Atmos and TrueHD 7.1 playback on 5.1 systems - Tests, Results, questions, experiences

[SeeMoreDigital]

I’ve seen this turn into arguments before, so I’ll throw in my two cents. The terminology for the required DD track is often referred to as a “DD core” but it is technically a separately encoded stream from the TrueHD track that could even be a different mix. The TrueHD and DD tracks are combined (maybe where the term “core” comes from) and need to be demuxed to ascertain the differences. See my John Lennon’s Gimme Some truth example above.

When lossless Dolby True HD audio streams are muxed within the m2ts container, they have to contain a lossy Dolby Digital 'core as a mandatory requirement.

Where some confusion lies is that unlike lossless DTS-HD MA streams, the lossy Dolby Digital core is automatically removed when re-muxing into the .mkv container.

It is not possible to create conformant Blu-ray disc .m2ts files using Dolby TrueHD audio streams unless they contain is a lossy DD core. Even if the core has been encoded at the lowest possible bit-rate of zero.

EDIT: By-the-way, in the past I have created, authored and burned dozen of Blu-ray 'discs' (for old work colleagues show reals). So I do know what I'm talking about!

 

[harync]

Down mixed is not how Atmos works. All sounds are present in the 5.1 or 7.1 bed, they have to be otherwise someone playing it through a Dolby True HD decoder that doesn't understand Atmos would have things missing. The Atmos object data both says what the sound is and how it moves, and how to remove it from the bed. If it didn't work that way every Atmos blu ray would need two True HD tracks, once for the Atmos mix and one to play on devices that don't understand Atmos.

An important consideration here is if the album was mixed in a way so that non-Atmos playback gives a similar experience as Atmos playback. If the mixer wanted, the 7.1 bed would give the same distribution of sound and Atmos would further refine location or put sounds in the height speakers. If no attention was given to localization for non-Atmos playback, a sound could play in 3 speakers in a 5.1 system, but play only in the front left ceiling speaker in an Atmos 5.1.4 system. This is the case for REM’s Automatic for the people, which was one of the very first Atmos albums.

Since DSOTM already has a dedicated 5.1 mix, it makes sense to include it. I haven’t listened to the Atmos mix without my height speakers, but I would guess it would be less discrete and not intended for non-Atmos playback.

 

[harync]

When lossless Dolby True HD audio streams are muxed within the m2ts container, they have to contain a lossy Dolby Digital 'core as a mandatory requirement.

Where some confusion lies is that unlike lossless DTS-HD MA streams, the lossy Dolby Digital core is automatically removed when re-muxing into the .mkv container.

It is not possible to create conformant Blu-ray disc .m2ts files using Dolby TrueHD audio streams unless they contain is a lossy DD core. Even if the core has been encoded at the lowest possible bit-rate of zero.

I think where the confusion lies is that the TrueHD and DD tracks can be completely different mixes. The term “core” implies the DD mix is derived from the TrueHD mix when that is not necessarily the case.

It would be interesting to see if the DSOTM 50th Anniversary DD5.1 “core” is derived from the Atmos mix or the previous 5.1 SACD mix.

 

[SeeMoreDigital]

I think where the confusion lies is that the TrueHD and DD tracks can be completely different mixes. The term “core” implies the DD mix is derived from the TrueHD mix when that is not necessarily the case.

You are indeed correct in this regard. Indeed it's technically possible to encode a lossy Dolby Digital 'test tone' and use that as the core!

More recently however, I've come across a few Atmos authored discs that include a Dolby Digital EX core...

 

[Owen Smith]

Every Blu-ray disc that has been encoded with Dolby TrueHD (with or without Atmos) has a Dolby Digital core. Look in the .m2ts contained file.

But it's not actually a "core" in any meaningful sense of the word "core". It is not used at all when playing the Dolby True HD soundtrack, therefore it is not core to anything. It is simply an alternate soundtrack. Dolby can call it a "core" if they want but it is a lie.

This contrasts with DTS HD MA (or any extended DTS format eg DTS 24/96) where the DTS soundtrack is held as "core plus extensions". Old equipment can play the DTS core only, newer equipment can play the core and add the extensions to get the new format. But even when playing DTS HD MA, the core is being read and used.

 

[himey]

Just like the term "core" isn't truly a core, it is a separate track, the term "bed" is used to refer the 5.1/7.1 ground channels, when actually, bed channels are something different.
Although the terms aren't technically correct, I think used in the proper context, they are fine. Most people don't care enough to distinguish between the differences, and the ones that do, can look it up themselves. They don't need a lesson, every time it is used technically incorrectly.

 

[Owen Smith]

They don't need a lesson, every time it is used technically incorrectly.

I have a hard time not giving one every time it is used incorrectly. It's just part of being an engineer.

 

[SeeMoreDigital]

But it's not actually a "core" in any meaningful sense of the word "core". It is not used at all when playing the Dolby True HD soundtrack, therefore it is not core to anything. It is simply an alternate soundtrack. Dolby can call it a "core" if they want but it is a lie.

Whatever 'you' want to call it, in the case of Blu-ray disc media, the lossy Dolby Digital stream is embedded within the lossless Dolby TrueHD stream and can only be extracted from the lossless Dolby TrueHD stream using software and/or when muxing to the Matroska container!

The lossy Dolby Digital stream was designed to be always active in hardware playback devices so it could be passed via SPDIF to those who had older AVR's.

 

[Owen Smith]

Whatever 'you' want to call it, in the case of Blu-ray disc media, the lossy Dolby Digital stream is embedded within the lossless Dolby TrueHD stream and can only be extracted from the lossless Dolby TrueHD stream using software and/or when muxing to the Matroska container!

The lossy Dolby Digital stream was designed to be always active in hardware playback devices so it could be passed via SPDIF to those who had older AVR's.

I believe this to be incorrect. The lossy Dolby Digital stream is entirely separate on the Blu Ray so that devices which know absolutely nothing about Dolby True HD can still output it.

 

[himey]

Clean up aisle 5.

 

[SeeMoreDigital]

I believe this to be incorrect. The lossy Dolby Digital stream is entirely separate on the Blu Ray so that devices which know absolutely nothing about Dolby True HD can still output it.

No.... It is not an entirely separate stream on a Blu-ray authored disc... Either do your research or learn how to create compliant Dolby TrueHD audio streams for Blu-ray authored discs - Like I have had to do!

This needs to move on now!

 

[kfbkfb]

Anyone know the default channel mapping for Dolby TrueHD 7.1 (may contain Atmos) -> DD 5.1 (I'll be listening to the DD 5.1 track on this Pink Floyd Atmos mix)?


Kirk Bayne

 

[Owen Smith]

No.... It is not an entirely separate stream on a Blu-ray authored disc... Either do your research or learn how to create compliant Dolby TrueHD audio streams for Blu-ray authored discs - Like I have had to do!

This needs to move on now!

Do you have a reference that I and others that haven't signed Dolby NDAs can read describing this? Dolby love hiding things.

 

[kfbkfb]

FYI - just tried my ABC SDE disc on my old Magnavox (Funai OEM) Blu-ray player (made in 2009), the DD 5.1 from the TrueHD track doesn't appear as a separate AUDIO menu selection.


Kirk Bayne

 

[Owen Smith]

FYI - just tried my ABC SDE disc on my old Magnavox (Funai OEM) Blu-ray player (made in 2009), the DD 5.1 from the TrueHD track doesn't appear as a separate AUDIO menu selection.

Thanks for checking that and reporting. That tallies with what @SeeMoreDigital said, but is entirely at odds with everything I have read on the subject. I hate Dolby as a company, why can't they publish all the specs?

 

[himey]

just tried my ABC SDE disc on my old Magnavox (Funai OEM) Blu-ray player (made in 2009), the DD 5.1 from the TrueHD track doesn't appear as a separate AUDIO menu selection.


Kirk Bayne

LOL

 

[kfbkfb]

P. 16 - NB500MG9 MAGNAVOX Blu-ray player (mentioned above) - owners manual:
DIGITAL OUT jack (COAXIAL)...Dolby Digital will be output instead of Dolby Digital Plus and Dolby TrueHD...


Kirk Bayne

 

[Horbus]

Thanks for checking that and reporting. That tallies with what @SeeMoreDigital said, but is entirely at odds with everything I have read on the subject. I hate Dolby as a company, why can't they publish all the specs?

Intellectual property??

 

[SeeMoreDigital]

Hmmm...

In-case people were not aware, Dolby TrueHD is nearing 20 years of age. And Dolby Atmos is over 10 years old!

There's been plenty of time to understand how they function. Even deconstruct them...

 

[mutant_matt]

You can almost certainly select the DD 5.1 track using the Audio button on your player's remote, I recall seeing the extra DD 5.1 track there on a couple of discs.

Most players indeed have this, mine does. If you listen/watch stuff via KODI (like I do), then this is definitely an option too...