# Perceptual Quality of Audio-Visual Content with Common Video and Audio Degradations
## 9 Discussion and Comparison among Experiments
### On the Auditory Component Effect  
This analysis investigates the effect of audio impairments for equivalent A-TCs in Experiments 2 and 3. Figure 13 shows a comparison between the MQSAT values (MQS among different A-TCs) gathered from these experiments. Similarly to what was done in the previous analysis, we organized the results according to the audio distortion (background noise, chop, clip and echo). The differences between the average MQS values for the equivalent test conditions in Experiment 2 and Experiment 3 were verified using a Two-sample \(t\)-test analysis. Table 13 reports this analysis and highlights the equivalent conditions where the difference between results in Experiment 2 and Experiment 3 are significantly different. Figure 13a shows the results obtained for the background noise distortion. For this scenario, the equivalent test conditions A-TC0 and A-TC1 reported statistically significant differences, as for the case of A-TC3, results were very similar for both experiments. Considering that Experiment 3 included visual distortions in addition to the audio distortions in Experiment 2, results in Figure 13a suggest that the background noise (audio-only distortions) affected the overall audio-visual quality at a similar level than the background noise plus the visual distortion (audio + video distortions). Similarly, Figure 13b presents the quality scores sequences with chop distortions. Results for equivalent test conditions A-TC6 and A-TC8 reported a significant difference in the \(t\)-test analysis. More particularly, results for A-TC8 shows that there is a difference between results with and without video distortions. This might suggest that chop type distortions by themselves do not have a strong impact on the overall quality. Figure 13c presents the scores for clipping distortions. These results are very similar to the ones observed in the background noise scenario. These results suggest that the combination of clipping and visual distortions (Audio + Video distortions) affected the audio-visual quality at the same level that the clipping distortion on its own (audio-only distortion). None of the equivalent test conditions reported significant differences in the \(t\)-test analysis. Figure 13d presents the results for echo distortions. Test condition A-TC14, which reported a significant difference, suggests that video distortions had a higher impact on the perceived quality. As for test condition A-TC16, results seem to suggest that the audio distortion (echo) and the audio plus video distortion from Experiment 3 had an equivalent impact on the perceived quality. However, this test condition did not report a significant difference in the \(t\)-test analysis. Figure 12: Comparison of MQS values values for: (**a**) Experiment 1 versus Experiment 3 and (**b**) Experiment 2 versus Experiment 3. One particular detail that is common to all four audio distortion scenarios is the differences between the equivalent V-TC0 test conditions. Table 13 reports that such differences are statistically significant, plus, in all four cases, a relative higher MQS average was reported for Experiment 3. One possible interpretation of these results is that commonly, speech and audio perceptual tests tend to present a more narrow range of quality when compared to a video perceptual study [7]. Indeed, Experiment 2 contains distortions only in the audio component; meanwhile, Experiment 3 combines both audio and video distortions. This is confirmed by results presented in Figure 11b, where V-TC0 reported a significant difference, only this time it was Experiment 1 (video-only distortions) that had a higher MQS average when compared to Experiment 3.