Observation impulse response by two relatively prime pseudorandom sequences

A crosscorrelation method using two pseudo-random sequences whose periods are relatively prime is introduced to measure the impulse response of a bandpass system with improved signal-to-noise ratio. One pseudorandom sequence is driven by d-times faster clock than the other and is switched after the polarity of the other sequence. The switched signal is used as an input of the bandpass system. The PR-sequence, which is defined as an arithmetic product of the slower sequence and the decimated faster sequence by d, is prepared. It is shown that the cross-correlation between the PR-sequence and the decimated output of the system equals the impulse response of the system. The example of the practical implementation of this system is described for room acoustics measurement. The experimental results are shown and the final signal-to-noise ratio is compared with the theoretial values.