In this article, Edgar Rothermich asks whether it is really possible to mix for Dolby Atmos without first investing in suitable loudspeaker monitoring?
To answer whether you can mix Dolby Atmos on headphones, I will look at five important aspects of this topic that need to be considered. Instead of one final answer, I will provide five answers.
Two things to be aware of before I start. When talking about headphones, I refer to the binaural mode of headphone listening, not stereo headphones. Also, the discussion is mainly about mixing Dolby Atmos for music.
1 - Requirements From Dolby For Mixing Dolby Atmos
The requirements for mixing in Dolby Atmos are less restrictive when mixing for music than for film. Dolby even ended the studio certification program in late 2020, so technically, you can mix in Dolby Atmos in any self-proclaimed Dolby Atmos studio. Dolby's requirements are now more like suggestions because they are not enforced. They provide some guidelines on how to set up a studio, and for the actual mixing in Dolby Atmos, they have the following recommendation: Mix with a discrete speaker layout of at least 7.1.4 while checking the binaural headphone mix during mixing. So this is then the first answer:
Answer 1: Mix on 7.1.4 and only use Headphones to check your mix.
2 - Bedroom Dolby Atmos Producer
Besides the requirements, here is the reality. Mixing in Dolby Atmos used to be something only a handful of sound engineers performed on big-budget movies on a few big dubbing stages. Now with Dolby Atmos being the standard also for smaller productions and TV shows, it has trickled down to smaller studios.
A similar development is happening with Dolby Atmos Music right now. The first Atmos mixes for music were done in big studios like Blackbird or Capitol Records by a handful of top engineers. Now, many studios are crunching the numbers and looking at their crystal ball to decide if it is feasible to upgrade to DolbyAtmos.
But then, in October 2021, Apple changed the game with the Logic Pro update 10.7, providing Dolby Atmos Renderer integration built into Logic Pro (free of charge).
Nuendo and DaVinci are two DAWs with Dolby Atmos integration already; however, Logic Pro is the first DAW with a vast user base from top producers and film composers down to the bedroom producers. Most Logic users definitely won't think about upgrading to the recommended 7.1.4 system to mix in Dolby Atmos. They will mix their song in Dolby Atmos using headphones and upload it to DistroKid to get it on Apple Music as soon as possible. So if you ask any of those users if you can mix in Dolby Atmos, their answer would be, "Yes, that's all that I have". So that would be our second answer:
Answer 2: Yes, you can mix in Dolby Atmos using headphones because that is the only available choice for many users.
3 - User Experience
Now let's look at how the end consumer listens to the Dolby Atmos content. It is estimated that 80% of music is listened to over headphones. Applying that to Dolby Atmos music consumption, you could end with 80% of headphone listening (in binaural mode), maybe 19% listen for some sort of speaker virtualization (smart speaker, soundbar, etc.) and maybe 1% over a dedicated 7.1.4 system. That 1% might be only 0.1% because most people with a 7.1.4 speaker setup are sound engineers in their studio and some home theater enthusiasts.
So instead of asking if we "can" mix Atmos over headphones, shouldn't the question rather be whether we "should" mix Atmos over headphones? Who do we serve when we monitor over a speaker system that virtually nobody has? Shouldn't we create our Dolby Atmos mix closer to "real-world listening conditions"? So, how about this answer?
Answer 3: Yes, we should mix in Dolby Atmos using headphones because that is how consumers are listening to it.
4 - Distribution
For this consideration, let's look at the Dolby Atmos distribution chain. There are two significant problems with the whole concept of listening to Dolby Atmos in Binaural Mode. The Dolby Atmos Renderer application lets you set each of the 128 channels to any of the four Binaural Render Modes, representing three different HRTF algorithms (near, mid, far) plus "off", which disables Binaural Rendering for that channel. These Binaural Render Modes give the mixing engineer great flexibility to adjust the Binaural experience to sound closer to the discrete speaker experience. The problem is, all that Binaural Render Mode metadata is ignored with the older DD+JOC codec that Apple is using to stream to their subscribers. Only the modern AC4-IMS codec, used by Tidal and Amazon for their headphone playback, uses the Binaural Render metadata. In addition, Apple does not even use the Atmos Renderer engine at all and, instead, uses their own Spatial Audio technology for headphone virtualization (and speaker virtualization).
So the strange situation is that you can check your Dolby Atmos mix on headphones, but that is only a QC step for Tidal subscribers. When monitoring the Dolby Atmos Renderer in Binaural Mode, whatever you hear will be different from what the 72 million subscribers to Apple Music will hear.
The only clumsy workaround is to use the mp4 export in the Dolby Atmos Renderer and playback that file on your iPhone. However, what about all those Logic Pro Atmos Bedroom Producers mixing over headphones? They will be in for a big surprise when they hear their mix on Apple Music. Even if they would be aware of that minor "issue", Logic doesn't provide the mp4 export workaround. Even worse, the parameter in Logic where you enabled Dolby Atmos is labeled "Spatial Audio", which might suggest that Logic is using Apple's Spatial Audio engine. However, that is not the case. In Logic, "Spatial Audio" is just another word for "Immersive Audio" or "3D Audio".
So what is the answer under these circumstances?
Answer 4: Yes, you might want to mix Dolby Atmos in Binaural Mode for your target audience but better check how it sounds through Appleās' Spatial Audio engine.
5 - Personalized HRTF
This last aspect might be the most important one. It has to do with HRTF, that mysterious "Head Related Transfer Function" that makes Binaural Audio such a convincing immersive 3-dimensional sound experience. Or does it? The problem is that the algorithms used in various applications for Binaural Rendering, including Dolby Atmos, are based on Standardized HRTFs. That is one of the reasons why some people experience a realistic 3-dimensional sound over headphones, while others find the experience not convincing at all. It depends on whether the size and shape of people's heads and ears are close to the dimensions used as a model for the Binaural Renderer.
The only way to deliver a true 3D experience is by using "Personalized HRTFs". That means a person's head and ears are measured, and that data (already an AES standard as a so-called SOFA file) needs to be used by the Binaural Renderer when that person listens through headphones. A lot of research is going on at the moment by big companies, and although it might take years for mass implementation, I hope this will be an option for audio production sooner than later.
If a mixing engineer could load their Personalized HRTF file into the Renderer, then placing a signal with the Panner anywhere in the 3D space would result in a precise localization when listening over headphones. Your brain would not know the difference. In that case, the Binaural Renderer would be more accurate than playing over dedicated speakers.
So the answer for one is:
Answer 5: You definitely could mix Dolby Atmos over headphones if you would have the option to utilize your Personalized HRTF in the Binaural Renderer.
Further Reading
I hope you find the information in this article useful. If you think about starting to mix in Dolby Atmos or want to find out more and dive deeper, I released the first comprehensive Atmos book, "Mixing in Dolby Atmos - How it Works". On 284 pages, I cover the Dolby Atmos Render software (v3.7) in great detail, but also provide a lot of information about the Dolby Atmos eco-system, delivery mechanisms, all the various file formats, and new workflows for mixing and mastering in Dolby Atmos. All that with a lot of unique signal flow diagrams and graphics.
In my other book release, "Logic Pro - What's new in 10.7, I explain the new Dolby Atmos integration into Logic Pro with signal flow diagrams that show how the Dolby Atmos Renderer is integrated in Logic.
More information about my books (available as pdf, iBook, Kindle, and printed book) with many screenshots on my website.