Observation of reverberation curves by two relatively prime pseudorandom sequences

The pseudorandom sequence whose periods are relatively prime are introduced to measure reverberation decay curves in a room. One pseudorandom sequence is driven by d-times faster clock than the other and is switched after the polarity of the other sequence. After radiating the switched signal from a loudspeaker, the crosscorrelation between the switching sequence and d-times decimated envelope sequence of a microphone output is calculated. The decay curve obtained by the integration of the crosscorrelation through the formula given by Schroeder equals the ensemble average of the envelope of decay curves driven by white noise. It is shown that the decimation serves not only to decrease the amount of computation but also to increase the signal to noise ratio of the measured decay curves.