2531.540506380100125160200250315400500630800100012501600200025003150400050006300800010000

(1)

reproducing spatial sound properties of auditoria

Angelo Farina (1) and Lamberto Tronchin ⁽²⁾

(1) Dipartimento di Ingegneria Industriale, Università di Parma, Via delle Scienze 181/A Parma, 43100 ITALY

HTTP://pcfarina.eng.unipr.it - mail: angelo.farina@unipr.it

(2) DIENCA - CIARM, Università di Bologna, Viale Risorgimento 2 Bologna, 40136 ITALY

HTTP://www.ciarm.ing.unibo.it - mail: lamberto.tronchin@unibo.it

(2)

Topics

• This paper is a tribute to M. Gerzon, who had foreseen 3D impulse response measurements and 3D Auralization obtained by convolution.

• The advantages (and disadavantages) of employing measured IRs

• Comparison between Auralizations based on calculated and measured IRs

(e.g. Theatre “La Fenice”, Venice)

• Different approaches to 3D Auralization

(3)

10-Sep-08 Farina, Tronchin, RADS

Concept (Gerzon, 1975)

Portable PC with 4- channels sound board Original Room

Sound Source

SoundField Microphone

B-format 4-channels signal (WXYZ) Measurement of B-format

Impulse Responses

MLS or sweep excitation signal

Convolution of dry signals with the B-format Impulse

Responses Sound Source

Mono Mic.

B-format Imp. Resp.

of the original room

B-format 4-channels signal (WXYZ) Convolver

Ambisonics decoder

Speaker array in the reproduction room

(4)

The measurements of IRs:

1. In case something happens to the original

space (e.g.: La Fenice theater) they contain a detailed “acoustical photography” which is

preserved for the posterity

2. They can be used for studio sound processing, as artificial reverb and surround filters for

today’s and tomorrow’s musical productions

3. Several configurations of listening rooms could be developed, by means of multichannel

auralization, for subjective tests

(5)

Theatre la Fenice, Venice

• The first theatre was realised in 1792 by Gian Antonio Selva, after the burning of Teatro San Benedetto

• In December 1836 the theatre burned down again and was rebuilt by G. and T. Meduna the year after

• The theatre was closed in 1995 for maintainance; it had to open again in February 1, 1996, but it

burned two days before (January 29, 1996)

• A few weeks before the fire, L.Tronchin measured binaural impulse responses

(6)

Impulse Responses of La Fenice

In 27 positions a series of binaural impulse responses (with gun shots) was recorded

Each recording is consequently a

stereo file at 16 bits, 48 kHz

During

measurements the room was perfectly fitted, whilst the stage was empty (no scenery)

Point n. 12

(7)

Example n. 1 – La Fenice

• Dry music

• Convolution with

experimental I.R. (pt. 12)

• Convolution with simulated IR

Overture alle Nozze di Figaro di Mozart

Preludio al primo atto della Traviata di G.Verdi

• Dry music

• Convolution with

experimental I.R. (pt. 12)

• Convolution with simulated IR

Stop

(8)

Example n. 2 – Paris vs ...la petit Paris

Citè de la Musique, Parigi Auditorium di Parma

Stop

(9)

Advanced IR capture and rendering ( project)

• Description of the measurement technique

• Analysis of some acoustical parameters of some theaters measured

• Description of the processing methods to be employed for transforming the measured data in audible reconstructions of the original spaces

• Description of the usage of the measured data for studio processing, musical production and for scientific Auralization tests

(10)

Sound propagation in rooms

Direct Sound

Reflected Sound

Receiver Direct Sound

Reflected Sound

Point Source

(11)

Measurement process

• The desidered result is the linear impulse response of the acoustic propagation h(t). It can be recovered by knowing the test signal x(t) and the measured system output y(t). It is necessary to exclude the effect of the not-linear part K and of the background noise n(t).

Not-linear, time variant

system K[x(t)]

Noise n(t)

input x(t)

+ output y(t) linear system

w(t)⊗h(t) distorted signal

w(t)

(12)

Test signal: Log Sine Sweep

x(t) is a sine signal, which frequency is varied

exponentially with time, starting at f₁ and ending at f₂.

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

⋅

⎟⎟⎠

⎜⎜ ⎞

⎝

⎛

⋅

⋅ π

= ⋅ ^⎟⎟^⎠

⎜⎜ ⎞

⎝

⋅ ⎛

1 e

f ln f

T f

sin 2 )

t (

x ¹

2

f ln f T

t

1 2 1

(13)

Deconvolution of Log Sine Sweep

The “time reversal mirror” technique is emplyed: the

system’s impulse response is obtained by convolving the measured signal y(t) with the time-reversal of the test signal x(-t). As the log sine sweep does not have a

“white” spectrum, proper equalization is required

Test Signal x(t) Inverse Filter z(t)

(14)

Test Signal – x(t)

(15)

Measured signal - y(t)

The not-linear behaviour of the loudspeaker causes many harmonics to appear

(16)

Inverse Filter – z(t)

The deconvolution of the IR is obtained convolving the measured signal y(t) with the inverse filter z(t) [equalized, time-reversed x(t)]

(17)

Result of the deconvolution

The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders

2° 1°

5° 3°

(18)

Measurement Setup

The measurement method incorporates all the known techniques:

Binaural

B-format (1^st order Ambisonics)

WFS (Wave Field Synthesis, circular array)

ITU 5.1 surround (Williams MMA, OCT, INA, etc.) Binaural Room Scanning

M. Poletti high-order virtual microphones

Any multichannel auralization systems nowadays available is supported

(19)

Measurement Parameters

• Test Signal: pre-equalized sweep

Start Frequency 22 Hz End Frequency 22 kHz

Sweep length 15 s

Silence between sweeps 10 s

Type of sweep LOG

z Deconvolution:

(20)

Transducers (sound source #1)

• Equalized, omnidirectional sound source:

Dodechaedron for mid-high frequencies One-way Subwoofer (<120 Hz)

Dodech. LookLine D200

60.0 70.0 80.0 90.0 100.0 110.0 120.0

25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000

Frequency (Hz)

Sound Power Level (dB)

Unequalized Equalized

Lw,tot = 94.8 dB Lw,tot = 106.9 dB

(21)

Transducers (sound source #2)

• Genelec S30D reference studio monitor:

Three-ways, active multi-amped, AES/EBU Frequency range 37 Hz – 44 kHz (+/- 3 dB)

1000 Hz

-40 -35 -30 -25 -20 -15 -10 -5 0 0

30

60

90

120

150 180

210 240 270

300 330

250 Hz

-40 -35 -30 -25 -20 -15 -10 -5 0 0

30

60

90

120

150 180

210 240 270

300 330

2000 Hz

-40 -35 -30 -25 -20 -15 -10 -5 0 0

30

60

90

120

150 180

210 240 270

300 330

4000 Hz

-40 -35 -30 -25 -20 -15 -10 -5 0 0

30

60

90

120

150 180

210 240 270

300 330

8000 Hz

-40 -35 -30 -25 -20 -15 -10 -5 0 0

30

60

90

120

150 180

210 240 270

300 330

16000 Hz

-40 -35 -30 -25 -20 -15 -10 -5 0 0

30

60

90

120

150 180

210 240 270

300 330

(22)

Transducers (microphones)

• 3 types of microphones:

Binaural dummy head (Neumann KU-100) 2 Cardioids in ORTF placement (Neumann K- 140)

B-Format 4 channels (Soundfield ST-250)

Turntable

Binaural dummy head Cardioids (ORTF) Soundfield Microphone

(23)

Other hardware equipment

• Rotating Table:

Outline ET-1

z Computer and sound card:

– Signum Data Futureclient P-IV 1.8 GHz

– Aardvark Pro Q-10 (8 ch., 96 kHz, 24 bits)

(24)

Measurement procedure

• A single measurement session play backs 36 times the test signal, and simultaneusly record the 8 microphonic channels

(25)

Theatres measured

N. Theatre N. sources/receivers

1 Uhara Hall, Kobe, Japan 2/2

2 Noh Drama Theater, Kobe, Japan 2/2

3 Kirishima Concert Hall, Kirishima, Japan 3/3 4 Greek Theater in Siracusa, Italy 2/1 5 Greek-Roman Theater in Taormina, Italy 3/2

6 Auditorium of Parma, Italy 3/3

7 Auditorium of Rome (Sala 700), Italy 3/2 8 Auditorium of Rome (Sala 1200), Italy 3/3 9 Auditorium of Rome (Sala 2700), Italy 3/5

10 Bergamo Cathedral, Italy 2/1

11 Teatro Valli, Reggio Emilia, Italy 5/1 12 Sydney Opera House, Opera Theatre 4/2 13 Sydney Opera House, Concert Hall 3/3 14 Sydney Opera House, The Studio 3/1

15 Tearo Regio, Parma, Italy 6/1

Reverberation Time T20

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

31.5 63 125 250 500 1000 2000 4000 8000 16000

Frequency (Hz)

T20 (s)

Uhara

Noh

Kirishima

Siracusa

Taormina

Audit. Parma

Roma-700

Roma-1200

Roma-2700

Bergamo Cathedral Valli-RE

SOH Concert Hall

SOH-Opera Theatre SOH-The Studio Regio Parma

(26)

Uhara Hall, Kobe, Japan

T 20= 1.44 s

(27)

Noh theater, Kobe, Japan

T 20= 1.14 s

(28)

Kirishima Concert Hall, Japan

(29)

Kirishima Concert Hall, Japan

T 20= 1.93 s

(30)

Greek Theater in Siracusa

T 20= 0.65 s

(31)

Roman Theater in Taormina

T 20= 1.15 s

(32)

Parma Auditorium, Italy

T 20= 2.08 s

(33)

Rome Auditorium, 700 seats

T 20= 2.04 s

(34)

T 20= 2.10 s

(35)

T 20= 2.56 s

(36)

Bergamo’s Cathedral, Italy

T 20= 2.95 s

(37)

Teatro Valli, Reggio Emilia, Italy

T 20= 1.55 s

(38)

Sydney Opera House

(39)

Sydney Opera House – opera theatre

T 20= 1.16 s

(40)

Sydney Opera House – concert hall

T 20= 2.04 s

(41)

Sydney Opera House – the studio

T 20= 0.76 s

(42)

Teatro Regio in Parma (Italy)

T 20= 1.11 s

(43)

Acoustical Parameters (ISO 3382)

z Center Time T_S:

( )

∫ ( )

∫

∞

τ

⋅ τ

τ

⋅ τ

=

0 2 0

2

s

d p

d p T

( ) ( ) _⎥^⎥

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

⋅

=

∫

∞ ms ms

dτ τ p

dτ τ p C

80 2 80

0 2

80 10 lg

z Clarity C₈₀:

( ) ( )

100 d p

d p D

0 2 ms 50

0 2

⋅ τ

τ

⋅ τ

=

∫

z Definition D: ∞

20 dB

z Reverberation Time T₂₀:

T₂₀/3

(44)

Acoustical Parameters (ISO 3382)

•

^Strength: ^G ⁼^SPL⁻^L^w ⁺³¹ ^dB

( ) ( )

∫ ( )

∫

τ

⋅ τ

τ

⋅ τ

= ₈₀_ms

ms 0

2 W ms 80

ms 5

W Y

d h

h

z LFC: LFC

( )

∫ ( )

∫

⋅

= _ms

ms W ms

ms Y

d h

LF ₈₀

0 2 80

5 2

τ τ

τ

z LF: τ

( )

( ) ( )

( ) ∫ ( )

∫

∞

−

∞

−

∞

−

τ

⋅ + τ

⋅ τ

τ

⋅ + τ

⋅ τ

= τ ρ

d t h d h

d t h h

2 s 2

d

s d

z IACC:

(45)

Analysis of spatial attributes

(46)

Polar diagrams of IACC and (1-LF)

IACC Auditorium Parma - Sorgente a sx

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0

10 20

30 40

50 60

70

80

90

100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290

300 310

320 330

340 350 Sorgente

IACC Auditorium Roma (Sala 1200) - Sorgente a sx

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0

10 20

30 40

50 60

70 80

90

100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290

300 310

320 330

340 350 Sorgente

(1-LF) Auditorium Parma – Sorgente a sx

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0

10 20

30 40

50 60

70

80

90

100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290

300 310

320 330

340 350 Sorgente

(1-LF) Auditorium Roma (Sala 1200) – Sorgente a sx

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0

10 20

30 40

50 60

70 80

90

100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290

300 310

320 330

340 350 Sorgente

Auditorium 1-LF IACC Parma 0.725 0.266 Roma 0.676 0.344

(47)

Auralization by convolution

• The basic method consists in convolution of a dry signal with a set of

impulse responses corresponding to the required output format for surround (2 to 24 channels).

• The convolution operation can nowadays be implemented very

efficiently on a modern PC through an ancient algorithm (equally-partitioned FFT processing, Stockam 1966).

(48)

Auralization types

• Stereo (ORTF on 2 standard loudspeakers at +/- 30°)

• Rotation-tracking reproduction on headphones (Binaural Room Scanning)

• Full 3D Ambisonics 1^st order (decoding the B-format signal)

• ITU 5.1 (from different 5-mikes layouts)

• 2D Ambisonics 3^rd order (from Mark Poletti’s circular array microphone)

• Wave Field Synthesis (from the circular array of Soundfield microphones)

• Hybrid methods (Ambiophonics)

(49)

ORTF Stereo

Playback occurs over a pair of loudspeakers, in the standard configuration at angles of +/- 30°, each being fed by the signal of the

corresponding microphone

2 Microphones

60°

2 Loudspeakers

(50)

Binaural (Stereo Dipole)

Reproduction occurs over 2 loudspeakers angled at +/- 10°, being fed through a “cross-talk cancellation” digital filtering system

…

2 3

1

Original 2-channels recording of the signals coming from N sources

d_1l d_1r

d_2l d_2r

x_r

x_l

Cross-talk canceller

d_Nl d_Nr N

20°

(51)

Binaural (Stereo Dipole#2)

L R

hll hrr

hlr hrl Binaural

stereo signal yl yr

pl pr

xl

xr

convolver

fll

flr

frl

frr

yl y_r

(52)

Binaural (Stereo Dipole#3)

( )( )

( )

( ) ( )

⎪⎪

⎪

⎩

⎪⎪

⎪

⎨

⎧

⊗

−

⊗

=

⊗

=

⊗

−

=

⊗

−

=

⊗

=

rl lr

rr ll

ll rr

rl rl

lr lr

rr ll

h h

InvFilter InvDen

InvDen h

f

InvDen h

f

InvDen h

f

InvDen h

f C(ω) = FFT(h_ll)⋅FFT(h_rr)− FFT(h_lr)⋅FFT(h_rl)

( ) [ ( )]

[ ( )^ω ] ( ) ( )^ω^ω ^ε ^ω

ω = ⋅ +

C C

Conj

C InvDen Conj

h_ll

h_lr

h_rl

h_rr

f_ll

f_lr

f_rl

f_rr

(53)

Binaural (Dual Stereo Dipole)

advantages advantages: :

3D sound reproduction3D sound reproduction

RotatingRotating ofof the headthe head

The cross-The cross-talk talk filtersfilters could

could equaliseequalise alsoalso the the loudspeakers

loudspeakers

disadvantages disadvantages^:^:

Low frequenciesLow frequencies

ColorationColoration outsideoutside the the

““sweetsweet spotspot””

Scheme

Subwoofer

(54)

Binaural (Dual Stereo Dipole#2)

Frontal Rear

Quested 2108 monitors Quested F11P monitors

(55)

Ambisonics 3D 1^st order

Reproduction occurs over an array of 8-24 loudspeakers, through an Ambisonics decoder

Original Room

Sound Source

SoundField Microphone

B-format 4- channels signal

(WXYZ) Ambisonics decoder

Speaker array in the reproduction room

(56)

Rooms for Ambisonics 3D 1^st order

University of Parma

University of Bologna

(57)

ITU 5.1 surround

• Williams MMA

Schematic of the setup C : Cardioid, 0°

L, R : Cardioid, ± 40°

LS, RS : Cardioid, ± 120°

z INA-5

L, R : Cardioid, ± 90°

(58)

ITU 5.1 surround

OCT

73 cm

L, R : Super Cardioid, ± 90°

(59)

Virtual high-order microphones (M. Poletti)

One of the two ORTF cardioid is

employed, which samples 36 positions along a 110 mm-radius

circumference

1 , 0 6 n

n 3

cos D

1 , 0 4 n

n 2

cos D

1 , 0 2 n

n cos

D 1 D

n , 3

n , 2

n , 1

0

⎟ =

⎠

⎜ ⎞

⎝

⎛ ⋅ϑ+ ⋅π

=

⎟ =

⎠

⎜ ⎞

⎝

⎛ ⋅ϑ+ ⋅π

=

⎟ =

⎠

⎜ ⎞

⎝

⎛ϑ+ ⋅π

=

From these 36 impulse responses it =

is possible to derive the response of cylindrical harmonics microphones (2D Ambisonics) up to 5th order.

0 1 0

90

180

270 0

1 0

90

180

270 0

1 0

90

180

270 0

1 0

90

180 270

(60)

Wave Field Synthesis (WFS)

Flow diagram of the process

microphones

loudspeakers

Original space Virtual space

WFS

(61)

Hybrid methods (Ambiophonics)

Ambiophonics 3D (10 loudspeakers):

(62)

Hybrid methods (Ambiophonics#2)

(63)

Conclusions

• The spatial informations have to be accurately sampled, making it possible to store, analyze and preserve these

“3D acoustical photographies” of existing musical spaces for the posterity

• Many different kinds of impulse-response measurements are required for different 3D auralization methods: a proper set-up should include all different approaches

• Once the impulse responses are stored in suitable multichannel formats, they become available for surround productions with today technologies (ITU 5.1, 1st order Ambisonics) and future, more advanced methods (high order Ambisonics, WFS, Ambiophonics)

• The only point which requires substantial enhancements:

sound sources used for IR measurements

(64)

Future enhancements

Sound source for realistic

emulation of an human singer

(65)

Future enhancements

Omnidirectional sound source with enhanced power frequency response

Dodech. LookLine D300 + Sub Audio Pro B2.27

60 70 80 90 100 110 120

25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000

Frequency (Hz)

Sound Power Level (dB)

Unequalized Equalized Lw,tot = 100.5 dB

Lw,tot = 108.4 dB

(66)

Acknowledgements

This research was started thanks to the support of Waves, Tel Aviv, Israel (www.waves.com)

For years 2004 and 2005 the research is also supported by the Italian Ministry for the

University and Research (MIUR)

During 2004 a new web site will be started:

www.acoustics.net

This will provide free access to the whole data- base, and it will be possible to add contributions.