D80

D80 is the Definition parameter for music, calculated as the ratio of sound energy arriving within the first 80 milliseconds to the total sound energy, expressed as a decimal or percentage. It is the energy-ratio equivalent of C80 (Clarity for music) and is defined in ISO 3382-1:2009. D80 values above 0.50 indicate that the early sound field dominates, favoring clarity and articulation in music. Lower values indicate a more reverberant quality where individual notes blend together. The mathematical relationship is D80 = 1/(1 + 10^(−C80/10)). Optimal D80 values for concert halls are typically 0.40–0.60, representing the balance between definition and fullness that characterizes the best performance spaces. D80 is less commonly reported than C80 in practice because the logarithmic C80 scale is more intuitive for comparing differences. Both parameters are extracted from measured impulse responses and should be spatially averaged per ISO 3382-1.