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An Introduction to Sound Rendering

An Introduction to Sound Rendering. Anish Chandak achandak@cs.unc.edu COMP 770 (Spring’09). Sound Rendering: An Overview. Scientific Visualization. Specular Reflection. Late Reverberation. Acoustic Geometry -- surface simplification. Scattering. Personalized HRTFs for 3D sound.

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An Introduction to Sound Rendering

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  1. An Introduction to Sound Rendering AnishChandak achandak@cs.unc.edu COMP 770 (Spring’09) © Copyright 2009 Anish Chandak

  2. Sound Rendering: An Overview Scientific Visualization Specular Reflection Late Reverberation Acoustic Geometry -- surface simplification Scattering Personalized HRTFs for 3D sound Acoustic Material -- absorption coefficient -- scattering coefficient Diffraction Refraction Digital Signal Processing Source Modeling -- area source -- emitting characteristics -- sound signal Doppler Effect Interpolation for Dynamic Scenes Attenuation Rendering (Sweet Audio!) Modeling Propagation © Copyright 2009 Anish Chandak

  3. Sound Rendering: An Overview Scientific Visualization Specular Reflection Late Reverberation Acoustic Geometry -- surface simplification Scattering Personalized HRTFs for 3D sound Acoustic Material -- absorption coefficient -- scattering coefficient Diffraction Refraction Digital Signal Processing Source Modeling -- area source -- emitting characteristics -- sound signal Doppler Effect Interpolation for Dynamic Scenes Attenuation Rendering (Sweet Audio!) Modeling Propagation © Copyright 2009 Anish Chandak

  4. Applications • Advanced Interfaces • Multi-sensory Visualization Minority Report (2002) Multi-variate Data Visualization © Copyright 2009 Anish Chandak

  5. Applications • Games • VR Training Medical Personnel Training Game (Half-Life 2) © Copyright 2009 Anish Chandak

  6. Applications • Acoustic Prototyping Symphony Hall, Boston Level Editor, Half Life © Copyright 2009 Anish Chandak

  7. Modeling Acoustics vs. Graphics Acoustic Geometry -- surface simplification • Low geometric details vs. High geometric details Acoustic Material -- absorption coefficient -- scattering coefficient Source Modeling -- area source -- emitting characteristics -- sound signal Modeling © Copyright 2009 Anish Chandak

  8. Propagation Acoustics vs. Graphics Specular Reflection • 343 m/s vs. 300,000,000 m/s • 20 to 20K Hz vs. RGB • 17 m to 17 cm vs. 700 to 400 nm Scattering Diffraction Refraction Doppler Effect Attenuation Propagation © Copyright 2009 Anish Chandak

  9. Rendering Acoustics vs. Graphics Late Reverberation • Compute intensive DSP vs. Simple addition of colors • 44.1 KHz vs. 30 Hz • Psychoacoustics vs. Visual psychophysics Personalized HRTFs for 3D sound Digital Signal Processing Interpolation for Dynamic Scenes Rendering (Sweet Audio!) © Copyright 2009 Anish Chandak

  10. Sound Propagation in Games • Strict time budget for audio simulations • Games are dynamic • Moving sound sources • Moving listeners • Moving scene geometry • Trade-off speed with the accuracy of the simulation • Static environment effects (assigned to regions in the scene) © Copyright 2009 Anish Chandak

  11. Sound Propagation Approaches • Numerical Methods • Solve Helmholtz Wave Equation • Accurate • Compute intensive (fourth power of frequency) • Independent of model complexity • Methods: FEM, BEM, FDTD, DWM • Geometric Methods • Ray-Approximation of Wave Equation • High-frequency approximation • Fast • Dependent on model complexity • Methods: Image Source/Beam Tracing, Frustum Tracing, Ray Tracing/Phonon Tracing © Copyright 2009 Anish Chandak

  12. Beam Tracing for Sound Propagation • [Funkhouser,1998] • Demo • Input: point sound source, point listener, scene geometry with acoustic properties • Output: pressure impulse response (IR) • Rendering: convolve IR with audio signal of sound source • Note: audio signal is a function of pressure © Copyright 2009 Anish Chandak

  13. Beam Tracing for Sound Propagation Source Modeling -- area source -- emitting characteristics -- sound signal Propagation Acoustic Geometry -- surface simplification Acoustic Material -- absorption coefficient -- scattering coefficient Late Reverberation Personalized HRTFs for 3D sound Digital Signal Processing [Funkhouser,1998] © Copyright 2009 Anish Chandak

  14. Example: Input [Funkhouser,1998] © Copyright 2009 Anish Chandak

  15. Step 1 (pre-processing)Spatial Subdivision • Partition 3D space into convex regions (BSP Tree). • Build adjacency graph. [Wikipedia, Binary space partitioning] [Funkhouser,1998] © Copyright 2009 Anish Chandak

  16. Example: Step 1 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  17. Step 2 (pre-processing)Beam Tracing • Compute Beam Tree • Node Information • Cell ID • Beam and its apex • Cell boundary • Parent node ID • Attenuation © Copyright 2009 Anish Chandak

  18. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  19. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  20. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  21. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  22. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  23. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  24. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  25. Example: Step 2 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  26. Step 3 (interactive)Path Generation • Find cell, C, containing listener (log N) • For each beam in C check for listener is inside it • Yes, then a path exist • Attenuation, path length, and direction can be computed quickly • Construct path by traversing the beam tree • Compute Impulse Response (IR) © Copyright 2009 Anish Chandak

  27. Example: Step 3 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  28. Example: Step 3 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  29. Example: Step 3 [Funkhouser,1998] © Copyright 2009 Anish Chandak

  30. Step 4 (interactive)Auralization • Convolve IR with input sound signal • Use the directional paths to simulate 3D audio using HRTFs * = Impulse Response (IR) = * Sound Signal Output Audio © Copyright 2009 Anish Chandak

  31. Ray Tracing for Sound Propagation • [Krokstad,1968] [Kulowski,1984] • Input: spherical sound source, spherical listener, scene geometry with acoustic properties • Output: energy impulse response (IR) • Rendering: • convert energy IR into pressure IR • convolve IR with audio signal of sound source • Note: audio signal is a function of pressure © Copyright 2009 Anish Chandak

  32. Shoot Sound Rays(Step 1) L S Shoot Rays From Source Sound Source Listener Scene Geometry © Copyright 2009 Anish Chandak

  33. Trace Sound Rays(Step 2) L S © Copyright 2009 Anish Chandak

  34. Specular Reflection(Step 3) L S • Based on Reflection Coefficient • Annihilate Or Energy Based © Copyright 2009 Anish Chandak

  35. Diffuse Reflection(Step 3) L S • Based on Scattering • Coefficient • Annihilate or Choose a random direction © Copyright 2009 Anish Chandak

  36. Construct Energy Histogram(Step 3) L S Collect Rays at the Listener © Copyright 2009 Anish Chandak

  37. Construct Pressure IR from Energy Histogram(Step 4) • To compute sound signal at a point add sound pressure of all contributions • Phase angles of pn and pm are different and for quite a large number of components [Kuttruff,2007] © Copyright 2009 Anish Chandak

  38. Auralization(Step 4) • Convolve IR with input sound signal • Use the directional paths to simulate 3D audio using HRTFs * = Impulse Response (IR) = * Sound Signal Output Audio © Copyright 2009 Anish Chandak

  39. Advanced Topic: Acoustic Rendering Equation • Equivalent to rendering equation in computer graphics [Kajiya, 1986] • Time dependent equation • Typically solved in frequency space • Very recent development [Siltanen, 2007] • Lot of potential to apply graphics techniques of rendering to acoustic rendering equation © Copyright 2009 Anish Chandak

  40. Advanced Topic: Acoustic Surface Simplification Visual Geometry Acoustic Geometry [Vorländer,2007] © Copyright 2009 Anish Chandak

  41. Advanced Topic: HRTFs for 3D sound Inter-aural Time Difference (ITD) Inter-aural Level Difference (ILD) HRTF = Head Related Transfer Function. Encodes ILD, ITD, and much more. © Copyright 2009 Anish Chandak

  42. COMP 770 Course Project Suggestions • Sound + Visual (Parameterized Sound) • Integrating Sounds and Motions in Virtual Environments (http://search.ebscohost.com/login.aspx?direct=true&db=aph&AN=289953&site=ehost-live) • Presence: Teleoperators & Virtual Environments (Journal) (http://search.ebscohost.com/login.aspx?direct=true&db=aph&jid=VTE&site=ehost-live) • Acoustic Radiosity Simulation • A modified radiosity algorithm for integrated visual and auditory rendering (doi:10.1016/0097-8493(93)90112-M) • Samuel Siltanen, TapioLokki, and LauriSavioja, “ACOUSTIC RADIANCE TRANSFER METHOD,” in The 19th International Congress on Acoustics (ICA) (Madrid, 2007), http://www.sea-acustica.es/WEB_ICA_07/fchrs/papers/rba-05-008.pdf. • Building Evacuation Using Sound Cues • Virtual Acoustic Technology: Its Role in the Development of an Auditory Navigation Beacon for Building Evacuation • Building Acoustics (Journal) (http://www.ingentaconnect.com/content/mscp/bac) © Copyright 2009 Anish Chandak

  43. Reading List • Rudolf Rabenstein, Oliver Schips, and ErStenger, “Acoustic rendering of buildings,” in In 5th International Conference on Building Simulation, 1997, 8—10 • Funkhouser, T., Carlbom, I., Elko, G., Pingali, G., Sondhi, M., and West, J. 1998. A beam tracing approach to acoustic modeling for interactive virtual environments. In Proceedings of the 25th Annual Conference on Computer Graphics and interactive Techniques SIGGRAPH '98. ACM, New York, NY, 21-32. • Peter Svensson, "The Early History of Ray Tracing in Room Acoustics". • Funkhouser, Thomas and Tsingos, Nicolas and Jot, Jean-Marc, "Survey of Methods for Modeling Sound Propagation in Interactive Virtual Environment Systems," Presence and Teleoperation, 2003. © Copyright 2009 Anish Chandak

  44. Additional References • Michael Vorländer, Auralization: Fundamentals of Acoustics, Modelling, Simulation, Algorithms and Acoustic Virtual Reality, 2007. • Samuel Siltanen et al., “The room acoustic rendering equation,” The Journal of the Acoustical Society of America 122, no. 3 (2007): 1624-1635, doi:10.1121/1.2766781. • Kajiya, J. T. 1986. The rendering equation. In Proceedings of the 13th Annual Conference on Computer Graphics and interactive Techniques D. C. Evans and R. J. Athay, Eds. SIGGRAPH '86. • U. Krockstadt. Calculating the acoustical room response by the use of a ray tracing technique. Journal of Sound and Vibrations, 8(18):118-125, 1968. • U. Kulowski. Algorithmic representation of the ray tracing technique. Applied Acoustics, 18:449-469, 1984. • Heinrich Kuttruff, Acoustics, 2007.   © Copyright 2009 Anish Chandak

  45. Questions? © Copyright 2009 Anish Chandak

  46. Modeling Sound Material [Embrechts,2001] [Christensen,2005] [Tsingos,2007] © Copyright 2009 Anish Chandak

  47. Sound Source Modeling Volumetric Sound Source Directional Sound Source Complex Vibration Source © Copyright 2009 Anish Chandak

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