Journal of the Audio Engineering Society

2015 April - Volume 63 Number 4


Parametric Spatial Audio Processing of Spaced Microphone Array Recordings for Multichannel Reproduction

Authors: Politis, Archontis; Laitinen, Mikko-Ville; Ahonen, Jukka; Pulkki, Ville

There are two major categories of recording approaches for multichannel sound reproduction: coincident and spaced microphone arrays. Coincident techniques assume that the microphones are essentially at the same point in space and they provide stable localization of discrete sound events. In contrast, spaced techniques provide a better enveloping sense of the ambient reverberant sound, at the expense of localization performance. In this research a parametric processing method is presented for spaced microphone array recordings using the principles of Directional Audio Coding (DirAC), knowledge of the array configuration, and the directional response of the microphones. The method achieves equal or better quality relative to the standard high-quality version of DirAC and it improves the common direct playback of such recordings by offering improved and stable localization cues and reduction of coloration issues at all frequencies.

Although recent research showed the connection between timbre and emotion with sustaining musical instruments, this research investigates the connection for nonsustaining instruments, such as plucked string, pitched percussion, and keyboard sounds. Pairwise listening tests considered eight emotional categories. Results showed that the harpsichord, marimba, vibraphone, and xylophone were highly rated for positive emotional categories; the guitar, harp, and plucked violin were highly rated for negative emotional categories; and the piano was rated emotionally neutral. By correlating timbral features with the listener rankings, we found that decay slope and density of significant harmonics were the relevant timbral features for many emotional characteristics. There were differences in emotional characteristics due to early release.

As the percentage of the population with hearing loss increases, broadcasters are receiving more complaints about the difficulty in understanding dialog in the presence of background sound and music. This article explores these issues, reviews previously proposed solutions, and presents an object-based approach that can be implemented within MPEG-H to give listeners control of their audio mix. An object-based approach to clean audio, combined with methods to isolate sounds that are important to the narrative and meaning of a broadcast has the potential to enable users to have complete control of the relative levels of all aspects of audio from TV broadcast. This approach was demonstrated at the University of Salford campus in 2013.

The center of a spherical wave radiating from a loudspeaker is defined as its acoustic center. This study investigates how the acoustic center of a closed-box loudspeaker is shifted when the loudspeaker is placed in a linear array composed of two or three identical loudspeakers. In order to estimate the acoustic center based on wave fronts, the proposed method measures the sound pressure around the loudspeaker with an array of microphones, and then uses the beamforming method for the reduction of experimental errors. The acoustic center of the loudspeaker at one side is shifted in the opposite direction of the other two loudspeakers, and that of the center loudspeaker is shifted further away from the diaphragm. This implies that the acoustic center of each loudspeaker in a linear array can be shifted differently depending on the relative position of the loudspeaker in the array. Sound field control using an array can be more accurate by taking into consideration the shift of acoustic centers.

Engineering reports

Audio recordings for mobile devices are predominantly mono-channel, in part, because stereo transducers are too large to be mounted on hand-held devices. By using array signal processing and omnidirectional, dipole cardioid elements, two-channel stereophony can simulate a stereo microphone. In addition, 5.1 surround sound can also be realized with a special microphone arrangement. To synthesize the desired beam patterns, optimized beamformers were designed with the aid of least-square and convex optimization techniques. Two-channel stereophonic recording configurations (including a broadside array and a curved array) and a 5.1 surround sound configuration were developed and evaluated with objective and subjective tests. For two-channel stereophonic recording, the results show that the broadside array and curved array outperform the conventional M-S technique. The 5.1 array has achieved similar recording quality as conventional systems.

Motivated by the fact that more than thirty thousand firearm homicides occur on the American continent every year, law enforcement agencies have been deploying gunshot detection systems to reduce the use of illegal firearms in high-crime urban areas. This article provides a comprehensive review of gunshot detection technologies, including commercially available systems and current research. Discussions consider the following: (1) the acoustic signatures of small firearms, (2) muzzle blast waves and their propagation in outdoor spaces, (3) history of gunshot detection, (4) gunshot-detection methods, (5) electroacoustic-sensor methods, (6) firearm identification, (7) shooter localization in urban environments, and (8) hit-rate analysis. Given the current status of gunshot detection technology, there are a number of technical issues that remain unaddressed and merit research and development. Quantifying the efficacy of gunshot detection in reducing firearm violence and crime is difficult given the available research in this field.


[Feature] Music for games is going through a gradual transformation from “pre-cooked” to “cooked-on-the-fly.” There is still, though, something of a disconnection between the academic studies of the subject and real-world implementations in commercial systems. Music and audio manipulation can be used to communicate emotional mood and impact in games. Headphones are becoming increasingly important as a way of listening to games, requiring solutions to creating a convincing experience for the user.

Hearing Loops, The Preferred Assistive Listening Technology

Authors: Kaufmann, Thomas; Sterkens, Juliette; Woodgate, John. M.

[Feature] This article discusses the benefits of hearing loops as an effective and user-friendly assistive listening technology and summarizes the current progress of adoption in the United States. Research shows that audio frequency induction loops are strongly preferred by hearing aid users over FM and IR systems and allow venues to provide their hard-of-hearing patrons with the optimal and most convenient listening experience.

[Feature] Although there are many ways to approach classical music recording and mixing, it is the end result that is truly important—a mostly accurate capture of a large ensemble that generates a compelling listening experience. I say “mostly accurate,” as in certain cases we may be trying to present an enhanced experience, with a “larger than life” presentation. Extra-low-frequency content, a wider perspective, more reverb, and clarity in low-level details and slightly exaggerated solo balances are all important areas of attention in modern recording. This stems from the very practical problem of trying to capture the experience of listening to a full orchestra in a great hall and then reproduce it over medium-quality loudspeakers or a pair of inexpensive headphones.

Special Issue on Music Induced Hearing Disorders, Call for Papers


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