Atmos vs 5.1

[LuvMyQuad]

Why would you want to select the 5.1 mix? It's in lossy Dolby Digital AC3 and while it can be at 640kbps (the max for AC3) it is far more likely to be at a lower bit rate and sound poor as a result. Much better in my view to play the 7.1 MLP and have your AVR fold the two sets of rears together to get 5.1 (or 5.0 in my case), it's a trivial thing for your AVR to do and likely an identical mix to the AC3 5.1. I suspect the AC3 is always generated automatically from the 7.1 MLP in the Atmos workflow, even if there is a separate DTS HD MA 5.1 mix on the disc it seems unlikely to me that will be put into the Atmos workflow just for the AC3 5.1.

I agree with what you say. I don't want to choose the 5.1, and i dont. In fact I never rip the 5.1 substream and choose the 7.1, rip to flac, for my son to play on his non atmos system.

What I'm saying is in many cases, the AC3 is the only 5.1 version on the disk. Who is it backward compatible for? How does someone with straight 5.1, (and I mean strictly 5.1 with only 6 channels, not 8 for 7.1) select that playback mode. For such a system, that is the only multichannel option available that can play with no loss of information. Playing the 7.1 will simply lose the rears. There is no menu option to choose 5.1. How does the disc player know to choose that stream? Is it hardwired to look for a 5.1 stream? Default to stereo if it doesn't find one?

I did at one time in the early 2000s i used a Pioneer universal disc player. It didnt play blurays, only SACD, DVDA, etc. It was strictly 5.1. 7.1 was not yet a common format. Can we assume that the 5.1 AC3 stream is meant to provide backward compatibility for that vintage gear? But again, that old Pioneer wouldn't play a bluray at all anyway. By the time blurays arrived, 7.1 gear had become the norm. This is in spite of the fact that there was next to no 7.1 software to take advantage of it.

Once there were 7.1 capable disc players, it's no problem. The player downmixes to 5.1 and feeds the 5,1 AVR

I guess the real question is, in the interest of backward compatability, what scenario will facilitate the playback of that 5.1 stream? Who is that backward compatability targeting exactly?

 

[mandrix]

I'm trying to think if I've ever encountered > 5.1 AC3 on a Blu Ray. I have somewhere an old AC3 encoder but I believe it only does 5.1.
Unless of course you're talking about Atmos DD+.

 

[inspclouseau]

I know where you are coming from and I feel much the same way. Atmos on a non-atmos 5.1 system, like mine, is a hit and miss experience. The recent Bowie Ziggy Stardust, for example, was a disappointment. I don't want to see the dedicated 5.1 mixes disappear but it looks like that will be the case more often than not.

I agree with you wavelength. We are at an age now that because we started collecting music/concert 5.1 dvd's when they first started being produced (1980-something.. ) Any quality 5.1 DTS MA that is from a band we like or music re-dos in 5.1 is a bonus these days.. We likely purchase. We have pretty much run out of room with so much to choose from in our house anyway.. sure love going through them as we play music. Fun.
We do not stream for two reasons. The first is the fact that living in the sticks, we have poor/SLOW, but inexpensive reliable internet. We could pay for another/different outfit but it is OUT of the question to pipe it to us. $$$$$$$$$ The other is the music rental bit that is destroying physical media. We are being nickle and dimed to death as it is. A shame seeing this. We own 3 Oppo players that play our disks flawlessly. One for the 5.3 system. One for a 2 channel Decware tube amp. And the last one that is pretty much not used in the bedroom cabinet. We are all set. As I have said before my intent is not to piss anyone off, my intent is just the truth. A few here have asked smug questions that I just ignore, as they obviously don't want to hear it from me anyway. This outfit is a good one though with a lot of people who obviously just love music......View attachment 1731786967160.jpeg
All the best~ Mike

 

[Owen Smith]

What I'm saying is in many cases, the AC3 is the only 5.1 version on the disk. Who is it backward compatible for?

People with non HDMI AVRs that only have an optical or coax audio in. The blu ray player outputs the AC3 substream to coax and optical, and outputs the entire of the Atmos with all substreams to HDMI. If you are using an HDMI AVR it is the AVR's job to decide how to downgrade or render it to your speaker layout.

 

[mandrix]

I agree with you wavelength. We are at an age now that because we started collecting music/concert 5.1 dvd's when they first started being produced (1980-something.. ) Any quality 5.1 DTS MA that is from a band we like or music re-dos in 5.1 is a bonus these days.. We likely purchase. We have pretty much run out of room with so much to choose from in our house anyway.. sure love going through them as we play music. Fun.
We do not stream for two reasons. The first is the fact that living in the sticks, we have poor/SLOW, but inexpensive reliable internet. We could pay for another/different outfit but it is OUT of the question to pipe it to us. $$$$$$$$$ The other is the music rental bit that is destroying physical media. We are being nickle and dimed to death as it is. A shame seeing this. We own 3 Oppo players that play our disks flawlessly. One for the 5.3 system. One for a 2 channel Decware tube amp. And the last one that is pretty much not used in the bedroom cabinet. We are all set. As I have said before my intent is not to piss anyone off, my intent is just the truth. A few here have asked smug questions that I just ignore, as they obviously don't want to hear it from me anyway. This outfit is a good one though with a lot of people who obviously just love music......View attachment 111037
All the best~ MikeView attachment 111036

Sucks about the internet . I live sort of in the boonies, and thought ADSL was as good as I would ever get, and it took many years to get it . I had satellite internet for a few years before ADSL.
But our electric co-op put in for fiber grants, and since they owned the power poles they ran/are running to every meter.
So the impossible finally happened in August, and I now have 2 gig fiber and for a reasonable cost.

 

[jimfisheye]

Huh??? Is that supposed to be a response to my question?

It is, yes.

Disc player HDMI -> AVR, right?

Disc player is sending encoded Atmos data signal to AVR. It doesn't need any information from the AVR. It's sending the full encoded signal in all cases.

The AVR has the Atmos decoder software hidden in its firmware. It decodes the full Atmos datastream to 9.1.6. We're still inside the box at this point. The Atmos decoder doesn't need to know anything about the connected speakers. It's decoding the full signal.

Now any speaker management settings in the AVR take over.
Set for 1:1 with the full speaker array connected? Then is passes the Atmos output 1:1. Set the management for a smaller speaker array and the multichannel output is downmixed accordingly.

The Atmos decoder never needs to know about the connected speakers. That job is left to the AVR. On HTPC (software player/computer/interface/amps) you set the output on the Dolby reference player.

 

[LuvMyQuad]

It is, yes.

Disc player HDMI -> AVR, right?

Disc player is sending encoded Atmos data signal to AVR. It doesn't need any information from the AVR. It's sending the full encoded signal in all cases.

The AVR has the Atmos decoder software hidden in its firmware. It decodes the full Atmos datastream to 9.1.6. We're still inside the box at this point. The Atmos decoder doesn't need to know anything about the connected speakers. It's decoding the full signal.

Now any speaker management settings in the AVR take over.
Set for 1:1 with the full speaker array connected? Then is passes the Atmos output 1:1. Set the management for a smaller speaker array and the multichannel output is downmixed accordingly.

The Atmos decoder never needs to know about the connected speakers. That job is left to the AVR. On HTPC (software player/computer/interface/amps) you set the output on the Dolby reference player.

I know how it works, the question has nothing to do with Atmos. It was how the disk player knows to play the 5.1 AC3 stream when there is no atmos or 7.1 compatability.

 

[Mr. Afternoon]

I know how it works, the question has nothing to do with Atmos. It was how the disk player knows to play the 5.1 AC3 stream when there is no atmos or 7.1 compatability.

From what I understand, Dolby Atmos (on Blu-ray) is an extension of Dolby TrueHD, which in turn is an extension of Dolby Digital. Each "extension" is stored as supplementary metadata which is optional, to retain backwards compatibility. If a device doesn't support or understand any of the metadata, it can simply discard it and play the "core" stream. For example, on a setup that supports TrueHD, but not Atmos, it would interpret the core stream and the supplementary TrueHD metadata but discard the Atmos metadata upon playback.

 

[LuvMyQuad]

So there must be some hiarchy inside the disk player that just searches for the best surround substream it's compatable with and plays it. If the disc player is only capable of 5.1, it plays the AC3 substream which all True HD releases seem to have.

As far as I can tell, the only stream that makes use of metadata is the True HD Atmos stream. The 5.1 AC3 substream is independant and can be ripped quite easily without any special decoding or software.

 

[jimfisheye]

I know how it works, the question has nothing to do with Atmos. It was how the disk player knows to play the 5.1 AC3 stream when there is no atmos or 7.1 compatability.

An Atmos encoded file includes a 5.1 folddown in AC3. An older "incompatible" AVR will see an incoming AC3 stream and be blind to the rest of the data. The disc player is sending the same datastream the whole time.

"Compatible" AVRs might have different choices to parse that datastream. Some models might be programmed to choose the highest quality and not even give you the option to choose the "legacy" stream as some people mentioned.

Seems off putting indeed to buy a combo box of amp channels, audio interface, DACs, and decoder codecs, and then be told what to do in how to use them! But you knew I'd say something like that.

 

[LuvMyQuad]

Seems off putting indeed to buy a combo box of amp channels, audio interface, DACs, and decoder codecs, and then be told what to do in how to use them! But you knew I'd say something like that.

Indeed. There is no way to choose the AC3 substream on these releases.

 

[Mr. Afternoon]

So there must be some hiarchy inside the disk player that just searches for the best surround substream it's compatable with and plays it. If the disc player is only capable of 5.1, it plays the AC3 substream which all True HD releases seem to have.

My understanding may very well be wrong but here's what I got.

The "hierarchy" is not based on channel configuration but codec support. If the player supports TrueHD, it will pull the TrueHD audio and downmix it for the channels the user has. Downmix flags are additional metadata set in the file of the codec.

For Dolby Digital and TrueHD, there are no separate mixes aside from the one that is encoded. However, there are customizable downmix parameters (such as gain and pan) that are used to present a multichannel mix on a lesser number of speakers.

For TrueHD, what it (supposedly) does is that it stores a stereo downmix in the first substream. Then it stores data to correct and transform that downmix to 5.1 in the second substream. If the original mix is 7.1, then it stores data in to correct and transform that downmix to 7.1 in the third substream. And then, if the original mix is Atmos...that fourth substream gets used. Because of the nature of TrueHD not actually storing separate mixes, all these substreams are generated from the downmix co-efficient sets by the person who encoded the audio, if they bothered to change them from anything other than the default.

Atmos in TrueHD is interesting, because it's described by Dolby as "16ch presentation" and can be stored as either a fixed amount of channels, audio objects, or both.

TL;DR: That 5.1 AC3 core in TrueHD Atmos isn't actually a dedicated 5.1 mix, it's just a downmix.

 

[kfbkfb]

Anyone know if Atmos mixing engineers spend time (=money) to change the TrueHD (containing Atmos) -> DD 5.1 downmix parameters or do they leave them at the defaults (I don't know if DD+ [containing Atmos] has a downmix -> DD 5.1)?


Kirk Bayne