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Journal of the Audio Engineering Society

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2010 July/August - Volume 58 Number 7/8

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Papers

Parametric Spring Reverberation Effect

Authors: Välimäki, Vesa; Parker, Julian; Abel, Jonathan S.

The unique sonic quality of spring reverberation, and its historical importance in many musical genres, motivated implementing this sound with modern digital signal processing techniques. Spring reverberation produces chirplike responses. Rather than attempt to reproduce the physical vibrations of springs, this research uses a parametric model to duplicate their sound. The basic model consists of a spectral delay filter placed into a feedback loop with a long delay line and a selectable loop gain. A delay line is modulated with a strongly correlated random-number sequence. Parameters such as delay time, chirp shape, and decay rate can be adjusted.

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Reverse Engineering of a Mix

Authors: Barchiesi, Daniele; Reiss, Joshua

In order to remaster an old recording made before modern digital processing, reverse engineering the original mix would allow for improving on the final mix. Two algorithms based on least-squares optimization allow the parameters of time-invariant processes, such as gains, delays, panning and filtering, to be estimated if a raw multitrack recording and the final targeted mix are both available. Theoretical and experimental results show that under specific assumptions the proposed method can precisely and efficiently retrieve the original mixing parameters.

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Engineering reports

Closed-Box Loudspeaker with a Series Capacitor

Authors: Thiele, Neville

Adding a series capacitor to a closed-box loudspeaker modestly extends the low-frequency response, enabling the use of a smaller enclosure. In addition, the capacitor offers substantial protection against excessive voice-coil excursions from subsonic input signals. The capacitor converts a second-order system to third order. A design procedure for the composite system in closed form is provided, allowing the resulting transfer function to be optimized for group delay, frequency response, and cone excursion.

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Acoustical Design of a Bluetooth Earphone Using Simulated Annealing Optimization

Authors: Bai, Mingsian R.; Kuo, Yu-Chih

Because a designer of a Bluetooth earphone is faced with conflicting requirements arising from sensitivity, distortion, bandwidth, and miniaturization, a systematic way of meeting these requirements would be useful. Based on a lumped-parameter model, the design process uses a simulated annealing algorithm, which is essential to a random-search technique. For the microspeaker and associated enclosure, a lumped-parameter model predicts the frequency response. Experimental results of the approach are presented, illustrating that the 3GPP2 standards can be met.

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Standards and Information Documents

AES Standards Committee News

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Features

Time-Frequency Processing of Spatial Audio

Authors: Rumsey, Francis

[Feature] Time–frequency processing of spatial audio signals is an important area of current research. It enables elements of composite sounds to be isolated and managed selectively, and it is used in format conversion processes such as upmixing and downmixing. Time–frequency processing is also an important element of some low bit-rate coding schemes, and it is shown how stereo microphone signals can be processed directly for MPEG-Surround applications.

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