## 4 Evaluation Procedure
### Subjective Evaluation  
The subjective evaluation of the \(BL\) ARA mix model was a challenging procedure consisting of a MUSHRA test (see Appendix A Figure A4). It was set up in the laboratory with stereo loudspeakers propagating the real environment, and the subjects answering an electronic questionnaire. A user-friendly graphical user interface (GUI) facilitated the evaluation system's usability (see Appendix A Figure A1). The system produced test samples and adapted the virtual component into the real source in real-time.  
The evaluation test consisted of the following three parts: (a) demographics and technographics, (b) discrimination test, and (c) MUSHRA test. The subjects participated in the tests without any training. A number of 78 participants were recruited through email and other online communication channels.  
Prior to the testing procedure, all subjects signed a statement of consent. The first part of the test required the participants to fill in their personal demographic and technographic information (see Appendix A Figure A2). The questionnaires were submitted anonymously. In the second part, a discrimination test aimed to separate the subjects (see Appendix A Figure A3) according to their experience in sound perception. This discrimination test included: (a) a loudness comparison test of two different tones, (b) a perception test, in which one of two tones heard separately was to be identified as a partial of a subsequent complex tone, and (c) a spatial perception test, in which subjects had to find the position of a virtual sound in a hypothetical virtual sonic environment. The number of the correct responses assigned the subject to one of the following categories: \"Naive\", \"Beginners\", \"Experienced\", or \"Experts\".  
\begin{table}
\begin{tabular}{c c} \hline \hline
**ARA Components 10 ms** & \(BL\) (Phons) \\ \hline Virtual Input “Test-1” & 77.17 \\ \hline Real Input Forest & 72.46 \\ \hline \(BL\) Virtual Output “Test-1” & 72.85 \\ \hline \hline \end{tabular}
\end{table}
Table 4: \(BL\) Inputs and Output of “Test-1—Forest”.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**ARA Components** & \(BL\) **Low Mix (Phons)** & \(BL\) **Mid Mix (Phons)** & \(BL\) **High Mix (Phons)** \\ \hline Virtual Input “Test-1” & 77.17 & 77.17 & 77.17 \\ Real Input Traffic & 72.46 & 72.46 & 72.46 \\ \(BL\) Virtual Output “Test-1” & 72.85 & 74.64 & 75.89 \\ \hline \end{tabular}
\end{table}
Table 5: \(BL\) ARA mix modes benchmarks.  
The third part of the evaluation was the MUSHRA test, Appendix A Figure A4. The MUSHRA test consisted of five alternatives: the _BL_ ARA mix and four other mixes. More specifically, it was comprised of: (a) the original virtual source, (b) the _BL_ adapted ARA mix virtual source, (c) the original virtual source with 3.5 kHz bandwidth, (d) the original virtual source with 7 kHz bandwidth, and (e) the original virtual source with 10 kHz bandwidth. The MUSHRA's sound content is composed of industrial sounds, which represent the real environment, and an artificial sound, (called Test-2), in looping playback mode, which represents the virtual component. At first, the subjects needed to push a button to let the system propagate a complete ARA mix in real-time. To evaluate the outcome, the participants used a Likert-type scale with the following rating options: 1. Bad, 2. Poor, 3. Fair, 4. Good, 5. Excellent.  
This methodology produces qualitative data, which describe subjects' subjective experience, to be collected in a quantitative form. The _BL_ mix mode (low mix mode, mid mix mode, or high mix mode) was chosen randomly before the start of the test.