Time Variance in Measured Room Impulse Responses

Time variance is unavoidable in room impulse response (RIR) measurements, as the fluctuations in the atmospheric conditions and air movement prevent any room from being perfectly steady. However, the effect of such changes on RIRs has received little attention so far, although it is known to cause energy loss when RIRs are averaged for the purpose of enhancing their signal-to-noise ratio. In this work, we focus on the influence of spatio-temporal fluctuations in the speed of sound on RIR energy loss. We introduce a new approach of examining the relation between time-variance-related energy loss of averaged RIRs and the decrease in their cross-correlation over time. We show that even when the measurements are compensated for the global changes in the speed of sound, the small fluctuations still contribute to the RIR dissimilarity. The results also indicate that the RIRs become less correlated with the growing time separation between measurements. This shows that the short-term running cross-correlation is a good metric for estimating the time-variance-related energy loss in RIRs. The research presented in this work is a step towards more robust acoustic measurements and compensation of time-variance-related artifacts in measured signals.