General Discussion Technical question about Dolby Atmos on streaming (1 Viewer)

[Jesse Skeen]

I like to think I've been pretty well-versed in sound for more than 30 years, but Atmos just baffles me. I have tons of questions about how it works but here I'll just ask why on some services it works on some devices but not others. I thought the Atmos data was already in the Dolby Digital Plus signal, so why would some devices only get 5.1 Dolby Digital Plus from some services and not have the Atmos triggered? I know Dolby Digital Plus has to be supported, for example my LG TV only passes standard Dolby Digital and so I know there's no way of getting Atmos from that. But for example my Chromecast gets Dolby Atmos from Netflix which is delivered via Dolby Digital Plus, yet my Roku Stick only gets 5.1 DD+ on the same material. Why would a Dolby Digital Plus signal even exist without the Atmos data included? If the receiver doesn't support Atmos, it already falls back on the core track.

 

[Sam Posten]

Dolby digital plus is the base layer and Atmos is data that sits on top of it

 

[Josh Dial]

Also, some services lock Atmos/DTS:X to 4k streams only. For example, if you stream Hawkeye on Disney+ in 1080p the audio signal will show up on your receiver as Atmos, but it will actually only be the Dolby Digtial 7.1 bed layer. If you stream Hawkeye on Disney+ in 4k the audio signal will show up on your receiver as Atmos and your receiver will actually play the height channels. Basically, Disney only gives you true Atmos on the 4k streams.

Amazon does the same thing.

Netflix, on the other hand, lets you stream Atmos audio over the 1080p streams.

Additionally, some services periodically throttle back their Atmos/DTS:X tracks during periods of high traffic. If you try watching Hawkeye on Disney+ on Christmas day afternoon, you might only get the Dolby Digital bed layer during peak viewing.

 

[Jesse Skeen]

I’ve noticed Atmos is only on 4K streams most of the time, I have 4K so no worries there, but I know it’s still possible to have Atmos on any Dolby Digital Plus signal. Shortly after Atmos first came out Vudu put up a few trailers for it, and my oldest Roku made before Atmos existed can still stream those with no issues. So Atmos is still a separate “layer” in addition to Dolby Digital Plus that can be stripped out? Seems very strange, on discs any Blu-Ray player no matter how old can bitstream them to an Atmos receiver.

Even with 4K, not every device can get Atmos from Netflix- my Roku and Chromecast are both 4K but only the Chromecast can get Atmos from Netflix, the Roku only gets Dolby Digital Plus 5.1 but does get Atmos from other services.

 

[JohnRice]

There's no simple answer. When you have many different streaming services and even more devices, things can get confusing. Essentially, the audio stream can be downgraded from the maximum just like the video quality and resolution can, depending on various circumstances. Home Atmos is also extremely limited. If you want the best from all your streaming, in most but not all cases, you're best off spending the $ for an AppleTV 4K. It almost always provides the best from all services. There are exceptions, such as Hulu not having 4K or anything over 2 channel audio for a long time, but that's in the past now.

 

[Jesse Skeen]

I have an Apple TV also, I like it but it still has a few issues- I've found multiple devices are needed both to get the best quality out of some services and also avoid annoying interfaces on them. The time bar appearing at the beginning of most movies on the Apple TV annoyed me at first but in the last update they changed it so it's now easier to get rid of. Atmos on that is even more confusing, as it normally sends out PCM for everything that isn't Atmos and as far as I know that can't carry Atmos data- hence why Blu-Ray players need to be set to bitstream for it and not PCM. My receiver doesn't even display an audio format other than Atmos when it's passing that, on everything else it will show whether it's Dolby Digital Plus or TrueHD. But I won't even try to make sense out of that...

 

[Carlo_M]

My continuing complaint with AppleTV Atmos (music) is that on two different receivers (Denon 4400 and 4500) connected via Monoprice 8K HDMI (so it's not a cable bandwidth issue) there are audio dropouts at the beginning of a streamed Atmos enabled album, and if that album has "gapless playback" tracks (i.e. tracks that blend one song into the next) there is a split second audio dropout.

They're all like this (at least the ones I've tested) but the most blatantly obvious offender is The Beatles Abbey Road (2019 mix) with the Atmos soundtrack. I never hear the opening bass line of Come Together, and the medley on the second side of the album (#vinylreference #imold) has that split second dropout between the songs that are supposed to be one long medley.

I have a long standing trouble ticket in with Apple via their Feedback app...no luck.

 

[Jesse Skeen]

Yeah, there's definitely an issue with Music. I've learned if the beginning of a song is cut off, wait til the Atmos signal locks in then pause and scan back to the beginning. The gaps between tracks are a huge problem. There is even a test "album" from Dolby Labs titled "Functional Testing" that has some music divided into short tracks specifically for testing gapless playback, and it fails.

I've started using Kodi with an NVidia Shield to watch Disney Plus (and avoid their annoying interface), and that lets you access EVERY audio track that's available. There are still separate Atmos and plain 5.1 tracks in addition to a 2-channel track in AAC format, so some devices are only getting the 5.1 track.

 

[Todd Erwin]

So Atmos is still a separate “layer” in addition to Dolby Digital Plus that can be stripped out? Seems very strange

Strange, indeed. To some extent, I think it comes down to how the content is encoded, particularly the DD+ track, or the particular chipset the streaming device has on-board. Why do I say that? Two examples:

1. Netflix does stream in Dolby Atmos on more recent Roku devices, notably their two models that are also Dolby Vision-capable, the Ultra (2020 edition, aka 4800X), Streaming Stick 4K (3820X), and Streaming Stick 4K+ (3821X). I have read in other forums users reporting that the Express 4K+ is also capable of streaming Netflix in Atmos. So it must be chipset-related, although I had previously thought it had to do with the simple fact that both the Ultra and Streaming Stick 4K/4K+ had a Dolby chipset onboard, so it could be some other chipset.

2. On the Roku stand alone app for Paramount+, the ONLY piece of content that currently streams in Dolby Atmos is the movie Rumble. Every other title listed as Dolby Atmos only streams in DD+ 5.1 on all of my Roku devices, including the ones I use when travelling, Premiere and Streaming Stick+. This leads me to believe that it is an encoding issue that is not compatible with Roku (even though, supposedly, Roku devices do not actually do any audio decoding). Unfortunately, HDR has been disabled on Paramount+ since December 2021, with hopes of being re-instated for late May or early June, but they keep moving the goal posts on that.

 

[Todd Erwin]

Hulu not having 4K or anything over 2 channel audio

Hulu now streams in 4K HDR10 (DV is still broken) and DD+ 5.1 (finally).

 

[Carlo_M]

I've learned if the beginning of a song is cut off, wait til the Atmos signal locks in then pause and scan back to the beginning. The gaps between tracks are a huge problem. There is even a test "album" from Dolby Labs titled "Functional Testing" that has some music divided into short tracks specifically for testing gapless playback, and it fails.

In my ongoing frustration with Apple's implementation of it, I had mentioned how Abbey Road in Atmos is one of the easiest ways to observe the two big issues I find in Atmos music playback through my AppleTV 4K (2021 versions, certified HDMI 2.1 cable to Denon AVR-4500h). Again, I'm postulating as to the cause as I'm not an engineer:

• When an Atmos album first begins, most (all?) AVRs need a second to detect the signal. So if there is no "padding" of say the ATV4K sending a signal to the AVR "hey this is an Atmos stream" and instead just sends the music, you will not hear the first split second or so until the AVR detects and decodes the stream. This is most evident in that I always miss the first part of the bass line in Come Together.
• Gapless playback is not enabled for Atmos. So songs that should run together (like the medley on side 2 of Abbey Road) instead have a split second gap (shorter than the initial detection gap, this can sound more like a "stutter" in the music) rather than seamlessly going from song to song with any audible pause/break.

What's ironic is that I'm testing out my new speakers in 5.1 music so I chose the Rock in Spatial Audio playlist on my AppleTV. Come Together was the 4th song on that playlist. Guess what? I heard the entire bass line in the intro. WTH? In fact as it progresses down the playlist...I'm not losing any introductory notes on songs. So they can put out an uninterrupted Atmos stream for songs that aren't even on the same album but somehow can't (or didn't bother to) do it for songs that actually aren't supposed to have pauses between them? Come on, Apple.

 

[Jesse Skeen]

Just checked an Atmos title on Netflix using Kodi (the only way to get the full quality while avoiding their absolutely infuriating interface) and there is no separate 5.1 track on that, just Atmos and 2-channel, so odd that some devices won't pass on the Atmos from that.

 

[Todd Erwin]

Just checked an Atmos title on Netflix using Kodi (the only way to get the full quality while avoiding their absolutely infuriating interface) and there is no separate 5.1 track on that, just Atmos and 2-channel, so odd that some devices won't pass on the Atmos from that.

That is why I think it is a combination of encoding and chipset.