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Authors: Geiger, Ralf; Yu, Rongshan; Herre, Jürgen; Rahardja, Susanto; Kim, Sang-wook; Lin, Xiao; Schmidt, Markus
Recently the MPEG Audio standardization group has successfully concluded the standardization process on technology for lossless coding of audio signals. A summary of the scalable lossless coding (SLS) technology as one of the results of this standardization work is given. MPEG-4 scalable lossless coding provides a fine-grain scalable lossless extension of the well-known MPEG-4 AAC perceptual audio coder up to fully lossless reconstruction at word lengths and sampling rates typically used for high-resolution audio. The underlying innovative technology is described in detail and its performance is characterized for lossless and near lossless representation, both in conjunction with an AAC coder and as a stand-alone compression engine. A number of application scenarios for the new technology are discussed.
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Authors: Hawksford, Malcolm J.
A concept for a digital loudspeaker array, composed of clusters of micro-radiating elements that form individual digital-to-acoustic converters, is studied. In this scheme a large-scale array is composed of subgroups of micro clusters. To accommodate the finite resolution of each cluster, noise shaping is proposed and parallels are drawn with the processes used in digital-to-analog converters. Various elemental array geometries for each micro cluster are investigated by mapping transduction output into three-dimensional space to reveal the spatial distribution of both noise and distortion, which result from noncoincident and quantized digital-to-acoustic elements.
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Authors: Bai, Mingsian R.; Chen, Rong-liang
[Engineering Report] Miniature loudspeakers are key components to many 3C (computer, communication, and consumer electronics) products, especially for portable devices such as mobile phones, PDAs, and MP3 players. Due to size limitation, miniature loudspeakers suffer from the problem of low output level. To gain higher output, one tends to drive the miniature loudspeaker over the excursion limit and induce nonlinear distortion. Thus how to best reconcile the conflicting requirements of nonlinear distortion and acoustic output is extremely crucial in the design of such loudspeakers. To address the issue, a systematic procedure is presented to pinpoint optimal designs appropriate for miniature dynamic moving-coil loudspeakers. The optimization procedure is based on an electroacoustic model established by using the test-box method. Characteristics including voice-coil impedance, frequency response, and harmonic distortion are evaluated. The results show that significant improvement in output performance and excursion limitation has been gained by using the optimal design.
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Authors: Sang, Jinqui; Qiu, Xiaojun
[Engineering Report] An analytical model for an ultrasonic piezoelectric flexural transducer is presented, which consists of a circular piezoelectric unimorph and an aluminum cone. The aluminum cone amplifies sound radiation from the mechanical vibration of the unimorph. The proposed model includes an equivalent electromechanical circuit with parameters derived through energy analysis and an acoustic analysis based on the acoustic radiation impedance transformation characteristics of the finite conical horn. A general agreement has been achieved between the simulation and the experimental results.
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Authors: Staff, AES
[Feature] Audio systems often take advantage of the subtleties of human perception. Is it possible to hear the effect of using extra-high sampling frequencies, or the effect of packet loss when using different types of error concealment? Does stereo make a difference to loudspeaker timbre and what sort of sound quality compromises are acceptable for mobile multimedia?
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