OpenLoop Dereverberation of Multichannel Room Impulse Responses Bowon
Open-Loop Dereverberation of Multichannel Room Impulse Responses Bowon Lee, Mark A. Hasegawa-Johnson, and Camille Goudeseune Department of Electrical and Computer Engineering Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign
Audio Display for a Virtual Reality Theater (Beckman Cube)
Audio Demo (Plywood Cube)
Introduction q Free-Field Audio Display q Sound Control at Multiple Points q Open-Loop Inversion of Room Impulse Responses q Image Source Method to Estimate Room Impulse Responses
Problem Formulation q Consider a Multichannel System: L sound sources and M control points
Problem Formulation (Continued) q Transfer function G from L sound sources to M control points
Problem Formulation (Continued) q Inverse transfer function H from M desired control points to L sound sources
Problem Formulation (Continued) q Multichannel System from M desired control points to M actual control points
Problem Formulation (Continued) q We do not know the transfer function G, a matrix of exact room impulse responses q Create inverse H^ using the estimation of the room impulse responses G^ instead of G :
Problem Formulation (Continued) q How to Estimate the Room Impulse Responses? q How to Find the Inverse Transfer Function H^ ?
Estimation of the Room Impulse Responses: Image Source Method q Two-Dimensional Illustration
Image Source Method (Continued) q : Reflection coefficient of the wall (uniform) q : Index of the image source location q : Distance between the image source and receiver q : Impulse arrival time
Computing the Inverse Transfer Function q Room impulse responses are non-minimum phase in most cases q Therefore, they are not exactly invertible q Solution: Use regularization and modeling delay
Computing the Inverse Transfer Function: Regularization q Add a small constant β to the diagonal components before the inversion :
Computing the Inverse Transfer Function: Modeling Delay q Delay the inverse transfer function to make it a delayed causal sequence
Computing the Inverse Transfer Function Example in 1 -D Case
Experiment: 2 X 2 (L = M = 2) Case q Starter Pistol as a Sound Source : Best Approximation of a Point Source
SPL of a Starter Pistol
Comparison of Measured and Simulated Room Impulse Responses (First 20 ms)
Comparison of Measured and Simulated Room Impulse Responses (After 100 ms)
One More Problem: Image Source Method is only Accurate for t < 100 ms
One More Problem: Image Source Method is only Accurate for t < 100 ms q Solution: Apply a Tapering Window
Results: 12 d. B Dereverberation
Summary q Open-Loop Inversion of Room Impulse Responses q Estimation of Room Impulse Responses by Image Source Method q Measurement of Room Impulse Responses using a Starter Pistol q 12 d. B Dereverberation
- Slides: 24