Journal of the Audio Engineering Society

2005 April - Volume 53 Number 4


System measurement using pseudorandom filtered noise and music sequences is investigated. A single-pass technique is used to evaluate simultaneously the transfer function and the spectral-domain signal-to-distortion ratio that is applicable to amplifiers, signal processors, digital-to-analog converters, loudspeakers, and perceptual coders. The technique is extended to include a simplified Volterra model expressed as a power series and linear filter bank where for compliant systems, nonlinear distortion can be estimated for an arbitrary excitation without a need for remeasurement.

Reverberators play a vital role in immersive audio reproduction. Conventional methods for synthesizing reverberation generally are either computationally intensive or ineffective in producing a natural sensation of environmental settings. A synthesis technique is developed using discrete virtual source representation in an effort to overcome these difficulties. In comparison with the finite-element method (FEM) and the boundary-element method (BEM), which rely on complex numerical operations, the present method is based on a simple representation of the sound field with a distribution of discrete simple sources close to the boundary. The complex strengths of the virtual sources are then calculated by solving a frequency-domain least-squares problem. Parameters such as the geometry, size, and wall absorption of the room are naturally incorporated into the synthesis process. The filtering property of human hearing is also considered in a nonuniform sampling procedure to further simplify the computation. Numerical simulations are carried out for a rectangular room model and a concert hall to investigate the effects of room parameters on the synthesis performance. Subjective listening experiments demonstrate that the present technique is capable of rendering remarkable realism of reverberation.

At its fundamental resonance frequency, the conversion efficiency of a direct-radiator loudspeaker can be substantially greater than its rated efficiency. The behavior of a movingcoil direct-radiator loudspeaker near resonance is analyzed and ways are suggested in which this behavior might be used to increase the sensitivity of closed-box low-frequency loudspeaker systems.

Picking spectral snapshots from an original tone is a successful approach to finding basis spectra in wavetable matching of musical instrument tones. Spectral snapshot selection usually requires optimization by a sophisticated technique such as a genetic algorithm (GA). GA selection is compared to a straightforward local search method, which first selects an initial set of basis spectra from the original tone by some simple selection strategy, and then modifies and improves them. Matching results for a range of instruments show that local search, when using the best composite results found by various simple selection strategies, is as effective as the GA. Moreover, surprisingly, starting from various initial basis spectra, local search can usually find several different matches, all with errors within 1% of the best solution, indicating that there are many near-optimal solutions in the wavetable search space.

[Feature Article] In this article we review recent AES convention papers relating to multichannel spatial audio systems and techniques. Approaches continue to be divided between those based on some acoustical theory designed to render a specified soundfield or wavefront accurately at a listening position or over a certain area (wavefield synthesis and ambisonics may be considered as examples) and those based on an extension of stereophonic principles (5.1 is an example). The latter typically rely on the generation of appropriate perceptual cues at the listening position to create a stereophonic illusion but may be more or less accurate in their exact rendering of acoustical events. Typically, the more loudspeakers that are employed, the more meaningful it becomes to consider the rendering of soundfields that stand up to some form of formal analysis. Somewhere along the line that links the extremes of stereophonic approaches and soundfield-reconstruction approaches, these concepts meet and meaningful evaluation must consider both perceptual and acoustical factors.

Shake, Rattle, And Roll: Gettiing Immersed In Multisensory, Interactiive Music Via Broadband Networks

Authors: Woszczyk, Wieslaw; Cooperstock, Jeremy; Roston, John; Martens, William

[feature] Broadband Internet (transmission rates more than a gigabit per second) enables bidirectional real-time transmission of multiple streams of audio, video, and motion data with latency dependent on distance plus network and processing delays. In this article we describe a new immersive multisensory environment recently constructed at McGill University, designed for network-based communication for music performance coordinated between remote sites, potentially over great distance. The system’s architecture allows participants to experience the music with greatly enhanced presence through the use of multiple sensors and effectors and high-resolution multimodal transmission channels. Up to 24 channels of audio, digital video, and four channels of vibration can be sent and received over the network simultaneously, allowing a number of diverse applications such as remote music teaching, student auditions, jam sessions and concerts, recording sessions, and postproduction for remotely-captured live events. The technical and operational challenges of this undertaking are described, as well as potential future applications.

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A Comparison between Local Search and Genetic Algorithm Methods for Wavetable Matching

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