In This Section
Journal of the AES
2008 December - Volume 56 Number 12
Fractional delay filters, which allow for delays that are not aligned at samples values, are important in many signal processing algorithms. Lagrange interpolation is frequently used for this purpose in situations where delay values change frequently, because filter coefficients can be calculated from explicit formulas. The large number of algorithms for Lagrange interpolation necessitates an analysis of their computational effort. A novel structure that is efficient, scalable, and well suited for parallel hardware or software implementation is described.
Hierarchical Bandwidth Limitations of Surround Sound—Part I: Psychoacoustically Hierarchical Transform
In order to reduce the increase data rate of multichannel surround sound, a hierarchical bandwidth limiting technique is proposed. In this approach, the original signals are transformed into a hierarchical representation, which is then band-limited and re-transformed back into the original representation. Subjective listening tests were used to evaluate two such approaches: Gerzon MSBTF and Karhumen–Lòeve transforms. The results showed that the signal-dependent hierarchical encoding performed better than the signal-independent techniques, but both techniques were better than conventional methods.
Because conventional sigma–delta modulators have a proclivity toward instability when excited by high-amplitude audio signals, a modified detection process incorporates an energy metric. This new paradigm uses the sums of the energy in the filter integrators as part of the five-sample look-ahead. Unlike a conventional sigma–delta modulator, which only considers the filter output, this approach also lowers the stored energy within the filter. As an intrinsic tradeoff, increased stability at high levels increases noise modulation. An energy-balance algorithm can use a highly parallel matrix operation for computational efficiency.
When using multiple drivers in a linear array structure to achieve an increased soundfield level, the designer must consider the spatially dependent frequency response of the array. By using specifically designed weights for the array elements, the array can be made to have a spatial all-pass characteristic such that there is minimal variation in the frequency response of the array with respect to angle. Weights that achieve this property correspond to FIR filter approximations of all-pass filters. A search algorithm for such approximations is described, and examples are provided to demonstrate the design freedoms of the proposed approach, including the use of crossover-filter configurations.
Correction to “Nonlinear Distortion Synthesis Using the Split-Sideband Method, with Applications to Adaptive Signal Processing”
Standards and Information Documents
AES Standards Committee News
Preferred sampling frequencies; serial transmission format; flutter measurement; serial multichannel interface; extended file format for audio; ATM networks; analog recording; transfer technologies; grounding & EMC
In this article we summarize a number of recent AES convention papers, describing new findings relating to the perception of reproduced sound. These include the perception of auralized urban soundscapes as well as the interesting topic of how the blind might detect obstacles by auditory means. Further papers relate to novel methods for measuring speech quality, loudness calculation for objects in complex scenes, and the detection of sound signals at very high frequencies. Although there is no central theme linking these papers, they provide insights into some fascinating avenues of various kinds of perceptual research.
For wireless microphone operators below 698 MHz, the FCC’s recent actions yield little to be concerned about and much to be thankful for. The frequencies above 698 MHz will be gone starting in February of 2009 (in an action announced years ago and unrelated to new devices) but the rules for the new TV Band Devices (TVBDs) are so stringent that it is unlikely any interference will be caused to wireless mic systems, even to those operating illegally. In addition to setting very high technical requirements for TVBDs, the FCC finds that it is in the public interest to provide spectrum space for wireless microphones even if they are operated without the required license.
125th Convention Report, San Francisco
125th Convention Exhibitors
127th Convention, New York, Call for Papers
Index to Volume 56