ISO 3382 acoustical parameters

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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
 g t'dt'
0
t
B
0

A
0
16 November 2012
2
Acoustical Parameters (ISO 3382)
 g t'dt'
2
t
t
3
Schroeder’s BW Integration
Pressure Impulse Response
Stationary Sound Decay (in dB)
Energetic Impulse Response (in dB)
16 November 2012
Acoustical Parameters (ISO 3382)
4
Reverberation time T20
Lp
(dB)
-5 dB
45 dB
-25
dB
Time (s)
T20
16 November 2012
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
16 November 2012
Acoustical Parameters (ISO 3382)
Detrimental Energy
7
Early-Late parameters

Clarity Index C80 (symphonic music):
 80 ms 2

  p τ   dτ 

C80  10  lg  0


2
  p τ   dτ 
 80 ms


Optimal Value = +/- 1 dB
Clarity Index C50 (speech):
 50 ms 2

  p τ   dτ 

C50  10  lg  0


2
  p τ   dτ 
 80 ms

16 November 2012
Optimal Value = +/- 1 dB
Acoustical Parameters (ISO 3382)
8
Early-Late parameters
50ms
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
16 November 2012
Acoustical Parameters (ISO 3382)
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Other acoustical parameters
SPL at 10 m
•
Strenght:
G  SPL  Lw  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
80 ms
 h    d
2
Y

Lateral Fraction:
J LF 
5 ms
80 ms
 h    d
2
W
0 ms
80 ms
 h    h    d
Y

LFC:
J LFC 
W
5 ms
80 ms
 hW    d
2
0 ms
16 November 2012
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)
16 November 2012
Acoustical Parameters (ISO 3382)
12
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()
80ms
t  
 pL  pR   t  d
80 ms
0
80ms
80ms
0
0
2
p
 L  d 
16 November 2012
IACCE  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()
80 ms
 h8    d
2
J LF 
5 ms
80 ms
 ho    d
2
0 ms
16 November 2012
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
16 November 2012
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)
16 November 2012
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)
20
The Aurora Acoustical Parameters plugin
16 November 2012
Acoustical Parameters (ISO 3382)
21
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