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Echo and Bounce

Echo and Bounce. Marc O’Morain. Presentation. About 15 Minutes of PowerPoint 5 Minutes of video and demonstration Please ask questions at any time. A Rabbit. A Visual Proxy. A Physical Proxy. An Audio Proxy. This project will explore the idea of using an audio proxy

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Echo and Bounce

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  1. Echo and Bounce Marc O’Morain

  2. Presentation • About 15 Minutes of PowerPoint • 5 Minutes of video and demonstration • Please ask questions at any time

  3. A Rabbit

  4. A Visual Proxy

  5. A Physical Proxy

  6. An Audio Proxy • This project will explore the idea of using an audio proxy • A proxy to generate sound Visual Proxy Physical Proxy Audio Proxy Realistic Graphics Realistic Movement Realistic Sound

  7. Past Research • Synthesizing Sounds from Rigid-Body Simulations. • O'Brien, J. F.Shen, C., Gatchalian, (SIGGRAPH 2002) • Synthesizing Sounds from Physically Based Motion. • O'Brien, J. F., Cook, P. R., Essl G., (SIGGRAPH 2001) • FoleyAutomatic: Physically-based Sound Effects for Interactive Simulation and Animation • K. van den Doel, P. G. Kry and D. K. Pai, (SIGGRAPH 2001)

  8. Why? • Why is this useful? • No need to record sounds • Information needed is in physics engine already • What is new? • Level of detail • Using mass springs – no pre-computation

  9. What is an Audio Proxy • What is an audio proxy made of? • Masses and Springs • Tetrahedra • How do we build one?

  10. Mass Spring Mass Spring System

  11. Natural Length Mass Spring System • When a spring is at rest it has no resultant effect on masses • When compressed, pushes two masses away from each other • When extended, pulls two masses toward each other

  12. 3D Meshes • A triangular mesh can approximate any 3D surface • Commonly used in graphics • Just a skin: • No Volume • No Density

  13. Tetrahedra • A Tetrahedron is a 4 sided shape (Triangular based pyramid) • Made from 4 triangles • Collection of tetrahedra can approximate any 3D volume

  14. Mass Spring Tetrahedra • Create tetrahedra from mass-spring system: • Soft body of any shape can be created • This is how all objects in the project are represented

  15. of a second 65536 16-bit 0 Digital Audio + - Time Amplitude

  16. Sound Generation Sound Generation

  17. Sound Generation Apply A Force Resultant Vibration

  18. Sound Generation For each face: • Find displacement at each vertex • Find average displacement • Multiply by area Wave ampltiude = (Average displacement * area)

  19. Vibration to Sound Time

  20. Up Sampling • Take samples at quite a low granularity • Fit a hermite curve to the sample data • Re-sample from curve at higher resolution • Sample at CD-quality

  21. Audio Buffer Do 5 simulation steps, then send audio to sound card. 1st Major Problem • The Sound was crackling • Reason: • Hermite curve blends between 4 values • Don’t know what is coming in the future • Assume Zero • Curve goes below zero (unsigned short) -0.00007f = 65536

  22. A Click @ 33Hz 65536 16-bit 0

  23. Simulation Simulation

  24. Mass Stability • Each Mass in the system has a ‘short term memory’ (Last 5 timesteps) • At each timestep: current movement is added to memory • If the mass does not remember moving: • It is ‘stable’ • Masses will stay stable until an external force acts on them (Newtons 1st Law)

  25. Audio Proxy Stability • Simulating a stable mass is free • If all the masses are stable, the entire proxy is stable • Simulating a stable proxy is free

  26. A Physics Engine • This is not a physics engine • All external forces will come from a physics engine • When a collision happens, the physics engine will provide: • The Point of collision • A Force

  27. Objects in Model Space • All objects are kept in model space • (All at the origin) • All models are independent from each other • Simulate all models seperately

  28. Levels of Detail Levels of Detail

  29. Levels of Detail Because this project uses: • Up sampling • Separate Models Different timesteps for each model: • Small timestep for close objects • Larger timestep when further away

  30. Different Sampling Rates Low Sampling Rate Higher Sampling Rate

  31. Levels of Detail • Simulation time is proportional to: • Number of masses in the system • Number of springs in the system • System with s springs and m masses: • Time t per calculation is:

  32. Levels of Detail 6 Tetrahedra 24 Tetrahedra 166 Tetrahedra

  33. Variable Level Of Detail Listener is far away – Low level of detail

  34. Variable Level Of Detail Listener is medium distance - Higher level of detail

  35. Variable Level Of Detail Listener is very close - Highest level of detail

  36. Resonance

  37. Top View 3D View Front View Side View A Screenshot

  38. A Screenshot Sound Wave (Left and right channels)

  39. A Screenshot Field Of Vision (Blue Cone)

  40. A Screenshot Level of Detail Selection

  41. A Screenshot Click to apply a force

  42. Echo and Bounce Now for some videos and a demonstration

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