1. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Computation of room acoustics using programable video hardware Marcin Jędrzejewski Krzysztof Marasek

2. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Presentation plan Acoustics computational methods Graphical Processing Unit ( GPU ) – programming model Used acoustic model Used algorithms and data structures Implementation on GPU Results Conclusions and further work Demo movie

3. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Room acoustics Geometrical methods - Beam tracing Not very scaleable Ray tracing Point sound source Receiver aproximated by sphere Each position change requires recomputation - Image sources Computationally ineffective Echogram:

4. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Room representation 3D geometry Walls are made of polygons Each wall contains information on its absorption coeficient Scene contains also positions of sound source and receiver

5. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair GPU – programming model Streaming processor - the same program is executed parallely but with different data on input. Each program produces output data. Programs that are executed are also known as kernels or Pixel Shaders HLSL as programming language, very similar to C++ Input and output data is stored in a form of textures which are blocks of memory stored on video card

6. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Program execution Data (like rays) are loaded to input texture Quad (rectangle composed of two triangles) is rendered, for each processed texel, pixel shader is executed HLSL program can read from many different textures but can write up to 16 floating point values (using MRT) Many passes of this algorithm

7. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Acoustics model One frequency band is used for material absorption High number of reflections (~15 - 25) No diffraction, refraction, diffusion – purely specular model

8. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Space division algorithms used Constructive Solid Geometry (CSG) : to remove all illegal geometry Binary Space Partitioning (BSP) : to partition space into convex subspaces Portal calculation – to find ways between subspaces Further subspaces division required for efficient GPU implementation

9. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Execution flow 1.CSG, BSP, Portals,... 2.Generation of rays on sphere surface, uploading textures to video card 3.Propagation of rays through portals and reflecting them from walls 4.Retrieving video memory with computed rays and building echogram 5.Using echogram to generate spatial sound Loading textures: state data and data structures Data structures computation Multipass rendering Building echogram Auralization Real time Precomputation phase 1 2 3 4 5

10. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Results Almost 100 mln ray - triangle intersections checks per second Computation of above 16000 rays with 10 reflections in two room enviroment takes ~30ms ModelPoly countPrecomputationCPUGPU Two rooms241,4s0,5s0,016s House1921,89s0,37s0,025s Office3904,54s0,82s0,027s Church3901,09s0,82s0,033s

11. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair

12. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Conclusions and further work Real-time computation of echogram with the use of ray tracing algorithm CPU can execute other code parallely when GPU is computing ray reflections Making use of NVIDIA Geforce 6800 or ATI X800 cards Making use of PCI-Express architecture (even 16ms speed up possible) Mapping cone or pyramid tracing algorithms for early reflections and using raytracing for late reverberation Better optimizations with model 3 of PS and VS

13. M. Jędrzejewski, K.Marasek, Warsaw ICCVG, 22-24.09.2004 Multimedia Chair Demo movie