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Two-Way Acoustic Window using Wave Field Synthesis

Two-Way Acoustic Window using Wave Field Synthesis. Timo Haapsaari. Laboratory of Acoustics and Audio Signal Processing. April 1 0, 2007. Outline. Aims of the project System description Wave Field Synthesis Acoustic echo canceller Performance analysis Results of listening tests

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Two-Way Acoustic Window using Wave Field Synthesis

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  1. Two-Way Acoustic Window using Wave Field Synthesis Timo Haapsaari Laboratory of Acoustics and Audio Signal Processing April10, 2007

  2. Outline • Aims of the project • System description • Wave Field Synthesis • Acoustic echo canceller • Performance analysis • Results of listening tests • Conclusion

  3. Aims of the project • What is a virtual acoustic window?

  4. System description - Hardware

  5. System description - Hardware

  6. Wave Field Synthesis • Originates from Huygens’ principle (1690) • If the effect of a source Ω is known on surface S, sound pressure in volume V can be synthesized with continuous distribution of monopole and dipole sources on surface S

  7. Wave Field Synthesis • Simplification needed for realization • Reducing surface S to a plane (z=0) and further to a line is possible • Using a line array of monopole loudspeakers provides almost correct solution

  8. Wave Field Synthesis • Creation of virtual audio sources with line array of loudspeakers by delaying and attenuating signals accordingly • Wave Field Extrapolation (WFE) • Extrapolation from 4 microphones to 12 loudspeakers • Sources in front the array also possible • Bringing someone ‘through’ the opening next to you

  9. Multichannel acoustic echo canceller

  10. Performance analysis • A real time demonstrator was built • Good localization of multiple sound sources, even in highly reverberant room • Stable echo canceller enables normal conversation • Echo reduction of 5-7 dB achieved in simulations with wide band noise (16 coefficients) • With 64 coefficients: 11-14 dB • Whole system runs on one Pentium4 class PC

  11. Listening Test Description Methods: • Adaptive beamformer (GSC) + WFS • WFE • Close-talk microphones + WFS • Direct playback with two loudspeakers

  12. Listening Test Description Method: Direct playback with two loudspeakers

  13. Listening Test Description Method: Close-talk microphones+WFS

  14. Listening Test Description Method: Adaptive beamformer (GSC)+WFS

  15. Listening Test Description Method: Wave field extrapolation (WFE)

  16. Listening Test Description Aspects: • Spatial naturalness (quality of spatial image) • Coloration • Distance of the sound sources • Separation of the sound sources

  17. Listening Test Results

  18. Listening Test Results

  19. Conclusions • New aspects to communications system • Opening to an another space • Real spatial sound • Persistent communication • Viable solution for home-to-home conversation • With flush-mounted or panel speakers no visible equipment • Room for improvement with echo canceller • Computational load • Longer filters, system specific equalization • Other solutions, e. g. frequency shifter • WFE offers clear potential for usability in acoustic opening

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