How Personalized HRTF kicks Atmos up a Notch

If big tech was to be believed, Dolby Atmos on headphones has already been the most immersive thing since going into a real-world concert – however, this has only ever been true for a certain subset of people: Those with a head shape close enough to the average model used in rendering to actually make the soundstage of Atmos feel truly 3D for headphone users. For many others, myself included, the result was more akin to an overly widened stereo effect with extra reverb thrown in.

What IS Dolby Atmos anyway?

Dolby Atmos, referred to by some companies as “Spatial Audio” is a surround standard that differs from any other popular standard that came prior (think Dolby Digital, DTS, etc.) by being based on objects, rather than hard-coded speaker channels (5.1, 7.1 etc.). Each music track or sound effect can be treated as an individual object that content creators can position anywhere in 3D space. The main benefit to this kind of system is its scalability. Any Dolby Atmos system will know how many speakers are connected to it and can translate individual object positions to be best represented on whatever playback system you’re listening on – from 12+ speaker installations down to mono. By simulating the way sound gets blocked, diffused, and scattered by the listeners head, fully immersive 3D surround is also possible using stereo headphones on devices that support Dolby Atmos playback. This now includes most phones, Mac and Windows computers, and more – and the list of supported devices is growing consistently.

The Dolby Atmos Renderer in Logic Pro (included since 10.7) showing different objects and their position in space relative to the listener. Image source: Apple.

The current Problem with Headphones

As I mentioned, Atmos also allows for fully immersive surround sound playback on stereo headphones when playing content on a compatible device. This is where having a way to tell the device your listening on what the actual shape of your head and ears looks like can make a world of a difference. HRTF, or Head Related Transfer Function is a way to model how sound gets perceived by humans and to simulate truly 3-dimensional sonic environments using regular stereo headphones.

“Surround with only two speakers?” is what I always hear people asking… that statement will then be followed by the realization that we only have two ears soon after. And that’s exactly where HRTF comes in. The way our brains can locate exactly where a sound is originating from is largely based on the way the shape and size of our head and ears will boost and attenuate certain frequencies and affect the timing of sounds arriving at each of our two ears.

For a while now, many virtual surround and immersive audio standards relied solely on a mean average head and ear shape to create this virtual sonic space meaning that certain directionality just wouldn’t translate for many people. Our brains are especially picky about sounds that play in front of us or behind us – arguably one of the hardest things to approximate in a virtual space and so far the main challenge for Atmos in headphones.

So, to make binaural (or headphone-based) immersive audio as convincing as possible there is no way around getting a 3D image of the listener’s head and ears. This is something that various companies like Genelec, Audeze, and Dolby already offer but so far it’s requiring the use specific 3rd party apps and wouldn’t translate to your native music and media consumption apps on your phone, computer, or tablet.

“Personalized Spatial Audio”

Apple making “Personalized Spatial Audio” a built-in feature of iOS 16 will be a huge step in their race to achieve industry-wide adoption of the Dolby Atmos format for music and audiovisual content. Using the TrueDepth camera on FaceID-enabled iPhones, a camera that not only sees visual light but can create a 3D map of a subject in real time, this should be a much more straightforward process that’ll bring custom HRTF to not just their own AirPods and Beats headphones but in fact any kind of headphone available.

Hopefully, the profile created via this scan will be something that us creators can use to monitor in Logic Pro and maybe even 3rd party DAWs with the relevant Dolby Atmos plugin suite. If so, this will be a great step forward in not only making Spatial Audio more convincing to listeners, but also make it more feasible to create this type of content purely using headphones. With the Dolby plugin suite now included in DAWs like Logic, Nuendo, and ProTools, I hope we’ll be seeing a rapid influx of independent artists utilizing immersive audio to create captivating sonic experiences and help rethink the way we listen to musik.

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Featured image credit: Apple