The true duration of the impulse response used to estimate reverberation time

Since Schroeder [1965], reverberation time can be computed from the impulse response. Some other studies have shown the advantages of this method leading often to more accurate results than the classical ones. But, it can be shown that, when background noise is an important energetic part of the impulse response, Schroeder's method must be revised. A theoretical approach is proposed showing the influence of background noise and the integration boundaries in Schroeder's equation. Hence, a new upper limit of integration is defined based on regression lines to model background noise and decay. The intersection defines t' being the useful length of the impulse response. Experiments were processed in a large factory hall. Comparisons between classical reverberation time measurements and Schroeder's method are made showing good results even for the lowest values of signal-to-noise ratio.