# Perceptual Quality of Audio-Visual Content with Common Video and Audio Degradations
## 7 Perceptual Experiment 2 (Audio-Only)
\begin{table}
\begin{tabular}{l c c} \hline \hline
**BG Noise** & **Noise** & **SNR (dB)** \\ \hline HRC1\({}_{E2}\) & car & 15 \\ HRC2\({}_{E2}\) & babble & 10 \\ HRC3\({}_{E2}\) & office & 10 \\ HRC4\({}_{E2}\) & road & 5 \\ ANC1\({}_{E2}\) & - & - \\ \hline
**Chop** & **Period (s)** & **Rate (Chops/s)** & **Mode** \\ \hline HRC5\({}_{E2}\) & 0.02 & 1 & previous \\ HRC6\({}_{E2}\) & 0.02 & 2 & zeros \\ HRC7\({}_{E2}\) & 0.04 & 2 & previous \\ HRC8\({}_{E2}\) & 0.02 & 5 & zeros \\ ANC2\({}_{E2}\) & - & - & - \\ \hline
**Clipping** & \multicolumn{2}{c}{**Multiplier**} \\ \hline HRC9\({}_{E2}\) & & 11 & \\ HRC10\({}_{E2}\) & & 15 & \\ HRC11\({}_{E2}\) & & 25 & \\ HRC12\({}_{E2}\) & & 55 & \\ ANC3\({}_{E2}\) & & - & \\ \hline
**Echo** & **Alpha (\%)** & **Delay (ms)** & **Feedback (\%)** \\ \hline HRC13\({}_{E2}\) & 0.5 & 25 & 0 \\ HRC14\({}_{E2}\) & 0.3 & 100 & 0 \\ HRC15\({}_{E2}\) & 0.175 & 140 & 0.8 \\ HRC16\({}_{E2}\) & 0.3 & 180 & 0.8 \\ ANC4\({}_{E2}\) & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 8: HRC and ANC corresponding parameters used in Experiment 2. Figure 7: Mean Quality Score (MQS), and its respective spread of scores, for the different Hypothetical Reference Circuit (HRC) in Experiment 2. For Background Noise, combining the type of noise and the SNR value associated with it resulted in four HRCs (Table 8). By observing the results for HRC2 (noise = bable, SNR = 10 dB) and HRC3 (noise = office, SNR = 10 dB), we notice that the babble noise was perceived by participants as more annoying than the office noise. Similar results were observed in a previous study using only the audio component [30]. For Chop, each HRC corresponds to the combination of three parameters: rate, period, and mode (Table 8). The reported \(\text{MQS}_{\text{HRC}}\) values vary from 3.5 to 2.5, decreasing from HRC5 to HRC8. Notice that the \(\text{MQS}_{\text{HRC}}\) values decrease as the chop rate increases, independent of the period or the chop mode. For the particular case of HRC6 (rate = 2 chops/s, mode = zeros) and HRC7 (rate = 2 chops/s, mode = previous), repeating previous portions of samples (previous mode) was slightly more annoying than inserting silence portions (zeros mode). For Clip, a multiplier factor was the only parameter assigned to each HRC. The reported \(\text{MQS}_{\text{HRC}}\) values varied from 3 to 1.5, decreasing from HRC9 to HRC12. Clip results presented the lower \(\text{MQS}_{\text{HRC}}\) values among all 4 types of audio distortions, which indicates that clipped distortions were perceived as the most annoying ones. Finally, for Echo, each HRC was associated with the combination of three parameters: alpha, delay, and feedback (Table 8). The reported \(\text{MQS}_{\text{HRC}}\) values vary from 3.7 and 1.7, decreasing from HRC13 to HRC16 with an abrupt drop in the \(\text{MQS}_{\text{HRC}}\) between HRC14 and HRC15. This drop might be related to the inclusion of a feedback percentage, which affected the perceived quality in a similar way as observed in previous studies [30]. Figure 5(b) presents the \(\text{MCS}_{\text{HRC}}\) values for each HRC, corresponding to the four audio distortions groups. As observed in the previous \(\text{MQS}_{\text{HRC}}\) results, the range where these values vary is very small, fluctuating around '3' (\"Neutral\" Content). Almost no difference was observed between scores for distorted conditions (HRCs) and no-distorted conditions (ANCs). This indicates that, for this experiment, participants were not able to trace a correspondence between the perceived quality and the content of the sequence. Figure 8: Mean Quality Score (\(\text{MQS}_{\text{HRC}}\)) and Mean Content Score (\(\text{MCS}_{\text{HRC}}\)) for the different Hypothetical Reference Circuit (HRC) in Experiment 2.