In real room acoustical measurements, the assumption of time-invariant system is usually not verified. A measurement technique was set-up with the purposes of monitoring the acoustical media, searching for time variance phenomena, for low SNR situations. A probe test signal in the ultrasonic band is sent to the room by using a parametric loudspeaker array, with high polar pattern directivity, simultaneous with the test signal frames. The relevant parameters to establish time-variance and associated thresholds are then estimated from the acquired ultrasonic sound. The valid test signal frames, which pass the thresholds test, are labelled with a weighting factor depending on its significance. Otherwise, the frames are rejected, not entering on the averaging process. Results are presented and discussed herein.
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