Atmos vs 5.1

[LuvMyQuad]

Indeed, which is why I'm surprised that some discs also have an AC3 track you can select from the menus. That means two AC3 tracks on the disc, why?

It could be the same track

 

[SeeMoreDigital]

Indeed, which is why I'm surprised that some discs also have an AC3 track you can select from the menus. That means two AC3 tracks on the disc, why?

I can't say I've seen this on a Blu-ray Audio disc. However Blu-ray movie discs often offer multiple lossy Dolby Digital tracks for different languages.

 

[SeeMoreDigital]

For anyone curious, I created multiple mixdowns of a song that is 5:04 for the sake of comparing the sizes:

TrueHD Atmos = 227MB
---------------------------
TrueHD stereo = 62MB
TrueHD 5.1 = 152MB
TrueHD 7.1 = 199MB
AC3 (640 kb/s) = 23.1MB

Out of interest... What software's did you use to create these encodes?

 

[Owen Smith]

It could be the same track

They could be bitwise identical, but they may have to be two separate copies. Nothing I've seen says one of them can point at the other.

 

[Methuselah’s Grandpa]

Out of interest... What software's did you use to create these encodes?

DME (Dolby Media Encoder)

 

[Nyad]

I’m no expert, but I doubt it.

I have noticed that my quadio discs can start in audio modes that are inconsistent. Right off the bat I can’t state which, but my Oppo 105 can show me which stream is being decoded. Not to mention the on-screen display on the quadio itself. That leads me to believe that the disc has “default” information on it that the disc player follows.

I have a thing with outputting Quad into my Sony STR-DN1080 (budget 5.1.2 Atmos receiver) from my Oppo 103, where the Sony won't recognise the Quad and defaults to stereo unless there is a silent center channel present, very annoying

 

[Methuselah’s Grandpa]

Ok, I went back and created one last encode (5.1 448 kb/s ac3).

AC3 (448 kb/s) = 16.2MB
AC3 (640 kb/s) = 23.1MB
TrueHD stereo = 62MB
TrueHD 5.1 = 152MB
TrueHD 7.1 = 199MB
TrueHD Atmos = 227MB
---------------------------
...considering these file sizes, it would seem to me that the TrueHD 5.1 & the TrueHD stereo presentation are part of the TrueHD Atmos mix & not stored separately. There's only 28MB difference between the TrueHD 7.1 file and the TrueHD Atmos file.

The 4 sub-streams of a TrueHD Atmos file would appear to include the 7.1 mix (199MB), the lossy 5.1 core(16 to 23MB), & the Atmos metadata but there's just not enough room leftover for anything else stored separately.


The efficiency of TrueHD Atmos is actually quite remarkable. I wish I was smart enough to understand how exactly the codec is able to keep track of all those separate mixed elements & objects while not technically storing all of them in their own separate channels. To be able to do all of that & then offer up different lossless and lossy presentations of that mix depending on the playback scenario and hardware in such a reasonable file size is impressive.