Depthrow: a Physics-based Audio Game

We present an interactive audio game designed around the auditory perception of distance and the use of physics-based models for simulations of the dynamics, the sound source, and the acoustical environment. The game consists in throwing a virtual sounding object inside a virtual open-ended tube which is inclined. The task is to keep the object inside the tube, in other words the user should adjust the initial velocity applied to the object such that the latter does not fall out at the far end of the tube. The position of the object inside the tube is provided by continuous audio feedback. User performance is closely related to its ability to perceive the dynamic distance of the object in the virtual tube. Therefore, this game represents a potential tool for exploring the usability of auditory distance information in interaction design. 1. ARCHITECTURE OF THE INTERFACE The game prototype has been developed as a complex Max/MSP patch where three interacting physics-based models enable to simulate, respectively, the dynamics of the environment (an inclined plane), the sound source (a rolling ball), and to render the acoustical properties of the environment (an open-ended tube). The action of throwing is performed using a Wii Remote which provides, among other things, a 3D accelerometer, a vibration actuator, several buttons, and Bluetooth connectivity. The three physics-based models are connected in a top-down chain structure. Figure 1 shows the main Max/MSP patch. The throwing force applied to the virtual ball is captured (gesture mapping) by means of the accelerometer and provides the input to the computation (integration) of the initial velocity with which the ball is getting thrown inside the inclined tube. Then the initial velocity provides the input to the simulation of the inclined plane. The resulting velocity of the ball moving along the inclined plane drives the real-time synthesis of a rolling sound, which constitutes the audio input to a spatialization process (simulation of a tube), while the distance currently covered controls the distance parameter of the spatialization model. The latter conveys auditory information about the relative position of the sound source inside the virtual tube. The vibration actuator is exploited for providing tactile feedback: for example when the object comes back to the user’s hand, or when the ball falls over. 1http://www.cycling74.com/products/maxmsp 2The handed wireless controller for Nintendo’s Wii console. Thanks to Masayuki Akamatsu for his [aka.wiiremote] Max object (available at http://www.iamas.ac.jp/∼aka/max/). Figure 1: The main Max/MSP patch 2. PHYSICS-BASED MODELS