This option enables you to measure reverberation times in the filterbands 50Hz to 10kHz or in broadband values (A- and C- or Z-weighted).
Although the reverberation time is defined as the time it takes for the sound level to decay by 60dB, the presence of background noise will make this difficult to measure. The normal way is then to measure decays of 20 or 30dB and then extrapolate the results to 60dB. In the Nor118 a 20dB range is used and the figures are then normalised to 60dB. Reverberation times measured this way are often denoted T20.
The instrument employs the integrated impulse response method or schroeder method to calculate the decay.