A monophonic audio source intended to re-create the sound of a physical object existing in physical space. Sound objects are perceived by the listener to remain “attached” to a physical object whether that object stays still or moves over time. Crucially, sound objects are panned in the listener’s ears as the listener moves through physical space and turns her head.

Audio AR projects that use directional audio and some for of head-tracking often place many sound objects throughout an environment.

Locational audio is audio you hear only when physically within a pre-defined geographic region assigned to that particular audio..

Audio AR often uses directional in combination with locational audio.

Directional audio is audio that is panned in the listener’s stereo field to give the effect that it is coming from a certain physical location. Directional audio is essentially the creation of virtual “sound objects” that represent objects in physical space that emit audio. These objects can be stationary or mobile, just like IRL; a tree can emit a sound or a car can drive by you from left to right.

Audio AR often uses directional in combination with locational audio.

Audio AR that is related to a specific location in the real world and can only be experienced on that site. For example, a piece that enhances a specific public park with audio requires listeners to be in that park to experience the piece.

Audio AR related to movement through or interaction with the proximate landscape rather than presence at a specific site (see Absolute Location-Based). These pieces often can benefit from being experienced in disparate landscapes with the physical differences providing interesting variation to the audio experience.

Binaural recording is a method of recording sound that uses two microphones, arranged with the intent to create a 3-D stereo sound sensation for the listener of actually being in the room with the performers or instruments. This effect is often created using a technique known as “dummy head recording”, wherein a mannequin head is outfitted with a microphone in each ear. By mimicking the way humans hear with two ears on either side of our heads, a more realistic representation of an audioscape can be created for playback on headphones.

Audio AR projects often use binaural recordings to enhance the realism of the ambient audio.

An inertial measurement unit (IMU) is an electronic device that measures and reports a body’s specific force, angular rate, and sometimes the magnetic field surroundings the body, using a combination of accelerometers and gyroscopes, sometimes also magnetometers.

Audio AR makes use of IMUs both in mobile phones and various wearables to position sound objects in space and create realistic panning affects.

Ambisonics is a full-sphere surround sound format: in addition to the horizontal plane, it covers sound sources above and below the listener. Ambisonics mimics audio in the real world by using multiple tracks to allow for the placing and moving of sounds throughout this full-sphere.

Audio AR can take advantage of ambisonic recordings to augment audio environments with an additional spatialized layer.

Any of a multitude of techniques used to track the position and orientation of an individual’s head. This is crucial for displaying accurate content in VR and visual AR as well as for audio AR pieces to position sound objects dynamically. Accuracy in 3D space as well as latency over time are both crucial to create realistic effects. IMUs are often used for this purpose.

HRTF can be described as the modifications to a sound from a direction in free air to the sound as it arrives at the eardrum. These modifications include the shape of the listener’s outer ear, the shape of the listener’s head and body, the acoustic characteristics of the space in which the sound is played, and so on. All these characteristics will influence how (or whether) a listener can accurately tell what direction a sound is coming from.

Audio AR can use HRTF as a method of placing sound objects such that they seem to be realistically and consistently placed in relation to physical space.