echo and bounce
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Presentation
• About 15 Minutes of PowerPoint
• 5 Minutes of video and demonstration
• Please ask questions at any time
An Audio Proxy
• This project will explore the idea of using an audio proxy
• A proxy to generate sound
VisualProxy
PhysicalProxy
AudioProxy
Realistic Movement Realistic SoundRealistic Graphics
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)
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
What is an Audio Proxy
• What is an audio proxy made of?– Masses and Springs– Tetrahedra
• How do we build one?
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
Natural Length
3D Meshes
• A triangular mesh can approximate any 3D surface
• Commonly used in graphics
• Just a skin:– No Volume– No Density
Tetrahedra
• A Tetrahedron is a 4 sided shape(Triangular based pyramid)
• Made from 4 triangles
• Collection of tetrahedra can approximate any 3D volume
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
Sound Generation
For each face:• Find displacement at each
vertex• Find average displacement• Multiply by area
Wave ampltiude =(Average displacement * area)
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
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 zeroAudio Buffer
Do 5 simulation steps, then send audio to sound card.
(unsigned short) -0.00007f = 65536
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)
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
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
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
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
tt
1
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:
mst