RECORDING CONCERT HALL RECORDING CONCERT HALL ACOUSTICS FOR - - PowerPoint PPT Presentation

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: farina@unipr.it

(2) K.S. Waves Inc., Azrieli Center, Tel Aviv, ISRAEL

HTTP://www.waves.com - mail:regev@waves.com

Multichannel Audio - The New Reality 24th AES International Conference June 26 - 28, 2003

Background Background

• The title of this paper is exactly the same

employed by Michael Gerzon in its JAES paper (Vol. 23, Number 7, 1975)

• He first proposed to collect impulse responses

measured in famous theatres, with a microphone capable of capturing the complete spatial information

• 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

• The main goal is to measure an huge

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

• 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

• Description of the measurement technique
• Analysis of some acoustical parameters of the

first theaters already 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 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

• 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

• f the background noise n(t).

Not-linear, time variant system K[x(t)] Noise n(t) input x(t)

+

• utput y(t)

linear system w(t)⊗h(t) distorted signal w(t)

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Test Test signal signal: Log : Log Sine Sine Sweep Sweep

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

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

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⎥ ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎢ ⎣ ⎡ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ − ⋅ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⋅ ⋅ π ⋅ =

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⋅

1 e f f ln T f 2 sin ) t ( x

1 2

f f ln T t 1 2 1

Deconvolution Deconvolution of

• f Log

Log Sine Sine Sweep 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)

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

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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)]

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Result Result of

• f the

the deconvolution deconvolution

The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders 1° 2° 3° 5°

Measurement Setup Measurement Setup

The measurement method incorporates all the known

techniques:

– Binaural – B-format (1st 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

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

• 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

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Deconvolution:

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

• Equalized, omnidirectional sound source:

–

Dodechaedron for mid-high frequencies

–

Subwoofer

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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)

• 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
• 1

• 1
• 5

30 60 90 120 150 180 210 240 270 300 330

250 Hz

• 40
• 35
• 30
• 25
• 20
• 1

• 1
• 5

30 60 90 120 150 180 210 240 270 300 330

2000 Hz

• 40
• 35
• 30
• 25
• 20
• 1

• 1
• 5

30 60 90 120 150 180 210 240 270 300 330

4000 Hz

• 40
• 35
• 30
• 25
• 20
• 1

• 1
• 5

30 60 90 120 150 180 210 240 270 300 330

8000 Hz

• 40
• 35
• 30
• 25
• 20
• 1

• 1
• 5

30 60 90 120 150 180 210 240 270 300 330

16000 Hz

• 40
• 35
• 30
• 25
• 20
• 1

• 1
• 5

30 60 90 120 150 180 210 240 270 300 330

Transducers Transducers ( (microphones 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) 24th AES International Conference

Braccio rotante Testa artificiale binaurale Cardioidi ORTF Microfono Soundfield

Other Other hardware hardware equipment equipment

• Rotating Table:

–

Outline ET-1

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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

• A single measurement session play backs 36

times the test signal, and simultaneusly record the 8 microphonic channels

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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

0.5 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

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• Center Time TS:

( ) ( )

∫ ∫

∞ ∞

τ ⋅ τ τ ⋅ τ ⋅ τ =

2 2 s

d p d p T

( ) ( )

⎥ ⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎢ ⎣ ⎡ ⋅ ⋅ ⋅ =

∫ ∫

∞ ms ms

dτ τ p dτ τ p C

80 2 80 2 80

lg 10

• Clarity C80:

( ) ( )

100 d p d p D

2 ms 50 2

⋅ τ ⋅ τ τ ⋅ τ =

∫ ∫

∞

• Definition D:

30 T

30

/2

20 T20/3

• Reverberation Time T20:

Acoustical Acoustical Parameters Parameters

• Strenght:

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dB 31 L SPL G

w +

− =

( ) ( ) ( )

∫ ∫

τ ⋅ τ τ ⋅ τ ⋅ τ =

ms 80 ms 2 W 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 2 80 5 2

τ τ τ τ

• 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

• IACC:

Analysis of spatial attributes Analysis of spatial attributes

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Polar Polar diagrams diagrams of

• f IACC and (1

IACC and (1-

• LF)

LF)

IACC Auditorium Parma - Sorgente a sx

0.05 0.1 0.15 0.2 0.25 0.3 0.35 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

0.05 0.1 0.15 0.2 0.25 0.3 0.35 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

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 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

0.1 0.2 0.3 0.4 0.5 0.6 0.7 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

Auralization Auralization by by convolution convolution

• The

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

• f impulse responses corresponding to

the required

• utput

format for surround (2 to 24 channels).

• The

convolution

• peration

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

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Auralization Auralization types types

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

reproduction

• n

headphones (Binaural Room Scanning)

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

signal)

• ITU 5.1 (from different 5-mikes layouts)
• 2D Ambisonics 3rd order (from Mark Poletti’s

circular array microphone)

• Wave Field Synthesis (from the circular array of

Soundfield microphones)

• Hybrid methods (Ambiophonics)

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ORTF Stereo ORTF Stereo

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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) )

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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

d1l xr xl

Cross-talk canceller

d1r d2l d2r dNl dNr N

20°

Ambisonics Ambisonics 3D 1 3D 1st

st order

• rder

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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

• Williams MMA

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Schematic of the setup C : Cardioid, 0° L, R : Cardioid, ± 40° LS, RS : Cardioid, ± 120°

• 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

• OCT

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73 cm

Schematic of the setup C : Cardioid, 0° L, R : Super Cardioid, ± 90° LS, RS : Cardioid, ± 180°

Virtual Virtual high high-

• order
• rder

microphones microphones (M. (M. Poletti Poletti) )

• One
• f

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

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1 , n 6 n 3 cos D 1 , n 4 n 2 cos D 1 , n 2 n cos D 1 D

n , 3 n , 2 n , 1

= ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π ⋅ + ϑ ⋅ = = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π ⋅ + ϑ ⋅ = = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ π ⋅ + ϑ = =

From these 36 impulse responses it is possible to derive the response of cylindrical harmonics microphones (2D Ambisonics) up to 5th order.

1 90 180 270 1 90 180 270 1 90 180 270

1 90 180 270

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

• Flow diagram of the process

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microphones loudspeakers Original space Virtual space WFS

Hybrid Hybrid methods methods ( (Ambiophonics Ambiophonics) )

• Ambiophonics 3D (10 loudspeakers):

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Conclusions Conclusions

• 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