3D Audio Technology Explained

This article provides a comprehensive overview of 3D audio technology, exploring its history, current state, key concepts, and formats. It aims to clarify how spatial audio enhances the listening experience across various media.

Have you ever wanted to transport yourself into the heart of a concert hall or immerse yourself in the sounds of nature without leaving the comfort of home? With the emergence of spatial audio, this easily becomes a reality.

Introduction to Spatial Audio Today

Broadly speaking, “spatial audio” is defined by a listener’s ability to hear sounds moving in a three-dimensional way. While surround sound has been used in music and cinema for over 30 years, today’s concept of spatial audio became more prominent starting about ten years ago as VR headsets like the Oculus Rift became widely available, and video game developers began to push the limits of the medium.

Artists have been experimenting with a range of emerging audio formats over the years, many of which feel like precursors to today’s spatial audio field. Janet Cardiff and George Bures Miller have been making audio walks for over 30 years, which utilize binaural recordings of narrative fragments that correspond to site-specific walking routes. Other artists have used unique field recording techniques and multi-speaker installations to push what’s possible with immersive, three-dimensional audio; examples include Jacob Kirkegaard’s spatially recorded and composed TESTIMONIUM series, and Barry Truax’s multi-speaker sound pieces (especially The Bells of Salzburg). These early spatial works also build on Pauline Oliveros’ idea of deep listening, which can be seen as a foundational concept in spatial audio production as it emphasizes close, attentive listening as the basis for creating immersive audio experiences.

Spatial audio is an innovative technology that creates a three-dimensional listening experience, making it seem as if sound is coming from various directions and distances. Unlike traditional stereo sound, where audio is delivered through two channels (left and right), spatial audio adds an extra dimension by incorporating height. This technology allows you to perceive sound as though it's coming from specific locations around you, mimicking how sound travels in real life.

For the purposes of our work, we’ve been defining spatial audio as a listener’s ability to play back recorded sound as an immersive, headphone-enabled audio experience. This can happen in one of two ways: either the listener is stationary and sounds move around them, or the listener’s movement is tracked through space using head-tracking headphones and the sounds change based on their movements.

The State of Spatial Audio Technology

On the technical side of things, spatial audio involves a series of recently developed tools and products that can bring a sonic environment to life. Thanks to advancements in hardware (such as head-tracking headphones, earbuds, and VR headsets) and software capabilities (such as real-time rendering, object-based audio, and game development environments), listeners are now able to play a participatory role in sonic experiences that were previously static.

While artists and video games have experimented with various degrees of spatial audio for many years now, we’re currently entering a period where mainstream technology is beginning to support it. Apple’s 3rd generation AirPods, AirPods Pro and AirPods Max all currently support head tracking, which we’ve now tested across a range of mixes and devices. Android has announced that support for head tracking is coming soon, and streaming platforms such as Apple Music, Tidal, Netflix and the Amazon-owned podcast network Wondery have also either begun to offer content with spatial audio support or announced that they will be integrating it soon.

Currently, audio-only experiences such as podcasts are much less prominent than games, music, and video that support spatial audio. While podcasts’ broad listenership makes them an opportune format to expand into spatial audio, distribution is a challenge. That’s because currently, most podcasts are hosted by third-party podcast publishing platforms and RSS feeds that aren’t set up to handle large, multi-channel audio files.

How Does Spatial Audio Work?

The Science of Spatial Audio

Unlike stereo or surround sound, spatial audio uses sophisticated algorithms, advanced processing techniques, and specialized hardware to recreate lifelike soundscapes. Using object-based sound technology, such as Dolby Atmos, sound objects (including vocals, instruments, or effects) are strategically assigned to specific locations in a 3D space rather than a fixed channel.

Say you’re listening to spatial audio on a single speaker, like Sonos Era 300. To produce sound that feels like it’s coming from above, upward-firing drivers in the speaker bounce sound off the walls and ceiling, which get reflected to a specific location in the room. Because audio isn’t being projected in one direction, as is the case with mono and stereo sound, your content feels like it’s hitting you from every direction.

A standout quality of Dolby Atmos is its ability to adapt to various hardware and playback setups. Whether listening on headphones, a smart speaker, or a complete home theater system, Dolby Atmos optimizes the sound to your environment for a more realistic listening experience.

Foundational Spatial Audio Concepts and Formats

To get a sense of the current spatial audio field, we’ve found it helpful to review a few foundational concepts and audio formats. These have been developed over the years by the industry and by audio engineers as they’ve attempted to record more lifelike and immersive sonic experiences - from early record players to the first surround-sound systems in movie theaters.

Channel-Based Audio

Currently, channel-based audio is the standard for music, radio, and TV. With this long-standing format, sound is recorded linearly, and each input channel directly correlates to an output channel. While channel-based audio can create the effect of different sounds coming from different directions - such as with a stereo recording that has guitar playing from the left-hand speaker, and drums playing from the right-hand speaker - a listener’s movement and/or position in space has no effect on audio playback.

Binaural Audio

First developed in the late 1800s, binaural audio introduced the idea that if you record sound in the same way that ears hear, the audio quality will be much more lifelike. To record binaural audio, you mimic the acoustics of a human head by using a microphone in the shape of a head that contains tiny microphones inside each ear canal. This technique accounts for the impact of “head shadow” (the way a noise that’s behind a listener sounds muted), and “ear to sense space” (the slight time delay caused by the distance between a listener’s two ears).

Binaural audio records sound in the same way that ears hear by using microphones placed inside the ears of a dummy head.

Surround Sound

Developed in the 1940s as a way to make theatrical experiences more immersive, surround sound is the precursor to the field of spatial audio. Surround sound connects various audio channels to specific speakers which are strategically placed in a theater, performance space, or room to maximize the sensation of being enveloped in sound. One popular surround sound configuration is known as “5.1,” which places five speakers and one subwoofer across a horizontal axis. Another popular format is “7.1,” which adds an additional two speakers to the horizontal array, and “7.1.2” adds yet another two speakers above the listener. When mixing for surround-sound playback, an audio engineer will build a sonic mix with each discrete speaker in mind.

Ambisonic Audio

Ambisonic is an audio format that uses a specialized microphone to record a 360-degree sound field. While it was first developed in the 1970s, it has become more widely used as a spatial audio format over the last 10 years for 360-degree VR videos in particular. Ambisonic recordings capture audio in all directions, which means the audio files can be used for a vast variety of configurations and formats. They also enable a listener to experience a sound field in its entirety by turning their head in different directions, with a completely unique sonic experience accessible across the entire 360-degree spectrum.

Ambisonic microphones can record an entire 360-degree sound field. While ambisonic recordings can be challenging to work with, they do offer a great deal of flexibility during the mixing process.

Object-Based Audio

Spatial audio introduced the concept of mixing sounds in 3D space. This is possible thanks to object-based audio, in which sounds are placed in a 3D scene and attached to “objects” that move in various ways as a listener interacts with them, or as time passes. To use an example from the gaming world, object-based audio enables the sound from components of the game - such as speaking characters or ambient noises - to move as a player navigates an environment. Object-based audio is important because it enables producers to construct spatial mixes based on how they want various sounds to be positioned around a listener in 3D space over time. With object-based audio, sounds can be placed in a 3D scene and attached to “objects” that move in various ways as a listener interacts with them, or as time passes.

Proprietary Spatial Audio Formats

Dolby Atmos

A key player in today’s spatial audio field, Dolby Atmos is an immersive sound format that incorporates an object-based approach on top of traditional channel-based formats. Designed by the company Dolby as a spatial audio format specifically for use in cinemas, it has recently been expanded to work with music and audio-only experiences. In addition to traditional surround-sound setups, it can also integrate object-based technology as a way to produce an immersive sound field in any given space. We've found Atmos beneficial because mixes automatically reconfigure for different environments - whether you’re playing the audio in your car, through your home stereo, or with headphones. While Dolby Atmos is a versatile spatial audio format, because of its technical requirements and licensing agreements, using it requires special decoding software and hardware.

Mach1

We've also been experimenting with Mach1, a spatial audio framework that works well across a range of platforms including the web. Mixing with Mach1 is similar to mixing with ambisonics, and it integrates well into a traditional podcast mixing workflow enabling a degree of creative flexibility. We explore Dolby Atmos and Mach1 in greater depth in the Mixing section of this guide.

Understanding Spatial Movement

When wearing head-tracking headphones, a listener can move their head to experience spatial audio interactively.

Head-Tracked Audio

Head-tracked audio uses the head-tracking capabilities of headphones or a headset to map a listener’s movement so that when they look from side to side or up and down, they can experience a soundscape interactively. Head tracking mimics the experience of moving through an environment and hearing things differently as you get closer to, or farther from, various sound sources. Head-locked audio, on the other hand, is not interactive. Most headphone-enabled spatial audio relies on head tracking to create an immersive effect, with the exception of binaural audio, which is often considered a head-locked spatial audio format.

HRTF, ITD, and ILD

Head Related Transfer Function (HRTF) is the idea that each listener has a unique head, and therefore will produce specific HRTF data, which conveys the listener’s head size, ear shape, and the angle and position their head is pointed. HRTF is primarily determined by “interaural time differences” (ITD), the difference in the time it takes a sound to reach your left ear vs. your right ear, and “interaural level differences” (ILD), the difference in a sound’s loudness as it moves from one ear to the other.

Localization

Localization describes how well a listener can discern the direction of a sound source in a spatial audio experience. Contextual factors, such as how the audio is experienced and whether or not there are accompanying visuals, can profoundly influence the effect of localization.

3DoF and 6DoF

In the field of head-tracked spatial audio, 3DoF refers to an experience that offers a listener “three degrees of freedom,” and describes how movement will affect playback: a listener can rotate their head left to right (as if saying “no”), shake their head up and down (as if nodding “yes”), and tilt their head side to side (as if touching their ear to their shoulder). With 3DoF, a sound source will seem fixed in space as a listener moves their head to hear it from different positions.

Building on this, 6DoF refers to “six degrees of freedom.” The additional degrees of movement supported by 6DoF spatial audio include walking forwards or backwards, stepping from side to side, and climbing up and down.

3D Audio vs. Standard Surround Sound

Perhaps the most important component of a dynamic, engrossing home theater experience is audio. Advanced audio formats allow for true surround sound unlike anything before. Arguably the most immersive surround sound formatting, 3D audio completely encircles viewers in rich cinematic soundscapes.

Your standard 5.1-channel surround sound setup provides a pretty great aural experience when watching movies, but it doesn't come as close to capturing the full potential of a home theater. The primary issue is the lack of verticality. Sound comes from the left and right and a bit from behind, but that's still a fairly basic layout due to the lack of height channels.

If you want to achieve more nuanced and detailed sound, you need two things: a more complex speaker setup and the right audio format to get the most out of that equipment. That's where 3D audio formats like Dolby Atmos and Auro-3D come into the picture.

The difference between 3D audio formats and less sophisticated options starts at the sound mixing stage. In a standard environment, sound engineers use faders to pan sounds across the different channels. With a format like Auro-3D, however, this process becomes much more refined and accurate, allowing for aural sensations like thunder to boom over the viewer's head.

The addition of height into the soundscape is where 3D audio formats really set themselves apart. Imagine watching Independence Day and actually hearing the alien spaceships moving into position over your head. Dolby Atmos, DTS:X, Auro-3D and other members of this new class of audio formatting continue to pave the way for a more immersive home theater experience.

To take full advantage of the latest audio formats - especially from Dolby Atmos and DTS:X, which allow for more robust surround and height channel setups compared to Auro 3D - you need high-quality equipment that supports 3D sound. State-of-the-art Denon AV receivers like the AVR-X8500H feature anywhere from 9.2 (can be set up as 5.2.4 or 7.2.2), to 11.2 (can be set up as 7.2.4 or 9.2.2), to 13.2 (can be set up as 7.2.6 or 9.2.4) surround sound channels, and includes 4K Ultra HD video capabilities.

Experiencing Spatial Audio

When you press play, you expect sound to fill your ears. But what if it could fill your space? Unlike traditional stereo, which plays left and right, spatial audio creates a three-dimensional soundscape with audio from in front, behind, above, or to the sides. From cinematic sound effects to layered music production, spatial audio brings a level of depth and realism that fits naturally into film, music, and gaming.

For years, stereo and surround sound have shaped how we hear music and media. Stereo splits audio into two channels: left and right. It’s simple and familiar, but it lacks depth and vertical movement. Surround sound uses multiple speakers placed around the room to create directionality, typically in front, beside, and behind the listener.

Spatial audio goes further, using software to simulate full 3D space including height, distance, and movement. It can create an immersive sound field from just a soundbar, a pair of headphones, or even built-in speakers.

And unlike surround setups, spatial audio doesn’t require a fixed listening position. Is spatial audio the same as Dolby Atmos?No. Spatial audio is a broad category of 3D sound technologies. Dolby Atmos is one specific format that uses object-based mixing to place sounds in space. It's one way to deliver spatial audio.

Listening to Spatial Audio at Home

To experience your music and movies in spatial audio from the comfort of home, you’ll need two things: a Dolby-Atmos supported streaming service and a compatible device. Below are a few types of devices you can use to play Dolby Atmos content:

• Headphones: One of the most popular ways to experience spatial audio is with a pair of headphones. Over-ear headphones like Sonos Ace have the ability to create an exceptional acoustic seal around your ears, making you feel completely surrounded by what’s playing.
• Smart speaker: If you want to experience spatial audio out loud instead of using headphones, some smart speakers - like Sonos Era 300 - can fill a large space with immersive Dolby Atmos content. No matter where you are in the room, it will feel like the music is playing all around you.
• Soundbar: Similar to a smart speaker, some high-end soundbars, like Sonos Arc Ultra, can support spatial audio for movies and TV shows for a theater-like experience. These systems often include upward-firing drivers to bounce sound off the ceiling to create an all-encompassing effect.
• Gaming console: If you want to put yourself inside your games, certain consoles and PCs with compatible sound cards can deliver a truly lifelike experience when playing content mixed in Dolby Atmos.
• Virtual reality (VR) headset: Some VR headsets provide spatial audio as part of their virtual experiences. When pairing spatial audio with VR content, these headsets can offer an incredibly immersive audio-visual experience.

Spatial Audio: Key Differences

Feature	Stereo	Surround Sound	Spatial Audio
Channels	2 (Left, Right)	5.1, 7.1, etc.	Object-based
Directionality	Horizontal	Horizontal	3D (Horizontal and Vertical)
Immersion	Basic	Enhanced	Highly Immersive
Listening Position	Not Fixed	Fixed	Not Fixed

Why Should I Listen with Spatial Audio?

Spatial audio brings you closer to the creator's original intent, allowing you to hear your content the way it was meant to be heard. When listening to music, you'll feel as if you're in the recording studio, surrounded by every instrument and nuanced detail. When watching a movie, the explosions will reverberate around you, the dialogue will appear to come from specific corners of the room, and ambient sounds will transport you into the center of the scene - it's like having a private cinema right in your living room.

Spatial audio enriches your emotional connection to your content by making it more engaging and lifelike.

Experience Spatial Audio with Sonos

Spatial audio represents a groundbreaking leap in the way we enjoy our favorite movies, music, and games. Its ability to create immersive, lifelike audio environments opens up new dimensions of entertainment where sound isn’t just heard but felt. Sonos Era 300 or Sonos Arc Ultra speakers feature cutting-edge technology that allow you to effortlessly experience spatial audio at home.