos soundtracks in previously released movies to just do some sort of Auto remaster to the 7.1.2 bed channels and call it a day.

As Traunwieser says, it will depend on the project, the mixer, the budget and time. I have zero doubts that some "bare minimum effort" Atmos upmixes from old content exist, where you could put your ear right up to the .4s and hear almost nothing throughout the movie. This is exactly why if an old(er) movie I love is released and it doesn't have an Atmos upmix, I don't ever say "No Atmos, No Sale". The recently released Star Trek First Contact UHD is a perfect example. No Atmos, but the soundtrack they employ is very dynamic and impactful. I'm happy with it.

But the original Star Wars and Matrix trilogies are upmixes, and I can tell you there's a decent amount of .4 action there. Now the other question can come into play. How much time and effort did the mixer spend to place unique objects in discrete parts of the .4, that's an open question. For older non Atmos materials they do have to put effort to put things in those channels as there's no height information on the original tracks for the software to automatically place in the overheads (unless they just want to duplicate the rear/surround channels). But for Atmos theatrical downmixes, as Traunwieser says, they can spend a ton of time making sure the overhead sounds are mapped discretely and correctly in the home mix...or they can let the automated workflow within the renderer (which he did confirm exists and some mixers employ) do the work of folding down the theatrical mix into the nearfield mix.

EDIT: full disclosure I have experience using both Pro Tools and Logic Pro DAWs because I used to record my own music. At the time I didn't have the Atmos renderer installed (no need for it, I have enough difficulty filling up 2 channels lol) but that's why it's all starting to make sense to me, the difference between the bed channels and objects.

 

[Carlo_M]

As I wrote that last edit comment, I realized it's been quite a while since I launched Logic Pro (life, work, ugh). I long ago gave up the license for Pro Tools because it's just too $$$ and Apple gives you a lot for free that Pro Tools nickels and dimes (like thousands of nickels and dimes lol) you for.

Turns out, if you have a Logic Pro license (which I paid for years ago) as soon as you upgrade your client you have the Atmos renderer built in! I haven't messed with it yet (have to work) but I took some screenshots of the Help screens.

Maybe come the weekend I'll try my hand at messing around with older stuff I'd recorded.

 

[Carlo_M]

Also keep in mind that's only Apple's implementation of Atmos. Here's Pro Tools implementation:

Avid – Mixing Dolby Atmos Music – What You Need and More

Want to create immersive music mixes? Find out what audio gear you need for mixing in Dolby Atmos—it’s less than you think

www.avid.com

The videos at the bottom of that page "Configure the renderer" and "Prepare your mix" are very insightful.

And here's their Atmos resource page. As you can tell they have a more fulsome implementation than Logic (at least at first glance). But that makes sense as Logic Pro tries to be friendly for both professionals and hobbyists whereas Pro Tools is the industry standard.

Watch those videos on that page. They even have one for "rendering your mix" for delivery to streaming services which, John T is very critical of in terms of sound quality.