1997 JUNE, VOLUME 45 NUMBER 6

CONTENT

President's Message: The Evolution of Standards Elizabeth A. Cohen p. 443

PAPERS

Digital Parametric Equalizer Design with Prescribed Nyquist-Frequency Gain
Sophocles J. Orfanidis p. 444
A new class of second-order digital parametric equalizers is shown that closely matches its analog counterpart over the entire Nyquist interval. This digital configuration does not suffer from the prewarping effect of the bilinear transformation. An additional degree of freedom is introduced in this design, namely, gain at the Nyquist frequency.

Virtual Sound Source Positioning Using Vector Base Amplitude Panning
Ville Pulkki p. 456
A vector-based reformulation of amplitude panning is shown that uses simple and computationally efficient equations for accurate, virtual sound-source positioning. This method, vector base amplitude panning (VBAP), makes possible the creation of two-dimensional and three-dimensional sound fields using multiple loudspeakers that are set in an arbitrary placement. It is claimed that VBAP produces virtual sound sources that are as sharp as those possible with current loudspeaker configurations that use amplitude panning.

ENGINEERING REPORTS

Digital-Domain Dithering of Sigma-Delta Modulators Using Bit Flipping
Anthony J. Magrath and Mark B. Sandler p. 467
A new technique is introduced for dithering sigma-delta modulators directly in the digital domain, eliminating the need for an analog dither source or the use of chaos. This reduces the analog circuit complexity. The system design reduces noise modulation at low input levels and extends the dynamic range by reverting back to an undithered modulator at high input levels.

Digital Power Amplification Using Sigma-Delta Modulation and Bit Flipping
Anthony J. Magrath and Mark B. Sandler p. 476
A novel data conversion scheme suitable for power digital-to-analog conversion is based on a modified sigma-delta modulator. It is proposed that the digital-to-analog converter translate a 44.1/48-kHz format pulse-code-modulated (PCM) digital audio signal to an oversampled single-bit signal. This signal then controls a high-power MOSFET switch. Its output signal is passively filtered to reconstitute the analog signal, which can then be applied directly to the loudspeaker.

LETTERS TO THE EDITOR

Comments on "Spice Models for Vacuum-Tube Amplifiers" Eric K. Pritchard p. 488
Author's Reply W. Marshall Leach, Jr. p. 489
Comments on "Spice Models for Vacuum-Tube Amplifiers" Fridiric Broydi. Evelyne Clavelier, and Charles Hymowitz p. 490
Charles Rydel p. 491
Author's Reply W. Marshall Leach, Jr. p. 493 CORRECTIONS

Corrections to "Digital Signal Processing Tools for Loudspeaker Evaluation and Discrete-Time Crossover Design" Malcolm Omar Hawksford p. 497

STANDARDS AND INFORMATION DOCUMENTS

AES Standards Committee News p. 498
Computer audio; flutter; multiple-contact connector database

FEATURES

The AES Technical Council and Its Committees Tim Shelton p. 502

DEPARTMENTS

News of the Sections p. 508
Sound Track p. 516
Upcoming Meetings p. 517
New Products and Services p. 518
Available Literature p. 521
Membership Information p. 522
In Memoriam p. 531
Sections Contacts Directory p. 532
AES Conventions and Conferences p. 536