Journal of the Audio Engineering Society

2003 January/February - Volume 51 Number 1/2

Papers


[feature article] The AES 22nd International Conference, held recently in Espoo, Finland, highlighted themes of vital importance to the future of audio engineering. Prominent among these was a clear challenge for audio engineers to look at the authoring of audio content in an entirely new way compared to traditional approaches used in the creation of content for the entertainment industry.

In the 2002 November issue,1 the affiliations for the authors should have read: Kelly Fitz, School of Electrical Engineering and Computer Science, Washington State University, Pullman, WA 99164-2752, USA; and Lippold Haken, Department of Electrical and Computer Engineering, University of Illinois, Urbana-Champaign, Urbana-Champaign, IL 61801, USA.

A study of the modified discrete cosine transform (MDCT) and its implications for audio coding and error concealment is presented from the perspective of Fourier frequency analysis. A relationship between MDCT and DFT via shifted discrete fourier transform (SDFT) is established, which provides a possible fast implementation of MDCT employing a fast Fourier transform (FFT) routine. The concept of time-domain alias cancellation (TDAC), the symmetric and nonorthogonal properties of MDCT, is analyzed and illustrated with intuitive examples. New insights are given for innovative solutions in audio codec design and MDCTdomain audio processing such as error concealment.

Earlier work that simplified the calculation of loudspeaker horn characteristics below the horn cutoff frequency is further investigated, leading to a more secure foundation for the computations. The complex wavenumber is used by means of which acoustic losses are introduced. remains complex at all times. It also allows the presence of a complex ß throughout the mathematics, which in turn ensures that the mathematics does not break down at and below the so-called horn cutoff frequency since there is a complex part at all frequencies. This leads to a smooth calculation over the whole frequency range of interest and, in particular, right through the cutoff frequency.

Frequency-warped filters have recently been applied successfully to a number of audio applications. The idea of all-pass delay elements replacing unit delays in digital filters allows for focusing enhanced frequency resolution on the lowest (or highest) frequencies and enables a good match to the psychoacoustical Bark scale. Kautz filters can be seen as a further generalization, where each all-pass element may be different, allowing also complexconjugate poles. This enables an arbitrary allocation of frequency resolution to filter design, such as modeling and equalization (inverse modeling) of linear systems. Strategies for using Kautz filters in audio applications are formulated. Case studies of loudspeaker equalization, room response modeling, and guitar body modeling for sound synthesis are presented.

Traditionally, electronic equalization has used linear filters of low complexity. The nature of spectral and temporal distortions of rooms limits useful equalization to minimum-phase filters of relatively low order, despite the existence of new and powerful digital signal processing tools. The high Q and non-minimum-phase nature of the room loudspeaker 'listener transfer function, caused by wave interference effects, creates severe problems for more complete equalization. A typical professional listening room and three cinema acoustic environments were used to investigate the difficulties inherent for more ambitious equalization approaches.

Corrections


Correction to: "On the Use of Time-Frequency Reassignment in Additive Sound Modeling"

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Standards and Information Documents


AES Standards Committee News

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Features


114th Convention Preview, Amsterdam

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    Calendar

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    Exhibitors

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    Exhibit Previews

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Virtual and Synthetic Audio

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115th Convention, New York, Call for Papers

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Departments


News of the Sections

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Upcoming Meetings

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Sound Track

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Available Literature

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Membership Information

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Advertiser Internet Directory

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In Memoriam

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Sections Contacts Directory

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AES Conventions and Conferences

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Extras


Cover & Sustaining Members List

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VIP List & Editorial Staff

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