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Journal of the Audio Engineering Society

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2008 March - Volume 56 Number 3

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Papers

Digital Audio Antiquing-Signal Processing Methods for Imitating the Sound Quality of Historical Recordings

Authors: Välimäki, Vesa; González, Sira; Kimmelma, Ossi; Parviainen, Jukka

Processing modern audio files to make them appear to have originated from historic technology, called antiquing, is the inverse of restoring old recordings. Simulating both global and local degradations of older technologies can be useful in such applications as testing restoration algorithms. A theoretical analysis of old recordings combined with numerous case studies results in a convincing imitation of historic phonograph and gramophone recordings. This work was motivated by a museum that wanted to show how audio technology has evolved over the last 150 years.

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Evaluation of HE-ACC, AC-3, and E-AC-3 Codecs

Authors: Gaston, Leslie; Sanders, Richard

A carefully controlled independent double-blind test with 27 listeners compared the Dolby Digital AC-3 standard compression codec with newer bandwidth extended codecs, Advanced Audio Coding Plus HE-AAC and Dolby Digital Plus E-AC-3. Subjective tests of this kind require a listening space that is physically and acoustically appropriate for detecting auditory nuances, mostly conforming to the standards of ITU-R BS.1116-1. Out of a large library of samples, a subset was selected based on their ability to challenge compression codecs. On average, AC-3 sounded better than the other two codecs.

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Sound Field Analysis along a Circle and Its Applications to HRTF Interpolation

Authors: Ajdler, Thibaut; Faller, Christof; Sbaiz, Luciano; Vetterli, Martin

The sampling and interpolation of the sound field along a circle is studied, and an angular sampling theorem is presented. Application of these results can be found in the problem of interpolating coarsely sampled head-related transfer functions (HRTFs). The proposed method interpolates HRTFs in a sub-band domain. For the low temporal frequencies satisfying the sampling theorem, HRTFs can be interpolated very precisely. At higher frequencies, the angular interpolation is carried out in a complex temporal envelope domain to limit aliasing. Numerical simulations indicate that the proposed method performs better in a mean square error sense than conventional interpolation methods.

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A New Method for Measuring Distortion Using a Multitone Stimulus and Noncoherence

Authors: Temme, Steve; Brunet, Pascal

A new approach for measuring distortion provides a continuous distortion curve versus frequency, and the method is suitable for use with noise, music, and multitone stimuli. Distortion measures are derived from dual-channel analysis of the noncoherence between the stimulus and the response. The mathematics is based on Volterra theory, which is an extension of linear system theory but applied to nonlinear systems. Because the technique uses standard signal processing, the approach is simple, accurate, and repeatable.

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Forensic Audio Analysis

Authors: Rumsey, Francis

[Feature] Although a relatively small and specialized field, the domain of forensic audio analysis gives rise to some interesting applications of audio processing in the service of voice identification and recording authentication. Some of the most important topics involved in such work were covered in papers presented at the AES 122nd and 123rd Conventions and a workshop at the 123rd. One aspect has to do with the tracking of vocal features or parameters in the identification or elimination of voice samples, while the second involves the authentication of recordings, including the intriguing use of the electric network frequency as a remarkably reliable "watermark" when dealing with digital audio recordings.

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