A method is proposed that provides an approximation of the acoustic energy decay (energy–time curve) in room impulse responses generated using the image-source technique. A geometrical analysis of the image-source principle leads to a closed-form expression describing the energy decay curve, with the resulting formula being valid for a uniform as well as nonuniform definition of the enclosure’s six absorption coefficients. The accuracy of the proposed approximation is demonstrated on the basis of impulse-response simulations involving various room sizes and reverberation levels, with uniform and nonuniform sound absorption coefficients. An application example for the proposed method is illustrated by considering the task of predicting an enclosure’s reflection coefficients in order to achieve a specific reverberation level. The technique presented in this work enables designers to undertake a preliminary analysis of a simulated reverberant environment without the need for time-consuming image-method simulations.

In many research fields of engineering and acoustics, the image-source model represents one of the most popular tools for the simulation of sound fields in virtual reverberant environments. This can be seen as a result from the relative simplicity and flexibility of this particular method. However, the associated computational costs constitute a well known drawback of image-source implementations, as the required simulation times grow exponentially with the considered reflection order. This paper proposes a method that allows for a fast synthesis of room impulse responses according to the image-source technique. This is achieved by modeling the diffuse reverberation tail as decaying random noise, where the decay envelope for the considered acoustic environment is determined according to a recently proposed method for the prediction of energy decay curves in image-source simulations. The diffuse reverberation model presented in this paper thus produces impulse responses that are representative of the specific virtual environment under consideration (within the general assumptions of geometrical room acoustics), in contrast to other artificial reverberation techniques developed on the basis of perceptual measures or assuming a purely exponential energy decay. Furthermore, since image-source simulations are only used for the computation of the early reflections, the proposed approach achieves a reduction of the computational requirements by up to two orders of magnitude for the simulation of full-length room impulse responses, compared to a standard image-source implementation.

The image-source method has become a ubiquitous tool in many fields of acoustics and signal processing. A technique was recently proposed to predict the energy decay (energy-time curve) in room impulse responses simulated using the image-source model. The present paper demonstrates how this technique can be efficiently used to determine the enclosure's absorption coefficients in order to achieve a desired reverberation level, even with a non-uniform distribution of the sound absorption in the room. As shown in this work, classical expressions for the prediction of an enclosure's reverberation time, such as Sabine and Eyring's formulae, do not provide accurate results when used in conjunction with the image method. The proposed approach hence ensures that the image-source model effectively generates impulse responses with a proper reverberation time, which is of particular importance, for instance, for the purpose of assessing the performance of audio signal processing algorithms operating in reverberant conditions.

In noisy and reverberant environments, the problem of acoustic source localisation and tracking (ASLT) using an array of microphones presents a number of challenging difficulties. One of the main issues when considering real-world situations involving human speakers is the temporally discontinuous nature of speech signals: the presence of silence gaps in the speech can easily misguide the tracking algorithm, even in practical environments with low to moderate noise and reverberation levels. A natural extension of currently available sound source tracking algorithms is the integration of a voice activity detection (VAD) scheme. We describe a new ASLT algorithm based on a particle filtering (PF) approach, where VAD measurements are fused within the statistical framework of the PF implementation. Tracking accuracy results for the proposed method is presented on the basis of synthetic audio samples generated with the image method, whereas performance results obtained with a real-time implementation of the algorithm, and using real audio data recorded in a reverberant room, are published elsewhere. Compared to a previously proposed PF algorithm, the experimental results demonstrate the improved robustness of the method described in this work when tracking sources emitting real-world speech signals, which typically involve significant silence gaps between utterances.