Acoustical parameters Acoustical parameters
ISO 3382
ISO 3382
ISO 3382 acoustical parameters
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 t
20
' '
g t d t
t
2
' '
g t d t
t 2
0
' '
Schroeder’s BW Integration
Pressure 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
T
20ISO 3382 Reverberation Time(s)
Early Decay Time (EDT):
extrapolated from 0 to -10 dB
Reverberation Time T 10 : extrapolated from -5 to -15 dB
Reverberation Time T 20 : extrapolated from -5 to -25 dB
Reverberation Time T 30 :
extrapolated from -5 to -35 dB
Early – Late energy evaluation
Useful Energy Detrimental Energy
Early-Late parameters
ms ms
dτ τ
p
dτ τ
p C
80
2 80
0 2
80
10 lg
Clarity Index C 80 (symphonic music):
Clarity Index C 50 (speech):
Optimal Value = +/- 1 dB
Optimal Value = +/- 1 dB
ms ms
dτ τ
p
dτ τ
p C
50
2 50
0 2
50
10 lg
Early-Late parameters
Center Time t S :
0 2 0
2
d p
d p
t
s
100 d
p
d p
D
0 2 ms 50
0 2
Definition Index D:
Other acoustical parameters
• Strenght: G SPL L w 31 dB
d t h
d h
d t h
h t
s 2 d 2
s d
IACC:
SPL at 10 m
Other acoustical parameters
msms W ms
ms
W Y
LFC
d h
d h
h
J
800
2 80
5
LFC:
ms
ms W ms
ms Y LF
d h
d h
J 80
0
2 80
5
2
Lateral Fraction:
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)
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
Right Right
80 ms 80 ms
p pLL(())
p pRR(())
t t 1 ms ... 1 ms
Max IACC
d t p
d p
d t p
p
t
Ems 80
0 2R ms
80 0
2L ms 80
0
R L
Lateral Fraction (LF) spatial parameter
• Another “spatial” parameter is the Lateral Fraction J
LF• 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
msms o ms
ms LF
d h
d h
J
800 2 80
5 2 8
hhoo(())
hh88(())
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 evident
IACCe - 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)
IACCe B&K4100
Cortex Head Neumann
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
IACCe B&K4100
Cortex Head Neumann
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?
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
