2531.540506380100125160200250315400500630800100012501600200025003150400050006300800010000125001600020000Lw (dB)

RECORDING CONCERT HALL RECORDING CONCERT HALL

ACOUSTICS FOR POSTERITY ACOUSTICS FOR POSTERITY

Angelo Farina ⁽¹⁾ – Regev Ayalon ⁽²⁾

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

HTTP://pcfarina.eng.unipr.it - mail: [email protected]

(2) K.S. Waves Inc., Azrieli Center, Tel Aviv, ISRAEL HTTP://www.waves.com - mail:[email protected]

Multichannel Audio - The New Reality

24th AES International Conference

June 26 - 28, 2003

Background Background

z The title of this paper is exactly the same employed by Michael Gerzon in its JAES paper (Vol. 23, Number 7, 1975)

z He first proposed to collect impulse responses measured in famous theatres, with a

microphone capable of capturing the complete spatial information

z This paper is consequently basically a tribute to M.Gerzon, who had foreseen most of the modern multichannel audio applications,

including impulse response measurements

and auralization obtained by convolution.

Goals Goals

z The main goal is to measure an huge

collection of impulse response in famous theatres, concert halls, cathedrals, etc.

z These impulse responses have two main uses:

1. In case something happens to the original space (remember the case of 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

Topics Topics

z Description of the measurement technique

z Analysis of some acoustical parameters of the first theaters already measured

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

spaces

z Description of the usage of the measured data

for studio processing and production

Sound

Sound propagation propagation in in rooms rooms

Direct Sound

Reflected Sound

Receiver Direct Sound

Reflected Sound

Point Source

Measurement

Measurement process process

z 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)

24th AES International Conference

Test

Test signal signal : Log : Log Sine Sine Sweep Sweep

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

variable exponentially with time, starting at f ₁ and ending at f ₂ .

24th AES International Conference

⎥ ⎥

⎥ ⎥

⎦

⎤

⎢ ⎢

⎢ ⎢

⎣

⎡

⎟⎟

⎟ ⎟

⎠

⎞

⎜⎜

⎜ ⎜

⎝

⎛

−

⋅

⎟⎟ ⎠

⎜⎜ ⎞

⎝

⎛

⋅

⋅ π

= ⋅ ^{⎟⎟ ⎠}

⎜⎜ ⎞

⎝

⋅ ⎛

1 e

f ln f

T f

sin 2 )

t (

x ¹

2

f ln f T

t

1

2

1

Deconvolution

Deconvolution of of Log Log Sine Sine Sweep Sweep

z 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)

Test

Test Signal Signal – – x(t) x(t)

Measured

Measured signal signal - - y(t) y(t)

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

24th AES International Conference

Inverse

Inverse Filter Filter – – z(t) z(t)

The deconvolution of the system’s impulse response is obtained convolving the measured signal y(t) with the inverse filter z(t) [equalized, time-reversed x(t)]

24th AES International Conference

Result

Result of of the the deconvolution deconvolution

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

2° 1°

5° 3°

Measurement Setup Measurement Setup

z 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

z This measurement setup has been named “Waves2003”, as it is being employed for the collection of impulse response to be employed together with the new convolution software being developed by KS Waves ltd.

24th AES International Conference

“ “ Waves2003 Waves2003 ” ” Measurement Measurement Parameters

Parameters

z 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

24th AES International Conference

z Deconvolution:

Transducers

Transducers (sound source #1) (sound source #1)

z Equalized, omnidirectional sound source:

– Dodechaedron for mid-high frequencies

– Subwoofer

24th AES International Conference

Radiated sound power level

40 50 60 70 80 90 100

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 12500 16000 20000

Frequency (Hz)

Lw (dB)

Unequalized Equalized

Transducers

Transducers (sound source #2) (sound source #2)

z 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

Transducers

Transducers ( ( microphones microphones ) )

z 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)

24th AES International Conference

Braccio rotante Testa artificiale binaurale

Cardioidi ORTF Microfono Soundfield

Other

Other hardware hardware equipment equipment

z Rotating Table ^:

– Outline ET-1

24th AES International Conference z Computer and sound card:

– Signum Data Futureclient P-IV 1.8 GHz

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

Measurement

Measurement procedure procedure

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

24th AES International Conference

Theatres

Theatres measured 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

Reverberatiuon Time T20

0 0.5 1 1.5 2 2.5 3 3.5

31.5 63 125 250 500 1000 2000 4000 8000 16000

Frequency (Hz)

T20 (s)

Uhara Noh Kirishima Siracusa Taormina Parma Roma-700 Roma-1200 Roma-2700

Uhara

Uhara Hall, Kobe, Hall, Kobe, Japan Japan

Noh Noh theater theater , Kobe, , Kobe, Japan Japan

Kirishima

Kirishima Concert Hall, Concert Hall, Japan Japan

Kirishima

Kirishima Concert Hall, Concert Hall, Japan Japan

Greek

Greek Theater Theater in Siracusa in Siracusa

Roman

Roman Theater Theater in Taormina in Taormina

Parma Auditorium, Italy

Parma Auditorium, Italy

Rome Rome Auditorium, 700 Auditorium, 700 seats seats

Rome Rome Auditorium, 1200 Auditorium, 1200 seats seats

Rome Rome Auditorium, 2700 Auditorium, 2700 seats seats

Bergamo

Bergamo ’ ’ s s Cathedral Cathedral , Italy , Italy

Teatro Valli, Reggio Emilia, Italy

Teatro Valli, Reggio Emilia, Italy

Acoustical

Acoustical Parameters Parameters

24th AES International Conference z Center Time T _S :

( )

∫ ( )

∫

∞

∞

τ

⋅ 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 C ₈₀ :

( ) ( )

100 d p

d p D

0 2 ms 50

0 2

⋅ τ

⋅ τ

τ

⋅ τ

=

∫

∫

z Definition D:

z

30

z

T

/2 20

T

/3

z Reverberation Time T ₂₀ :

Acoustical

Acoustical Parameters Parameters

z Strenght:

24th AES International Conference

dB 31

L SPL

G = −

+

( ) ( )

∫ ( )

∫

τ

⋅ τ

τ

⋅ τ

⋅ τ

= _80ms

ms 0

2 W ms 80

ms 5

W Y

d h

d h

h

z LFC:

( )

∫ ( )

∫

⋅

⋅

=

ms W ms

ms Y

d h

d h

LF

0 2 80

5 2

τ τ

τ

z LF: τ

( )

( ) ( )

( ) ∫ ( )

∫

∫

∞

∞

−

∞

∞

−

∞

∞

−

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:

Analysis of spatial attributes Analysis of spatial attributes

24th AES International Conference

Polar

Polar diagrams diagrams of of IACC and (1 IACC and (1 - - LF) 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

140 150 170 160 180 200 190

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

140 150 170 160 180 200 190

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

Auralization

Auralization by by convolution convolution

z 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).

z The convolution operation can nowadays be implemented very

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

24th AES International Conference

Auralization

Auralization types types

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

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

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

z ITU 5.1 (from different 5-mikes layouts)

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

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

z Hybrid methods (Ambiophonics)

24th AES International Conference

ORTF Stereo ORTF Stereo

24th AES International Conference

z 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

Binaural

Binaural (Stereo (Stereo Dipole Dipole ) )

24th AES International Conference

z 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

x_r

x_l

Cross-talk canceller

d_1r d_2l d_2r

d_Nl d_Nr N

20°

Ambisonics

Ambisonics 3D 1 3D 1 ^{st st} order order

24th AES International Conference z 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

ITU 5.1 surround ITU 5.1 surround

z Williams MMA

24th AES International Conference

Schematic of the setup C : Cardioid, 0°

L, R : Cardioid, ± 40°

LS, RS : Cardioid, ± 120°

z INA-5

Schematic of the setup C : Cardioid, 0°

L, R : Cardioid, ± 90°

LS, RS : Cardioid, ± 150°

ITU 5.1 surround ITU 5.1 surround

z OCT

24th AES International Conference

73 cm

Schematic of the setup C : Cardioid, 0°

L, R : Super Cardioid, ± 90°

LS, RS : Cardioid, ± 180°

Virtual

Virtual high high - - order order microphones

microphones (M. (M. Poletti Poletti ) )

z One of the two ORTF cardioid is employed, which samples 36 positions along a 100 mm-radius circumference

24th AES International Conference

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.

1 0

90

180

270 0

1 0

90

180

270 0

1 0

90

180

270 0

1 0

90

180 270

Wave Wave Field Field Synthesis Synthesis (WFS) (WFS)

z Flow diagram of the process

24th AES International Conference

microphones

loudspeakers

Original space Virtual space

WFS

Hybrid

Hybrid methods methods ( ( Ambiophonics Ambiophonics ) )

z Ambiophonics 3D (10 loudspeakers):

24th AES International Conference

Conclusions Conclusions

z Main advantages of the new measurement method “Waves 2003”:

- Almost all previously known measurement techniques are incorporated in a single, coherent approach

- The spatial informations are accurately sampled, making it possible to store, analyze and preserve these “3D acoustical photographies” of existing musical spaces for the posterity

- The impulse response are stored in many different formats, allowing for their usage for surround productions with today technlogies (ITU 5.1, 1st order Ambisonics) and future, more advanced methods (high order Ambisonics, WFS, Ambiophonics)

24th AES International Conference