corr - Correlation

The computation of decay time parameters are made by a least-squares fit of a straight line to the chosen level range of the decay curve. For the decay times to be meaningful descriptors of the reverberation, the decay curve should approximate a straight line. To provide an indication of the linearity of the decay curve, the decay time parameters are accompanied by a correlation coefficient describing how well the straight line fits the decay curve. If the coefficient is close to –1.0 the decay curve is linear in the chosen range and frequency band.

The early decay time (EDT) will not be accompanied by a corresponding correlation coefficient, because it is always computed from the uppermost part of the decay curve which normally displays some curvature due to the influence of the direct sound.

The calculation is described in [2003: ISO/CD 3382-2 Acoustics – Measurement of the reverberation time – Part 2: Ordinary rooms, Appendix B.2].