2004 June, Volume 52 Number 6

CONTENT

PAPERS

Efficient Generation of Multichannel Dither Signals
Robert A. Wannamaker   579
When a dither source is needed for multichannel quantization, efficient techniques reduce the computational burden of computing each channel independently. By using appropriate matrix transformations, a single rectangular probability density function (RPDF) random number per sample per channel can be used to produce independent identically distributed (iid) triangular probability density function (TPDF) dither for each channel. After quantization, the errors in each channel are uncorrelated with one another and each has an input-independent mean and variance.

Time-Quantized Frequency Modulation, Time-Domain Dither, Dispersive Codes and Parametrically Controlled Noise Shaping in SDM
M. O. J. Hawksford   587
Comparing sigma-delta modulator (SDM) performance to a mathematically equivalent coding technique based on linear frequency modulation (LFM) and time-domain quantization provides additional insight into the noise behavior of SDM. Normally if the conclusions drawn from studies of linear quantization and triangular dither are applied to SDM, then the two-level quantizer range is violated and instability results. Nevertheless, the chaotic-like loop behavior of high-order SDM even with apparent suboptimal dither demonstrates low correlation distortion and is shown here to be insensitive to dither statistics. The LFM model applies ditherin the time domain rather than the amplitude domain and does not violate these assumptions.

Augmented Reality Audio for Mobile and Wearable Appliances
Aki Härmä, Julia Jakka, Miikka Tikander, Matti Karjalainen, Tapio Lokki, Jarmo Hiipakka, and Gaëtan Lorho   618
In a portable device, integrating environmental sounds with synthetically generated audio leads to the concept of a wearable device that produces augmented reality. Listeners wear a headset configuration that includes a binaural microphone and stereophonic headphones. In addition to feeding sounds of the environment to the headphones, an auxiliary input provides the means for reproducing recorded audio in a virtual space. Listening tests with a prototype system showed that some experienced listeners found it difficult to distinguish between real and virtual sources.

Room Sizing and Optimization at Low Frequencies
Trevor J. Cox, Peter D'Antonio, and Mark R. Avis   640
In critical listening environments, the modes in a room of low volume produce an uneven frequency response and extended decay rates at low frequencies. Using a cost metric based on minimizing the deviations from the flattest possible modal response, the authors propose a new method for choosing the appropriate dimensions for a room of a given volume. While there is a numerically optimum solution, many local minima are equivalent in terms of quality, which then allows for incorporating the physical constraints of real buildings.

LETTERS TO THE EDITOR

Comments on "Wavefront Sculpture Technology"
Chao Jiang and Yong Shen   652

Author's Reply
M. Urban, C. Heil, and P. Bauman   653

CORRECTIONS

Correction to "Graphing, Interpretation, and Comparison of Results of Loudspeaker Nonlinear Distortion Measurements"
A. Voishvillo, A. Terekhov, E. Czerwinski, and S. Alexandrov   655

Correction to "Historical Perspectives and Technology Overview of Loudspeakers for Sound Reinforcement"
J. Eargle and M. Gander   655

STANDARDS AND INFORMATION DOCUMENTS

AES Standards Committee News   656
Audio measurements; metadata

FEATURES

How Loud Is My Broadcast?   662

DEPARTMENTS

Review of Acoustical Patents   659
News of the Sections   670
Upcoming Meetings   673
Sound Track   675
New Products and Developments   676
Available Literature   678
Membership Information   679
Advertiser Internet Directory   689
In Memoriam   689
Sections Contacts Directory   690
AES Conventions and Conferences   696

FPO For the cover:

2004 June, Volume 52 Number 6

spine: 2004 June, Volume 52 Number 6