Transcript Diapositiva 1

University of Parma
Industrial Engineering Department
HTTP://ied.unipr.it
“Underwater applications of the Brahma and
Citymap technologies for the Interreg project:
“MANagement of anthropogenic NOISE and
its impacts on terrestrial and marine habitats
in sensitive areas”
Author: Angelo Farina – HTTP://www.angelofarina.it
E-mail: [email protected] – Skype: angelo.farina
Goals
• Explanation of the Ambisonics technology, as
currently employed in room acoustics
• Brahma: the first underwater 4-channels digital
sound recorder
• A tetrahedrical hydrophone array for Brahma
• Sound source localization from Ambisonics
(B-format) recordings
• Noise immission mapping employing a modified
version of the CITYMAP computer program
Ambisonics technology
• Ambisonics was invented in the seventies by
Michael Gerzon (UK)
• It was initially a method for recording a 4channel stream, which later was played back
inside a special loudspeaker rig
• It is based on the pressure-velocity
decomposition of the sound field at a point
• It makes it possible to capture the complete
three-dimensional sound field, and to reproduce
it quite faithfully
Ambisonics recording and playback
Original Room
Ambisonics decoder
Sound Source
SoundField Microphone
B-format 4 channels signal
(WXYZ)
Speaker array in the
reproduction room
Reproduction occurs over an array of 8-24 loudspeakers,
through an Ambisonics decoder
Ambisonics Technology
Recording
Processing
Decoding
Speaker-feeds
Playback
Encoding
B-Format
The Soundfield microphone
• This microphone is equipped with 4
subcardioid capsules, placed on the faces
of a thetraedron
• The signal are analogically processed in
its own special control box, which derives 4
“B-format” signals
• These signals are:
• W : omnidirectional (sound pressure)
• X,Y,Z : the three figure-of-eight
microphones aligned with the ISO
cartesian reference system – these
signals are the cartesian components
of the “particle velocity” vector
Other tetrahedrical microphones
• Trinnov, DPA, CoreSound, Brahma are other microphone
systems which record natively the A-format signals,
which later are digitally converted to B-format
The B-format components
• Physically, W is a signal
proportional to the pressure,
XYZ are signals proportional
to the three Cartesian
components of the particle
velocity
• when a sound wave
impinges over the
microphone from the
“negative” direction of the xaxis, the signal on the X
output will have polarity
reversed with respect to the
W signal
A-format to B-format
• The A-format signals are the “raw” signals coming from
the 4 capsules, loated at 4 of the 8 vertexes of a cube,
typically at locations FLU-FRD-BLD-BRU
A-format to B-format
• The A-format signals are converted to the B-format signals by
matrixing:
W' = FLU+FRD+BLD+BRU
X' = FLU+FRD-BLD-BRU
Y' = FLU-FRD+BLD-BRU
Z' = FLU-FRD-BLD+BRU
• and then applying proper filtering:
Recording
Recording
Processing
Decoding and Playback
Encoding
X
Y
Directional
components:
velocity
Z
W
Soundfield
Microphone
Omnidirectional
component:
pressure
B-FORMAT
Polar Diagram
Encoding (synthetic B-format)
Recording
Processing
Decoding and Playback
Encoding
0
1
W
=0,707 *s(t)
X
=cos(A)cos(E) *s(t)
Y
=sin(A)cos(E) *s(t)
Z
=sin(E) *s(t)
X Y  Z 1
2
s(t)=
2
2
Processing
Recording
Processing
Decoding and Playback
Encoding
w'  w
x'  x  cos(R)  y  sin(R)
y '  x  sin(R)  y  cos(R)
 X '  k11 X  k12W  k13Y  k14 Z
W '  k X  k W  k Y  k Z

21
22
23
24

Y '  k 31 X  k 32W  k 33Y  k 34 Z
Z '  k 41 X  k 42W  k 43Y  k 44 Z
Rotation
z'  z
w'  w
x'  x
y '  y  cos(T )  z  sin(T )
z '  y  sin(T )  z  cos(T )
Tilt
w'  w
x'  x  cos(T )  z  sin(T )
y'  y
z '  x  sin(T )  z  cos(T )
Tumble
Decoding & Playback
Recording
Processing
z
Decoding and Playback
Encoding

1
Fi   G 1  W  G 2  X  cos( )  Y  cos( )  Z  cos(  ) 
2
r

y

x
Each speaker feed is
simply a weighted sum
of the 4 B-format signals.
The weighting
coefficients are
computed by the cosines
of the angles between
the loudspeaker and the
three Cartesian axes
Software for Ambisonics decoding
Audiomulch VST
host
Gerzonic bPlayer
Gerzonic Emigrator
Software for Ambisonics processing
Visual Virtual Microphone by David McGriffy (freeware)
Rooms for Ambisonics playback
ASK (UNIPR) – Reggio Emilia
University of Ferrara
University of Bologna
Rooms for Ambisonics playback
University of Parma (Casa della Musica)
BRAHMA: 4-channels recorder
• A Zoom H2 digital sound recorder is modified in India,
allowing 4 independent inputs with phantom power supply
BRAHMA: 4-channels recorder
• The standard microphone system is usually a terahedrical
probe equipped with 4 cardioid electrect microphones
Hydrophones for Brahma
• Brahma provides phantom power (5V) for transducers
equipped with integral electronics. Hence the ideal
hydrophone is the Acquarian Audio H2A:
Aquarian Audio Products
A division of AFAB Enterprises
1004 Commercial Ave. #225 Anacortes, WA 98221 USA
(360) 299-0372 www.AquarianAudio.com
Sensitivity:
Frequency range:
-180dB re: 1V/Pa
<10 Hz to >100KHz
Polar Response:
Operating depth:
Output impedance:
Omnidirectional
<80 meters
Power:
Physical:
Dimensions:
Mass:
1 K
0.6 mA
(+/-4dB 20Hz-4.5KHz)
(approximate sensitivity @100KHz
= -220dB re: 1V/Pa)
(horizontal)
(typical)
(typical)
(cable and output plug excluded)
25mm x 46mm
105 grams
Underwater probe for Brahma
• For underwater recordings, a special setup of 4 screwmounted hydrophones is available:
Underwater case for Brahma
• Due to the small size (like a cigarette packet) it is easy to
insert the Brahma inside a waterproof cylindrical
container, sealed with O-rings
• An external lead-acid battery can be included for
continuous operation up to one week (in level-activated
recording mode)
cable
6V 12 Ah battery
BRAHMA: 4-channels recorder
• The probe can be mounted on a weighted base, allowing
for underwater placement of the recorded, inside a
waterproof case. However, the cables are long enough
(15m) also for keeping the recorder on the boat
BRAHMA: 4-channels underwater
recorder
• The system is aligned vertically by means of a bubble
scope, and horizontally by means of a magnetic compass:
BRAHMA: 4-channels underwater
recorder
• Once placed on the sea bed, the system is usually well
accepted (and ignored) by the marine life:
Brahmavolver: the processing software
• Brahma records A-format signals. They can be converted
to standard B-format by means of the Brahmavolver
program, running on Linux / Windows / Mac-OSX
BRAHMA: technical specs
•
•
•
•
•
•
•
•
Sampling rates: 44.1 kHz, 48 kHz, 96 kHz (2 ch. only)
Recording format: 1 or 2 stereo WAV files on SD card
Bit Resolution: 16 or 24 bits
3 fixed gain settings, with 20 dB steps (traceable)
Memory usage: 1.9 Gbytes/h (@ 44.1 kHz, 24 bits, 4 ch.)
Recording time: more than 16 hours (with 32 Gb SD card)
Power Supply: 6 V DC, 200 mA max
Automatic recording when programmable threshold is
exceeded
• The SD card can be read and erased through the USB
port
Source localization from B-format signals
• At every instant, the source position is known in spherical
coordinates by analyzing the B-format signal
z
buoy
boat
q
y

 = azimuth - q = elevation
Tetrahedrical hydrophonic
probe
x
Trajectory from multiple recording buoys
• Employing several buoys, the complete trajectory can be
triangulated
The CITYAMP computer program
• Developed by University of Parma and
Italian Ministry for the Environment in 1995
during the EU-funded DISIA project
• CITYMAP makes it possible to map the
sound pressure level in large urban areas,
due to noise sources such as roads,
railways and industrial plants
Sound sources
• CITYMAP manages 4 types of sound
sources:
– Roads
– Railways
– Wide-area industrial plants
– “point sources”
• CITYMAP contains an comprehensive database of noise emission of Italian vehicles
(cars, trucks, motorbikes, trains, etc.)
Measurements of noise emission
• The emission data base is formed on recordings
of vehicle pass-bys recorded in octave bands,
with 0.5s time resolution, so that the time profile
of each pass-by was obtained
90
Livello Sonoro (dBA)
85
Integrating this area, the
Single Event Level (SEL) is
obtained:
SEL = Leq + 10log[T]
80
75
70
65
60
0
1
2
3
4
5
6
Tempo (s)
Time profile of the pass-by of a car - d=7.5 m
Data-Base of SEL – road vehicles
• Averaging over a large number of pass-bys,the typical
value of SEL was obtained for 5 categories of vehicles, 8
speeds and 5 types of rolling surfaces:
Vehicle Type
V1 - cars
V2 – small trucks, bus;
V3 – heavy trucks, double-decker bus;
V4 - TIR;
V5 - motorbykes.
Velocity ranges
C1 - 0<V<25 km/h acceler.;
C2 - 25<V<50 km/h acceler.;
C3 - 0<V<25 km/h deceler.;
C4 - 25<V<50 km/h deceler.;
C5 - 50<V<70 km/h;
C6 - 70<V<90 km/h;
C7 - 90<V<110 km/h;
C8 - V > 110 km/h.
Type of rolling surface:
A1 – standard bitume – slope negligible;
A2 – standard bitume, slope > +5%;
A3 –standard bitume, slope < -5%;
A4 - pavé, slope negligible;
A5 – sound absorbing road pavement, slope negligible.
Data-Base of SEL – railway vehicles
• Averaging over a large number of pass-bys,the typical
value of SEL was obtained for 3 categories of vehicles, 4
speeds and 2 types of rolling surfaces:
Vehicle type
V1 – freight train;
V2 – passenger (regional);
V3 – passenger (intercity);
Speed ranges
C1 - 0<V<60 km/h
C2 - 60<V<90 km/h
C3 - 90<V<120
C4 - V > 120 km/h.
Type of rails
A1 – Continuous Welded Rail on concrete sleepers and ballast;
A2 – Short rails with open joints on wood sleepers and ballast.
km/h
Computation formulas
• First of all, we get the Leq at 7.5m from axis of
the road:
 5  SELi  Lasfalto ,i  Lpendenza ,i

Ni 


10
L eq ,7.5m  10  lg  10

 
16

3600

 i1 
 
• Or from the axis of the track (railways):
 3  SELi  Lbinario ,i  Lpendenza ,i

Ni
Li  


10
L eq ,7.5m  10  lg  10


 
16

3600
100

 i1 
 
Propagation at distant receivers
• The total sound power emitted by each segment
of linear source is regrouped at its center:
LW  Leq,7.5m  10 lg  7.5  L
• Then the sound level at a distance d is
computed as if it was a point source:
 e d 

L eq  L W  10  lg
2
4d 
• At each receiver, the contribuition of all segments
of roads and railways are energetically summed
Effects of screens
• CITYMAP computes a simplified screening effect due to
obstacles, such as building or noise barriers:
 = B + C -A
C
B
A
f

L  10  lg 1 + 40    

c
Frequency f is assumed equal
to 340 Hz
CITYMAP software architecture
Geographical Information Service
(GIS) - Cartografia Digitale
Misure di Potenza (ISO 3744)
Source Manager
Misure di Direttività (balloons)
Certificati di prova
dei materiali
AutoCad (TM)
Material Manager
Dati di traffico
stradale e ferroviario
File di Interscambio
(.DXF)
data base
emissione
veicoli
data base
R, 
CITYMAP.EXE
Programma di Interfaccia - CITYMAP.EXE
data base
L w ,Qq
Ray CAD
File di descrizione
geometrica e di
emissione sonora (.CMP)
Geometry File (.RAY)
CITYMAP.EXE
Pyramid Tracer (DISIAPYR.EXE)
Structured SPL file (.GRD)
Unstructured SPL file (.DAT)
Surfer (TM)
SPL Contour Maps (.DXF or .WMF)
CITYMAP reads the
geometry from a DXF file, the
traffic flow data are inserted,
the emission value of each
vehicle is read from the database, or from a specific SPK
file for point sources.
Citymap computes the sound
pressure level at a number of
receivers, which can be
located also on a regular grid.
The resulting GRD file is later
post-processed by Surfer, for
creating the map
Geometry definition in AutoCAD
• Relevant entities are 3DPOLY on layers named as
STRADE, BINARI, CASE, BARRIERE
Import of DXF file in Citymap
• It is possible to select what entities are to be
imported, and if they have to be appended
Traffic flow data for roads and railways
• Clicking on an entity, a new window appears,
making it easy to assign traffic data.
Single-point computation
• It is very fast to compute the sound pressure level in
selected points (entity CIRCLE on layer PUNTI)
Computation on a grid of receivers
• It is also possible to define a regular grid of receivers, for
charting SPL maps
Post-processing with Surfer
• Surfer converts the GRD file created by Citymap in a
countor map chart
From Surfer back to AutoCAD
• Finally the contour map is imported back over the
original plan, for showing the noise map
Underwater extension of Citymap
• If Citymap is to be employed for underwater applications,
two main modifications are required:
– A new data-base of marine noise sources needs to be compiled
– The propagation algorithm must be replaced with a more realistic
one, which takes into account the inhomogeneous medium and
the multiple reflections between sea surface and sea floor.
• The first task is accomplished by performing thousands
of recording of pass-by recordings with various types of
boats, at various speeds, and with different sea state
• The second task requires a substantial effort for the
software developer, who will have to rewrite completely
the subroutine which performs the computations
Example of usage of Underwater
Citymap
• Mapping of underwater sound pressure level due to a
boat along a trajectory
Times and costs
• The prototype of the recording buoy has just
been finalized and tested! – the cost has been
anticipated by UNIPR and AIDA (our spinoff
company)
• The series production of buoys will start at
beginning of 2010. The estimated cost is 3000 €
each, and it is scheduled to build 6 of them
• The recordings for compiling the source emission
database will begin in summer 2010, and will last
6 months, employing 3 buoys and 2 people (12
man-months, 25.000 €)
Times and costs
• The recordings for performing surveys in the
selected marine sites will also start in summer
2010. The total number of buoys will be 6 (3
used also for boat recordings, 3 only for site
surveys), and a lot of work will be required fopr
deploying and recvering the buoys. The estimate
cost for the surveys is 25.000 €
• The modification of the Citymap program will tale
one year for one programmer (cost 25.000 €)
• The analysis of the survey recordings and the
elaboration of noise maps is also to be defined,
depending on the amount of data to be
processed and on the extension of the areas to
be mapped. It is actually estimated at 6.000 €
Internet resources
All the papers previously published by Angelo Farina can
be downloaded from his personal web site:
www.angelofarina.it
The CITYMAP program can be downloaded from:
www.angelofarina.it/Public/Disia
Its use is free for academic research in public institutions
(password issued on request)