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Journal of the Audio Engineering Society

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2007 December - Volume 55 Number 12

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Papers

Degradation Decomposition of the Perceived Quality of Speech Signals on the Basis of a Perceptual Modeling Approach

Authors: Beerends, John G.; Busz, Bartosz; Oudshoorn, Paul; Van Vugt, Jeroen; Ahmed, Kamal; Niamut, Omar

The authors discuss the way we perceive the quality of a speech signal and how different degradations contribute to the overall perceived speech (listening) quality. More specifically, ITU-T Recommendation P.862 (perceptual evaluation of speech quality—PESQ), which provides a perceptual modeling approach with which the subjectively perceived speech quality can be predicted, is used as a starting point for a degradation decomposition algorithm. This algorithm decomposes the perceived degradation into three different contributions by finding specific degradation indicators that quantify the impact of each type of degradation separately. The first degradation indicator quantifies the impact of additive noise as found in many speech-processing situations, such as when unwanted background noise is sent over a voice connection. The second degradation indicator quantifies the impact of linear timeinvariant frequency response distortions as, for example, introduced by a band-limited telephone system. The last degradation indicator quantifies the impact of the time-varying behavior of the system under test. This time response degradation indicator quantifies the impact of temporal signal loss, as found with packet loss in modern digital speech connections, and the impact of pulses (clicks) as found in many speech-processing systems.

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Comparison of Four Subwoofer Measurement Techniques

Authors: Melon, Manuel; Langrenne, Christophe; Rousseau, David; Herzog, Philippe

Acoustic measurements of loudspeakers are difficult to perform at very low frequencies, and therefore their interpretation is often tricky. Four subwoofer measurement techniques are compared in terms of frequency response and directivity. The methods were selected with an attempt to avoid assumptions about the behavior of the loudspeakers: anechoic room, pseudo free field, reference chamber, and field separation. Three subwoofers were tested: two closedbox systems and an active/passive system. Discrepancies between the results are discussed and explained where possible.

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Analysis of Multiactuator Panels in the Space-Time Wavenumber Domain

Authors: Pueo, Basilio; López, José J.; Escolano, José; Bleda, Sergio

A methodology for the analysis of the radiation characteristics and spatial performance of loudspeaker arrays for wave field synthesis (WFS) reproduction is presented. It is based on the wavenumber domain analysis, where the source radiation is decomposed into plane waves for arbitrary angles of incidence. The method deals with the measurement and analysis of the radiation performance, evaluation of the spatial aliasing frequency, and associated sampling artifacts for linear loudspeaker arrays. A detailed description of the parameters that modify spatial aliasing artifacts, such as array directivity and truncation effects by geometry, is also given. The method is validated at the laboratory with two multiactuator panel arrangements and a dynamic loudspeaker array, all presenting the same transducer spacing. Simulations and experimental results are discussed through several case studies, comparing dynamic loudspeaker arrays and multiactuator panels in WFS operation. Moreover, a study of the consequences for the wavefield when splitting the panels to accommodate a lower number of exciters is also addressed.

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Adaptive Wave Field Synthesis for Sound Field Reproduction: Theory, Experiments, and Future Perspectives

Authors: Gauthier, Philippe-aubert; Berry, Alain

Wave field synthesis (WFS) is a sound field reproduction technology that assumes that the reproduction environment is anechoic. A real reproduction space thus reduces the objective accuracy of WFS. Adaptive wave field synthesis (AWFS) is defined as a combination of WFS and active compensation. With AWFS the reproduction errors are minimized along with a departure penalty from the WFS solution. Analysis based on the singular value decomposition connects WFS, active compensation, and Ambisonics. The decomposition allows the practical implementation of AWFS based on independent radiation mode control. Results of experiments in different rooms support the theoretical propositions and show the efficiency of AWFS for sound field reproduction.

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High Resolution Audio

Authors: Rumsey, Francis

[Feature] Significant developments in the field of high resolution audio, reported at the 31st International Conference held in London earlier this year, are summarised here. This will include discussion on how to avoid bottlenecks where quality could be compromised, and how to maintain and encourage high resolution audio in an ever-changing marketplace.

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