estimation of sound source direction using parabolic reflection board 2008 risp international...
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Estimation of Sound Source Direction Using Parabolic Reflection Board
2008 RISP International Workshop on Nonlinear Circuits and Signal Processing (NCSP’08)
6-8 March, 2008 Watermark Hotel, Australia
Tetsuya Takiguchi, Ryoichi Takashima and Yasuo Ariki
Kobe University, Japan
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Table of Contents
Introduction Purpose of Sound-source-direction Estimation Conventional Technique
Proposed Method Parabolic Reflection Board Active Microphone
Experiments Summary and Future Work
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Purpose of Sound-source-direction Estimation
Noise suppression by forming directivity toward the target signal source
Noise disturb the speech recognition
Speech
Noise
Noise
If the system direction of the target signal source, …
Directivity
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Purpose of Sound-source-direction Estimation
Search robot for disaster victims
Estimation of speaker for the meeting system
Help !!
A is talking now.
Sound-source-direction estimation technique is necessary for various systems
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Conventional Techniques
Microphone Arrays Use of simultaneous phase information from
microphone arrays to estimate the direction of the signal arrival.
30-channel arrays 32-channel arrays
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Proposed Method
Two or more microphones are necessary for conventional method
It is difficult to estimate of the signal arrival using only a single microphone
Goal: Sound-source-direction estimation using only a single microphone
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Active microphone with Parabolic Reflector
Proposed Method
Microphone
Parabolic reflector
Diameter: 12cm
The reflector and its associated microphone rotate together
Rotationmanually
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Parabolic Reflection Board
Focal point Focal point
Any wave, where the sound source is located directly in front of the parabolic surface, is reflected toward the focal point.
No reflection waves, where the sound source is not located directly in front of the parabolic surface, will travel toward the focal point.
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Observed Signal at the Focal Point
The signal is coming from directly in front of the parabolic surface
Distance difference between path s1 and s2 to the focal point:
QP+PO = QP+PH = 2d
d : distance of the focal point
s1 : Direct sounds2 : Reflection sound
O-d
HP Q
2d
s1
s2
a
d2Directrix
Focal point
Parabolic surface
Time difference for all reflection paths is equal to 2d/a.
Time difference to the focal point:
a : sound speed
(depending only on ‘d’)
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Observed Signal at the Focal Point
The signal is coming from directly in front of the parabolic surface
Observed signal at the focal point
In the frequency domain
Power spectrum
)()()( tsAtstx
)()()( 2 SeASX j
:)(ts:)( ts :ADirect sound
Reflection soundReflection coefficient
The use of parabolic reflector can increase the power gain of the signalarriving from the front of the parabolic reflector according to )(H
)()(1)()(22222 HSeASX j
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Observed Signal at the Focal Point
The sound source is not located directly in front of the parabolic surface.
O: Focal point
Parabolic surface
P
Tangential line
(Input Signal)
(Reflected Signal)
degrees
No reflection waves will travel toward the focal point!
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Selection of Direction Having Maximum Power
1. A microphone is set up at the focal point.
2. The microphone rotates and the power of the target signal observed at each angle is calculated.
3. The direction having maximum power is selected as the sound source direction.
M
mi
imX
Mi
1 1
2);(log
1maxargˆ
Microphone
i : angle of the parabolic reflector
Rotation manually
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Experiment Conditions
90cm
60cm
30cm
Parabola Reflector
Loud speaker
Microphone
Target source: 90 degrees
Source signal: white noise (5 sec)
The angle of the microphone with the parabolic reflector is changed manually from 0 degrees to 180 degrees at an interval of 10 degrees.
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Average Power Versus Angle of Microphone
•Average log-power spectrum at 90 degrees is maximum value.•The power decreases as the direction of the microphone becomes farther from the direction of the target sound source.
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With / Without the Parabolic Reflector
with reflector
without reflector
(The directivity of the microphone is set up opposite the sound source)
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3D Power Spectrum of the Observed Signal
Pow
er [
dB]
Frequency [Hz] 410x
Angle of mic. [degree]
Effect is not so great for the low-frequency components of the signal.Power spectrum becomes larger as the angle of parabolic reflector is closer to 90 degrees.
Low-frequency: diffraction of the sound wave
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Power spectrum of the signal observed without reflector
0 5 10 15 20 245
10
15
20
25
30
35
40
45
50
55
60
The shape of the spectrum is not flat.
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Summary
A sound-source-direction estimation method using a single microphone only.
New Proposed Method :
Active microphone with parabolic reflection board is able to estimate the sound source direction using only a single microphone.
In future work :
research for short signal (for example, speech)
form of the parabolic reflector
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Comparison with Any Reflector