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Journal of the Audio Engineering Society

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2008 January/February - Volume 56 Number 1/2

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Papers

Objective Measurement of Perceived Auditory Quality in Multichannel Audio Compression Coding Systems

Authors: Choi, Inyong; Shinn-Cunningham, Barbara G.; Chon, Sang Bae; Sung, Koeng-Mo

An objective method that predicts perceived audio quality in multichannel compression coding systems is described. This method, which takes into account degradation in both spatial and timbral quality, extends previous approaches by incorporating a binaural hearing model. Spatial quality uses three interaural distortions metrics: time difference, level difference, and cross-correlation coefficient. Timbral quality uses 10 nonspatial statistics. Predictions of perceived quality are comparable or better than other models.

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Control of Synthesized Vibrato during Portamento Musical Pitch Transitions

Authors: Maher, Robert C.

Vocal vibrato, a naturally occurring pitch oscillation in singing, requires careful analysis in the vicinity of portamento transitions from one pitch to another. Measurements show that singers manage to align pitch transitions to the natural shape of the vibrato cycle. Vibrato continuity is preferred to timing accuracy. Although singers do not report being conscious of this subtlety, the characteristic is quite consistent. These results show that in order to mimic natural vocal vibrato, a vocal synthesizer must synchronize the main pitch transition and the phase of the vibrato oscillator.

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A New HRTF Interpolation Approach for Fast Synthesis of Dynamic Environmental Interaction

Authors: Keyrouz, Fakheredine; Diepold, Klaus

In order to achieve a realistic rendering of moving sound sources and changes in listener position with real-time virtual auditory spaces, a very dense grid of head-related transfer functions (HRTFs) is required for interpolation. A new binaural interpolation algorithm based on a block Loewner matrix is proposed to avoid artifacts with dynamic changes in the HRTF. Compared to existing algorithms, the new method is both accurate and efficient. Subjective tests were used to verify the technique.

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Nonlinear Intermodulation of Two Coherent Acoustic Progressive Waves Emitted by a Wide-Bandwidth Loudspeaker

Authors: Lemarquand, Guy; Bruneau, Michel

The usual assumption that air provides a linear medium for sound propagation is not valid at high intensities. An analytic procedure and experimental measurements show that when two harmonic waves propagate, an intermodulation phenomenon appears because nonlinear acoustic phenomena occur in fluid media. Regardless of the quality of the loudspeaker, high-fidelity sound reproduction is theoretically impossible with high particle velocity.

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Understanding Sigma-Delta Modulation: The Solved and Unsolved Issues

Authors: Reiss, Joshua D.

[Feature] Sigma–delta modulation is the most popular form of analog-to-digital conversion used in audio applications. It is also commonly used in D/A converters, sample-rate converters, and digital power amplifiers. In this tutorial the theory behind the operation of sigma–delta modulation is introduced and explained. We explain how performance is assessed and resolve some discrepancies between theoretical and experimental results. We discuss the issues of usage, such as limit cycles, idle tones, harmonic distortion, noise modulation, dead zones, and stability. We characterize the current state of knowledge concerning these issues and look at what are the most significant problems that still need to be resolved. Finally, practical examples are given to illustrate the concepts presented.

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DSP in Loudspeakers

Authors: Rumsey, Francis

[Feature] Digital signal processing is used increasingly in loudspeakers to compensate for a range of linear and nonlinear distortion processes that typically arise. DSP can also be used in crossover design and for controlling the spatial radiation characteristics of loudspeakers or loudspeaker arrays. This requires the detailed understanding and modeling of the acoustical deficiencies and behavior of transducers and cabinets. In this article we summarize a number of papers describing recent research in this field; they were all presented at the AES 32nd International Conference, held in Denmark in September 2007.

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Anatomy of the Soundscape: Evolving Perspectives

Authors: Krause, Bernie

[Feature] The concept of the soundscape was first introduced by R. Murray Schafer in his 1977 book Tuning of the World. Schafer’s definition of soundscape includes all of the sound from a particular environment that reaches the human ear. Schafer considered that we are linked to the natural world through its perceived voice, and he encouraged us to exam - ine what first stirred human communities to form sound into cohesive and expressive patterns such as music, dance, and even speech. In the past several years, mostly as a result of technological developments in field recording and data analysis, it has become necessary to focus more specifically on the complex sources of soundscape acoustics in order to more accurately explain and probe the roots of this phenomenon. In the following article the soundscape is described as comprised of three basic active acoustic sources : biophony, geophony, and anthrophony. These sources are sometimes independent of one another while at other times intrinsically related in various combinations. In addition, the active soundscape can only be understood in light of the passive surrounding environment in which the source is transmitted. The connection between the natural soundscape and early human culture and spirituality will be addressed. Further - more, this article will touch on the ways in which natural soundscapes are currently thought to be linked to the fields of ecological resource management, geology, medicine, biology, physics, sociology, and many other disciplines.

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