Android Spatial Audio: Types, Formats & More

Spatial audio refers to sound that is processed to give the listener a sense of space and dimension. Unlike regular stereo audio which sends the same sounds to both ears, spatial audio adds subtle differences between the left and right audio channels to mimic real-world acoustics. This allows the listener to perceive sound as occurring at different locations and distances around them, creating a more immersive listening experience.

The concept of spatial audio dates back to the 1930s when engineers began experimenting with stereo sound for films. However, the technology did not become widespread until the introduction of surround sound home theater systems in the 1970s and 1980s. More recently, spatial audio has seen renewed interest with the rise of virtual and augmented reality headsets which aim to fully immerse the user.

On a technical level, spatial audio works by applying filters and effects to the audio to simulate the ways soundwaves behave in a real 3D environment. Sounds can be processed to seem like they are coming from behind, above, below or anywhere around the listener. Reverb effects are added to make sounds appear far away or in a large space. Even the shape of the listener’s ears can be simulated so that sound interacts realistically based on head position and orientation.

There are many benefits offered by spatial audio compared to traditional stereo. It creates a more natural listening experience that reduces listening fatigue. Spatial audio allows for greater perceptibility of distinct sounds and improves comprehension for dialog-heavy content. It also enables more creative audio production and sound design possibilities. Use cases range from gaming and movies to emerging technologies like self-driving cars which can use spatial audio to increase situational awareness.

Types of Spatial Audio

There are several techniques used to create spatial audio effects and immerse listeners in surround sound. The main types of spatial audio include:

Binaural Audio

Binaural audio simulates the listening experience of our ears. It is recorded using two microphones to capture sound from two different positions, similar to how human ears pick up audio cues to locate sounds in space. This creates a 3D soundscape when played back using headphones. The audio seems to come from all around the listener.

Surround Sound

Surround sound systems use multiple speakers to envelop listeners in audio from different directions. The most common setups are 5.1 with speakers in front, behind, and a subwoofer, or 7.1 which adds side speakers. The multiple audio channels create the illusion of sound sources placed spatially around the room.

Object-Based Audio

Object-based audio involves mixing various sounds as individual audio objects. These objects can then be dynamically positioned and moved anywhere in the 3D space during playback based on metadata. For instance, a helicopter sound effect could move from left to right to match the action on screen.

Ambisonics

Ambisonics is a full-sphere surround sound technique. It captures sound from all directions using special microphones, then encodes audio with directional information. This lets audio be adapted to different speaker layouts while retaining immersion and spatialization. Ambisonics is the basis for platforms like YouTube’s spatial audio.

Spatial Audio Formats

There are several key spatial audio formats that are driving immersive audio experiences:

Dolby Atmos was originally developed for cinemas and later adapted for home entertainment systems. It creates immersive audio by adding height channels, allowing sounds to be placed and moved in a 3D space [1].

DTS:X is a competing format from DTS that also provides object-based spatial audio. Like Dolby Atmos, it introduces height channels for 3D audio placement [2].

Sony 360 Reality Audio is an immersive audio format focused on music reproduction over headphones. It uses object-based spatial audio to create a 360-degree sound field [3].

MPEG-H is an open standard audio format developed by the Moving Pictures Experts Group that supports immersive sound experiences. It allows for adaptive audio streaming and rendering based on a device’s speaker configuration [3].

Spatial Audio on Android

Native spatial audio support was introduced in Android 9 Pie in 2018. This allowed Android devices to render spatial audio content and take advantage of hardware acceleration. Initially, support was limited to select devices like the Samsung Galaxy S9. However, spatial audio support has expanded across Android devices from many OEMs like Samsung, Sony, Xiaomi, Oppo and more. Most modern Android smartphones support spatial audio playback.

To develop spatial audio enabled apps for Android, developers can utilize the Spatializer API introduced in Android 13. This API provides methods to apply spatial audio effects like reverb to audio streams. Developers can also use third-party SDKs like the Gaudio SDK which simplifies spatial audio implementation with features like head-tracking and room simulation.[1]

Overall, Android offers full-fledged native spatial audio capabilities that enable immersive audio experiences on mobile. With wider device support and APIs/SDKs, developing spatial audio apps on Android is easier than ever.

Developing Spatial Audio Apps on Android

There are several tools and SDKs available for developing spatial audio apps on Android devices:

The Android Spatial Audio SDK provides APIs for spatial audio rendering and head-tracking. Developers can use it to create immersive audio experiences by positioning sounds in 3D space around the user. The SDK supports multiple spatial audio formats and head-tracking sensors.

Google Resonance is an audio SDK focused on spatial audio and 3D sound propagation effects. It features room modeling, occlusion, and environmental reverb to simulate how sound interacts with virtual environments. Resonance works across mobile, desktop, and VR platforms.

Unity and Unreal Engine have built-in spatial audio engines and plugins like Ambisonics Toolkit. These game engines provide 3D mixing, audio propagation, and HRTF-based spatialization out of the box for building spatial audio into games and VR/AR apps.

When developing for spatial audio, it’s important to optimize assets for 3D and test extensively on target devices. Spatial audio mixing should consider acoustics and environment modeling. Performance is also critical for low-latency head-tracking.

Optimizing Spatial Audio Content

Optimizing spatial audio content involves careful attention during the mixing and mastering process. Mixing for spatial audio requires balancing elements across a three-dimensional space rather than just left and right channels. The stereo field must be expanded to place sounds around the listener while retaining clarity and intelligibility. Key considerations include using reverb, EQ, and stereo width enhancements to give elements a sense of space and depth. Panning can help place sounds, but avoid hard-panning in spatial audio.

Mastering for spatial audio should focus on creating a cohesive listening experience. Subtle, wide stereo enhancement can help fill out the sound field. Since spatial audio relies on crosstalk cancellation, excessive stereo width can cause phasing issues. Moderately compressing and limiting the mix helps maintain dynamic range while preventing clipping. The goal is a balanced, smooth master that translates well to various playback systems.

Binaural rendering is a crucial step in optimizing spatial audio content. It involves filtering audio into left and right ear signals to simulate human hearing and natural sound localization cues. HRTF (head-related transfer functions) algorithms place sounds at precise points around the head. High-quality binaural rendering creates an immersive, three-dimensional experience and avoids inside-the-head or other unnatural localization. Careful binaural mixing helps each element find its place in the surround soundscape.

Distributing Spatial Audio

With the rise of spatial audio, content creators are looking for ways to distribute mixes to listeners. While spatial audio is still an emerging technology, there are a few distribution options available.

For streaming, some platforms like Apple Music, Amazon Music HD, and Tidal support Dolby Atmos music tracks which can provide an immersive listening experience. However, platform support is still limited. Podcast platforms like Spotify have begun early experiments with distributing spatial audio mixes.

For digital downloads, sites like HDtracks allow users to purchase and download spatial audio albums in formats like Dolby Atmos. However, consumer adoption of premium music downloads has declined over the years as streaming has become more popular.

Physical media such as Blu-ray discs can support spatial audio formats. For example, some Blu-ray movies contain immersive Dolby Atmos surround sound mixes. However, physical media represents a small portion of today’s media consumption.

Overall, distributing spatial audio is still a challenge. As more streaming platforms add support and spatial audio production tools improve, content creators will have more options to share their immersive mixes with listeners.

Spatial Audio Hardware

Spatial audio requires specialized hardware in order to create the immersive experience. On the playback side, spatial audio enabled headphones or speakers are needed. These have additional drivers and acoustic components to create the surround sound effect and accurate positional audio (Magnetic Magazine, 2023). Popular options include the Apple AirPods Pro and Max headphones which have spatial audio support built-in. Many other headphone manufacturers like Sony and Bose also offer spatial audio models. High-end audiophile headphones with multiple drivers are capable of more convincing spatial audio reproduction.

For spatial audio capture, microphone arrays are used to record sound sources from various directions. Specially designed spatial audio microphones like the Zoom FSM-8 and Sennheiser AMBEO VR capture sound in a spherical pattern. This allows capturing the accurate position and movement of sounds in a 3D space. These can then be encoded into spatial audio formats.

As spatial audio gains traction, more hardware options targeted for spatial audio creation and playback will become available. The improved immersion and realism offered by spatial audio will drive consumer demand for compatible devices (AudioScenic, 2022).

Use Cases

Spatial audio has a wide range of use cases across different industries. Some of the key use cases include:

Gaming

Spatial audio can create more immersive gaming experiences by simulating 3D sound environments. This allows gamers to hear sounds coming from different directions, with distance cues and occlusion effects. Major gaming platforms like PlayStation 5 and Xbox Series X support spatial audio technologies.

VR/AR

Spatial audio is crucial for creating believable virtual environments in VR and AR. It provides important auditory cues about objects and events, enhancing immersion. Spatial audio tracks head movements in VR/AR headsets to ensure sounds update realistically as users look around virtual spaces.

Music

Music listening is a major use case, with spatial audio able to recreate the experience of listening to music live. Platforms like Apple Music and Tidal allow users to stream music in spatial formats. This provides a surround sound experience and makes listeners feel like they’re at a concert.

Film

Many blockbuster films now use spatial audio when mixing their soundtracks, to create more immersive theater experiences. Objects on screen can be given distinct spatialized sounds placing them accurately within the cinema sound system.

Broadcasting

Spatial audio is being adopted by broadcasting, to make content more engaging. For example, sports broadcasts can spatialize crowd noise and commentator voices. News broadcasts can make reporters in the field sound distant and environmental sounds more realistic.

Future of Spatial Audio

Spatial audio is an exciting and rapidly evolving field. As immersive technologies like VR/AR continue to advance, spatial audio will play an increasingly vital role in creating truly convincing virtual experiences. Several key developments and trends will shape the future landscape of spatial audio:

New formats like MPE are emerging as potential successors or alternatives to current standards like Dolby Atmos. MPE aims to improve spatial positioning and deliver more customized audio based on an individual’s anatomy. Brandenburg’s team is pioneering this new format.

Machine learning is being applied to spatial audio creation and processing. AI-generated spatial audio could automate laborious tasks like mixing and allow for more personalized soundscapes tuned to each user.Idavar predicts ML and personalization will shape the future of the field.

New capture and reconstruction techniques will provide more lifelike spatial audio that fully mimics the acoustics of real spaces. Companies are developing advanced microphone arrays and algorithms to capture and reproduce the full complexity of real-world auditory scenes.

Major challenges include streaming and compression of massive spatial audio data sets, as well as developing more advanced auditory displays and interfaces. Cost, complexity, and compatibility issues will need to be overcome for spatial audio to achieve mainstream adoption.

But the future looks bright. With many major players investing heavily, spatial audio is poised to transform gaming, entertainment, communication, and even productivity or accessibility applications.