Quality and impairment are measured with distinct MOS variants.

Evidence

The direct measure of quality is simply called the MOS value, and the measure of impairment between reference and test cases is called the degradation mean opinion score (DMOS). — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2349

Categorization

• DEFINE: Distinguishes MOS (direct quality) from DMOS (degradation between reference and test).