autodirective dual microphone digital signal processing technology to build an optimal directional...
TRANSCRIPT
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.
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Common microphone typesCommon microphone types
Omnidirectional
Hyper-cardioid Super-cardioid
Bi-directional (figure eight) Bi-directional (dB plot)
Cardioid
=
Dis
tan
ce f
act
or
= 1
Dis
tan
ce f
act
or
= 1
.7
Dis
tan
ce f
act
or
= 2
.0
Dis
tan
ce f
act
or
= 1
.9
Dis
tan
ce f
act
or
= 1
.7
Null
Null
Null
Null
Null
Null
Null
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The Optimal Directivity MicrophoneThe Optimal Directivity Microphone
AbilityAbility: automatically change: automatically change the directivity pattern the directivity pattern
ObjectiveObjective: the best: the best signal-to-noise ratio in signal-to-noise ratio in varying acoustic conditions. varying acoustic conditions.
ChallengeChallenge: Fast adaptation: Fast adaptation with minimal distortion with minimal distortion
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Electronic Directional MicrophoneElectronic Directional Microphone
F(t)
-
R(t)
D(t)
Plain wave
d
S(t) +
=T
=0.5T
=0
)1)((),( )cos(2 TfjefSfY
2
)cos(2sin)(2),(
TffSfY
velocitysound,/ ccdT
cos),(
,1/:Assuming
TffP
Tcfd
Normalized polar pattern as a function of (fixed frequency)
Delay
EQ(,)
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Autodirective Dual MicrophoneAutodirective Dual Microphone
Autodirective Dual Microphone schematic
F(t)
DSP
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)
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 band
4.4. Combine from bandsCombine from bands
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Adaptive Directivity BlockAdaptive Directivity Block
-
Delay
+
rk(n)
rk(n-)
Control
fk(n) dk(n)
g( n, , )
s
cos),( TffP
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
330
340
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
Ad
dit
ion
al P
roc
ess
ing
Additional ProcessingAdditional Processing Noise 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 (<5ms)Low latency (<5ms)
No proximity effectNo proximity effect
Low sensitivity to wind and other turbulencesLow sensitivity to wind and other turbulences
Easy integration with other Alango technologiesEasy integration with other Alango technologies
Low demands to constituting SPL sensorsLow demands to constituting SPL sensors
Easy integration into mobile and other devicesEasy integration into mobile and other devices
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ADM applicationsADM applications
Cellular 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
Reporter’s microphoneReporter’s 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
Hands-free car kitsHands-free 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 mic) (regular mic)
In the close-talk (handset ) mode, ADM creates “Bubble Of Sensitivity” (BOS) muting outside sounds
ADMADM
Microphones
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 mic) (regular mic)
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: [email protected]