Two-Way%20Acoustic%20Window%20using%20Wave%20Field%20Synthesis - PowerPoint PPT Presentation

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Two-Way%20Acoustic%20Window%20using%20Wave%20Field%20Synthesis

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Originates from Huygens' principle (1690) If the effect of a source O is known on surface S, sound pressure in volume V ... Reducing surface S to a plane (z=0) ... – PowerPoint PPT presentation

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Title: Two-Way%20Acoustic%20Window%20using%20Wave%20Field%20Synthesis


1
Two-Way Acoustic Window using Wave Field
Synthesis
Timo Haapsaari
Laboratory of Acoustics and Audio Signal
Processing
April 10, 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 O 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 (z0) 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 microphonesWFS

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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