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Noise represents one of the most significant disturbances in measured room impulse responses (RIRs), and it has a potentially large impact on evaluation of the decay parameters. In order to reduce noise effects, various methods have been applied, including truncation of an RIR. In this paper, a procedure for the response truncation based on a model of RIR (nonlinear decay model) is presented. The model is represented by an exponential decay plus stationary noise. Unknown parameters of the model are calculated by an optimization that minimizes the difference between the curve generated by the model and the target one of the response to be truncated. Different curves can be applied in the optimization-absolute value of the RIR, logarithmic decay curve, and Schroeder curve obtained by the backward integration of the RIR. The proposed procedure is tested on various synthesized and measured impulse responses. It is compared with the procedure taken from the literature, often applied in practice.

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The absorption of sound in air represents one of the main problems of the scale model measurements. This absorption, especially at higher frequencies, is considerably greater than the value determined by the law of acoustical similarity between the full scale and the scale model. Different alternatives are applied for compensation of the excess air absorption including a numerical compensation. In this paper, a modified approach to numerical compensation is proposed. It is based on compensation of the sound decay only, and not background noise. As a consequence, there is no an increase of background noise in the compensated impulse response. The results obtained by the proposed procedure are compared to the corresponding ones obtained by the other procedures.

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