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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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Estimation of sound source direction using parabolic reflection board

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


Table of contents
Table of Contents Reflection Board

  • Introduction

    • Purpose of Sound-source-direction Estimation

    • Conventional Technique

  • Proposed Method

    • Parabolic Reflection Board

    • Active Microphone

  • Experiments

  • Summary and Future Work


Purpose of sound source direction estimation
Purpose of Sound-source-direction Estimation Reflection Board

  • Noise suppression by forming directivity toward the target signal source

If the system direction of the target signal source, …

Noise disturb the speech recognition

Noise

Directivity

Noise

Speech


Purpose of sound source direction estimation1
Purpose of Sound-source-direction Estimation Reflection Board

Search robot for disaster victims

Estimation of speaker for the meeting system

Help !!

Sound-source-direction estimation technique is necessary for various systems

A is talking now.


Conventional techniques
Conventional Techniques Reflection Board

  • Microphone Arrays

    • Use of simultaneous phase information from microphone arrays to estimate the direction of the signal arrival.

30-channel arrays

32-channel arrays


Proposed method
Proposed Method Reflection Board

Two or more microphones are necessary for conventional method

It is difficult to estimateof the signal arrival using only a single microphone

Goal: Sound-source-direction estimation

using only a single microphone


Proposed method1

Active microphone with Parabolic Reflector Reflection Board

Proposed Method

Diameter: 12cm

Microphone

Rotation

manually

Parabolic reflector

The reflector and its associated microphone rotate together


Parabolic reflection board
Parabolic Reflection Board Reflection Board

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.

Focal point

Focal point


Observed signal at the focal point
Observed Signal at the Focal Point Reflection Board

The signal is coming from directly infront of the parabolic surface

s1 : Direct sound

2d

s2: Reflection sound

Q

P

s2

H

Distance difference between path s1 and s2 to the focal point:

QP+PO = QP+PH = 2d

d : distance of the focal point

s1

-d

O

Focal point

Time difference to the focal point:

a: sound speed

(depending only on ‘d’)

Parabolic surface

Directrix

Time difference for all reflection paths is equal to 2d/a.


Observed signal at the focal point1
Observed Signal at the Focal Point Reflection Board

The signal is coming from directly in front of the parabolic surface

  • Observed signal at the focal point

  • In the frequency domain

  • Power spectrum

Direct sound

Reflection coefficient

Reflection sound

The use of parabolic reflector can increase the power gain of the signal

arriving from the front of the parabolic reflector according to


Observed signal at the focal point2
Observed Signal at the Focal Point Reflection Board

The sound source is not located directly in front of the parabolic surface.

(Input Signal)

P

degrees

O: Focal point

Tangential line

(Reflected Signal)

Parabolic surface

No reflection waves will travel toward the focal point!


Selection of direction having maximum power
Selection of Direction Having Maximum Power Reflection Board

A microphone is set up at the focal point.

The microphone rotates and the power of the target signal observed at each angle is calculated.

The direction having maximum power is selected as the sound source direction.

Rotation manually

Microphone

i : angle of the parabolic reflector


Experiment conditions
Experiment Conditions Reflection Board

Parabola Reflector

Target source: 90 degrees

Source signal: white noise

(5 sec)

Microphone

30cm

Loud speaker

60cm

90cm

The angle of the microphone with the parabolic reflector is changed manually from 0 degrees to 180 degrees at an interval of 10 degrees.


Average power versus angle of microphone
Average Power Versus Angle of Microphone Reflection Board

  • 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.


With without the parabolic reflector
With / Without the Parabolic Reflector Reflection Board

with reflector

without reflector

(The directivity of the microphone is set up opposite the sound source)


3d power spectrum of the observed signal
3D Power Spectrum of the Observed Signal Reflection Board

Low-frequency:

diffraction of the sound wave

Power [dB]

Angle of mic.

[degree]

Frequency [Hz]

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.


Power spectrum of the signal observed without reflector
Power spectrum of the signal observed without reflector Reflection Board

The shape of the spectrum is not flat.


Summary
Summary Reflection Board

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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