This is a highly specialised compact disc for the calibration and conformation of accuracy of acoustical reverberation time measuring instruments as made by Bruel & Kjaer and Nortronics, amongst others. It contains a set of accurately calculated sinusoids recorded at fsd for 5 seconds, after which the signal decays exponentially to noise with accurately known reverberation times. The decays are calibrated in reverberation time (the time to decay by 60dB).
With this CD it is possible to check the accuracy of reverberation time measuring instruments. This should be done on a regular basis as per British Standards.