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Journal of the Audio Engineering Society

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2006 November - Volume 54 Number 11

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Papers

Multiple-Loudspeaker Playback of Stereo Signals

Authors: Faller, Christof

A perceptually motivated spatial decomposition for two-channel stereo audio signals, capturing the information about the virtual sound stage, is proposed. The spatial decomposition allows resynthesizing audio signals for playback over sound systems other than twochannel stereo. With the use of more front loudspeakers the width of the virtual sound stage can be increased beyond ±30° and the sweet-spot region is extended. Optionally, lateral independent sound components can be played back separately over loudspeakers on the sides of a listener to increase listener envelopment. It is also explained how the spatial decomposition can be used with surround sound and wavefield synthesis–based audio systems.

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Structural and Acoustic Analysis of Multiactuator Panels

Authors: Kuster, Martin; De Vries, Diemer; Beer, Daniel; Brix, Sandra

Multiactuator panels are a possible solution to satisfying the requirement of a large number of loudspeaker channels inherent in wavefield synthesis. The structural acoustic behavior of multiactuator panels has been measured with a laser Doppler vibrometer, and acoustic radiation simulation has been performed using a discretized Rayleigh I integral. The analysis showed that, due to large structural damping, the acoustic radiation is generated almost entirely by the structural near field around the excitation point on the panel, but it is influenced to a large extent by the panel dimensions and the exciter position. The radiation principle of a distributed-mode loudspeaker from the literature is briefly contrasted.

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Synthesis and Implementation of Virtual Bass System with a Phase-Vocoder Approach

Authors: Bai, Mingsian R.; Lin, Wan-chi

A bass enhancement technique based on a phase-vocoder approach is presented. Instead of direct bass boosting, the proposed method creates a bass impression by exploiting the psychoacoustic properties of humans. This technique is most useful in audio reproduction using small loudspeakers that have no low-frequency capability, where direct boosting will likely result in nonlinear distortions. In light of psychoacoustics, the bass effect is synthesized by augmenting the original signals with high-frequency harmonics. Unlike conventional methods that rely on nonlinear processing, the proposed method performs the required frequency transformation by using a phase-vocoder approach. Apart from frequency transformation, another key element of the proposed technique is the magnitude adjustment of the generated harmonics. The underlying principle for magnitude adjustment is based on a polynomial model of equal-loudness contours. The method is implemented on a digital signal processor with the aid of multirate signal processing. To validate the proposed technique, objective and subjective experiments are conducted for PC multimedia loudspeakers and handset loudspeakers. The subjective listening experiment followed the procedure of multistimuli with the hidden reference and anchor (MUSHRA), and the data were analyzed by using the multianalysis of variance (MANOVA) method. As indicated by the results, the proposed technique proved effective in rendering bass impression with acceptable audio quality.

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Validation of ITU-T P.563 Single-Ended Objective Speech Quality Measurement

Authors: Kurittu, Antti

[Engineering Report] ITU-T Recommendation P.563 defines a single-ended method for objective speech quality assessment. The P.563 objective speech quality measurement method predicts the subjective absolute category rating (ACR) listening quality. The accuracy of the P.563 algorithm was tested against data from subjective listening tests. It was found that P.563 compresses the corresponding MOS (mean opinion score) value range for coded speech. For AMR coded speech with GSM and 3G radio channel errors, the MOS value range was from about 1.2 to 4.0, while the corresponding P.563 MOS-LQO range was from about 3.0 to 3.6. The quality of the modulated noise reference unit (MNRU) and direct samples was predicted better.

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Using Game-Audio Tools to Build Audio Research Applications

Authors: Kelly, Michael

[Feature Article] Examples of such tools include listening-test software, measurement software, and tools with real-time controls that can be used to tune DSP algorithms. The process of getting audio in and out of the computer is not always clear to the uninitiated, even to an otherwise experienced programmer. This article is the first part of a two-part tutorial showing the steps required to access a computer’s audio hardware using high-level audio application programming interfaces (APIs), used primarily in the games industry. The tutorial shows how audio applications can be developed from scratch and tailored to the needs of the audio researcher. It is aimed at researchers in the audio field with some C or C++ programming experience but who are unfamiliar with audio input and output. The tutorial does not require an understanding of game-audio programming but provides the necessary background to produce real-time audio research tools. The second part of this article consists of online tutorials with step-by-step instructions for a number of widely or freely available audio APIs. To view the tutorials go to www.aes.org/tutorials/gameaudio/kelly. Only individual AES members using their personal logins are able to view the tutorials.

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Preventing Hearing Loss

Authors: Staff, AES

[Feature Article] Jan Voetmann, chair of the tutorial Hearing Loss—Causes, Preventative Measures, and Effects on Sound Professionals and the Audience, presented at the AES 120th Convention in Paris in May, introduced the event by explaining that the official limit for occupational noise is also used for evaluating the effects of listening to music. A sound level of 85 dBA for 8 hours of the day leads to an equivalent of around 100 dBA for a quarter of an hour, which is easily reached in leisure time by many people either in the home and yard, in clubs and discos, and at work. (For further information about equivalent noise levels see Noise Exposure on next page.) Short intervals with very high peak sound levels can still lie within the noise dose guidelines, even though they can be harmful. Voetmann said that it is difficult to find young people with normal hearing levels, based on informal data gathered at a university in Munich that showed common hearing losses consistent with listening to music at high levels. Gunshots, as experienced by hunters or soldiers, can reach 160 dB for a short period, and woodwind players in an orchestra can experience 128 dBC. If you go to a rock concert and stand in front of the loudspeakers you can experience 129 dBC. For an online sound demo, go to www.hei.org/education/soundpartners/guidelines.htm, where you can adjust a noise meter to hear the different sounds and sound intensities of everyday objects, courtesy the U.S. National Institute of Occupational Safety and Health.

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