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Trying to wrap my head around Arc, ARC, Dolby Digital, Dolby Digital Plus and Atmos


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I have or had every intention of purchasing the Arc and was really excited.

Now that it has been released I have about what it can and can not do with my current setup. It will be replacing my Beam that's connected to my Sony Bravia Android TV that purchase in 2018 though I believe it's a 2017 model.

So it has ARC but not eARC. What does this mean for me. I've been finding conflicting information.

My main concern is will I be able to get Atmos. I've read post that say yes and others that say no.

After spending lots of time googling info for my TV I have found that it supports Dolby Digital and Dolby Digital Plus (and honestly I don't know what it's outputting to my Beam). However no where do I see Atmos support or decoding for it. Will this mean no Atmos for me with the Arc or will the Atmos signals somehow be carried through the Dolby Digital Plus?

Please help... I may need to rethink my purchase. Normally I would speakers for my TV, not the other way around. 

Just FYI, I also have a pair of Sonos One's and a Sub Gen 2.

Thanks in advance for any feedback.

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Best answer by Airgetlam 20 May 2020, 15:45

First, split the concept of codec and transmission methods in your mind, they’re two different things. Optical is the transmission method, Dolby Digital is the codec. Now, take it one step further, with Atmos being the content on top of both of those concepts. 

Working backwards from the top, Atmos, by definition, has a multitude of speaker streams in it. This data is manifested in two different codecs, TrueHD, which carries all streams in an uncompressed manner, and Dolby Digital Plus, which carries a smaller number of discrete channels and may be in a lossy state. 

So, the carrier method of each of these is determined by available bandwidth. TrueHD, carrying the ‘ultimate’ expression of Atmos, requires so much bandwidth that it can only run across an eARC connection. Dolby Digital Plus can carry the ‘normal’ version of Atmos, and needs the bandwidth of ARC via HDMI, there’s just too much data to be carried across optical as it was designed. 

My personal opinion is that using a sound bar for Atmos, such as the Sonos Arc is unlikely to provide any significant audio difference between the two methods of transmission. If you have your own dedicated home theater with 20 + professionally installed and placed speakers, I would think eARC is the better way to go. But for the Arc, I suspect that regular Atmos across the Dolby Digital Plus transmission on HDMI ARC will be amazing. 

 

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First, split the concept of codec and transmission methods in your mind, they’re two different things. Optical is the transmission method, Dolby Digital is the codec. Now, take it one step further, with Atmos being the content on top of both of those concepts. 

Working backwards from the top, Atmos, by definition, has a multitude of speaker streams in it. This data is manifested in two different codecs, TrueHD, which carries all streams in an uncompressed manner, and Dolby Digital Plus, which carries a smaller number of discrete channels and may be in a lossy state. 

So, the carrier method of each of these is determined by available bandwidth. TrueHD, carrying the ‘ultimate’ expression of Atmos, requires so much bandwidth that it can only run across an eARC connection. Dolby Digital Plus can carry the ‘normal’ version of Atmos, and needs the bandwidth of ARC via HDMI, there’s just too much data to be carried across optical as it was designed. 

My personal opinion is that using a sound bar for Atmos, such as the Sonos Arc is unlikely to provide any significant audio difference between the two methods of transmission. If you have your own dedicated home theater with 20 + professionally installed and placed speakers, I would think eARC is the better way to go. But for the Arc, I suspect that regular Atmos across the Dolby Digital Plus transmission on HDMI ARC will be amazing. 

 

To add to what Bruce said above, another factor to consider is the source content.  Because TrueHD requires higher bandwidth, it is never used with streaming sources.  You’ll only get TrueHD from bluray disks.  Streaming sources are going to be in dolby digital plus to get your atmos format data.  In other words, if you only use streaming sources, then you don’t really need to be concerned about getting an eARC capably TV, your ARC capable TV is all you really need.

 

 

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Thanks both of you. That gives me some relief.

@Airgetlam you should teach this stuff. First time explained where I understood it. Appreciate you taking the time to do so.

@melvimbe that's good to know as the vast majority of my content is streamed.

What got me so worried is that more recent Sony Android TV's recently received an update and it specifically stated support for Atmos was included in the updated and my set was not on the list for that update.

I feel better placing a order now.

 

Thanks a million

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I’ll be ordering my Arc through Sonos so I have 100 days to make sure it’s what I want, it’s not cheap, I do have a Playbase 5.1 system so it’s not as if I really need one! It’s doubtful I’ll be returning it though, my Sonos speakers have always exceeded our expectations.

What got me so worried is that more recent Sony Android TV's recently received an update and it specifically stated support for Atmos was included in the updated and my set was not on the list for that update.

 

That could mean that your TV doesn’t support the Atmos format in it’s internal smart apps...the android part of your TV, while it does support Atmos when it comes in through an HDMI input.

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What got me so worried is that more recent Sony Android TV's recently received an update and it specifically stated support for Atmos was included in the updated and my set was not on the list for that update.

 

That could mean that your TV doesn’t support the Atmos format in it’s internal smart apps...the android part of your TV, while it does support Atmos when it comes in through an HDMI input.

Good point. Makes sense.  Guess time will tell. I'm coming from a Beam so either way it's still an upgrade. 

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I’ll be ordering my Arc through Sonos so I have 100 days to make sure it’s what I want, it’s not cheap, ....

You make an excellent point. Was wondering if I should order direct.  Have over 3 months to try it has won me over. 

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To add to what Bruce said above, another factor to consider is the source content.  Because TrueHD requires higher bandwidth, it is never used with streaming sources.  You’ll only get TrueHD from bluray disks.  Streaming sources are going to be in dolby digital plus to get your atmos format data.  In other words, if you only use streaming sources, then you don’t really need to be concerned about getting an eARC capably TV, your ARC capable TV is all you really need.

 

 

Unless you’ve an Apple TV for your streaming sources! If that’s the case and you’ve no earc, no Atmos!

Unless you’ve an Apple TV for your streaming sources! If that’s the case and you’ve no earc, no Atmos!

 

Not entirely true.  Apple TV only streams Apple content as Multi-Channel LPCM w/ Atmos.  Any other streaming app, Netflix, Amazon Prime Video, Disney+, etc., are streamed as DD+ w/ Atmos and are fully compatible with ARC.  I tested this myself last night. 

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Not sure I get your point, but I’ll say it again, if you’re using a Sonos Arc with an Apple TV box with a tv that only has arc, and want Atmos, it’s a no no.

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It’s irrelevant if Disney+, Amazon, Netflix are using DD+ for Atmos as there’s only two output options on Apple TV that will be sent to your Sonos arc, Dolby Digital 5.1, and Multichannel PCM, the first Which will not carry Atmos obviously, and the latter which is not supported by Sonos arc

Not sure I get your point, but I’ll say it again, if you’re using a Sonos Arc with an Apple TV box with a tv that only has arc, and want Atmos, it’s a no no.

 

My point is, once again, that is not entirely true.  Only the Apple sources won’t work with ARC.  All the other streaming services will give you Atmos over ARC when streamed on Apple TV 4K.  I experimented with it last night.  I played an Apple TV+ source (See with Jason Momoa) and my AVR said Multi-Channel 7.2.1.  Then I went to the Disney+ app and played Black Panther.  My AVR said “DD+ Atmos”.  Narcos: Mexico on Netflix?  “DD+ Atmos”.  Jack Ryan on Amazon Prime VIdeo?  “DD+ Atmos”.

So as I said, saying you cannot get Atmos from an Apple TV without eARC is not entirely true, for I watched 3 sources from an Apple TV 4K and got ARC compatible Atmos just fine.  And as one who isn’t going to purchase any Apple content, just use the other services, the Apple TV 4K suits me just fine. 

It’s irrelevant if Disney+, Amazon, Netflix are using DD+ for Atmos as there’s only two output options on Apple TV that will be sent to your Sonos arc, Dolby Digital 5.1, and Multichannel PCM, the first Which will not carry Atmos obviously, and the latter which is not supported by Sonos arc

 

Again, not true.  See above.  I actually tested it.  

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So your av receiver has taken the multichannel pcm that has come from the Apple TV and extracted the relevant codec (DD+ Atmos) as expected. Try this with a Sonos Arc, which will downconvert the multichannel pcm to stereo. It won’t work.

So your av receiver has taken the multichannel pcm that has come from the Apple TV and extracted the relevant codec (DD+ Atmos) as expected. Try this with a Sonos Arc, which will downconvert the multichannel pcm to stereo. It won’t work.

 

Nope.  If that were the case, my AVR would have said “Input = Multi-Channel 7.2.1” and “Output = DD+ Atmos”.  The input was “DD+ Atmos”.  Also, Multi-Channel LPCM isn’t a wrapper for DD+ to be extracted from.  It’s the rawest form of Multi-Channel audio there is, there is no “extracting” anything from it.   

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Ok perhaps I used the wrong terminology. Still, this makes no sense. Apple TV is outputting multichannel pcm, so I’ve no idea how it’s inputting dd+ to your receiver (over arc). Check again, if what you’re saying is true, then I suspect, regardless of what info your receiver is displaying, you’re only getting 2 channels outputting sound, then perhaps you’ve it upmixing via Dolby surround etc. 

Ok perhaps I used the wrong terminology. Still, this makes no sense. Apple TV is outputting multichannel pcm, so I’ve no idea how it’s inputting dd+ to your receiver (over arc). Check again, if what you’re saying is true, then I suspect, regardless of what info your receiver is displaying, you’re only getting 2 channels outputting sound, then perhaps you’ve it upmixing via Dolby surround etc. 

 

So my receiver is lying?  It’s telling me I’m getting DD+ w/ Atmos when I’m only getting stereo? That’s what you are going with?

Can you really not fathom it may be you who has it wrong?    Sorry, but my hands-on experiment trumps your specious speculation:  Apple TV 4K will output the audio format as is.  In the case of Apple sources, it is Multi-Channel LPCM.   In the case of apps that stream DD+ w/ Atmos, it is DD+ w/ Atmos.  

And by the way, why are you arguing?  This is something that should make you happy, seeing how Atmos partially works for ARC connections to Apple TV.  Instead you are making up nonsense (DD+ “extracted” from LPCM???) to justify your criticism?  

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Keep your knickers on!

First of all I’m argueing (discussing) because I wouldn’t like anyone to buy the arc with any false expectations from misleading/mistaken information

i didn’t make up anything, I used the wrong terminology, my mistake, partly because you were talking about Apple TV outputting multi channel pcm yet your receiver showing dd+ being input, that threw me.


The various 3rd party apps on the Apple TV using DD+ Atmos are being re-encoded by the Apple TV, which is outputting multichannel PCM, I trust we can agree on that… so, if Sonos Arc does not support multichannel pcm, anything, ANYTHING coming from the Apple TV will be downconverted to stereo.

Being an AV receiver it will handle multichannel pcm and somehow (I don’t  know) is giving you your DD+ Atmos.

This will not happen with the Sonos arc, I wish it would, but it won’t/can’t!! Meet here back in a few weeks when there’s conclusive testing instead of back and forth, as I will not yield in this, as it’s technical impossible!

 

The various 3rd party apps on the Apple TV using DD+ Atmos are being re-encoded by the Apple TV, which is outputting multichannel PCM, I trust we can agree on that… so, if Sonos Arc does not support multichannel pcm, anything, ANYTHING coming from the Apple TV will be downconverted to stereo.

 

 

Why are you claiming agreement on something that @jgatie has clearly disagreed with and personally tested to be false?

 

Why would an Apple TV take a DD+ signal from the netflix service and then re-encode it to a different, less likely to be supported format?  It makes sense for them to record their own content in a format they feel is superior, but there is nothing to gain by doing that with content already in DD+.

 

Being an AV receiver it will handle multichannel pcm and somehow (I don’t  know) is giving you your DD+ Atmos.

This will not happen with the Sonos arc, I wish it would, but it won’t/can’t!! Meet here back in a few weeks when there’s conclusive testing instead of back and forth, as I will not yield in this, as it’s technical impossible!

 

Do you have a link to tech docs on the Apple TV to support your claim? 

Keep your knickers on!

First of all I’m argueing (discussing) because I wouldn’t like anyone to buy the arc with any false expectations from misleading/mistaken information

i didn’t make up anything, I used the wrong terminology, my mistake, partly because you were talking about Apple TV outputting multi channel pcm yet your receiver showing dd+ being input, that threw me.

 

 


The various 3rd party apps on the Apple TV using DD+ Atmos are being re-encoded by the Apple TV, which is outputting multichannel PCM, I trust we can agree on that… so, if Sonos Arc does not support multichannel pcm, anything, ANYTHING coming from the Apple TV will be downconverted to stereo.

 

 

No, we cannot agree on that.  My actual experiments say otherwise.  Any source that is originally DD+ w/ Atmos is output as DD+ w/ Atmos.  Which makes perfect sense.  Why would the Apple TV change the audio stream if it doesn’t have to?

 

Being an AV receiver it will handle multichannel pcm and somehow (I don’t  know) is giving you your DD+ Atmos.

This will not happen with the Sonos arc, I wish it would, but it won’t/can’t!! Meet here back in a few weeks when there’s conclusive testing instead of back and forth, as I will not yield in this, as it’s technical impossible!

 

 

I don’t need to wait.  I’ve already seen the results.  

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Apple TV can be set to output either Dolby digital 5.1 OR Multichannel pcm, the latter must be selected if you’re to get Atmos. Google it.

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Ask Apple, it’s ridiculous, but it’s true

Apple TV can be set to output either Dolby digital 5.1 OR Multichannel pcm, the latter must be selected if you’re to get Atmos. Google it.

 

Actually, in the settings of my Apple TV 4K, audio can be set to “Change Format On/Off - Dolby Digital 5.1 (when On)” and “Immersive Audio - Atmos On/Off”. Nothing about Multi-Channel PCM.  I have Change Format set to Off and Atmos set to On, and I get DD+ w/ Atmos just fine from Netflix, Disney+, and Amazon Prime Video.  

Have you tried this on your Apple TV? 

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Yes long term owner and av receiver owner. I know the setting you’re referring to. I really feel like you’re shooting the messenger here. Whatever you’re experiencing now, the Sonos arc will not so this. Do a bit of research and you will see that if Apple TV is set to Change format (off) it’s outputting pcm.

From:  https://developer.dolby.com/blog/dolby-audio-support-on-apple-tv/

 

It is important to keep in mind that while the Apple TV supports Dolby Digital Plus, this does not mean the Apple TV is necessarily sending a Dolby Digital Plus bitstream over its HDMI® output. After it decodes the Dolby audio, the Apple TV sends the audio to your receiver via HDMI; how it sends the audio depends on the Apple TV settings as well as the capabilities of your HDMI-connected device.
 

 

Notice the bolded.  Seems like “it’s either LPCM or DD 5.1” isn’t so cut and dried.

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