Journal of the Audio Engineering Society

2003 September - Volume 51 Number 9


Digital Rights Management

Authors: Woodgate, John

[feature article] In one sense digital rights management, or DRM, has nothing to do with audio. However, rather in the same way that metadata (covered in the July/August issue) is data that relates to or describes audio information, DRM is concerned with the means by which the intellectual property rights in audio information is managed in electronic-commerce systems. Its importance cannot be nderestimated, as it is the primary means by which owners of audio content hope to get paid in the fast-growing world of e-commerce.

Not available.

Objective Measures of Listener Envelopment in Multichannel Surround Systems

Authors: Soulodre, Gilbert A.; Lavoie, Michel C.; Norcross, Scott G.

A common goal in multichannel musical recordings is to create a better approximation of the concert-hall experience than can be achieved with a traditional stereo reproduction system. Listener envelopment (LEV) is known to be an important part of good concert-hall acoustics and is therefore desirable in multichannel reproduction. In the present study a series of subjective tests were conducted to determine which acoustic parameters are important to the creation of LEV. It is shown that LEV can be controlled systematically in a home listening environment by varying the level and angular distribution of the late arriving sound. While the perceptual transition point between early and late energy has traditionally been set to 80 ms when predicting LEV, this matter has not been investigated rigorously. Subjective tests were conducted wherein the temporal and spatial distributions of the late energy were varied. A new frequency-dependent objective measure GSperc was derived, and it was shown to outperform other objective measures significantly.

Listening tests on four different loudspeakers were conducted over the course of 18 months using 36 different groups of listeners. The groups included 256 untrained listeners whose occupations fell into one of four categories: audio retailer, marketing and sales, professional audio reviewer, and college student. The loudspeaker preferences and performance of these listeners were compared to those of a panel of 12 trained listeners. Significant differences in performance, expressed in terms of the magnitude of the loudspeaker F statistic FL, were found among the different categories of listeners. The trained listeners were the most discriminating and reliable listeners, with mean FL values 3-27 times higher than the other four listener categories. Performance differences aside, loudspeaker preferences were generally consistent across all categories of listeners, providing evidence that the preferences of trained listeners can be safely extrapolated to a larger population. The highest rated loudspeakers had the flattest measured frequency response maintained uniformly off axis. Effects and interactions between training, programs, and loudspeakers are discussed.

Simplified head shapes, such as spheres and ellipsoids, have often been applied in the research of head-related transfer functions (HRTFs). However, the effects of the missing head-shape features in these simplified head models have not been thoroughly examined. Head shapes are represented using spherical harmonics, which allows the simplification of head shapes to be carried out in a controlled and systematic way. The KEMAR head shape is low-pass filtered to different degrees. The errors in both the head shape and the acoustic pressures introduced by the low-pass filters are studied. Guidelines are presented for examining the tradeoff between head-shape simplification and accuracy of pressure estimation. It is concluded that spherical harmonics above degree 11 may be ignored in the computation of HRTFs below 3 kHz.

Effects of Down-Mix Algorithms on Quality of Surround Sound

Authors: Zielinski, Slawomir K.; Rumsey, Francis; Bech, Søren

Eight down-mix algorithms were evaluated in terms of basic audio quality. The investigation was focused on the standard 5.1 multichannel audio setup (ITU-R BS.775-1) and limited to two listening positions. The results obtained are summarized and detailed specifications of the subjectively best algorithms are given. The effect of the presentation of moving pictures on the assessment of audio quality was also investigated. The results show that the exposure to a visual content has a considerable effect on the evaluation of the audio quality at the off-center position to some types of program material.

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