Patrones Polares Microfonos

7/27/2019 Patrones Polares Microfonos

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Microphone Techniques forStereo and Multichannel

Geoff Martin

Bang & Olufsen, Denmark


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What well look at How microphones behave

Monitoring environment What different microphoneconfigurations do for you

If something doesnt make sense,stop me and ask at any time!


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What is sound? Todays barometric pressure is

about 100 kPa

Sound is a change in that pressureover time

A microphone converts that pressure

change into a voltage change


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How to make a barometer

Airtight can Balloon


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How to make a barometer

Voltage

Voltage

Voltage

pressuremicrophone


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How to make a pressure microphone


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Pressure Microphone - Sensitivity

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Angle ofincidence

Sensitivity

(gain)

Sensitivity

S = 1

Angle of Incidence


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0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0

Pressure microphone - Sensitivity

Angle ofincidence

Sensitivity

Omnidirectional

S = 1


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Lets start again Well build another barometer

but this time without the sealed can

This means we are measuring thedifference in pressure on the front andback of the diaphragm

Pressure Difference = Pressure Gradient


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Pressure Gradient microphone - Construction

Supportingring Diaphragm


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Pressure Gradient microphone - Output

Voltage

Voltage

Voltage


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Pressure Gradient microphone - Sensitivity

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Angle of Incidence

Sensitivity

S = cos(angle)


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Pressure Gradient microphone - Sensitivity

0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0

Bidirectional

S = cos(angle)


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-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Lets add them

Angle of Incidence

Sensitivity


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Half-omni, half-bidirectional

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Angle of Incidence

Sensitivity

S = 0.5 + 0.5 cos(angle)


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0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0

Half-omni, half-bidirectional

S = 0.5 + 0.5 cos(angle)

Cardioidmicrophone


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Make your own Polar Patterns

100%0%Bidirectional

75%25%Hypercardioid

50%50%Cardioid

25%75%Subcardioid0%100%Omnidirectional

Pressure Gradient

(Bidirectional)

Pressure

(Omnidirectional)


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Polar Patterns

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1Omnidirectional

Subcardioid

Cardioid

Hypercardioid

Bidirectional


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-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Omnidirectional

0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0


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Subcardioid

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0


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Cardioid

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0


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Hypercardioid

0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


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Bidirectional

0.2

0.4

0.6

0.8

1

30

210

60

240

90

270

120

300

150

330

180 0

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


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Localisation in the real world

Left-right localisation relies on: Interaural time of arrival differences

(ITD) Interaural amplitude differences (IAD)

Front-back localisation relies on: Head rotation cues

Reflections off the pinnae Shoulder reflections


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Localization in the reproduced world

Phantom imagelocalization relies on:

Interchannelamplitude differences

Interchanneltime differences


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One version

or

or

or

or

or

1.12 ms15 dB30

0.44 ms5.5 dB20

0.2 ms2.5 dB10

0.0 ms0.0 dB0

! Time! Amp.Image position

Gert Simonsen 1983


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Other versionsInterchannel Amplitude vs. Phantom Image Angle

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70 80 90 100

Percentage of distance to loudspeaker

AmplitudeDifference(dB)

Simonsen (1984)

Webers (1968)

Theile (1988)

de Boer (1940)

Sengpiel (1992)


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Other versionsInterchannel Time Difference vs. Phantom Image Angle

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 10 20 30 40 50 60 70 80 90 100

Percentage of distance to loudspeaker

InterchannelTimeDifference(m

s)

Simonsen (1984)

Sengpiel


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Coincident Microphones

We assume identical time of arrival

Sensitivity differences produceinterchannel amplitude difference

S1

S2DS = 20 log10

Sn = Pn + Gn cos (!+"n)

!

!


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-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-150 -100 -50 0 50 100 150

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

90 Cardioids - Sensitivity Difference

Difference inSensitivity


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-150 -100 -50 0 50 100 150-60

-40

-20

0

20

40

60

-150 -100 -50 0 50 100 150-15

-10

-5

0

5

10

15


DifferenceinSensitiv

ity(dB)

Angle of Incidence ()


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A

ngleofElevation(deg)



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0 dB

5 dB

10 dB

15 dB

-5 dB

-10 dB

-15 dB


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-150 -100 -50 0 50 100 150

-30

-20

-10

0

10

20

30

-150 -100 -50 0 50 100 150

-30

-20

-10

0

10

20

30

90 Bidirectionals - Sensitivity Difference


S

ensitivityDiffere

nce


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-150 -100 -50 0 50 100 150

-30

-20

-10

0

10

20

30


S

ensitivityDiffere

nce

Same Polarity(in phase)

Opposite Polarity(Out of phase)


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0 dB

5 dB

10 dB

15 dB

-5 dB

-10 dB

-15 dB


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90 Hypercardioids - Sensitivity Difference

0 dB

5 dB

10 dB

15 dB

-5 dB

-10 dB

-15 dB


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Spaced Omnidirectionals - Time Difference

We assume identical amplitudes

Differences in distance to the

source produceinterchannel timedifference

!

d

D

D = dsin !

"T = D / c


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Time difference for 40 cm spacing


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Time difference for 40 cm spacing

0 ms

1 ms

2 ms

-1 ms

-2 ms


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Gain

Summ

ed

Pow

er

PanningLeft Right


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Coincident Microphones - Power Sum

SPower= 10 log10 (S12 + S22)

Sn = Pn + Gn cos (!+"n)!

!


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90 Cardioids - Power Sum

0

-10

-20

-30

-40

Summedpower(dB)


0 50 100 150-150 -100 -50

10


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-6 dB

-3 dB0 dB

+3 dB

-9 dB

-12 dB

-15 dB


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90 Bidirectionals - Power Sum

0

-10

-20

-30

-40

Sum

medpower(dB

)


0 50 100 150-150 -100 -50

10


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-10 dB

0 dB

-20 dB

-30 dB

-40 dB


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Correlation Coefficient An indicator of the relationship between two signals

Positive correlation: if one goes up, so does the other

Negative Correlation: If one goes up, the other goesdown

Correlation = 0: if one goes up, we dont know whatthe other will do

Geeky definition: the covariance divided by theproduct of the standard deviations


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Correlation Coefficient


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Correlation coefficient

Coincident directional mics, direct sound

Coincident mics have identical time ofarrival

Only differences are: Amplitude

Polarity

Correlation coefficient must be either1, 0 or -1


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Spaced mics, direct sound

Spaced mics have different times of arrival

This results in a phase difference

CorrelationCoefficient

Frequency (Hz)10

210

310

4

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


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Coincident directional, diffuse field

OmniSubcardioid

Cardioid

HypercardioidBidirectional


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30 cm spaced omnis in a diffuse field


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Conclusions Every recording situation requires a different

microphone configuration

Treat standard or textbook configurations only as

suggestions Understand the behaviour of the microphones and

their configuration but

Trust your ears!

www.tonmeister.ca/research www.hauptmikrofon.de

Michael Williamss AES papers


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Fukada TreeC (Card)

R / RS(Omni)

L(Card)

LS(Card)

L / LS(Omni)

a=b=c = 1 - 1.5 md = 0 - 2 m

L / R angle = 110 - 130

LS / RS angle = 60 - 90

d

a

bc b c

R(Card)

RS(Card)

d


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OCT Surround C(Card)

R(Hyper)

L(Hyper)

a = 8 cmb = 40 - 90 cm

c = 40 cm

d = 10 - 100 cm

a

b

RS(Card)

LS(Card)

c

d

b

d


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OCT Frontsystem + Hamasaki Square

a = 8 cm

b = 40 - 90 cm

c = ~100 cmCross side = 2 - 3 m

C(Card)

R

(Hyper)L

(Hyper) ab

RS

(Bi)LS(Bi)

c

b

R(Bi)

L(Bi)


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OCT Frontsystem + IRT CrossC(Card)

R(Hyper)

L(Hyper)

a = 8 cmb = 40 - 90 cm

c = ~100 cm

Cross side = 20 - 25 cm

a

b

RS(Card)

LS(Card)

c

b

R(Card)

L(Card)


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Klepko TechniqueC

(Hyper)R

(Hyper)L

(Hyper)

a = 17.5 cm

b = 125 cmL/R Angle +/- 30

a

RSLS

b

a


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Corey / Martin Tree C(Subcard) R

(Subcard)L

(Subcard)

a = 0 - 15 cmb = 60 - 80 cm

c = 60 - 90 cm

d = 30 cm

ab

RS(Card)

Aimed upwards

LS(Card)

Aimed upwards

c

b

d


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Martin Tree C(Bi - pointing downwards)

R(Bi)

L(Bi)

a = < 70 cm

LS/RS angle = 45 - 90

a

RS

(Bi)

LS

(Bi)

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Patrones Polares Microfonos