C80 Measurement

C80 measurement involves extracting the Clarity Index for music from a measured room impulse response. C80 is calculated as the logarithmic ratio of early energy (0–80 ms) to late energy (after 80 ms) in the impulse response per octave band, as defined in ISO 3382-1:2009 §4.3. Higher C80 values indicate clearer, more defined sound, while lower values indicate a more reverberant, blended quality. The measurement requires a high-quality impulse response with sufficient signal-to-noise ratio and accurate time alignment. Spatial averaging across multiple source-receiver positions is essential because C80 varies significantly with position. Typical targets for concert halls range from −2 dB to +2 dB (500–2000 Hz average). C80 measurement is standard practice in performance space commissioning and is always reported alongside RT60 and EDT. The 80 ms boundary relates to the psychoacoustic integration time for music perception.