# Flying a Quadcopter--An Audio Entertainment and Training Game for the Visually Impaired
## 2 Materials and Methods
### Sound Design
#### 2.3.1 Sonification Model  
Similar to other sonification techniques [3; 27; 28], our sonification model assigns audio information to objects, characters, and events in the game, such as the virtual quadcopter position, the next target's position, and sounds related to the way the user interacts with the environment, as shown in Table 1 and detailed below. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sound** & **Meaning** & **Rendering** & **Details** & **Activated** \\ \hline \multirow{3}{*}{Obstacle} & There is an obstacle in the & \multirow{3}{*}{\begin{tabular}{c} Short beep, with its play \\ frequency inversely \\ proportional to the distance \\ between the obstacle and the player. \\ \end{tabular} } & The scanning area is shaped & \multirow{3}{*}{Always} \\  & & & & as a cone that varies its angle \\ \cline{3-5}  & & & proportional to the distance \\ \cline{3-5}  & & & between the obstacle and the \\ \cline{3-5}  & & & player. \\ \hline \multirow{3}{*}{Target} & \multirow{3}{*}{\begin{tabular}{c} Direction of the next target \\ location. \\ \end{tabular} } & The target emits a click sound & \multirow{3}{*}{\begin{tabular}{c} The scanning area is \\ as a cone that varies its angle \\ and scanning distance based \\ on velocity, as detailed \\ below. \\ \end{tabular} } & \multirow{3}{*}{Always} \\  & & & & below. \\ \hline \multirow{3}{*}{\begin{tabular}{c} Altitude \\ same altitude as the player, \\ and target below the player. \\ \end{tabular} } & It conveys the difference in & \multirow{3}{*}{\begin{tabular}{c} Target above player: rising \\ beeps. \\ \end{tabular} } & \multirow{3}{*}{\
\begin{tabular}{c} The frequencies are specified \\ bellow. \\ four constant beeps. \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} Listening mode \\ Listening mode \\ \end{tabular} } \\  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Sonification model. The sonification model was implemented using two types of sound reflection and reverb simulations:  
1. Real-time sound reflections and reverberations, which were simulated using the features of Google Resonance Audio API. This method was used to generate every sound spatialized in the Unity game engine, such as target direction and the vehicle-generated sounds, for example, collision sounds and engine sounds. 2. Baked simulation. As the sounds from the interior of the vehicle are static, the approach was different. In this case, various samples of IR (impulse response recordings) have been recorded in different rooms and baked to a higher quality reverb with the help of Ableton Live Suite. These sounds are not localized in the Unity game engine. The obstacle sound. Similar to car parking sensors, the virtual vehicle warns the user if there is an obstacle in front of the player, and consequently, the sound becomes more pronounced if the user is closer to the obstacle. We convey the distance between the user and the obstacle this way. After testing the VR application with a visually impaired subject who had relevant experience with similar software, a problem with the encoding of the distance between the user and the obstacle was identified. Figure 7 shows the user moving the virtual vehicle in the direction of the blue arrow. The blue line on the left side of the figure represents the surface of a big obstacle. In this case, the \"parking sensor\" approach described above tells the user that the obstacle is farther away than it actually is because the collision happens with the left side of the vehicle (red circle in Figure 7) and the sensor offers information about the front of the vehicle. The solution proposed and tested with the visually impaired user was to create an adaptive scanning cone that scans the environment with the base of the cone oriented toward the direction of the movement vector (Figure 8). The angle of the cone is inversely proportional to the velocity of the virtual vehicle.