Room Response Equalization—A Review

Abstract

Room response equalization aims at improving the sound reproduction in rooms by applying advanced digital signal processing techniques to design an equalizer on the basis of one or more measurements of the room response. This topic has been intensively studied in the last 40 years, resulting in a number of effective techniques facing different aspects of the problem. This review paper aims at giving an overview of the existing methods following their historical evolution, and discussing pros and cons of each approach with relation to the room characteristics, as well as instrumental and perceptual measures. The review is concluded by a discussion on emerging topics and new trends. This paper aims to provide an up-to-date review on RRE, discussing the pros and the cons of each technique, following the historical evolution. It is worth underlining that the RRE problem is analyzed from the viewpoint of impulse response analysis. All approaches that are not directly based on RIR analysis (e.g., parametric or graphic equalizers) are not discussed. The reader is referred to [11] for a comprehensive review on this topic. Another research field related to RRE which is not addressed in this paper is sound spatialization. The reader is referred to [12] for a recent review.This review article is organized as follows: Section 2 describes the characteristics of room impulse responses and its perception by the human auditory system. Section 3 introduces the basic concept of RRE, explaining the main challenges in inverting room responses. Section 4 describes the approaches used for equalizer design following their historical evolution. Section 5 discusses pre-processing techniques used to cope for RIR variations by exploiting human perception. Section 6 covers the evolution from single-point to multi-point equalization using multiple microphones placed within the room. Section 7 reports adaptive approaches for RRE in the framework of single-point and multi-point equalization. Section 8 introduces innovative approaches following a wave-theoretical view on the problem. Section 9 describes instrumental and perceptual measures used for state-of-the-art evaluation of RRE approaches. Section 10 reports emerging methods and new trends in the field. Finally, Section 11 concludes this review. The Room Response and Its PerceptionThe characteristics of the room response in the time and frequency domain are related to the acoustic properties of the environment that influence human perception. Due to this aspect, it is sensible to shape the impulse response analysis in order to handle important issues that should be considered in the RRE procedure to reach a sound listening improvement. This includes knowledge on human perception and psychoacoustics to be exploited explicitly in the equalization procedure. Appl. Sci. 2018, 8, 16 4 of 47An impulse response, obtained from a sound source in a specific position of a real environment, can be divided into three parts [13]: (i) direct sound; (ii) early reflections, and (iii) late reflections, as r...

Low-Frequency Compensated Synthetic Impulse Responses For Improved Far-Field Speech Recognition

“…While the frequency response of an IR simulated using geometric methods is mostly flat due to the ray assumption, the response with room modes has visible irregularities, especially at low-frequencies where room resonance is most dominant. Room resonance is normally undesirable for sound field reproduction and various methods have been devised to remove this effect [26]. However, in this paper, we aim at compensating the missing room resonance by room EQ compensation, which helps reducing the performance gap between using simulated and real IRs for far-field ASR training.…”

22nd International Conference on Digital Audio Effects DAFx 2019 (2–6 September 2019, Birmingham, United Kingdom)

“…The presentation included excellent audio examples demonstrating the improvement obtained with some of the methods. Cecchi and her colleagues recently published a review article on the same topic [2].…”

Special Issue on “Sound and Music Computing”

“…Cecchi et al [1] have written the only review article for this special issue. Their long paper gives a complete overview of audio signal processing methods for the equalization of the loudspeaker-room response, which is a fundamental problem in sound reproduction.…”