Hej there,

I'm trying to understand the implementation of Dolby Atmos on the mac. It's not that straight forward, really. For example: I own a small quadrophenic setup at my mixing position. When I open the Audio-Midi-Setup on the mac I can set everything up. Playing some dolby-music through the music app (set to dolby automatic) I can hear a kind of dolby-mix. So, all right.

But: How does an atmos mix is downmixed to quadrophenic? Does somebody know that? Does the music app recognise my settings in the Audio-Midi-Setup? When I change it to something "bigger" like 5.1 or 5.1.2 (without the required speakers), it sounds different. So I assume the renderer is recognising the setup in Audio-Midi-Setup. But how is it downmixed? What happens to the center-channel or the LFE or the top speakers of an atmos-mix when using quadrophenic or some other formats?

I couldn't find any good information on this side of atmos. Maybe someone knows a place or can give me the information?

Cheers,
JC

I’m still getting a handle on Atmos myself, but as I understand it currently each object’s pan and level are vector based as opposed to speaker based, so it just uses a whole lot of math to reposition the sounds from a 3D space to surround or stereo space. The playback device recognizes your speaker configuration and renders the output automatically.

There’s a couple interviews and round tables with Andrew Scheps on YouTube where he talks the fun nerd stuff of the format. Check those out if you haven’t already.

Yeah, you are right. It's object based. So the idea is, that it will recognise what you have and do the best with the placement of the audio on your system. Also, there's the beds in an atmos-mix that are closest to the "old" surround format, where you send audio direct to a specific speaker. I get that and tried to mix some songs in Logic. It's fun.

But I try to understand what spatial audio in the music app is doing with atmos-mixes. Does it use the channels from the audio-midi-setup and applies some kind of downmix? I don't find any information on this topic.

Cheers,
JC

No macOS cannot do arbitrary decode of Atmos to arbitrary speaker configurations the only things it can do are:

- Bitstream it from a HDMI port or a supported USB-C to HDMI dongle to a external device that supports Atmos

- Play a binaural mix on AirPods

- Play some kind of downmix (it's unclear what) on the internal speakers of some MacBook Pro models.

I was under the impression that some macbooks and the new imacs are basically Atmos enabled devices, meaning they render the Atmos mix and play it back on the internal speaker setup. Basically like any Atmos enabled soundbar is rendering Atmos content. If I open the Atmos demo on the Dolby page on my M1 Air, it really tries to pan stuff behind me and rotate it.

Atmos sound bars do have complex speaker setups with upward and sideways firing drivers. They also have preceise relationships between the front firing drivers. This mean in the near field (where you don't have any room effects to worry about) you can do something similar to binaural rendering.

The macs are probably doing something similar however they have fewer drivers and are very limited in where they are and in what direction they are firing.

In any case such renders are very different to what you'd experience out of a speaker array or even a normal binaural render out of a pair of headphones.

I have a supported Macbook Pro and have tried the Dolby Demo page and frankly the Atmos stuff sound terrible compared to the Stereo.

Really funny that there's so little information on this matter. Is everything on the mac binaural? Even the spatial audio mix through the speakers on the newer macs?

I will try to test what's changing when you change Audio-MIDI-Settings.

It really is quite strange do you think about Isn’t it? I really spoken to people who would typically know the answer to this kind of think I’m somebody who would know the answer to this sort of thing particularly from Apple and Dolby but nobody seems to give a concrete answer to some pretty basic fundamental questions to how What is by all accounts eight basic set of circumstances which should have a consistent outcome across playback systems even if there are several I’ve never seen several listed with any sort of definitive explanation.

What’s more puzzling still is it in seem to get a good reason for the confusion I mean are there to do is explain what the technology actually does is an end result and I think we don’t have a lot more clarity an understanding of how we’re supposed to implement it they don’t even need to discuss the technology behind it in any sort of way just the basics as they were described for example don’t be digital 5.1 or what have you the lack of clarity is just very strange to me coming from both companies sides (Apple & Dolby respectively)

Hej,

so I did some tests with the Music App playing Atmos and the Audio-MIDI-Setup.

My setup:
Musik-App - Atmos turned to "Automatic"
Then I used different settings in Audio-MIDI-Setup and routed the outputs to Virtual Busses on my Apollo Interface and recorded that in Logic.

The result:
As far as I can see the Music App lets me play back a 5.1-Mix of an Atmos mixed track. I get all the channels correctly. If I switch to something smaller like Quadrophonic I seem to loose the center-signal and the LFE or they are mixed in very quietly. The important part is: When I switch to Quadrophenic no signal is coming through the other channels (that were beforehand used for Center and LFE). So, the Music App seem to recognise the settings in Audio-MIDI-Setup.

Anything above 5.1 isn't transmitted via my setup. So no 7.1.4 without some special receiver, it seems.

Don't know what to think of this. It seems kind of strange.
Cheers
JC

The graphs in this article I think do a great job show the different decode processes based on the selected output hardware: https://www.pro-tools-expert.com/pro...on-apple-music

Yes, Edgards Artikel ist great. Maybe he could chip in and share some infos on Atmos playback on a mac...

So Apple are distributing Atmos as EAC+JOC now a feature of this is it's backwards compatible with an EAC decoder that knows nothing about Atmos the decoder just ignores the Atmos metadata and the extra bed channels for the height and the object group channels.

So assuming macOS has EAC decoding in it, which is reasonable, that would explain you getting 5.1 out of the this setup.

I think dolby are trying to protect their revenue stream from licenses to hardware manufacturers by now allowing a software solution to exist in general OSes.

That could be it, even if I don‘t understand, what‘s happening with all the panning information in objects. Is the elevation-information ignored?

I would think that Apple should use the spatial-renderer it has to also playback on other audio-systems, that are connected to the mac. Would be great to have atmos through my apollo-interface… But that doesn‘t seem very likely.
Also, headphones through anything but the headphone-jack of the mac don‘t recieve the binaural atmos-mix. That‘s really a pity.

Well, you can connect your Atmos HDMI receiver to an Apple TV (and I think to a Mac too) for example and listen to the Spatial mixes on a discrete setup.
But directly on a Mac via your soundcard: no and I'm not assuming that will ever happen. The reason being that the number of people using such setup is minimal. There is a good case to be made for the creators of content but I'm thinking that Apple would provide additional tooling for that in the future if they want to enable creators to get an idea how the Spatial engine will process their music.
Note that Audio/Midi only supports 7.1 as a maximum. So even a 9.1 surround format is not supported.

Regarding the headphones: I think that playback of Spatial content on a supported mac is limited to rendering by using the internal speakers only and perhaps by using the apple headphones. Which is indeed a pity.
But as a last resort: try to set in Audio/Midi in the speaker configuration that it's a headphone and not a 2.0 speaker system.

Right, Apple TV seems to be the only real option.

But there should be an easy way for everyone who mixes atmos to check the playback. Apple should absolutely work on that. Atmos without this isn‘t going to work.

There is it's called the Dolby Reference Player but Dolby keep it locked up. Probably to protect the revenue stream from licenses from hardware devices for Atmos decoders.

Something linke that for Apple Spatial Audio would be good. I hope Apple is providing some form of monitoring-solution soon.

They did provide such tools for the iTunes store. In the past they created this plugin which you could insert on the masterbus or in your mastering tool of choice (they also provided AU Lab for people using DAW's not having audio unit support). You could select the rates and hear how your master would sound after being processed by iTunes store.

Updated version of that one with spatial would be welcome.

for some clarity-

apple spatial is a 5.1 downmix of the atmos ADM that is then processed by apple with a proprietary system IN THE HEADPHONES THEMSELVES to make "apple spatial audio"

it has nothing to do w/ the BIN file or binaural settings in the dolby renderer. all dolby metadata is ignored by apple at this point.

we're all hoping for an applet soon that will provide realtime monitoring of the spatial process just like apple did for MfIT back in the day.

keep in mind, as you work in atmos today, that the apple process can (and likely will) change in the future. so best practices at this point is to mix to physical speakers and BIN, back and forth to even them out, and then check Apple Spatial at the end and determine if anything is way outta whack in spatial. (I can tell you that certain spatialization stuff does not play nice with apple, put your Waves S1 away).

example: I did a song with some fun stuff on a guitar solo... sounded amazing in the room, disappeared in apple spatial. (!!)

for context: I've done about 100 atmos mixes from small to large artists. i don't go on here much (at all) so forgive me if my replies are slow.

thanks, R

What is inside a track provided by Apple Music is

#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-stereo-256-binaural",AUTOSELECT=YES,CHANNELS="2/-/BINAURAL",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-stereo-256",AUTOSELECT=YES,CHANNELS="2",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-stereo-256-downmix",AUTOSELECT=YES,CHANNELS="2/-/DOWNMIX",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-HE-stereo-64",AUTOSELECT=YES,CHANNELS="2",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-HE-stereo-64-binaural",AUTOSELECT=YES,CHANNELS="2/-/BINAURAL",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-HE-stereo-64-downmix",AUTOSELECT=YES,CHANNELS="2/-/DOWNMIX",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-stereo-128",AUTOSELECT=YES,CHANNELS="2",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-stereo-128-binaural",AUTOSELECT=YES,CHANNELS="2/-/BINAURAL",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-stereo-128-downmix",AUTOSELECT=YES,CHANNELS="2/-/DOWNMIX",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-alac-stereo-48000-24",AUTOSELECT=YES,CHANNELS="2",NAME="songEnhanced",SAMPLE-RATE=48000,BIT-DEPTH=24
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-atmos-2448",AUTOSELECT=YES,CHANNELS="16/JOC",NAME="songEnhanced"
#EXT-X-MEDIA :TYPE=AUDIO,GROUP-ID="audio-atmos-2768",AUTOSELECT=YES,CHANNELS="16/JOC",NAME="songEnhanced"

As you will notice there is a binaural render present, however it's unclear what it's used for as it's not used for what goes to Airpods that is derived from the EAC3/JOC.

The 'Dolby Metadata' is not exactly ignored by Apple the problem is that Apple are distributing in Dolby's EAC3/JOC and this format doesn't preserve the binaural metadata. In order to have the meta data present you need to use AC4. It's unclear they ended up with EAC3/JOC rather than AC4.