Copyright 2004 Ken Greenebaum Introduction to Interactive Sound Synthesis Lecture 24:Environment Ken Greenebaum

Copyright 2004 Ken Greenebaum And then there were 2 Two Classes left! Two Classes left! Discuss ambience/spatialization Discuss ambience/spatialization Final Review/Discussion Final Review/Discussion

Copyright 2004 Ken Greenebaum Assignment 7 revealed Many asked about the variable FIR filter Many asked about the variable FIR filter

Copyright 2004 Ken Greenebaum Filter design w/o DSP Use filter design sw like DSPlay Use filter design sw like DSPlay Design range of filters Design range of filters

Copyright 2004 Ken Greenebaum DSPlay 1Hz,1,2,3,4,5,6,7,8,9,10,20kHz

Copyright 2004 Ken Greenebaum 20kHz cutoff 48kHz sampling 31 order: 31 order: 500 order: 500 order:

Copyright 2004 Ken Greenebaum What did we observe? Symmetry Symmetry Leads to linear phase response Leads to linear phase response Resemble sinc function Resemble sinc function Narrower the main lobe Narrower the main lobe Sharper transition from pass to stop band Sharper transition from pass to stop band

Copyright 2004 Ken Greenebaum Recall FT of ideal low pass filter FT of ideal low pass filter Resembles sinc function Resembles sinc function Cutoff freq bounded between Cutoff freq bounded between DC and Nyquist DC and Nyquist We are dealing with noise We are dealing with noise Our solution isn’t critical Our solution isn’t critical

Copyright 2004 Ken Greenebaum Variable filter Solutions Solve for each using classic methods Solve for each using classic methods Delay/window Delay/window Solve optimally for parameter space Solve optimally for parameter space Create N-dimensional model Create N-dimensional model OR OR Solve for N cutoff frequencies Solve for N cutoff frequencies Cross fade between adjacent filters Cross fade between adjacent filters

Copyright 2004 Ken Greenebaum Reading more DESIGN AND IMPLEMENTATION OF VARIABLE FIR FILTERS DESIGN AND IMPLEMENTATION OF VARIABLE FIR FILTERS Djordje Babic Djordje Babic AudioAnecdotes: Rate Conversion

Copyright 2004 Ken Greenebaum Environment Synthesis is only one element Synthesis is only one element To fully model sound we need to: To fully model sound we need to: Synthesize sound Synthesize sound Called Raw or Dry sound Called Raw or Dry sound Model the environment Model the environment How sound is modified by the space How sound is modified by the space Model perception Model perception True 3D requires a pineal model True 3D requires a pineal model

Copyright 2004 Ken Greenebaum Environmental Modeling Atmospheric Losses Atmospheric Losses Delay Delay Echoes Echoes Near and distant Near and distant Occlusion Occlusion Doppler Doppler

Copyright 2004 Ken Greenebaum Environmental Modeling Freq specific atmospheric attenuation Freq specific atmospheric attenuation Modeled using low pass filter Modeled using low pass filter Delay Delay Straightforward for stationary objects Straightforward for stationary objects Occlusion Occlusion Considerably more complicated Considerably more complicated Refraction Refraction More complicated yet More complicated yet

Copyright 2004 Ken Greenebaum Delay Easy to compute object to ear delay Easy to compute object to ear delay Humans quite sensitive to phase information Humans quite sensitive to phase information Sample accuracy needed for high frequencies Sample accuracy needed for high frequencies Will discuss techniques Will discuss techniques

Copyright 2004 Ken Greenebaum Ray tracing sound More complicated than ray tracing light More complicated than ray tracing light Wavelength of sound significant Wavelength of sound significant Compared to size of objects modeled Compared to size of objects modeled Similar to lasers and small slits or holes Similar to lasers and small slits or holes Soundwaves interact destructively Soundwaves interact destructively Similar to coherent light interactions Similar to coherent light interactions

Copyright 2004 Ken Greenebaum Beam tracing sound 2 primitive sound sources 2 primitive sound sources Omni directional radiator Omni directional radiator Point source Point source Planar radiator Planar radiator Plane Plane Trace sound’s wavefronts & interactions Trace sound’s wavefronts & interactions

Copyright 2004 Ken Greenebaum Wavefront modeling sound models: Attenuation Attenuation Delay Delay Refraction Refraction Diffraction Diffraction Occlusion Occlusion Echo Echo Doppler Doppler

Copyright 2004 Ken Greenebaum Wavefront simulation Akin to digital (synthetic) holography Akin to digital (synthetic) holography Output may be: Output may be: Photographically reduced to wavelength scale Photographically reduced to wavelength scale Illuminated by reconstruction beam Illuminated by reconstruction beam To re-generate the true 3D object To re-generate the true 3D object

Copyright 2004 Ken Greenebaum Example synthetic hologram Enlarged: Enlarged:

Copyright 2004 Ken Greenebaum Sonic Holography Sometimes called STSF Sometimes called STSF Spatial transformation of sound fields Spatial transformation of sound fields Measure using an array of microphones Measure using an array of microphones Matched to < 5 degree phase Matched to < 5 degree phase Spacing < ½ wavelength of highest freq Spacing < ½ wavelength of highest freq

Copyright 2004 Ken Greenebaum Reproducing Doppler Can be accomplished w/o explicit Freq shift Can be accomplished w/o explicit Freq shift Frequency shifting Frequency shifting “falls out of the model” “falls out of the model” Based on O’Brien SIGGRAPH 2001 Based on O’Brien SIGGRAPH 2001

Copyright 2004 Ken Greenebaum Sound from physical vibration Accumulation buffer: Accumulation buffer:

Copyright 2004 Ken Greenebaum Accumulation buffer Doppler Add each pressure sample to accumulation buffer Add each pressure sample to accumulation buffer To location based on propagation delay To location based on propagation delay Based on sample rate and propagation Based on sample rate and propagation Put appropriate energy into adjacent buckets Put appropriate energy into adjacent buckets Filter to remove DC component Filter to remove DC component Otherwise object moving at constant rate would continue to build pressure Otherwise object moving at constant rate would continue to build pressure

Copyright 2004 Ken Greenebaum Accumulation buffer Doppler Red shift recession Red shift recession Automatically makes wavefronts farther apart Automatically makes wavefronts farther apart Effectively lowering the perceived frequency Effectively lowering the perceived frequency