AAutodirective utodirective DDual ual MMicrophoneicrophone

DDigital igital SSignal ignal PProcessing technology to build rocessing technology to build an optimal directional microphonean optimal directional microphone

Presented by Alexander Goldin

Copyright © 2003 Alango Ltd.

2

Common microphone typesCommon microphone types

Omnidirectional

Hyper-cardioid Super-cardioid

Bi-directional (figure eight) Bi-directional (dB plot)

Cardioid

=

Dis

tanc

e fa

ctor

= 1

Dis

tanc

e fa

ctor

= 1

.7

Dis

tanc

e fa

ctor

= 2

.0

Dis

tanc

e fa

ctor

= 1

.9

Dis

tanc

e fa

ctor

= 1

.7

Null

Null

Null

Null

Null

Null

Null

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The Optimal Directivity MicrophoneThe Optimal Directivity Microphone

AbilityAbility: automatically change: automatically changethe directivity patternthe directivity pattern

ObjectiveObjective: the best: the bestsignalsignal--toto--noise ratio innoise ratio invarying acoustic conditions.varying acoustic conditions.

ChallengeChallenge: Fast adaptation: Fast adaptationwith minimal distortionwith minimal distortion

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Electronic Directional MicrophoneElectronic Directional Microphone

F(t)

-

R(t)

D(t)

Θ

Plain wave

d

S(t) +

ττττ =T

ττττ =0.5T

ττττ =0

)1)((),( )cos(2 Θ+−−=Θ TfjefSfY τπ

2)cos(2sin)(2),( Θ+=Θ TffSfY τπ

velocitysound,/ −= ccdT

Θ+≈Θ

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Autodirective Dual MicrophoneAutodirective Dual Microphone

Autodirective Dual Microphone schematic

F(t)

DSP

Θ

Sound wave

d

S(t) A/D

R(n)

F(n) D(n)

R(t)

A/D

ADB 1

ADB M

f1(n)

fM(n)

r1(n)

rM(n)

d1(n)

dM(n)

R(n)

F(n)

D(n)

BPF 1

BPF M

BPF 1

BPF M

+

Adaptive Directivity

Blocks

DSP based dual microphoneDual microphone with variable polar pattern

F(t)

-

R(t)

D(t)

Θ

Sound wave

d

S(t) +

Delay

EQ( ,)

1.1. Divide both channels Divide both channels on subbandson subbands

2.2. Create an optimal Create an optimal microphone in every microphone in every frequency bandfrequency band

3.3. Equalize every bandEqualize every band4.4. Combine from bandsCombine from bands

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Adaptive Directivity BlockAdaptive Directivity Block

- Delay ττττ

+

rk(n) τ

rk(n-τ)

Control

fk(n) dk(n)

××××

g( n, τ, )

s

××××

Θ+≈Θ cos),( TffP τ

Adaptive Directivity Block schematic

ADB 1

ADB M

f1(n)

fM(n)

r1(n)

rM(n)

d1(n)

dM(n)

R(n)

F(n)

D(n)

BPF 1

BPF M

BPF 1

BPF M

+

Adaptive Directivity

Blocks

1.1. Estimate sensor difference Estimate sensor difference (gain “(gain “ss”)”)

2.2. Define the optimal delay “Define the optimal delay “ ””

3.3. Compute equalization gain “Compute equalization gain “gg” ” according to according to and and ;;

Autodirective Dual Microphone schematic

ADB functionalityADB functionality::

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Measured ADM polar patternMeasured ADM polar pattern

-30 -20 -10

0 10 0

10 20

30 40

50

60

70

80

90

100

110

120 130

140 150

160 170 180 190 200

210

220 230

240

250

260

270

280

290

300

310 320

330340 350

250Hz 500 Hz 1000 Hz 1500 Hz 2000 Hz 3000 Hz 4000 Hz

Ideal bi-directional (figure 8) pattern

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ADM and other Alango technologiesADM and other Alango technologies

ADB 1

ADB M

f1(n)

fM(n)

r1(n)

rM(n)

d1(n)

dM(n)

R(n)

F(n)

D(n)

BPF 1

BPF M

BPF 1

BPF M

+

Adaptive Directivity

Blocks

Addi

tiona

l Pro

cess

ing

Additional ProcessingAdditional ProcessingNoise SuppressionNoise Suppression

Multiband Dynamic Multiband Dynamic Range ReductionRange Reduction

Automatic Gain ControlAutomatic Gain Control

Other Alango technologies use the same Other Alango technologies use the same subband decomposition scheme.subband decomposition scheme.

Integration of technologies is easy without Integration of technologies is easy without extra MIPS, Memory or time delay required.extra MIPS, Memory or time delay required.

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ADM: summary of virtuesADM: summary of virtues

An optimal, adaptive polar pattern with a very An optimal, adaptive polar pattern with a very low adaptation time (around 5ms)low adaptation time (around 5ms)

Far and close talk operationsFar and close talk operations

Low latency (

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ADM applicationsADM applicationsCellular PhonesCellular Phones

ADM is perfect for cellular phones. ADM technology significantly improves signal quality for both speakerphone (far-talk) and handset (close-talk) phone usage.

Mic.2

Mic.1

Hearing aidsHearing aidsADM works very well in hearing aids. It provides high attenuation of ambient noise and other off-axis sounds. Mic.1 Mic.2

ReporterReporter’’s microphones microphoneADM excellent and adaptive directivity combined with its immunity to wind noise makes it ideal technology for such application.

Conference microphoneADM excellent directivity, lack of proximity effect and low sensitivity to popping and puffing sounds eliminates most of conference microphone problems.

Mic.2

Mic.1

HandsHands--free car kitsfree car kitsADM high directivity, immunity to wind noise and low components cost provides provides unparallel benefits

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ADM in cellular phonesADM in cellular phones

Outside BOSOutside BOS(regular (regular micmic) )

In the close-talk (handset ) mode, ADM creates “Bubble Of Sensitivity” (BOS) muting outside sounds

ADMADMMicrophones

Inside BOSInside BOS(ADM) (ADM)

Beam Of Beam Of SensitivitySensitivity

(BOS)(BOS)

In the far-talk (speakerphone ) mode, ADM creates “Beam Of Sensitivity” (BOS) attenuating outside soundsOutside BOSOutside BOS(regular (regular micmic) )

Inside BOSInside BOS(ADM) (ADM)

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Alango contact informationAlango contact information

www.alango.com

Headquarters: Edgar 1, Tirat-Carmel 39100, Israel

Telephone: +972 4 8580743

Fax: +972 4 8580621

e-mail: sound.info@alango.com