# Dynamic Range Compression and the Semantic Descriptor Aggressive
## 4 Perceptual Listening Experiments
### Listening Experiment 1 Method
#### 4.1.1 Listening Experiment 1 Results and Discussion  
The results from the listening test can be seen in Figure 4, where (a) shows the mean result for the descriptor aggressive with a 95% confidence interval for both songs and all time constant settings tested. As can be seen, there is little difference between the time constant settings for both the ratios tested, but there is a difference between the uncompressed material, the 4:1 ratio and the all-butttons mode. It is worth noting that the two all-butttons modes that measured highest for THD (see Table 3 for THD results) are not rated any higher than the other two all-butttons settings. An inspection of the FFT plots suggests this is a result of the even-order harmonics remaining at fairly consistent levels across the four settings, while the odd-order harmonics are attenuated as attack and release are slowed. This results in a lower THD measurement, which evidently does not result in a perceptually less aggressive sonic signature. It should be noted that many of the participants reported that the difference between some of the stimuli was small, and they found the test to be challenging. Therefore, the effect of listener \begin{table}
\begin{tabular}{c c} \hline \hline
**Setting** & **THD** \\ \hline A3R7 All & 1.58\% \\ A1R7 All & 1.51\% \\ A3R5 All & 0.54\% \\ A1R5 All & 0.50\% \\ A3R7 4:1 & 0.25\% \\ A1R7 4:1 & 0.24\% \\ A3R5 4:1 & 0.17\% \\ A1R5 4:1 & 0.16\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: THD measurements made using a 1 kHz tone and the time constants and ratios used in Listening Experiment 1.  
fatigue should be kept in mind. The ratings for distortion are illustrated in Figure 4b where a similar trend is visible. Once again, there is a difference between the ratios and the uncompressed material, but no difference between the different time constant settings for the two ratio settings. Thus, it appears that there is little perceptual difference between the time constant settings used in the current study, but the additional harmonic distortion created in the all-buttons mode is noticeable to the participants of the experiment. Audio features pertaining to the noise-like properties of sound (Roughness and Zero Crossing Rate) were extracted from the vocal tracks using MIRtoolbox for Matlab [34] and are presented in Table 5. The results for roughness show that the feature increases in value between the uncompressed audio and both ratio settings, and also between 4:1 and all-buttons mode. Within the time constant settings for each ratio, the results with the release time set to seven are the highest and this is largely comparable with the THD results shown in Table 4. However, the A1R7 combination for both ratio settings has slightly larger roughness values than the A3R7 combination, while the THD results highlight the A3R7 combination as having the largest amount of THD. The similarity in results within the ratio settings for roughness may be another reason why listeners rated the time constant settings comparably, despite the variation in THD. The values for zero crossing rate (ZCR) are less revealing, with no clear pattern in the results emerging, apart from an increase in ZCR when using compression. Figure 4: **(a) Results for the descriptor aggressive from listening experiment 1; **(b)** results for the distortion from listening experiment 1. Note, no significance was found between time constant settings, but significance was found between ratio settings.