116 th AES Convention Berlin, 8-11 May 2004 Measurement and 5.0 rendering of spatial impulse responses of rooms Angelo Farina 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
Topics This presentation is a tribute to M. Gerzon, who • had foreseen 3D impulse response measurements and 3D Auralization obtained by convolution. Comparison between Auralizations based on • calculated and measured IRs (e.g. Theatre “La Fenice”, Venice) The advantages (and disadavantages) of • employing measured IRs Possible approaches to Auralization over ITU 5.0 • “surround” systems 116 th AES Convention Berlin, 8-11 May 2004
Concept (Gerzon, 1975) Measurement of B-format Original Room Portable PC with 4- Impulse Responses channels sound board B-format Imp. Resp. Sound Source of the original room B-format 4-channels signal (WXYZ) SoundField Microphone MLS or sweep excitation signal Sound Source B-format 4-channels Ambisonics decoder signal (WXYZ) Mono Mic. Convolver Convolution of dry signals with the B-format Impulse Responses Speaker array in the reproduction room 116 th AES Convention Berlin, 8-11 May 2004
Why do we measure these IRs? In case something happens to the original 1. 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 (5.1) and tomorrow’s musical productions 3. Auralization in special listening rooms can be performed for subjective tests 116 th AES Convention Berlin, 8-11 May 2004
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, Tronchin measured binaural impulse responses • 116 th AES Convention Berlin, 8-11 May 2004
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. 12 116 th AES Convention Berlin, 8-11 May 2004
Numerical simulation vs. measurement Prelude 1° act “La Traviata” by G.Verdi Dry music • Convolution with • experimental I.R. (pt. 12) Convolution with • simulated IR Stop 116 th AES Convention Berlin, 8-11 May 2004
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 116 th AES Convention Berlin, 8-11 May 2004
Sound propagation in rooms 116 th AES Convention Berlin, 8-11 May 2004 Receiver Direct Sound Reflected Sound Direct Sound Reflected Sound Point Source
Measurement process 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). 116 th AES Convention Berlin, 8-11 May 2004
Test signal: Log Sine Sweep x(t) is a sine signal, which frequency is varied 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 ⎣ ⎦ 1 116 th AES Convention Berlin, 8-11 May 2004
Test Signal – x(t) 116 th AES Convention Berlin, 8-11 May 2004
Measured signal - y(t) � The not-linear behaviour of the loudspeaker causes many harmonics to appear 116 th AES Convention Berlin, 8-11 May 2004
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) 116 th AES Convention Berlin, 8-11 May 2004
Inverse Filter – z(t) The deconvolution of the IR is obtained convolving the measured signal y(t) with the inverse filter z(t) 116 th AES Convention Berlin, 8-11 May 2004
Result of the deconvolution 1° 2° 3° 5° The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders 116 th AES Convention Berlin, 8-11 May 2004
Maximum Lenght Sequence vs. Sweep 116 th AES Convention Berlin, 8-11 May 2004
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 116 th AES Convention Berlin, 8-11 May 2004
Transducers (sound source # 1) Equalized, omnidirectional sound source: • Dodechaedron for mid-high frequencies One-way Subwoofer (< 120 Hz) Dodech. LookLine D200 120.0 110.0 Sound Power Level (dB) Lw,tot = 106.9 dB 100.0 Unequalized 90.0 Equalized 80.0 Lw,tot = 94.8 dB 70.0 60.0 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) 116 th AES Convention Berlin, 8-11 May 2004
Transducers (sound source # 2) Genelec S30D reference studio monitor: • Three-ways, active multi-amped, AES/EBU Frequency range 37 Hz – 44 kHz (+ /- 3 dB) Genelec S30D 120.0 110.0 Sound Power Level (dB) 100.0 Lw,tot = 96.8 dB Power 90.0 Pressure 80.0 70.0 60.0 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) 116 th AES Convention Berlin, 8-11 May 2004
Directivity of transducers LookLine D200 dodechaedron 1000 Hz 250 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 90 270 90 270 -40 90 - 40 - 40 240 120 240 120 240 120 210 150 210 150 210 150 180 180 180 8000 Hz 16000 Hz 4000 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 90 270 90 270 90 - 40 - 40 - 40 240 120 240 120 240 120 210 150 210 150 210 150 180 180 180 116 th AES Convention Berlin, 8-11 May 2004
Directivity of transducers Genelec S30D reference studio monitor 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 90 270 90 270 90 -40 -40 -40 240 120 240 120 240 120 210 150 210 150 210 150 180 180 180 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 90 270 90 270 90 -40 -40 -40 240 120 240 120 240 120 210 150 210 150 210 150 180 180 180 116 th AES Convention Berlin, 8-11 May 2004
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) Soundfield Microphone Cardioids (ORTF) Turntable Binaural dummy head 116 th AES Convention Berlin, 8-11 May 2004
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