A review of the state-of-the-art approaches in detecting time-of-flight in room impulse responses

Detecting the correct peaks of reflections in room impulse responses (RIRs) is of interest for several applications. The time-of-flight (ToF) of these reflections peaks are needed, for example, in the application of Acoustic traveltime TOMography (ATOM) to reconstruct the indoor air temperature. Strictly speaking, the ToF of early reflections is used as an input dataset to reconstruct the air temperature using inverse algorithms. Here, the most popular benefit of using the ToF of early reflections is the possibility to reconstruct the indoor air temperature fields using a minimum number of transducers. In this context, there exist a wide variety of approaches to estimate the correct ToF of the reflection peaks. While literature empirically highlighted the potential of the majority of these methods to detect the correct peaks, they have not been compared to each other in terms of their advantages and limitations. This review paper provides a critical overview and a snapshot of the used detection methods of the ToF of reflection peaks with special focus on application of ATOM technique in the indoor areas. Meanwhile, it offers details and guidelines to improve the detection process of the ToF of reflection peaks in the RIRs reflectogram only in case the length of the short analysis time-windows is identified appropriately. Alternatively, a method designed to detect peaks in the measured reflectogram, excess coefficient technique, dynamic time warping approach and plane wave decomposition technique provide enhanced consistency and precision for the estimated ToF of early reflections. However, we discuss the short analysis timewindow procedure that is particularly well-suited to improve the estimation of the ToF of early reflections. Moreover, future outlook and research gaps are highlighted in the present review.