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 propagation propagation in in rooms rooms Sound Reflected Sound Direct Sound Point Source Receiver Direct Sound Reflected Sound

Measurement process process Measurement Noise n(t) Not-linear, distorted signal time variant output y(t) input x(t) linear system w(t) system + w(t) ⊗ h(t) K[x(t)] � 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). 24th AES International Conference

Test signal signal: Log : Log Sine Sine Sweep Sweep Test � x(t) is a sine signal, which frequency is variable exponentially with time, starting at f 1 and ending at f 2 . ⎡ ⎤ ⎛ ⎞ ⎛ ⎞ f ⎢ t ⎥ ⎜ ⋅ ⎜ ⎟ ⎟ 2 ln ⎜ ⎟ ⋅ π ⋅ ⋅ 2 f T ⎢ ⎥ ⎝ ⎠ T f ⎜ ⎟ = ⋅ − 1 1 x ( t ) sin e 1 ⎢ ⎥ ⎛ ⎞ ⎜ ⎟ f ⎜ ⎟ ⎜ ⎟ 2 ⎢ ⎥ ln ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ f ⎣ ⎦ 1 24th AES International Conference

Deconvolution of of Log Log Sine Sine Sweep Sweep Deconvolution � 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)

– x(t) x(t) Signal – Test Signal Test

Measured signal signal - - y(t) y(t) Measured � The not-linear behaviour of the loudspeaker causes many harmonics to appear 24th AES International Conference

Inverse Filter Filter – – z(t) z(t) Inverse 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 of of the the deconvolution deconvolution Result 2° 1° 3° 5° The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders

Measurement Setup 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 � 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 � Deconvolution: 24th AES International Conference

Transducers (sound source #1) (sound source #1) Transducers � Equalized, omnidirectional sound source: Dodechaedron for mid-high frequencies – Subwoofer – Radiated sound power level 100 90 80 Lw (dB) 70 60 50 40 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) Unequalized Equalized 24th AES International Conference

Transducers (sound source #2) (sound source #2) Transducers � Genelec S30D reference studio monitor: Three-ways, active multi-amped, AES/EBU – Frequency range 37 Hz – 44 kHz (+/- 3 dB) – 250 Hz 1000 Hz 2000 Hz 0 0 0 0 0 0 330 30 330 30 330 30 -5 -5 -5 -1 0 -1 0 -1 0 -1 5 -1 5 -1 5 300 60 300 60 300 60 -20 -20 -20 -25 -25 -25 -30 -30 -30 -35 -35 -35 270 -40 90 270 -40 90 270 -40 90 240 120 240 120 240 120 210 150 210 150 210 150 180 180 180 4000 Hz 8000 Hz 16000 Hz 0 0 0 0 0 0 330 30 330 30 330 30 -5 -5 -5 -1 0 -1 0 -1 0 -1 5 -1 5 -1 5 300 60 300 60 300 60 -20 -20 -20 -25 -25 -25 -30 -30 -30 -35 -35 -35 270 -40 90 270 -40 90 270 -40 90 240 120 240 120 240 120 210 150 210 150 210 150 180 180 180

Transducers ( (microphones microphones) ) Transducers � 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) – Microfono Soundfield Cardioidi ORTF Braccio rotante Testa artificiale binaurale 24th AES International Conference

Other hardware hardware equipment equipment Other � Rotating Table : Outline ET-1 – � Computer and sound card: – Signum Data Futureclient P-IV 1.8 GHz – Aardvark Pro Q-10 (8 ch., 96 kHz, 24 bits) 24th AES International Conference

Measurement procedure procedure Measurement � A single measurement session play backs 36 times the test signal, and simultaneusly record the 8 microphonic channels 24th AES International Conference

Theatres measured measured Theatres Reverberatiuon Time T20 N. Theatre N. sources/receivers 3.5 1 Uhara Hall, Kobe, Japan 2/2 2 Noh Drama Theater, Kobe, Japan 2/2 3 3 Kirishima Concert Hall, Kirishima, Japan 3/3 Uhara 4 Greek Theater in Siracusa, Italy 2/1 2.5 Noh 5 Greek-Roman Theater in Taormina, Italy 3/2 Kirishima 2 6 Auditorium of Parma, Italy 3/3 T20 (s) Siracusa 7 Auditorium of Rome (Sala 700), Italy 3/2 1.5 Taormina 8 Auditorium of Rome (Sala 1200), Italy 3/3 Parma 9 Auditorium of Rome (Sala 2700), Italy 3/5 1 Roma-700 10 Bergamo Cathedral, Italy 2/1 Roma-1200 11 Teatro Valli, Reggio Emilia, Italy 5/1 0.5 Roma-2700 0 31.5 63 125 250 500 1000 2000 4000 8000 16000 Frequency (Hz)

Hall, Kobe, Japan Japan Uhara Hall, Kobe, Uhara

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

Kirishima Concert Hall, Concert Hall, Japan Japan Kirishima

Kirishima Concert Hall, Concert Hall, Japan Japan Kirishima

Theater in Siracusa in Siracusa Greek Theater Greek

Roman Theater Theater in Taormina in Taormina Roman

Parma Auditorium, Italy Parma Auditorium, Italy

Rome Auditorium, 700 Auditorium, 700 seats seats Rome

Rome Auditorium, 1200 Auditorium, 1200 seats seats Rome

Rome Auditorium, 2700 Auditorium, 2700 seats seats Rome

Bergamo’ ’s s Cathedral Cathedral, Italy , Italy Bergamo

Teatro Valli, Reggio Emilia, Italy Teatro Valli, Reggio Emilia, Italy

Acoustical Parameters Parameters Acoustical � 30 20 � Reverberation Time T 20 : � T � /2 T 20 /3 � 30 ⎡ ⎤ ms 80 ( ) ∫ ⋅ p 2 τ d τ ⎢ ⎥ � Clarity C 80 : ⎢ ⎥ = ⋅ C 0 10 lg ⎢ ⎥ ∞ 80 ( ) ∫ ⋅ ⎢ p 2 τ d τ ⎥ ⎣ ⎦ ms 80 50 ms ( ) ∫ 2 τ ⋅ τ p d � Definition D: = 0 ⋅ D 100 ∞ ( ) ∫ 2 τ ⋅ τ p d 0 ∞ ( ) ∫ τ ⋅ 2 τ ⋅ τ p d � Center Time T S : = 0 T s ∞ ( ) ∫ 2 τ ⋅ τ p d 0 24th AES International Conference