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