Interactive acoustic modeling of virtual environments Nicolas Tsingos Nicolas TsingosREVES-INRIA

Acoustics in virtual environments Goal: realistic sound in virtual environments Evans & Sutherland Avery Fisher Hall Id Software Driving simulator Concert hall design Video game

Geometrical acoustics Represent sound waves as ray paths ray paths

Problem: modeling diffraction Current geometric methods ignore diffraction Newton’s “Principia” (1686)

Problem: modeling diffraction Ignoring diffraction causes discontinuities

A problem: sound diffraction Ignoring diffraction causes discontinuities

Outline Possible approaches Possible approaches Beam tracing algorithm Beam tracing algorithm Experimental results Conclusion

Possible approaches Wave formulation Wave formulation Huygens-Fresnel theory Huygens-Fresnel theory Fresnel ellipsoids Fresnel ellipsoids Geometrical theory of diffraction Geometrical theory of diffraction

Possible approaches Wave formulation Huygens-Fresnel theory Fresnel ellipsoids Geometrical theory of diffraction Geometrical theory of diffraction Equal angles source listener

Geometrical Theory of Diffraction Each sequence of diffracting edges and reflecting surfaces is modeled by a single shortest path Each sequence of diffracting edges and reflecting surfaces is modeled by a single shortest path At each edge, the acoustic field is modulated by a diffraction coefficient At each edge, the acoustic field is modulated by a diffraction coefficient source listener

Problem to solve Efficient enumeration and construction of diffracted and reflected paths in polygonal environments

Outline Motivation for diffraction Possible approaches Beam tracing algorithm Beam tracing algorithm Experimental results Conclusion

Example beam tracing

Outline Motivation for diffraction Possible approaches Beam tracing algorithm Experimental results Experimental results Conclusion

Experimental results Evaluate sound field continuity in a complex environment source listener ~1800 polygons

Experimental results Position along path Power (dB)

Reflection only Discontinuities Position along path Power (dB)

Diffraction only Position along path Power (dB) Continuous but low power

Reflection and diffraction Continuous reverberant sound Position along path Power (dB)

Applications Telepresence Telepresence Video games Video games Audio-visual production Audio-visual production Acoustic simulation of listening spaces Acoustic simulation of listening spaces

Video Performance Paths updated 20 times per second (R10k, 195 MHz)

Conclusion A beam tracing algorithm A beam tracing algorithm Efficient calculation of sound reflection and diffraction Scales well to large architectural environments Fast enough to support real-time audio rendering

Conclusion Diffraction … is an important acoustical effect is an important acoustical effect smoothes discontinuities smoothes discontinuities should be included in geometry-based acoustic simulation should be included in geometry-based acoustic simulation

Future work Signal processing Signal processing DSP hardware and software APIs Validation Validation Measurements Psychoacoustics Psychoacoustics Listening tests

Future work Signal processing Signal processing DSP hardware and software APIs Validation Validation Measurements Psychoacoustics Psychoacoustics Listening tests source wall panel

Validation in the “Bell Labs Box”

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