11 novembre 2010Parametri Acustici (ISO 3382) 1 Misura della risposta allimpulso Parametri Acustici...

11 novembre 2010 Parametri Acustici (ISO 3382) 1

Misura della risposta all’impulsoMisura della risposta all’impulsoParametri Acustici Parametri Acustici temporali e spazialitemporali e spaziali


Informazioni estraibili dalla Risposta Impulsiva

Energia Utile Energia Dannosa


Alcuni Descrittori Acustici


I parametri acustici (ISO 3382)

Tempo di Riverberazione Iniziale (EDT): estrapolato da 0 a -10 dB Tempo di riverberazione T10: estrapolato da -5 a -15 dB Tempo di riverberazione T20: estrapolato da -5 a -25 dB Tempo di riverberazione T30: estrapolato da -5 a -35 dB



ms80

2

ms80

0

2

80

dττp

dττp

lg10C

Indice di chiarezza C80 (musica sinfonica): Indice di chiarezza C50 (parlato):

Valore ottimale = +/- 1 dB

ms50

2

ms50

0

2

50

dττp

dττp

lg10C



Tempo baricentrico TS:

0

2

0

2

s

dp

dp

T

100

dp

dp

D

0

2

ms50

0

2

Indice di definizione D:



• Strenght: dB31LSPLG w

dthdh

dthh

t

2s

2d

sd

IACC:

SPL a 10 m



ms80

ms0

2W

ms80

ms5WY

dh

dhh

LFC LFC:

ms

ms

W

ms

ms

Y

dh

dh

LF 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

RightRight

80 ms80 ms

ppLL(())

ppRR(())

ms1...ms1ttMaxIACC

dtpdp

dtpp

t Ems80

0

2R

ms80

0

2L

ms80

0RL


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

ms80

ms0

2o

ms80

ms5

28

dh

dh

LF

hhoo(())

hh88(())


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

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


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

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


Il plug-in Aurora Acoustical Parameters

11 novembre 2010Parametri Acustici (ISO 3382) 1 Misura della risposta allimpulso Parametri Acustici...

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