# Musical Mix Clarity Prediction Using Decomposition and Perceptual Masking Thresholds
## 4 Model Evaluation
This suggests the masking effect of reverberation is more severe for transient sounds, which is in line with the greater effect reverberation has on the temporal axis of the spectrogram. Clipping appears to cause two different responses in the model output whereby some stimuli masking scores increase with degradation level and others decrease. The effect of this is almost symmetrical, keeping the median masking score relatively constant throughout the degradation levels whilst the interquartile range increases. Clipping had the effect of reducing \(AM_{R}\) (Equation (8)), as the dynamic range was decreased and the difference between the R and TSS components was reduced. However, in cases where there was very little residual energy, the \(AM_{\text{TSS}}\) (Equation (8)) was also reduced. Clipping can increase the harmonic density of transients which emphasises their spectrally broadband characteristic and thus increases the level of transient energy separated by the separation system. In  
Figure 6: L2 PM clarity model overall masking scores (Equation (10)) of the independent dataset at the seven levels of degradation for each method (detailed in Section 3.4), including the reference level of the examples without degradation. cases where the present signal is largely steady-state energy, such as a sustained Rhodes piano chord, clipping can emphasise the temporally constant and more slowly evolving nature of steady-state energy and increase the level of steady-state energy separated by the separation system. Moreover, additional harmonics generated from clipping such a signal are spectrally narrowband and temporally constant, and as such are considered to be steady-state by the separation system, further contributing to the level of steady-state energy extracted. Therefore, stimuli that were more noise-like at the reference level, receiving high masking scores, received even higher masking scores as more degradation was applied. Conversely, stimuli that had a low level of residual energy at the reference level received even lower masking scores at higher degradation levels, as the reduction of the R component masking was lesser than the reduction of TSS component masking. Whilst the effects of clipping may potentially increase the perception of clarity, given the more complex effect compared to the addition of pink noise or reverberation, the clipping applied at the highest levels of degradation is extreme. The resulting signals are very noise-like, and as such were expected receive high masking scores, which they did not in the case of stimuli that scored middle or low masking scores at the reference level. Figure 7: L3 PM clarity model overall masking scores (Equation (10)) of the independent dataset at the seven levels of degradation for each method (detailed in Section 3.4), including the reference level of the examples without degradation. The L3 PM clarity model responded similarly to the L2 PM clarity model for all degradation types. Figure 7 indicates that there was an increase of median masking score and convergence with increasing levels of degradation in the case of additional pink noise and reverberation. Moreover, there were somewhat diverging masking scores with a relatively constant median in the case of increasing levels of clipping. However, this response was muted in comparison to the response seen from the L2 PM clarity model. Application of the signal degradation had a greater effect on the separated higher frequency energy than on the separated low frequency energy; this was as a result of the STFT based separation system employed having frequency resolution which increases with bin index. When measured using linearly spaced scale-factor bands of the L2 PM, the high frequency bins represent a larger proportion of the scale-factor bands than when measured with more perceptually aligned scale-factor bands of the L3 PM.