Journal of the Audio Engineering Society

2008 May - Volume 56 Number 5


Subjective Intelligibility Evaluation in Multiple-Talker Situation for Virtual Acoustic Opening-Based Audio Environments

Authors: Beracoechea, J. A.; Torres-Guijarro, Soledad; García, L.; Casajús-Quirós, Francisco J.; Ortiz, L.

A virtual conferencing system, which couples two separated rooms as if they were a single virtual space connected by an open window, can be implemented in a variety of ways. This study examines the performance of four approaches using the metric of intelligibility with multiple simultaneous talks as the criterion. The problem is constrained by the amount of computation required, limitations on channel capacity, reverberation in the source space, and the difficulty using beamforming to isolate talkers and reduce acoustics contamination. Many improvements were not linear once a threshold level of performance was achieved.

Source Placement for Equalization in Small Enclosures

Authors: Stefanakis, Nick; Sarris, John; Cambourakis, George

A theoretical study explores the way in which sound equalization of the magnitude response in enclosed spaces can be achieved by controlling source locations. The optimization aims to create the desired sound pressure corresponding to that of a plane wave. Sources are placed so that they couple to the beneficial room modes while avoiding those modes that would degrade performance. Simulation results for a rectangular room and an automobile cavity show the benefits: reduced error and increased spatial robustness.

Development of a Super-Wide-Range Microphone for Sound Recording

Authors: Ono, Kazuho; Sugimoto, Takehiro; Tanabe, Hayao; Iwaki, Masakazu; Kurozumi, Koichi; Ando, Akio; Imanaga, Keishi

A new design for a super-wide-range microphone overcomes the conventional tradeoff between noise and bandwidth. Rather than reduce the size of the sensing element to extend the bandwidths to 100 kHz, this design explicitly takes advantage of high-frequency scattering by the microphone body and resonances of the diaphragm. This extends the frequency range, while still preserving the low noise of larger transducers. Laboratory measurements of the resulting omnidirectional electrostatic microphone validate the design approach.

The wavelet packet transform is particularly useful in analyzing the onset transients of piano tones as a means of capturing the unique attributes of such signals in an efficient way. This approach also allows the inhamonicity coefficients to be determined. By exploiting the fact that energy is concentrated in a few time-frequency blocks, a small number of such blocks, especially in the lower harmonics, are sufficient to accurately reconstruct the original waveform. Piano tones have rapidly rising onset transients resulting from the hammer striking the strings and before the string reaches steady state.

[Feature] The way in which loudspeakers interact with rooms has been the subject of study for many years, and the question of whether reflections can be perceptually benign or not is one that has aroused considerable debate. Rooms are a part of one’s natural perceptual experience, and there is evidence that the auditory perception process is finely evolved to concentrate primarily on first-arriving direct sounds. This has allowed humans to learn to survive in an acoustic environment filled with distracting reflections. Toole, for example, reviews the topic of loudspeakers and rooms in a recent paper in this journal (June 2006), and among his conclusions lies the suggestion that reflections may not always be the devil they are sometimes thought to be. Further evidence suggests that it matters whether reflections are spectrally distorted or not and that it only becomes possible to ignore them when they are sufficiently similar to the direct sound to be recognized as a repetition of such. There is also the question of whether room correction or adaptation is necessary for loudspeakers, as there is an increasing interest in systems that attempt to compensate for the effects of the room at low frequencies using signal processing. One needs to know just how much correction, if any, is desirable. In this article we summarize recent papers in the field that were presented at recent AES conferences and conventions.

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