11 novembre 2010 Parametri Acustici (ISO 3382) 1
Misura della risposta all’impulso Misura della risposta all’impulso
Parametri Acustici Parametri Acustici
temporali e spaziali
temporali e spaziali
Informazioni estraibili dalla Risposta Impulsiva
Energia Utile Energia Dannosa
11 novembre 2010 Parametri Acustici (ISO 3382) 3
Alcuni Descrittori Acustici
I parametri acustici (ISO 3382)
Tempo di Riverberazione Iniziale (EDT):
estrapolato da 0 a -10 dB
Tempo di riverberazione T 10 : estrapolato da -5 a -15 dB
Tempo di riverberazione T 20 : estrapolato da -5 a -25 dB
Tempo di riverberazione T 30 :
estrapolato da -5 a -35 dB
11 novembre 2010 Parametri Acustici (ISO 3382) 5
I parametri acustici (ISO 3382)
ms 80
2 ms 80
0 2
80
dτ τ
p
dτ τ
p lg
10 C
Indice di chiarezza C 80 (musica sinfonica):
Indice di chiarezza C 50 (parlato):
Valore ottimale = +/- 1 dB
ms 50
2 ms 50
0 2
50
dτ τ
p
dτ τ
p lg
10
C
I parametri acustici (ISO 3382)
Tempo baricentrico T S :
2 0
2
s
d p
d p
T
100 d
p
d p
D
0 2 ms 50
0 2
Indice di definizione D:
11 novembre 2010 Parametri Acustici (ISO 3382) 7
I parametri acustici (ISO 3382)
• 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 a 10 m
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)
11 novembre 2010 Speech Transmission Index 9
Microfono Soundfield
• The Soundfield microphone allows for simultaneous measurements of the omnidirectional pressure and of the three cartesian components of particle velocity (figure-of-8 patterns)
W X
Y Z
I parametri acustici (ISO 3382)
80 ms
2 ms
80 ms 5
W Y
d h
d h
h
LFC: LFC
ms
ms W ms
ms Y
d h
d h
LF 80
0
2 80
5
2
Lateral Fraction:
11 novembre 2010 Parametri Acustici (ISO 3382) 11
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 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
ms
80 2
8
d
h
hhoo(())
hh88(())
11 novembre 2010 Parametri Acustici (ISO 3382) 13
Are binaural measurents reproducible?
• Experiment performed in anechoic room - same loudspeaker, same
source and receiver positions, 5 binaural dummy heads
Are IACC measurents reproducible?
• Diffuse field - huge difference among the 4 dummy heads
IACCe - random incidence
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
IACCe B&K4100
Cortex Head Neumann
11 novembre 2010 Parametri Acustici (ISO 3382) 15
Are LF measurents reproducible?
• Experiment performed in the Auditorium of Parma - same
loudspeaker, same source and receiver positions, 4 pressure-
velocity microphones
Are LF measurents reproducible?
• At 25 m distance, the scatter is really big
Comparison LF - measure 2 - 25m distance
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
LF
Schoeps Neumann Soundfield B&K
11 novembre 2010 Parametri Acustici (ISO 3382) 17