Misura della risposta all’impulso Misura della risposta all’impulso Parametri Acustici Parametri Acustici temporali e spaziali temporali e spaziali

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

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

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 :

 

  

























0 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: 

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

I parametri acustici (ISO 3382)

   

  



















 _{80 ms}

ms 0

W 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:

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 p_LL(())

p p_RR(())

 

   

   

    ^{t t}  ^{1 ms ... 1 ms} 

Max IACC

d t p

d p

d t p

p

t

ms 80 2

R ms

80 2 L 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



  ^{  }

80

h

d

hh_oo(())

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

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

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

Are LF measurents reproducible?

• At 25 m distance, the scatter is really big

Comparison LF - measure 2 - 25m distance

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

LF

Schoeps Neumann Soundfield B&K

Il plug-in Aurora Acoustical Parameters