PSFC:
the Pioneer Sound Field Control System
at the University of Aizu Multimedia Center (Draft)

Katsumi Amano, Fumio Matsushita, and Hirofumi Yanagawa
Pioneer Electronic Corp.
2610 Hanazono 4-chome, Tokorozawa-shi; Saitama 359
voice: (0429)42-1151; fax: (0429)43-0395
{ama, mat, yana}@asd.pioneer.co.jp

Michael Cohen and Jens Herder
University of Aizu 965-80
voice: (0242)37-2537; fax: (0242)37-2549
{mcohen, herder}@u-aizu.ac.jp

Yoshiharu Koba and Mikio Tohyama
Kogakuin University
5-601 Dept. of Electronic Engineeering; 2665-1 Nagano-machi; Hachioji-shi, Tokyo 192
voice: (0246)25-8982; fax: (0426)25-8982
{koba@yamato, ctdeneuv@sin}.cc.kogakuin.ac.jp

Abstract

The PSFC, or Pioneer Sound Field Control System, is a DSP-driven hemispherical 14-loudspeaker array, installed at the University of Aizu Multimedia Center. Collocated with a large screen rear-projection stereographic display, the PSFC features realtime control of virtual room characteristics and direction of two separate sound sources, smoothly steering them around a configurable soundscape. The PSFC controls an entire sound field, including sound direction, virtual distance, and simulated environment (reverb level, room size and liveness) for each source. It can also configure a dry (DSP-less) switching matrix for direct directionalization. The PSFC speaker dome is about 14m in diameter, allowing about 20 users at once to comfortably stand or sit near its sweet spot.

System Description

System schematic

As a spatially immersive display, the large (3m x 9m) screen and speaker array combination crosses the intimacy of traditional HMD-style with the freedom of so-called "desktop VR" systems, allowing multiple users to share perspective. With such a speaker array, soundscape stabalization is natural (and no head-tracking is needed).

intimacy	audio	visual
	display
personal	headphones	HMD
	nearphones	desktop monitor
	transaural speakers	HDTV
multipersonal or social (spatially immersive displays)	speaker array	large-screen display
public	public address

Level vs. time for direct, reflected, and reverberant sound:
the effect of changing room size and reverberation via initial delay time and liveness

This interface configures both the presence (virtual room environment) and the source characteristics of the sound field. Ambience is set by combination (level and timing) of direct sound, discrete early reflections, and late diffuse reverberation. Direction is set by programming azimuth and elevation for two independent sources, which can move around with update of 100ms. Early reflection patterns, calculated via an image source model, are dynamically selected according to direction, while the reverberation patterns are exponentially decayed noise filters, independent of source position. Room liveness scales the reflection and reverberation tap amplitudes; a setting of 0 corresponds to a free-field or anechoic condition. Room size is set by programming delay for reflection (0-500ms). Reflection patterns can be chosen from one of twenty presets; overall volume is controlled by level. The ratio of direct:reverberant energy is a cue to source distance. For example, low gain and high liveness suggest a distant source, while high gain and low liveness suggest a close source. A pass-through mode configures null DSP with a switching matrix function.

Applications

We are developing a robust interface between the PSFC and graphical interfaces, including audio windows and VRML browsers. Our prototype is expected to be a fertile research platform, deploying applications related to teleconferencing, virtual concerts, hypermedia and VR.

For example, inspired by the cyclical nature of octaves and helical structure of a scale, we prepared a model of a piano-style keyboard which was then geometrically warped into a left-handed helical configuration, one octave/revolution, pitch mapped to height. Our model is being imported into (Open Inventor/)VRML, where it can be driven by MIDI events, realtime or sequenced, which stream is both synthesized by a sound module and spatialized by the PSFC, so that the sound of the respective notes is directionalized with respect to sinks, avatars of the human user, by default in the tube of the helix.

The PSFC's omnidirectional sound field complements the exaggerated visual display's inadequacies for immersion, since flying into the helix from the outside envelopes the listener as it overflows the visual system's field-of-view. The helical keyboard's multiple sinks are natural idioms for the PSFC, compensating for the fact that the speakers span only the upper hemisphere.

Acknowledgement

This research is supported in part by grants from the Fukushima Prefectural Foundation for the Advancement of Science and Education and the NTT Human Interface Laboratories.

References

Pioneer Electric Corporation (Ohmori R&D Laboratories). Sound field simulating system using multi-speaker reproduction (in Japanese). Journal of the Japan Acoustic Society. 48(4):275-278. 1992.
Michael Cohen. Integrating graphical and audio windows. Presence: Teleoperators and Virtual Environments, 1(4):468--481, Fall 1993.
Michael Cohen and Nobuo Koizumi. Audio windows for virtual concerts I. In Susumu Tachi, editor, Video Proc. ICAT/VRST: Int. Conf. Artificial Reality and Tele-Existence/Conf. on Virtual Reality Software and Technology, Makuhari, Chiba; Japan, November 1995.
Yoshiharu Koba. Virtual Acoustic System Using Multiple Loud Speakers (in Japanese). Masters Thesis, Kogakuin University. 1996.
Mikio Tohyama, Hideo Suzuki, and Yoichi Ando. The Nature and Technology of Acoustic Space. Academic Press. 1996. ISBN 0-12-692590-9.