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Augmented Reality Audio Games

30-06-2018 16:19

In this research the Augmented Reality Audio Game (ARAG) “Audio Legends” was designed, implemented and tested to evaluate the utilisation of gestural sonic interaction modalities in an Augmented Reality (AR) audio environment. The results were disseminated through the following publications in international scientific journals and conference proceedings, and can be found in the "Publications" section:

Rovithis, E., Moustakas, N., Floros, A., & Vogklis, K. (2019) Audio Legends: Investigating Sonic Interaction in an Augmented Reality Audio Game. Multimodal Technologies Interact.

Rovithis, E., Floros, A., Moustakas, N., Vogklis, K., & Kotsira, L. (2019). Bridging Audio and Augmented Reality towards a new Generation of Serious Audio-only Games. The Electronic Journal of e-Learning, 17(2), pp. 144-156

Moustakas, N., Floros, A., Rovithis, E., & Vogklis, K. (2019). Augmented Audio-Only Games:A New Generation of Immersive Acoustic Environments through Advanced Mixing. In Audio Engineering Society Convention 146. Audio Engineering Society (AES)

The Scenario of Audio Legends

Audio Legends is an Augmented Reality Audio Game (ARAG) designed to investigate sonic interaction as a means not only to navigate within the augmented environment, but also to interact with the virtual sounds by performing the necessary gestures for achieving the game’s objectives. To investigate the implications of such mechanics regarding the usability of the system and the immersion in the game world it was designed to include tasks that require different long- and closed-range interaction modalities. The scenario of the game's prototype draws on folktales of Corfu and more specifically it is based on the local myths regarding the protector of the island, Saint Spyridon, who is believed to have saved the island on four different occasions:

  • in the 16th century he ended famine by guiding Italian ships carrying wheat out of a storm to the starving Corfiots,
  • twice in the 17th century he fought the plague off the island by chasing and beating with a cross the half-old woman and half-beast disease
  • in the 18th century he defended the island against the naval siege of the Turks by destroying most of their fleet with a storm

To represent these achievements three Game Modes were designed respectively:

  • “the Famine”, in which players have to locate a virtual Italian sailor and then guide him to the finish point,
  • “the Plague”, in which players have to track down and then defeat in combat a virtual monster,
  • “the Siege”, in which players have to find the bombardment site and then shield themselves from incoming virtual canonballs.

The Game's Mechanics

All three Game Modes consist of two Interaction Phases, namely Exploration and Action. The former is related to locating the virtual sound and navigating to its proximity, whereas the latter, initiated when players enter a 5 meter radius around the sound, focuses on gestural behavior in response to virtual sonic stimuli.

In Exploration-phase standard ARA techniques regarding amplitude and panning facilitate the localisation of the virtual sound. The field of the game is divided into concentric proximity zones around the emitting source. The position of the player is GPS tracked and assigned to the respective zone. Amplitude is then scaled accordingly: the closer one gets to the source the louder one hears it. Stereo positioning is dynamically modified in relation to the direction the device is held at. In the "Famine" and "Plague" Game Modes the virtual sounds are only heard when the player's tablet is facing them, whereas in the "Siege" Game Mode the sound is heard independently of the device’s orientation. 

The Action-phase of each of the three Game Modes is designed as follows: In the "Famine", once players enter the virtual sound’s closest range, it becomes attached to them so that they can lead it to the required destination. Every 20 to 30 seconds the sound stops following them and moves to the closest one of pre-distributed positions along the possible tracks. Players must then recollect the sound and repeat that process until the completion of their objective. In the "Plague", the sound in the closest proximity zone moves between random positions within a 150o azimuth and 60o elevation conical field in front of the player, who needs to aim the device at the sound’s direction and perform an abrupt front and back gesture like hitting a nail with a hammer. Seven successful hits complete the mode’s objective. Finally, in the "Siege", the sound, originating from random positions within the same frontal cone, moves towards the player following a curved path. Players must estimate the sound’s trajectory and hold the device like a shield to block the anticipated impact. If they don’t succeed, the sound will pass right through them. Five successful saves complete the mode’s objective. 

Technical Implementation

Audio Legends was designed for an area of 120 x 46 meters. Outdoor positioning for the virtual sounds was based on GPS with the minimum attainable accuracy of 10 meters. The game was developed on Xcode 10.2 using Swift 5. A major design principle followed was the compatibility with as many iOS devices as possible. For this reason the bare basics Swift libraries were employed: Core Location (for GPS location events), MapBox (a library to display position on map), Core Motion (for device specific motions) and SceneKit (for rendering 3D audio). The end-user equipment consists of a binaural audio recording headset (Sennheiser Ambeo Smart Headset) and an iPad Air (early 2014 model). In Exploration-phase Core Location was combined with MapBox to create a mapping between the actual geographical coordinates of the user and the virtual 3D coordinates of SceneKit. The distance and the orientation in the virtual world (SceneKit) were used to render spatial audio. In Combat-phase the Core Motion library was used to get the orientation off the device and the SceneKit in order to render moving 3D audio targets. Geolocation was disabled during this phase and moving objects were always oriented in front of the player regardless of the orientation, in which they entered the scene. 

The sonic content of Audio Legends consists of recorded or electronically created samples, which were processed using various sound design software modules and audio editing, sequencing, and spatialiazation techniques.