It's clarifying time... at least a little.....
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Let's start with the end - which is what most people are really concerned with.
If you play an Atmos disc on equipment that is Atmos-capable it will be fully decoded and rendered as the author intended.
If you play an Atmos disc on equipment that is NOT Atmos-capable but is TrueHD capable...
It will be presented as TrueHD, without the special handling offered by Dolby Atmos.
NONE OF THE AUDIO CONTENT WILL BE DISCARDED.
(The Objects present in the Atmos mix will remain as part of the TrueHD surround channels.)
(We don't say that "you're hearing just the bed channels", which would be incorrect; we say that "you're hearing the TrueHD mix".)
If you play that Atmos disc on equipment that is TrueHD capable... but has fewer channels... (for example, on a 5.1 system)...
It will be presented as TrueHD, without the special handling offered by Dolby Atmos.
NONE OF THE AUDIO CONTENT WILL BE DISCARDED.
(The Objects present in the Atmos mix will remain as part of the TrueHD surround channels.)
(If the TrueHD mix contains more channels that you have speakers, they will be "mixed down to fit the channels you have" - just like other 7.1 TrueHD content.)
If the disc is authored according to the standard.... there is only actually a single mix.
The "TrueHD Mix" is actually PART OF the "Atmos Mix".
(And there's even a Dolby Digital Mix that is part of the TrueHD Mix.)
Assuming everything is configured correctly NO SOUNDS OR AUDIO OBJECTS ARE DISCARDED NO MATTER HOW YOU DECODE THAT MIX.
However, because Atmos has a lot more control over how the mix is rendered, it may SOUND DIFFERENT when decoded in various ways.
(No content will be discarded, but a given sound may be rendered at a different location, or a different level, in each mix.)
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Unfortunately, the terminology associated with Atmos is not especially intuitive, and can be quite confusing, unless you already know the details of how the whole system works.
The Dolby Atmos MIX contains Bed Channels and Objects; the playback system has Output Channels; and how they relate to each other is controlled by the Atmos Renderer.
To pick one common example:
If you play a Dolby Atmos mix in TrueHD, it DOES NOT contain "just the Bed Channels.
It actually contains the full TrueHD Mix, which includes both the Bed Channels, and all the Atmos objects.
There are two basic types of entities in an Atmos MIX: bed channels and objects.
Bed Channels are channels that correspond to the standard surround sound channels in TrueHD (Left Front, Right Front, Left Rear Surround).
There are also height bed channels (I believe those are optional).
In a theater, there may be multiple speakers assigned to each bed channels (so, for example, four or five speakers in the front left of the theater may all be assigned to the "Front Left Bed Channel").
In a home system each main (ground level) speaker is probably its own bed channel.
Objects are dynamic entities.
Each object is basically a sound clip with various parameters assigned to it.
Each object has a size, and a level, and a location, all of which can change dynamically (so an object can change size, change level, and move around over time).
In general (with certain exceptions), objects are NOT assigned to specific speakers.
Objects have the equivalent of physical locations and, when the audio is decoded, each object is assigned to one or more speakers by the Atmos rendering engine.
Here's where many people seem to become confused.
Let's say you play an Atmos mix in an Atmos equipped theater.
Various groups of speakers in the theater are assigned to the various Bed Channels (so, for example, the Left Front Bed Channel may play through the three or four speakers in the left front corner of the theater).
Each speaker may ALSO be addressed individually (a given speaker may be assigned to a bed, or as a separately addressable speaker, or both).
Each Bed Channel in the mix will be played through the entire group of speakers assigned to that Bed Channel.
Each Object will be played through the specific speaker or speakers chosen by the Atmos Renderer.
So, each Bed Channel will ALWAYS play through a specific speaker or group of speakers - and won't move around.
Each Object will play through whatever speaker or speakers it is sent to, any of which may or may not also be part of a bed group, and objects WILL move from speaker to speaker, and change size and volume.
(Note that, even if a certain sound appears only in the Bed Channels, it can still be panned in various directions if the sound engineer chooses to,)
In most home systems, the main channels used for TrueHD correspond to the Bed Channels in Atmos.... and those same speakers are ALSO used as the Object speakers.
There may also be height Bed Channels... or all height speakers may be "object speakers".
If this seems confusing.... here's what I find the easiest way to think of it.
The Bed Channels comprise a fixed mix - which can be played in TrueHD format - using your normal speakers.
IN ADDITION TO THAT, IF YOUR SYSTEM SUPPORTS ATMOS, individual Atmos objects can also be "pulled out of the mix and independently moved around".
Just to clear up the terminology:
When you play an Atmos disc in TrueHD...we don't say that "the objects are mixed down into the bed channels".
The TrueHD data stream ALREADY CONTAINS BOTH THE BED CHANNELS AND ALL THE OBJECT CONTENT.
(So, when you play that Atmos mix through a TrueHD system, you are hearing both the bed channels, and the objects, with nothing omitted or discarded.)
The TrueHD decoder simply plays them that way - WITHOUT pulling out the objects and rendering them separately as the Atmos Decoder would.
(You are hearing everything that belongs there - just without the "special handling" done by the Atmos renderer.)
(The Atmos decoder does NOT "decode everything, then mix it back down"; it only decodes things as far as necessary to begin with.)
It gets confusing because speakers are OUTPUT DEVICES.... and each of your speakers could be assigned to a bed channel, used as an object speaker, or both.
But the mix itself is made up of ENTITIES.... which may be assigned to output channels but are not themselves output channels.
And it gets more confusing because of where various operations are handled.
(And, yes, there are a few specific options that make the details even more complicated - like "pinned channels".)
From the Authoring side of things.....
The Sound Engineer creates a mix, which contains both Bed Channels and Objects.
(I suspect it may be possible, although somewhat odd, to create a mix that contains only bed channels or only objects. )
From that mix, the authoring software creates a set of data streams, including the "Atmos Mix" and the "TrueHD Mix".
(So, unless the author individually tweaks the various mixes, they all "appear" at the same time from the same master mix.)
There are also obviously default relationships, for example the loudness relationship between objects in the Atmos mix, and their counterparts in the TrueHD mix.
No
Your not getting it. It’s based off of 7.1 with metadata. When the metadata is decoded you get objects. The objects are rendered by whatever health channels you have available to be processed
It doesn’t work the oopposite way.
You're correct, I am definitely not getting it. If a 7.1.4 track isn't
down mixed to suite a 5.1.2 systems then how else would you describe it?
Talking about ceiling speakers just confuses the question/answer. Let's concentrate on the bed channels, if it's a 7.1 (.4) sound track and I'm playing it through a 5.1 (.2) systems. Aren't the 7 bed channels down mixed to the 5 bed speakers/channels that I have? If that's not down mixing then what is it?
Cheers
Gary
