# Perceptual Quality of Audio-Visual Content with Common Video and Audio Degradations
## 9 Discussion and Comparison among Experiments  
In this Section, quality and content responses across all three perceptual experiments are compared. We explore the results for equivalent test conditions in Experiments 1, 2 and 3. To this end, only the quality scores of the equivalent test conditions from each experiment are compared. The objective is to study the responses of equivalent test conditions used in different experimental scenarios (video-only distortions, audio-only distortions, and Audio + Video distortions). This analysis helps us understand how and at what level a particular test condition is affected by its accompanying component (impaired or unimpaired). For this particular analysis, labels assigned to the HRCs of Experiments 1, 2 and 3, were redefined. The goal was to compare equivalent HRCs across all three experiments. For this purpose, the term Video Test Condition (V-TC) was used to denote the test conditions for the video component (Table 10). In the same way, the term Audio Test Condition (A-TC) was used to denote the audio test conditions for the audio component (Table 11). These terms replaced the HRC labels used in previous sections. The analysis is divided into three parts: (1) the visual and (2) auditory component effects for equivalent test conditions, and (3) ranges of quality and content scores for the three experiments. This Section includes an  
Figure 10: Mean Quality Score (MOS\({}_{\text{HRC}}\)) and Mean Content Score (MCS\({}_{\text{HRC}}\)) for the different Hypothetical Reference Circuit (HRC) in Experiment 3.  
between the average MQS values for the equivalent test conditions in Experiment 1 and Experiment 3, a Two-sample \(t\)-test analysis was made. Table 12 reports this analysis and highlights the equivalent conditions where the difference between results in Experiment 1 and Experiment 3 are significantly different. Figure 10(a) depicts the results for the packet-loss distortion. Notice that, considering the same V-TCs, the scores were lower when the audio component was impaired (Experiment 3). This effect is more noticeable for V-TC2 and V-TC5 (differences are statistically significant). Figure 10(b) shows the same comparison for the frame-freezing distortion. More specifically, for V-TC7 and V-TC10 the scores for sequences with audio distortions are lower (differences are statistically significant). Audio distortions affected the audio-visual quality of sequences with packet-loss and frame-freezing distortions similarly. These results show that there is an impact of the audio quality on the perceived audio-visual quality. Moreover, given that the analysis is made per test condition, it looks like this impact did not depend on the content. However, a larger number of test conditions are necessary to analyze the effect of the media content. Results of equivalent test conditions from Experiments 1, 2, and 3 are compared in Figure 12. The scatter plot from Figure 11(a) shows a positive correlation between results from Experiment 1 and 3, where video distortions are compared. The plot also shows that scores from Experiment 1, with video distortions only, occupied a larger range in comparison to results from Experiment 3 (audio and video distortions). All markers appear above the red line independent of the type of video distortion (packet-loss or frame-freezing). Figure 11: Average MQS values for different video test conditions in Experiments 1 and 3.