Recording October 2023 - 20

The Wild World
of
Dolby Atmos Binaural Streaming
What Does This Mean for My Mix?
Long story short, it means that an Atmos mix will not sound the
same on Amazon Music and Tidal as it does on Apple Music.
While it's true that all three services are using the same ADM
BWF master file to create their binaural headphone experiences
for listeners, the tools and encoding they're using sound different.
One of the main differences centers around the " Near/Mid/
Far/Off " binaural settings that can be applied in the Dolby
Renderer [see the June 2023 RECORDING article for more].
These settings are saved as metadata in the ADM BWF file to
be used in the creation of the AC-4 binaural file further down
the line. Unfortunately, because DD+JOC is an older encoding
spec, it cannot support the use of these settings, and Apple has
to employ its own as part of its proprietary " psychoacoustic
tools " package. In some cases, they do not follow the metadata
instructions included in the ADM file.
One of the most important tools used by both Dolby and
Apple is essentially a room reverb to help create a virtual 3D
space for binaural playback. As with any two reverb algorithms,
these don't sound the same, and that difference will
affect the sound of a mix across the services.
Many of the processes involved in creating binaural playback
are proprietary, so it's impossible for us to know everything
that's happening behind the scenes in either case. But as
they've been developed separately, it's safe to assume they've
come up with different approaches in many, if not most, cases.
Apple Doesn't Follow the Binaural
Metadata " In Most Cases? "
Unlike traditional stereo, the binaural streaming experience
can be, has been and will continue to be updated via software
patches over time. When Spatial Audio launched in 2021, it was
only available to those with Apple head-tracking enabled headphones/AirPods.
A little more than a year ago, they opened it up
to everyone, but it required some fancy footwork on their part.
Today, if you listen to Apple Music with head-tracking enabled
headphones, you hear an updated version of the " original "
Spatial Audio.
Suppose you listen with any other kind of headphones. In
that case, you get a version that doesn't allow for head tracking
but does take the Near/Mid/Far/Off binaural metadata
into account while still running through the Apple psychoacoustic
tools rather than those from Dolby.
The upside is that the Atmos/Spatial Audio experience is
now available to many more Apple Music listeners, but at the
cost of mixing and mastering engineers now having a third set
of headphone variables to tackle.
20 RECORDING October 2023
In that Case, How Should I Approach My Atmos Mix?
I know...it's a lot to take in. So here are a few tips I hope will
help you navigate what is currently a complicated situation:
1. When in doubt, the speaker mix should be the most important
consideration. This may seem counterintuitive.
Most of our listeners today are on headphones. But as
I said earlier, binaural delivery has and will continue to
be updated regularly. Dolby and Apple are working to
make the headphone experience sound as much like the
speaker experience as they can. So, a mix tailored specifically
to one binaural fold-down may (will) not sound
the same in the future as it does today. But it will very
likely sound more like the speakers.
2. Listen to all versions of the binaural fold-down while you
mix. Ensure your Dolby Renderer is correctly set up to
deliver binaural playback to your headphones. If you're
a Logic user, you can monitor Dolby and both versions
of Apple Spatial binaural playback. If you don't use Logic,
you'll either need to find a way to monitor your mix
live through Logic as you work or create .MP4 files to
check your mixes on an Apple device.
3. Remember, they can't all be perfect! The stereo-mixing
process has always been an exercise in compromise.
While the specific compromises of an Atmos mix are different,
the process is the same. I've often described it as
trying to use one set of faders for the front-of-house mix
and three simultaneous monitor mixes! Making them all
perfect is impossible, but they can all be great with the
proper knowledge and a little work.
Keep Mixing!
It's a lot to juggle right now, but the good news is it's still the
early days in the adoption of immersive music. So keep on top
of the latest developments!
If our short history is any guide, you will likely continue to see
regular improvements that make our mixing lives easier.
Will Kennedy is a Los Angeles-based engineer who, with his
studio partner Matt Wallace, has (together and separately)
been behind the board for Maroon 5, Faith No More, O.A.R.,
3 Doors Down, The Replacements, OneRepublic, U2, Michael
Franti & Spearhead, The B-52s and many more. Check out their
Kali-equipped Dolby Atmos mix room and further adventures in
the July 2022 RECORDING issue, and don't forget the Dolby
Render walk-through this past June in RECORDING.
Recording October 2023

Table of Contents for the Digital Edition of Recording October 2023
