16 November 2012 Acoustical Parameters (ISO 3382) 1

Acoustical parameters Acoustical parameters ISO 3382ISO 3382

16 November 2012 Acoustical Parameters (ISO 3382) 2

ISO 3382 acoustical parameters

16 November 2012 Acoustical Parameters (ISO 3382) 3

From Impulse Response to Sound Decay

• Schroeder’s backward integral

• Makes it possible to reconstruct the decay of a stationary source by backward integration of the measured impulse response

0

A

B

t

g t d t2

0' '

g t d tt

2 ' '

g t d tt

2

0' '

16 November 2012 Acoustical Parameters (ISO 3382) 4

Schroeder’s BW IntegrationPressure Impulse Response

Energetic Impulse Response (in dB)

Stationary Sound Decay (in dB)

Reverberation time T20

Lp (dB)

Time (s)

45 dB

-5 dB

-25 dB

T20

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16 November 2012 Acoustical Parameters (ISO 3382) 6

ISO 3382 Reverberation Time(s)

Early Decay Time (EDT): extrapolated from 0 to -10 dB Reverberation Time T10: extrapolated from -5 to -15 dB Reverberation Time T20: extrapolated from -5 to -25 dB Reverberation Time T30: extrapolated from -5 to -35 dB

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Early – Late energy evaluationUseful Energy Detrimental Energy

16 November 2012 Acoustical Parameters (ISO 3382) 8

Early-Late parameters

ms

ms

dττp

dττp

C

80

2

80

0

2

80 lg10

Clarity Index C80 (symphonic music):

Clarity Index C50 (speech):

Optimal Value = +/- 1 dB

Optimal Value = +/- 1 dB

ms

ms

dττp

dττp

C

80

2

50

0

2

50 lg10

16 November 2012 Acoustical Parameters (ISO 3382) 9

Early-Late parameters

Center Time tS:

0

2

0

2

dp

dp

ts

100

dp

dp

D

0

2

ms50

0

2

Definition Index D:

Other acoustical parameters

• Strenght: dB31LSPLG w

dthdh

dthh

t

2s

2d

sd

IACC:

SPL at 10 m

16 November 2012 Acoustical Parameters (ISO 3382) 10

16 November 2012 Acoustical Parameters (ISO 3382) 11

Other acoustical parameters

ms

ms

W

ms

ms

WY

LFC

dh

dhh

J 80

0

2

80

5

LFC:

ms

ms

W

ms

ms

Y

LF

dh

dh

J 80

0

2

80

5

2

Lateral Fraction:

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Spatial analysis by directive impulse responses• The initial approach was to use directive microphones for gathering some information

about the spatial properties of the sound field “as perceived by the listener”• Two apparently different approaches emerged: binaural dummy heads and pressure-

velocity microphones:

Binaural Binaural microphone (left)microphone (left)

and and

Pressure-velocity Pressure-velocity microphone (right)microphone (right)

16 November 2012 Acoustical Parameters (ISO 3382) 13

IACC “objective” spatial parameter• It was attempted to “quantify” the “spatiality” of a room by means of

“objective” parameters, based on 2-channels impulse responses measured with directive microphones

• The most famous “spatial” parameter is IACC (Inter Aural Cross Correlation), based on binaural IR measurements

LeftLeft

RightRight

80 ms80 ms

ppLL(())

ppRR(())

ms1...ms1ttMaxIACC

dtpdp

dtpp

t Ems80

0

2R

ms80

0

2L

ms80

0RL

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Lateral Fraction (LF) spatial parameter• Another “spatial” parameter is the Lateral Fraction JLF

• This is defined from a 2-channels impulse response, the first channel is a standard omni microphone, the second channel is a “figure-of-eight” microphone:

Figure Figure of 8of 8

OmniOmni

ms

ms

o

ms

msLF

dh

dh

J 80

0

2

80

5

28

hhoo(())

hh88(())

16 November 2012 Acoustical Parameters (ISO 3382) 15

Are binaural measurents reproducible?• Experiment performed in anechoic room - same loudspeaker, same

source and receiver positions, 5 binaural dummy heads

Are IACC measurements reproducible?• 90° incidence - at low frequency IACC is almost 1, at high

frequency the difference between the heads becomes evidentIACCe - 90° incidence

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

31.5 63 125 250 500 1000 2000 4000 8000 16000

Frequency (Hz)

IAC

Ce

B&K4100

Cortex

Head

Neumann

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Are IACC measurements reproducible?

• Diffuse field - huge difference among the 4 dummy heads

IACCe - random incidence

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

31.5 63 125 250 500 1000 2000 4000 8000 16000

Frequency (Hz)

IAC

Ce

B&K4100

Cortex

Head

Neumann

16 November 2012 Acoustical Parameters (ISO 3382) 18

Are LF measurents reproducible?• Experiment performed in the Auditorium of Parma - same loudspeaker,

same source and receiver positions, 4 pressure-velocity microphones

• At 7.5 m distance, the results already exhibit significant scatter

Comparison LF - measure 1 - 7.5m distance

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

31.5 63 125 250 500 1000 2000 4000 8000 16000

Frequency (Hz)

LF

Schoeps

Neumann

Soundfield

B&K

Are LF measurents reproducible?

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16 November 2012 Acoustical Parameters (ISO 3382) 20

Are LF measurents reproducible?• At 25 m distance, the scatter is even larger

Comparison LF - measure 2 - 25m distance

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

31.5 63 125 250 500 1000 2000 4000 8000 16000

Frequency (Hz)

LF

Schoeps

Neumann

Soundfield

B&K

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The Aurora Acoustical Parameters plugin