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Last Updated: 20060821, mei

P4 - Instrumentation and Measurement

Thursday, October 5, 1:30 pm — 4:00 pm

Chair: Eric Benjamin, Dolby Laboratories - San Francisco, CA, USA

P4-1 A New Method for Measuring Distortion Using a Multitone Stimulus and NoncoherenceSteve Temme, Pascal Brunet, Listen, Inc. - Boston, MA, USA
A new approach for measuring distortion based on dual-channel analysis of noncoherence between a stimulus and response is presented. This method is easy to implement, provides a continuous distortion curve against frequency, and can be used with a multitone stimulus, noise, or even music. Multitone is a desirable test signal for fast frequency response measurements and also for assessing system nonlinearities. However, conventional single-channel multitone measurements are challenging because the number of intermodulation tones grows rapidly with the number of stimulus tones and makes it extremely difficult to separate harmonics from intermodulation products. By using dual-channel measurement techniques, only well-known, standard signal processing techniques are used, resulting in simplicity, accuracy, and repeatability.
Convention Paper 6877 (Purchase now)

P4-2 Gradient Microphone Design Using Miniature Microphone ArraysJuha Backman, Nokia Corporation - Espoo, Finland
The paper describes a method of using a dense array of miniature microphones (e.g., MEMS or miniature electret) to yield precise one-point multichannel gradient microphones. The signals obtained from individual microphones in the array are used to obtain an estimate for the zeroth, first-, and second-order components of the gradient of the sound field at the center of the array. (Higher orders of the gradient tend to be too noisy for actual sound recording purposes.) These can be used to form stereo or multichannel signals with adjustable polar patterns for recording purposes.
Convention Paper 6878 (Purchase now)

P4-3 Wind Generated Noise in Microphones—An Overview: Part IIEddy B. Brixen, DPA Microphones A/S - Allerød, Denmark, EBB-consult, Smorum, Denmark
When microphones are exposed to wind, noise is generated. The amount of noise generated depends on many factors: the speed and the direction of the wind being, of course, two of the important factors. However, the size, shape, and design principles of the microphones are also important factors. At higher wind speeds, not only is noise generated but also distortion is introduced, normally as a result of clipping. This paper is the second in a series of two. The first paper basically presented standard condenser microphones with 1st order characteristics. This paper presents a number of comparative measurements on electro dynamic microphones—basically some of the workhorses in the field.
Convention Paper 6879 (Purchase now)

P4-4 A Portable Record Player for Wax Cylinders Using both Laser-Beam Reflection and Stylus MethodsTohru Ifukube, The University of Tokyo - Meguro-ku, Tokyo, Japan; Yasuyuki Shimizu, Japan Women’s University - Bunkyou-ku, Tokyo, Japan
The wax phonograph cylinder invented by Thomas Edison in 1885 was the medium for recording sound until about 1930. Although a lot of historically valuable cylinders have been preserved all over the world, most of them changed in quality by recrystallization and had many cracks on their surfaces. We have developed a portable record player (3.4 kg-weight, 45 cm-width, 33 cm-length, and 10.5 cm-height) for the cylinders using both laser-beam reflection and stylus methods. In this paper the record player is shown to be useful for carrying it by hand and reproducing sounds in real time from damaged wax cylinders as well as the undamaged.
Convention Paper 6880 (Purchase now)

P4-5 High-Accuracy Full-Sphere Electro-Acoustic Polar Measurements at High Frequencies Using the HELS MethodHuancai Lu, Sean Wu, SenSound LLC - Grosse Point Farms, MI, USA; D. B. (Don) Keele, Jr., Harman International Industries - Northridge, CA, USA
Traditionally, high-accuracy full-sphere polar measurements require dense sampling of the sound field at very-fine angular increments, particularly at high frequencies. The proposed HELS (Helmholtz Equation Least Squares) method allows this restriction to be relaxed significantly. Using this method, far fewer sampling points are needed for full and accurate reconstruction of the radiated sound field. Depending on the required accuracy, sound fields can be reconstructed using only 10 to 20 percent of the number of sampling points required by conventional techniques. The HELS method allows accurate reconstruction even for sample spacing that violates the Nyquist spatial sampling rate in certain directions. This paper examines the convergence of HELS solutions via theory and simulation for reconstruction of the acoustic radiation patterns generated by a rectangular plate mounted on an infinite rigid flat baffle. In particular, the impact of the numbers of expansion terms and measurement points as well as errors imbedded in the input data on the resultant accuracy of reconstruction is analyzed.
Convention Paper 6881 (Purchase now)

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