Authors: Wannamaker, Robert A.
A comparative analysis of subtractively and nonsubtractively dithered quantizing systems, with and without noise-shaping error feedback, is presented. A review of the principal results prefaces the most thoroughgoing mathematical analysis of either system that currently exists in print. The relative advantages and disadvantages of each system are compared, addressing their inherent signal-to-noise ratios and the requirement for knowledge of the dither signal at the receiver in subtractive systems. It is shown that subtractively dithered systems can render the total error statistically independent of the input signal at the expense of requiring knowledge of the dither signal at the receiver. On the other hand, nonsubtractively dithered systems can at best render specified statistical moments of the total error independent of the input and will introduce greater total noise into the output, although they do not require knowledge of the dither signal at the receiver. The treatment extends to include new findings regarding signal correlations in subtractively and nonsubtractively dithered systems, and regarding subtractively dithered systems using spectrally colored dither signals and/or noise-shaping error feedback. The new results are proven as needed for purposes of comparison.
Authors: Moore, Brian C. J.; Tan, Chin-Tuan; Zacharov, Nick; Mattila, Ville-Veikko
The results of experiments in which subjects rated the perceived quality of speech and music that had been subjected to various forms of both linear and nonlinear distortion are reported. Experiment 1 made use of artificial distortions (such as ripples in frequency response combined with peak clipping). Experiment 2 included both artificial distortions and real distortions introduced by transducers. The results were compared with the predictions of a new model based on a weighted sum of predictions for linear distortion alone and for nonlinear distortion alone. There was a very good correspondence between the obtained and predicted ratings. Correlations were greater than 0.85 for speech stimuli and 0.90 for music stimuli. It is concluded that the new model can predict accurately the perceived quality of speech and music subjected to combined linear and nonlinear distortion.
Authors: Chiang, Wei-Hwa; Chao, Yi-Nuo; Lee, Jow-Yeh; Wu, Hui-Ping
The 256-seat Carrie Chang Music Hall is a remodeled lecture hall having a generally circular plan, 21.6 m in diameter. The room acoustics design focused on providing early reflections to compensate for high-frequency loss at the seats away from the direction of the sound source. This was realized by introducing convex curved walls on the stage and side boxes on the audience floor. Removing the original ceiling to increase the volume yielded a 1.02-s midfrequency early decay time (EDT). Evaluation of the overall impression with a tenor singing and a cello playing showed little difference among the seats with a 120° variation in viewing angle.
Authors: Barros, José Luis; Cárdenas, Jorge; Sommerhoff, Jorge
The directional characteristics of a piston mounted on a surface of zero impedance are studied. Zero and infinite acoustic impedance surfaces represent two extreme cases, although the most typical surfaces have infinite impedance. Zero acoustic impedance can be produced at discrete frequencies by using quarter-wave resonators. A two-dimensional model was simulated by multipole synthesis, which was then confirmed using experimental results. Because energy cannot flow tangentially on a surface with zero impedance, the directivity pattern was greatly sharpened. The results support the idea of using surface impedance as a means of controlling loudspeaker directivity patterns.
Authors: Errock, David
[feature] With high-definition television just around the corner, the audio industry faces a huge dilemma. Should it go all out to satisfy a similar consumer demand for high-resolution stereo and multichannel audio? Or will broadcasting and media chiefs settle permanently for the present system where audio data is compressed for greater quantity of channels and ease of storage, while sacrificing quality? If the latter happens it could indefinitely postpone the audio engineer’s quest for perfect sound reproduction. If the industry moves to a high-resolution format, record companies and broadcasters will be faced with the problem of moving these larger audio data signals between studios, which is currently cumbersome and expensive. There is, however, a revolutionary development, which could solve this problem in a realistic way: the Audio Engineering Society’s AES47 standard.
Authors: Staff, AES
[feature] In the last few years digital radio broadcasting has moved beyond the domain of research projects and trials and is beginning to take its place as a serious alternative to analog services in some parts of the world. The term digital radio is used here to refer to digital sound broadcasting systems of various types, including terrestrial and satellite systems. In the United States, in particular, the introduction of terrestrial digital radio has been slowed by a number of delays caused by standardization issues and decisions about audio coding algorithms, although satellite digital radio has been gaining ground for a few years. In parts of Europe and Canada, however, the Eureka 147 World DAB standard has been operating for some time, whereas satellite digital radio (at least for mobile reception) is less common. In the UK, for example, digital radio broadcasts have been on the air from the BBC for many years, although the market penetration of receivers has only recently become significant. In this article we describe the main audio features and differences of the most prominent systems in use.
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