1998 March, VOLUME 46 NUMBER 3

CONTENT

PAPERS

Thermal Time Constants and Dynamic Compressibility of Air in Fiber-Filled Loudspeaker Enclosures
Gavin R. Putland 139
The frequency response of a fiber-filled loudspeaker enclosure is influenced by the heat conduction between the fibers and the enclosed air. The heat conduction rate involves a time constant whose value is dependent upon which conditions are held constant during the heat transfer period. In this study, five constants are derived and their results compared to previous studies.

A Comparison of Computational Methods for Instantaneous Frequency and Group Delay of Discrete-Time Signals
V. C. Georgopoulos and D. Preis 152
A unified treatment of various computational methods for estimating the instantaneous frequency and group delay of discrete-time signals is given. Direct, phase-based methods are compared to the newer moment methods. Instantaneous frequency and group delay are mathematical duals of each other, so that an algorithm suitable for estimating one can be used, with a simple interchange of time and frequency variables, to estimate the other. A wide variety of test signals ar used to compare the performance of these methods, and their advantages and disadvantages compared.

ENGINEERING REPORTS

Subjective Evaluation of State-of-the-Art Two-Channel Audio Codecs
Gilbert A. Soulodre, Theodore Grusec, Michel Lavoie, and Louis Thibault 164
Several two-channel audio codecs were compared to a CD-quality reference in subjective double- blind tests. These studies were designed to determine the comparative audio quality of various codecs. The tests considered only audio quality with respect to bit rate for a series of codecs.

Methods for Reducing Audible Artifacts in a Wavelet-Based Broad-Band Denoising System
Pavan K. Ramarapu and Robert C. Maher 178
A denoising algorithm, which is based on the assumption that broad-band noise cannot be efficiently represented by any of the bases in a library of wavelets, has removed broad-band noise from recorded music signals. The goal of the system was to enhance the music without removing a perceptible amount of musical content. The results indicate that the broad-band noise was largely eliminated, although some minor artifacts, such as faint birdlike noise and warble did arise. These irregularities remain for future investigation.

STANDARDS AND INFORMATION DOCUMENTS

AES-5id-1997 AES information document for room acoustics and sound reinforcement systems - Loudspeaker modeling and measurement - Frequency and angular resolution for measuring, presenting, and predicting loudspeaker polar data 191

DRAFT AES3-1992 Amendment-3-xxxx DRAFT Amendment 3 to AES Recommended practice for digital audio engineering - Serial transmission format for two-channel linearly represented digital audio data (insert)

AES Standards Committee News 217
104th Convention meetings; representation of audio levels in articles and specifications

FEATURES

AES 104th Convention Preview, Amsterdam 226
Calendar 228
Exhibitors 230
Exhibit Previews 236
Student Delegate Assembly Established 254
Updates and Corrections to the 1997/1998 AES International Sections Directory 257
Updates to Review of Society's Sustaining Membership 261

DEPARTMENTS

Review of Acoustical Patents 222
News of the Sections 248
Sound Track 255
Upcoming Meetings 256
Available Literature 258
Membership Information 263
Sections Contacts Directory 267
AES Conventions and Conferences 272