ï~~The reproduced effect can be specified irrespective of the reproduction context and is, as much as
possible, preserved from one reproduction mode or listening room to another. The Out-- module allows to
compensate for the frequency response of the loudspeakers or headphones and for time lags due to the
geometry of the loudspeaker system. Additionnally, when the listening room is not acoustically neutral,
the processor can take into account measurements made at a reference listening position in order to
automatically perform the necessary corrections in the room effect synthesis, so that the perceived effect
at the reference position be as close as possible to the specification given by the user.
3. PERCEPTUAL CONTROL INTERFACE
The reproduced effect can be specified through a higher-level user-interface, which controls the different
signal processing modules in Spat- simultaneously. Its heart is a perceptual control module derived from
psychoacoustical research carried out at Ircam (Jullien 1995, Warusfel 1990). The perceptual approach
makes it possible to design a spatial processor which does not rely on a physical and geometrical
description of the virtual environment for synthesizing the artificial room effect (e.g. Moore 1983, Foster
& al. 1991). Instead, the user-interface is directly related to the perception of the reproduced sound by the
listener, which is described by a small number of mutually independent perceptual factors:
- source proximity, brilliance and warmth (energy and spectrum of direct sound and early reflections),
- room presence and envelopment (relative energies of direct sound, early and late room effect),
- running reverberance (early decay time), late reverberance (late decay time)
- heaviness and liveness (variation of decay time with frequency)
Each perceptual factor is related to a measurable acoustical criterion characterizing the sound
transformation. This allows to map the perceptual representation into signal processing parameters.
Consequently, virtual and measured acoustical qualities can be manipulated within a unified framework.
4. APPLICATIONS
By inserting a Spat.. processor in each channel of a mixing console or virtual mixing environment
(devoting one DSP to each source channel) the localization and room effect can be intuitively controlled
for each sound event. The mix can be produced in traditional as well as currently developing formats,
including 3/2-stereo or three-dimensional two-channel stereo (binaural or transaural recording). The
processor allows dynamic movements of sound sources and remote control through pointing or tracking
devices. The realism of the sound reproduction over headphones is substantially enhanced by interfacing
the spatial processor with a head-tracking device, and by the synthesis of a natural-sounding room effect.
Music, multimedia or virtual reality applications can benefit from a perceptually-oriented user interface
which is particularly suitable for dynamic interpolation processes between different acoustical qualities.
The Spat- library can also be used in the design of an electro-acoustic system allowing to dynamically
modify the acoustical quality of a large hall, for sound reinforcement or reverberation enhancement.
REFERENCES
J. Chowning, "The simulation of moving sound sources", J. Audio Eng. Soc., vol. 19, no. 1, 1971.
S. Foster, E. M. Wenzel, R. M. Taylor, "Real-time synthesis of complex acoustic environments", Proc.
IEEE Workshop on Applications of Digital Signal Processing to Audio and Acoustics, 1991.
J.-M. Jot, V. Larcher, O. Warusfel, "Digital signal processing issues in the context of binaural and
transaural stereophony", Proc. 98th Conv. Audio Eng. Soc., preprint 3980, 1995.
J.-P. Jullien, "Structured model for the representation and the control of room acoustical quality", Proc.
15th Internntional Conf. on Acoustics, 1995.
F. R Moore, "A general model for spatial processing of sounds", COmp. Music J., vol. 7, no. 6, 1983.
M. Puckette, "Combining event and signal processing in the Max graphical programming environment",
Computer Music Journal, vol. 15, no. 3, 1991.
G. Thiele, "The new sound format '3,2-stereo'", Proc. 94th Cony. Audio Eng. Soc., preprint 3550a, 1993.
0. Warusfel, "Etude des parametre lies k la prise de son pour les applications d'acoustique virtuelle",
Proc. l rst French Congress on Acoustics, 1990.
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