1	New measurement technique for 3D sound characterization in theatres A.Farina¹, L. Tronchin² ¹University of Parma, Italy ²University of Bologna, Italy
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4	Methods For mapping the direction of arrival of early reflections, three methods have been successfully tested: Good, old Ambisonics (1^st order B-format) A shotgun microphone over a turntable A spherical microphone array (Eigenmike™)
5	Previous experience At UNIPR and UNIBO we have 10+ years of experience employing 1^st-order Ambisonics microphones (Soundfield ^TM, DPA-4, Tetramic, Brahma)
6	Capturing Ambisonics signals A tetrahedrical microphone probe was developed by Gerzon and Craven, originating the Soundfield microphone
7	Soundfield microphones
8	Ambisonics signals The Soundfield (TM) microphone provides 4 signals: 1 omnidirectional (pressure, W) and 3 figure-of-8 (velocity, X, Y, Z)
9	Directivity of transducers
10	Advanced IR capture and rendering ( project) In 2003 Waves launched a large research project, aimed to capturing a huge set of 3D impulse responses in the most famous theatres of the world The measurments did employ three diffrent microphone systems, but here we are talking only about the Soundfield microphone, as in the original Gerzon’s suggestion More than 100 acoustical spaces were measured, including several historical sites, including the Greek/Roman theatres of SIracusa and Taormina, in SIcily
11	Measurement Setup The measurement method incorporated 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 available in 2003 was supported
12	Measurement Parameters Test Signal: pre-equalized sweep
13	Test Signal – x(t)
14	Measured signal - y(t) The not-linear behaviour of the loudspeaker causes many harmonics to appear
15	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)]
16	Result of the deconvolution The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders
17	Transducers (sound source #1) Equalized, omnidirectional sound source: Dodechaedron for mid-high frequencies One-way Subwoofer (<120 Hz)
18	Directivity of transducers LookLine D-200 dodechaedron
19	Directivity of transducers LookLine D-300 dodechaedron
20	Directivity of transducers Omnisonic 1000 dodechaedron
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)
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)
23	Other hardware equipment Rotating Table: Outline ET-1
24	Measurement procedure A single measurement session play backs 36 times the test signal, and simultaneusly record the 8 microphonic channels
25	Theatres measured
26	Greek Theater in Siracusa
27	Roman Theater in Taormina
28	Current use of Ambisonics 1^st order Ambisonics is still widely employed, as now it can be implemented employing very cheap equipment (Tetramic, Brahma) Pulsive sound sources are usually preferred for a number of reasons Portable, battery operated recorders make it very easy to collect a large number of impulse responses A new digital method of processing the signals provides much better polar response than those available form the original Soundfield microphone
29	Current use of Ambisonics Balloons or Firecrackers as sound source
30	Firecracker Vs. Dodechaedron Comparison in Patras’ Odeion
31	Firecracker Vs. Dodechaedron Comparison in Patras’ Odeion
32	Other pulsive sources Balloons, starter pistol
33	Balloons Large ballons have more pronounced low frequencies
34	Starter Pistol
35	The “clap machine” Good frequency response and repatibility
36	The “clap machine” Verification of the repeatibility
37	The “clap machine”
38	The “clap machine”
39	Current use of Ambisonics A portable digital recorder equipped with tetrahedrical microphone probe: BRAHMA
40	Conversion from A-format to B-format A 4x4 filter matrix is employed in the X-volver free plugin
41	ISO 3382 acoustical parameters Aurora plugin – processing the Odeion in Patra
42	ISO 3382 acoustical parameters Reverberation Time T30 – Odeion in Patras
43	ISO 3382 acoustical parameters Reverberation Time T30 – Audit. University of Patras
44	Spatial Analysis The direction of arrival can be found as follows: The Sound Intensity vector components are computed I_x=w·x I_y=w·y I_z=w·z Also the total energy density is computed De=sqrt(w·w+x·x+y·y+z·z) They are averaged over 1ms time slices The ratio between active intensity and energy density is finally computed I_mod = sqrt(I_x·I_x+I_y·I_y+I_z·I_z) R=I_mod/De And azimuth and elevation of reflections are found: Az = atan2(I_y,I_x) El = asin(I_z/I_mod)
45	Background image The Mercator projection is employed for creating a rectangular image covering the whole surface of the sphere
46	Image Composite Editor Creates a panoramic image ranging 360°horizontally and up to 180°vertically
47	Reflection Mapping We can now plot a circle for every reflection, at the Azimuth and Elevation found, over a standard Cartesian framework The radius of the circle is made proportional to the Sound Intensity level in dB The transparency of the circle is made proportional to the ratio R When R is low, the intensity is not indicating anymore a direction of arrival which can be perceived by the listeners When R is large (close to 1), the sound is strongly polarized in one direction, which can be easily perceived
48	Echo localization from B-format IR Visual Basic program for displaying reflections
49	Echo localization from B-format IR Odeion in Patras
50	Echo localization from B-format IR Odeion in Patras
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80	Hardware for 360° video
81	Video unwrapping
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