Acoustical parameters
ISO 3382
16 November 2012
Acoustical Parameters (ISO 3382)
1
ISO 3382 acoustical parameters
16 November 2012
Acoustical Parameters (ISO 3382)
2
From Impulse Response to Sound Decay
• Schroeder’s
backward integral
• Makes it possible to
reconstruct the decay
of a stationary source
 g t' dt'
by backward
integration of the
measured impulse
response

2
0
B
0
A
0
16 November 2012

t
Acoustical Parameters (ISO 3382)


t
g 2 t'dt'
g2 t'dt'
t
3
Schroeder’s BW Integration
Pressure Impulse Response
Stationary Sound Decay (in dB)
Energetic Impulse Response (in dB)
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Acoustical Parameters (ISO 3382)
4
Reverberation time T20
Lp
(dB)
-5 dB
45 dB
-25
dB
Time (s)
T20
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Acoustical Parameters (ISO 3382)
5
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
16 November 2012
Acoustical Parameters (ISO 3382)
6
Early – Late energy evaluation
Useful Energy
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Acoustical Parameters (ISO 3382)
Detrimental Energy
7
Early-Late parameters

Clarity Index C80 (symphonic music):
 80ms 2

  p τ   dτ 

C80  10  lg  0


2
  p τ   dτ 
 80ms


Optimal Value = +/- 1 dB
Clarity Index C50 (speech):
 50ms 2

  p τ   dτ 

C50  10  lg  0


2
  p τ   dτ 
 80ms

16 November 2012
Optimal Value = +/- 1 dB
Acoustical Parameters (ISO 3382)
8
Early-Late parameters
50 ms
2
p
  d

Definition Index D:
D
0

100
2
p
  d
0


Center Time tS:
ts 
2


p
    d
0

2
p
    d
0
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Acoustical Parameters (ISO 3382)
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Other acoustical parameters
SPL at 10 m
•
Strenght:
G  SPL  L w  31
dB


IACC:
t  
 h d  h s   t  d





2
h
 d  d 
16 November 2012
Acoustical Parameters (ISO 3382)
2
h
 s   t  d
10
Other acoustical parameters
80ms
 h    d
2
Y

Lateral Fraction:
J LF 
5 ms
80ms
 h    d
2
W
0 ms
80ms
 h    h    d
Y

LFC:
J LFC 
W
5 ms
80ms
 hW    d
2
0 ms
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Acoustical Parameters (ISO 3382)
11
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
microphone (left)
and
Pressure-velocity
microphone (right)
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Acoustical Parameters (ISO 3382)
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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
Left
pL()
Right
pR()
80 ms
t  
 p L  p R   t  d
80 ms
0
80 ms
80 ms
0
0

16 November 2012
p 2L   d 
IACC E  Max t 
t   1ms ...  1ms 
2
p
 R   t  d
Acoustical Parameters (ISO 3382)
13
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:
Omni
ho()
Figure
of 8
h8()
80ms
 h8    d
2
J LF 
5 ms
80ms
 ho    d
2
0 ms
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Acoustical Parameters (ISO 3382)
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Are binaural measurents reproducible?
• Experiment performed in anechoic room - same loudspeaker, same
source and receiver positions, 5 binaural dummy heads
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Acoustical Parameters (ISO 3382)
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Are IACC measurements reproducible?
• 90° incidence - at low frequency IACC is almost 1, at high
frequency the difference between the heads becomes evident
IACCe - 90° incidence
1
0.9
0.8
0.7
IACCe
0.6
B&K4100
Cortex
Head
Neumann
0.5
0.4
0.3
0.2
0.1
0
31.5
63
125
250
500
1000
2000
4000
8000
16000
Frequency (Hz)
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Acoustical Parameters (ISO 3382)
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Are IACC measurements reproducible?
• Diffuse field - huge difference among the 4 dummy heads
IACCe - random incidence
1
0.9
0.8
0.7
IACCe
0.6
B&K4100
Cortex
Head
Neumann
0.5
0.4
0.3
0.2
0.1
0
31.5
63
125
250
500
1000
2000
4000
8000
16000
Frequency (Hz)
16 November 2012
Acoustical Parameters (ISO 3382)
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Are LF measurents reproducible?
•
Experiment performed in the Auditorium of Parma - same loudspeaker,
same source and receiver positions, 4 pressure-velocity microphones
16 November 2012
Acoustical Parameters (ISO 3382)
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Are LF measurents reproducible?
• At 7.5 m distance, the results already exhibit significant scatter
Comparison LF - measure 1 - 7.5m distance
1
Schoeps
0.9
Neumann
0.8
Soundfield
B&K
0.7
LF
0.6
0.5
0.4
0.3
0.2
0.1
0
31.5
63
125
250
500
1000
2000
4000
8000
16000
Frequency (Hz)
16 November 2012
Acoustical Parameters (ISO 3382)
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Are LF measurents reproducible?
• At 25 m distance, the scatter is even larger
Comparison LF - measure 2 - 25m distance
1
Schoeps
0.9
Neumann
0.8
Soundfield
B&K
0.7
LF
0.6
0.5
0.4
0.3
0.2
0.1
0
31.5
63
125
250
500
1000
2000
4000
8000
16000
Frequency (Hz)
16 November 2012
Acoustical Parameters (ISO 3382)
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The Aurora Acoustical Parameters plugin
16 November 2012
Acoustical Parameters (ISO 3382)
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