What is the difference between 3D audio and spatial audio?

3D audio and spatial audio are audio technologies that aim to create an immersive listening experience by simulating how sound is perceived in the real world. Both technologies take into account how sound waves propagate and interact with the environment and listener to reproduce a three-dimensional soundscape.

3D audio refers to techniques that allow for sounds to be placed and moved in a 3D space, creating the illusion of sound sources being all around the listener. This is typically achieved through binaural audio techniques which take into account how the human ears receive sounds from different directions.

Spatial audio goes a step further by also incorporating room acoustics and environmental effects into the listening experience. Spatial audio aims to replicate how sound behaves in a real physical space, including how sound reflects off surfaces and changes as the listener moves around. This provides an extra layer of immersion and realism.

While there is some overlap between the two technologies, spatial audio focuses more on full environment modeling while 3D audio emphasizes 3D positional audio. In the following sections we’ll explore both concepts further.

Definition of 3D Audio

3D audio, also known as spatial audio, is a blanket term for immersive audio technologies that aim to fully surround the listener with sound and create the illusion of audible space and distance (Trusted Reviews, 2022). The goal of 3D audio is to mimic how human beings naturally hear sound in the real world, with audio coming at us from all directions due to how our ears are positioned on either side of our head. This provides auditory depth cues and allows us to locate sounds spatially.

With 3D audio, sound objects are mapped to virtual 3D space around the listener. Sophisticated 3D audio systems make use of head-related transfer functions (HRTFs), algorithms that simulate how sounds hit our ears from various points in space, taking into account the shape of the ears, head, and torso (Spotify, 2022). This allows for incredibly immersive audio that gives the illusion of true 360 degree sound.

Techniques Used for 3D Audio

There are a few key techniques used to create the 3D audio effect:

Binaural recording – This technique uses two microphones mounted in a dummy head to record sound from two ear positions. The sound is then played back through headphones to recreate the 3D effect. Binaural recording aims to simulate the listening experience of our ears and provides a very immersive 3D audio effect.[1]

Head-related transfer functions (HRTFs) – HRTFs are used to model how sound reaches our ears from any point around us. They capture the acoustic properties of our head, ears, and torso. HRTFs allow 3D audio effects to be added to existing audio without binaural recording. They enable converting stereo audio into 3D audio that can be played back through headphones. Some limitations exist in customizing HRTFs to individual anatomies.[2]

Room modeling – Modeling the impact of room acoustics is another technique for spatializing audio and adding a sense of space. Factors like room size, materials, and object placement are modeled to simulate how sound reflects and reverberates in a real physical environment. This provides cues that the brain uses to gauge distance and environment size.[3]

[1] https://en.wikipedia.org/wiki/3D_audio_effect
[2] https://www.endpointdev.com/blog/2020/12/3d-audio-fundamentals/
[3] https://sonicscoop.com/sound-all-around-a-3d-audio-primer/

Examples of 3D Audio Use Cases

3D audio has become increasingly popular in virtual reality applications, video games, and music. In VR, 3D audio helps create immersive experiences by simulating sounds coming from all directions, distances, and elevations. This allows users to feel like they are truly present in the virtual environment. Many VR games and experiences use 3D audio for directional sound effects, ambient background sounds, and dialog to enhance realism. Some examples include Beat Saber, Half-Life: Alyx, and Star Wars: Tales from the Galaxy’s Edge.

3D audio is also commonly used in modern video games to create surround soundscapes. Racing games like Forza Horizon use 3D audio for realistic engine sounds and environmental effects based on player position. First-person shooters like Call of Duty leverage 3D audio to simulate gunshots and footsteps coming from exact locations. Open-world games immerse players with 3D ambient noises and directional dialog. Wearing headphones with 3D audio enabled greatly enhances immersion in these games.

In the music industry, 3D audio allows mixing engineers to spatialize different elements of a song in a 360-degree soundfield. Musicians and producers can use 3D audio mixing techniques to create more vibrant, layered listening experiences. For example, certain instruments can be panned to one side while the vocals remain center-focused. Electronic music often makes creative use of 3D panning effects. When listened to using surround sound systems or spatial audio headphones, the 3D mix creates a feeling of being in the center of the music.

Sources:

https://www.highfidelity.com/blog/surprising-use-cases-for-3d-audio

https://www.highfidelity.com/blog/what-is-3d-audio

Definition of Spatial Audio

Spatial audio is a technology that allows sound to be reproduced in a way that creates the impression of true three-dimensional space (1). It uses advanced processing to make audio feel like it’s coming from all directions, moving around the listener as sound naturally would. The goal of spatial audio is to immerse the listener in sound by mimicking how we hear in the real world (2).

With spatial audio, sounds have distinct positions and distances relative to the listener. As the listener moves, the audio perspective shifts realistically. This creates a lifelike, surround sound experience. Spatial audio goes beyond standard stereo by adding a vertical dimension to the horizontal plane of stereo sound (3). The audio contains information about elevation and depth in addition to left/right panning.

Some key techniques used to create spatial audio include surround sound, object-based audio, ambisonics, wave field synthesis, and head-related transfer functions. These allow audio engineers to position and move sounds in a 3D space (1). Depending on the headphone or speaker setup, spatial audio can create the illusion that sounds are coming from all around or even from above and below the listener.

Sources:
(1) https://www.dolby.com/experience/home-entertainment/articles/what-is-spatial-audio/
(2) https://www.cnn.com/cnn-underscored/electronics/what-is-spatial-audio
(3) https://www.tomsguide.com/reference/what-is-apple-spatial-audio-how-it-works-and-how-to-use-it

Techniques Used for Spatial Audio

There are several key techniques used to create spatial audio effects:

Object-Based Audio

Object-based audio involves applying audio signals to individual sound sources or objects. The position and movement of each object is encoded, allowing each sound to be placed and moved independently in a 3D space (The Beginner’s Guide to Spatial Audio). This provides precise positioning and control over each sound element.

Scene-Based Audio

Scene-based audio aims to recreate an entire immersive environment. Sounds are fixed to locations in a 3D space to mimic a real-world scene. The listener’s position and orientation is tracked to blend audio sources realistically (Spatial Audio Techniques for Enterprise VR Applications).

Channel-Based Audio

Channel-based audio uses multiple channels routed to an array of speakers to produce directional audio effects. Sounds can be positioned by adjusting levels sent to different speakers. A simple example is stereo sound with left and right channels.

Ambisonics

Ambisonics encodes soundfield information rather than discrete channels. This allows the soundfield to be decoded for any speaker layout after recording. It provides full spherical surround sound that adjusts realistically as the listener moves through the space.

Examples of Spatial Audio Use Cases

Spatial audio is particularly useful for creating immersive experiences in virtual reality (VR) and augmented reality (AR). By using head tracking and processing audio in a way that mimics real-world acoustics, spatial audio can make VR and AR much more lifelike and engaging.

In VR applications, spatial audio allows sounds to change dynamically based on the listener’s perspective. For example, as you turn your head in a virtual environment, a sound that is on your left will shift to your right ear. This creates an incredibly compelling sense of presence and realism in VR worlds.

Spatial audio also enables realistic audio occlusion, reverb, and acoustic properties in VR and AR spaces. Sounds will be muffled if there is an object between the source and the listener, and environmental effects like echo can be simulated. This further heightens the immersiveness of the experience.

Major tech companies like Apple, Google, Meta, and Microsoft are actively developing spatial audio solutions for VR and AR. Spatial audio is considered an essential component of creating truly believable virtual and augmented environments.

For example, Apple notes that spatial audio on their AirPods Max headphones “takes movies, music, and more to the next level. Envelop yourself in sound that flows all around you with incredible definition. So you feel like you’re at the center of what you’re listening to.” https://www.softserveinc.com/en-us/blog/how-spatial-audio-meets-customer-needs

Key Differences Between 3D and Spatial Audio

There are some notable differences between 3D audio and spatial audio in terms of technique and use cases:

3D audio is designed to create the illusion of sound sources coming from specific fixed locations around the listener [1]. The auditory scene is anchored to the listener’s perspective and does not change if the listener moves. Common techniques for 3D audio include binaural recording, crosstalk cancellation, and ambisonics. 3D audio is often used in virtual reality experiences to immerse the user in a virtual environment.

Spatial audio refers more broadly to audio that conveys the impression of space and environment around the listener. In spatial audio, the auditory scene can shift realistically as the listener moves through space [2]. Object-based audio is a common technique for spatial audio, which allows audio sources to be positioned and moved independently in 3D space. Spatial audio is increasingly used in augmented reality, allowing virtual sound sources to blend naturally with the real physical environment.

In summary, 3D audio establishes an anchored, fixed soundscape from the listener’s perspective, while spatial audio allows the auditory scene to update realistically as the listener moves through an environment.

Overlaps Between 3D and Spatial Audio

While 3D audio and spatial audio have their differences, there are also some key overlaps between the two technologies. Both aim to create immersive audio environments that mimic how sounds are perceived in the real world. As the paper from the University of Washington explains, “Both terms are very general. ‘3-D sound’ usually implies the perception of point sources in 3-D space (could also be 2-D plane) whether the reproduction system employs 2, 3, 4, 5, etc. speakers.”

So in essence, both 3D and spatial audio use multi-speaker setups and advanced audio processing to simulate a realistic 3D soundscape. The key difference lies in the techniques used to position and render sounds in space, with 3D audio relying more on general localization and spatial audio using more advanced head-tracking and room modeling. But their shared goal is to immerse listeners in believable 3D audio environments.

Conclusion

In summary, while 3D audio and spatial audio share some similarities in their goal of creating an immersive listening experience, they utilize different techniques to achieve this. 3D audio aims to replicate a 3D space using HRTFs, object-based mixing, and binaural rendering. It focuses on the perception of sound sources coming from all around the listener. Spatial audio refers more broadly to any technique that allows the placement and movement of sound sources within a 3D space, using approaches like surround sound, ambisonics, and wave field synthesis.

Both 3D and spatial audio are providing enhanced, immersive audio experiences for applications like VR/AR, gaming, and entertainment. As audio technology continues to advance, the line between these two terms may blur. What is clear is that listener’s expectations for audio realism and immersion are increasing. Audio engineers now have more tools and techniques than ever before to meet this demand and craft engaging soundscapes that mimic how we hear in the real world.