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Open-Loop Dereverberation of Multichannel Room Impulse Responses

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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Open-Loop Dereverberation of Multichannel Room Impulse Responses

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  1. 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

  2. Audio Display for a Virtual Reality Theater (Beckman Cube)

  3. Audio Demo (Plywood Cube)

  4. 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

  5. Problem Formulation • Consider a Multichannel System:L sound sources and M control points

  6. Problem Formulation (Continued) • Transfer function G from L sound sources to M control points

  7. Problem Formulation (Continued) • Inverse transfer function H from M desired control points to L sound sources

  8. Problem Formulation (Continued) • Multichannel System from M desired control points to M actual control points

  9. 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 : ^ ^

  10. Problem Formulation (Continued) • How to Estimate the Room Impulse Responses? • How to Find the Inverse Transfer Function H ? ^

  11. Estimation of the Room Impulse Responses: Image Source Method • Two-Dimensional Illustration

  12. 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

  13. 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

  14. Computing the Inverse Transfer Function: Regularization • Add a small constant β to the diagonal components before the inversion :

  15. Computing the Inverse Transfer Function: Modeling Delay • Delay the inverse transfer function to make it a delayed causal sequence

  16. Computing the Inverse Transfer Function Example in 1-D Case

  17. Experiment: 2 X 2 (L = M = 2) Case • Starter Pistol as a Sound Source : Best Approximation of a Point Source

  18. SPL of a Starter Pistol

  19. Comparison of Measured and Simulated Room Impulse Responses (First 20 ms)

  20. Comparison of Measured and Simulated Room Impulse Responses (After 100 ms)

  21. One More Problem: Image Source Method is only Accurate for t < 100 ms

  22. One More Problem: Image Source Method is only Accurate for t < 100 ms • Solution: Apply a Tapering Window

  23. Results: 12 dB Dereverberation

  24. 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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