Environmental noise (also known as noise pollution)is a prevalent feature of any urban soundscape. Of the numerous environmental noise sources (e.g., aircrafts,road traffic, railways, industries, and construction),the World Health Organization(WHO) has identified road traffic noise as one of the main contributors to urban noise pollution..
With the strong growth of assistive and personal listening devices, natural sound rendering over headphones is becoming a necessity for prolonged listening in multimedia and virtual reality applications. The aim of natural sound rendering is to naturally recreate the sound scenes with the spatial and timbral quality as natural as possible, so as to achieve a truly immersive listening experience. However, rendering natural sound over headphones encounters many challenges. This tutorial article presents signal processing techniques to tackle these challenges to assist human listening.
We all are used to perceiving sound in a three-dimensional (3-D) world. In order to reproduce real-world sound in an enclosed room or theater, extensive study on how spatial sound can be created has been an active research topic for decades. Spatial audio is an illusion of creating sound objects that can be spatially positioned in a 3-D space by passing original sound tracks through a sound-rendering system and reproduced through multiple transducers, which are distributed around the listening space. The reproduced sound field aims to achieve a perception of spaciousness and sense of directivity of the sound objects. Ideally, such a sound reproduction system should give listeners a sense of an immersive 3-D sound experience. Spatial audio can primarily be divided into three types of sound reproduction techniques, namely, loudspeaker stereophony, binaural technology, and reconstruction using synthesis of the natural wave field [which includes Ambisonics and wave field synthesis (WFS)], as shown in Fig. 1(a).
In this review paper, we examine some of the recent advances in the parametric acoustic array (PAA) since it was first applied in air in 1983 by Yoneyama. These advances include numerical modelling for nonlinear acoustics, theoretical analysis and experimentation, signal processing techniques, implementation issues, applications of the parametric acoustic array, and some safety concerns in using the PAA in air. We also give a glimpse on some of the new work on the PAA and its new applications. This review paper gives a tutorial overview on some of the foundation work in the PAA, and serves as a prelude to the recent works that are reported by different research groups in this special issue.
The parametric loudspeaker provides an effective means of projecting sound in a highly directional manner without using large loudspeaker arrays to form sharp directional beams. It can be augmented with conventional loudspeakers to create a more immersive audio soundscape. Deployment of parametric loudspeakers in many public places where private messaging can make a difference in attracting attention, conveying messages without needing headphones, and creating private listening zones to reduce noise pollution. Digital signal processing plays a significant role in enhancing the aural quality of the parametric loudspeakers, and array processing can help to shape and steer the beam electronically. In addition, other signal processing techniques can also be applied to add more flexibility and improve the performance of parametric loudspeakers. These developments rely heavily on the latest techniques in acoustics and audio signal processing to overcome some of the current limitations in nonlinear acoustics modeling and ultrasonic transducers' technology. A useful feature in sound projection is to realize a highaccuracy digital beamsteering capability in air using an array of parametric loudspeakers. An in-depth study into the theoretical model of wave steering capability in parametric array in air can provide some hints on how we can best steer the demodulated signal in an efficient manner. As seen from this article, digital signal processing provides the main engine to achieve directional sound projection, and new digital processing techniques will be devised to provide a better quality, controllable audio beaming, and efficient sound focusing device in the future.
The problem of acoustic noise is becoming increasingly serious with the growing use of industrial and medical equipment, appliances, and consumer electronics. Active noise control (ANC), based on the principle of superposition, was developed in the early 20th century to help reduce noise. However, ANC is still not widely used owing to the effectiveness of control algorithms, and to the physical and economical constraints of practical applications. In this paper, we briefly introduce some fundamental ANC algorithms and theoretical analyses, and focus on recent advances on signal processing algorithms, implementation techniques, challenges for innovative applications, and open issues for further research and development of ANC systems.