Timbre (MOS-T) represents how faithfully the earbuds reproduce the frequency spectrum and temporal resolution (timing information). Distortion (MOS-D) represents non-linearities and added noise: higher scores mean cleaner reproduction. Immersiveness (MOS-I) represents perceived source width and positioning: how well virtual sound sources are defined in three-dimensional space. See here for an explanation of MDAQS, how it works, and how it was developed.