Streaming services all do their own atmos encoding

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zeerround

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Yesterday I went looking for the requirements for encoding Atmos for Tidal, because theirs' is a different format than I get when I use my commercial encoder and from when I use AWS media converter, and I wanted to learn how they do it.

What I found is that each streaming service does their own Atmos encoding. What you do is send them a giant wav file (ADM-BWAV, 48kHz, 24-bit, and 24fps timecode) from your Atmos Renderer, that has all the discrete channels, objects, metadata etc. and then they do the actual encoding from there.

So, each service will have the same "mix" but how they deliver it (object vs. channels, bed vs. objects, etc.) and at what quality will depend on the service and your device, etc. etc.

I also leaned that some services require you to remove any stereo version of your track, after releasing an atmos version.

Interesting stuff, but still didn't tell me the gory details of atmos encoding options.

FYI what I see is:

In my commercial atmos encoding case the 7.1 is the "bed" and all four height channels are really "objects". This is lossless with a True HD core.

In the AWS Atmos encoding case (at least the way I know how to set it up) I get (lossy) 12 bed channels, with the 7.1.4 channel layout (and Dolby Digital Plus with Dolby Atmos core).

Tidal Atmos is 15 (lossy) objects with LFE in the "bed" (and Dolby Digital Plus with Dolby Atmos core). I get 9.1.6 out of those with the A16 Realiser.

I don't have Apple Music Plus so don't know their specific format, but have seen reddit and other posts on the quality/bit rate differences between the various services.
 

zeerround

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good article here, from August of 2021:


Besides lots of technical detail (and intriguing hints) we have:

"Regarding the loudspeaker experience, TIDAL and Apple Music sound nearly identical. Lacking a compatible mobile device for TIDAL, I can’t comment on TIDAL’s binaural sound. But I’ve been enjoying TIDAL’s loudspeaker sound for many months now, and gain-adjusted albums on the two platforms almost completely null cancel.​
However, Apple Music on most receivers plays about 10db louder than TIDAL, making it more likely to hit the playback limiter. John Loose at Dolby chalks this difference up to the different dialnorm settings between the two platforms. Both platforms are working on this and Apple consumers should set iOS devices to Soundcheck ON for the best experience.​
The Affect Of The Bit Rate On the Height Channels
By far, my biggest issue with TIDAL and Apple Music is the 768kbps bitrate, they have chosen to use. (Blu-Ray doesn’t have this limitation). Atmos smartly delivers the most data to the LCR and Ls/Rs. But in a complex mix, soloing the ceiling channels often results in a cringe-worthy MP4 swish-fest.​
The entire mix might sound amazing, but don’t solo the Rtr channel with a client in the room. There is also a subtle and intermittent crackling issue heard more often in classical music that Dolby engineers are looking into now at my behest. And John Bowen, the audio wizard behind these great podcasts (here’s a link to the first in a series of excellent binaural podcasts Bowen has produced) has pointed out that…​
“The closer your pan is to the ‘listener,’ the more accentuated the crossover from one side to the other. This is most pronounced using FAR mode, and least using NEAR (or OFF). MID seems to most faithfully represent the loudspeaker mix. All of these observations are highly unscientific, and these things do change with updates.”​
That said, these are small artifacts in what has otherwise been an excellent technical roll-out of Atmos and now Spatial Audio-compatible consumer devices.​
Aesthetics
Listening to Dolby Atmos albums with TIDAL or Apple Music on loudspeakers in a calibrated 7.1.4 or 9.2.6 room is wonderful. It’s a quantum-leap over stereo and a huge improvement over surround sound.​
I feel like a kid in a candy store surfing Apple Music in 7.1.4. Spatial Audio on headphones is noticeably better than stereo on headphones, and gives producers new tools, but is a less startling difference when compared to loudspeakers."​

...
and goes on from there.
 
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