# Musical Mix Clarity Prediction Using Decomposition and Perceptual Masking Thresholds
## 5 Discussion  
All tested correlations showed significant (\(p<0.01\)) results, with a worst-case correlation of \(r=-0.6682\), \(rho=-0.6882\) to the subjective scores. This suggests a link between the underlying concept of transient, steady-state and residual masking and mix clarity perception. However, as the tested subjective dataset contained only 16 stimuli, the model may be overfit, and a larger test containing more participants and stimuli should be performed to validate these results. Previous work proposed a model of Inter-Band Relationship Analysis (IBR), which measures the correlation between dynamic ranges in three bands of the frequency spectrum over time [20; 21]. The best performing L2 PM model outperformed the IBR model scoring \(rho=-0.8382\) (\(p<0.01\)) versus \(rho=0.7882\) (\(p<0.01\)). As the IBR model simply utilises the dynamic range across three bands, it only has an incidental relationship to human perception. Furthermore, the IBR model is prone to being 'fooled' by some signals. For example, it would rate sustained pink noise and sustained full-bandwidth harmonic signals equally. The present model supersedes IBR by negating these shortcomings, and by relating more directly to human perception of auditory masking. The model also incorporates a greater awareness of the makeup of the signal being measured due to the TSR component separation employed. The L2 PM clarity model showed the strongest \(rho\) correlation, though was non-linear, with a Spearman's rank correlation test showing a stronger relationship than the Pearson correlation. This implementation of the model is also the least computationally expensive, as the L2 PM is less complex than the L3 PM. During independent testing, the model responded as expected to the addition of pink noise and reverberation, with the masking score increasing (clarity decreasing) as the degradation levels increased. The model's response to clipping was less uniform than that of the additional pink noise or reverberation, showing a more complex effect on the relationship of the R and TSS components of the signal. While the response is understandable in terms of how the model operates, it is not expected to be congruent with perception. Low perceived clarity scores, corresponding to high masking scores, would be uniformly expected for all stimuli at the highest levels of clipping degradation, showing a potential shortcoming of the model. However, given the strong correlation to the subjective scores, this shortcoming did not seem to have a greatly detrimental effect for the tested stimuli in this case. Though, improving the response to this kind of degradation would improve the robustness of the model in extreme cases. While the L3 PM has a more complex calculation of masking threshold and provides more efficient encoding in the context of MPEG compression compared to the L2 PM, the L3 PM clarity model unexpectedly had the weakest correlation to the subjective scores. It is suggested this was largely due to L3 PM's perceptually aligned scale-factor bands not providing emphasis on masking occurring in high frequency bands as in the L2 PM and modified L3 PM variations of the clarity model. This could indicate a greater importance of masking occurring between high frequency energy to the perception of clarity. In terms of independent testing, the L3 PM clarity model had a similar but less extreme response to all three degradation types than the L2 PM clarity model. The L3 PM is capable of calculating masking thresholds using shorter windows when transients occur, providing a higher time resolution and reducing pre-ringing artefacts in MPEG coding. Similarly, this window switching could be used in the clarity model to provide greater temporal resolution for masking occurring relating to transient passages in the signal under test. In the present testing only long windows were used, as none of the stimuli under test had transient content capable of triggering the short frame calculation.