# Perceptual Quality of Audio-Visual Content with Common Video and Audio Degradations
## 8 Perceptual Experiment 3 (Audio-Visual)  
In the last experiment, the goal was to estimate the overall quality of audio-visual video clips containing combinations of audio and video distortions. The video distortions were Bitrate compression, Packet-Loss, and Frame-Freezing, replicating the distortions in Experiment 1. The audio distortions were Background noise, Chop, Clip, and Echo, replicated conditions of Experiment 2. Forty (40) source stimuli were considered for this experiment. Both audio and video degradations were organized into sixteen (16) different HRCs. As with previous experiments, 4 anchors (ANCs) were included in the HRC set. Parameter details of both HRCs and ANCs are presented in Table 9. Altogether, 40 source stimuli were processed at 20 different test conditions (16 HRCs plus 4 ANCs). This resulted in 800 PVSs, containing different audio and video distortions. In each experimental session, the participant watched (only) 40 test stimuli out of the 800 test sequences, as recommended by the immersive methodology. These 800 sequences compose the third part of the UnB-AV dataset [47]. The sub-set is labelled as UnB-AV-Experiment-3 and is available for download along with the entire UnB-AV dataset. Figure 9 presents the average quality scores obtained for each HRC (i.e., the \(\text{MQS}_{\text{HRC}}\)), along with the individual scores given by each participant of Experiment 3. For each HRC, the \(\text{MQS}_{\text{HRC}}\) value is represented by the larger dot in the middle of the cloud of values. Notice that there is a certain consistency among results for different test conditions. This characteristic is more evident for extreme test conditions, i.e., test conditions with the higher (ANC1, ANC2, ANC3, and ANC4) and lower (HRC13, HRC14, HRC15, HRC16) quality levels. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Audio Component**} & \multicolumn{4}{c}{**Video Component**} \\ \hline  & \multicolumn{2}{c}{**Noise,**} & \multicolumn{2}{c}{**Chop-Period (s),**} & \multicolumn{2}{c}{**Clip**} & \multicolumn{2}{c}{**Echo-Alpha (\%),**} & \multicolumn{1}{c}{**Video**} & \multicolumn{1}{c}{**Bitrate**} & \multicolumn{1}{c}{**PacketLoss**} & \multicolumn{1}{c}{**Freezing**} \\
**HRC** & **SNR (dB)** & **Rate (Chop/s), Mode** & **Multiplier** & **Delay (ms), Feedback (\%)** & **Code** & **(kbps)** & **PLR** & **Pauses, Length (s)** \\ \hline HRC1\({}_{23}\) & car, 15 & - & - & - & - & H.264 & 16,000 & - & 1, 2 \\ HRC2\({}_{23}\) & - & - & - & 11 & - & H.264 & 16,000  
In Figure 10a,b, the \(\text{MQS}_{\text{HRC}}\) values gathered for each HRC in Experiment 3 are presented. For better visualization, \(\text{MQS}_{\text{HRC}}\) results were presented in two figures (a) and (b) organized by audio and video types of distortions, respectively. For each HRC, a confidence interval of 95% is included. From a general view, it can be observed that most \(\text{MQS}_{\text{HRC}}\) values fell in the range of 4.4 and 1.5 in the MQS scale. By observing the \(\text{MQS}_{\text{HRC}}\) values for the different audio distortions in Figure 10a, we notice that values vary along all different HRCs, which indicates that participants were able to perceive the variations among the different levels of quality when both audio and video degradations are present. With respect to the Chop type of distortion, the significant difference between HRC4 and HRC14, both with packet-losses, was determined by the combination of a chop rate (HRC4: 2 chops/s, HRC14: 5 chops/s) plus the BR and PLR parameters (HRC4: 8000 kbps, 1%, HRC14: 400 kbps, 8%). This, in accordance with the effects observed by these parameters in Experiments 1 and 2. For the Clip type of distortion, \(\text{MQS}_{\text{HRC}}\) values decrease progressively from HRC2 to HRC13. For the case of HRC2 and HRC3, where the clip multiplier is fixed in 11, an equivalence is expected in terms of bitrate (HRC2: H.264, 16,000 kbps, HRC3: H.265, 8000 kbps).