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