1
Underwater applications of the Brahma and
Citymap technologies for the Interreg
projectMANagement of anthropogenic NOISE and
its impacts on terrestrial and marine habitats in
sensitive areas
University of Parma Industrial Engineering
Department HTTP//ied.unipr.it
Author Angelo Farina HTTP//www.angelofarina.it
E-mail farina_at_unipr.it Skype angelo.farina
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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

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Ambisonics technology

• Ambisonics was invented in the seventies by
  Michael Gerzon (UK)
• It was initially a method for recording a
  4-channel 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

4
Ambisonics recording and playback

• Reproduction occurs over an array of 8-24
  loudspeakers, through an Ambisonics decoder

5
Ambisonics Technology
Recording
Processing
Decoding Speaker-feeds
Playback
Encoding B-Format
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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

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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

8
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 x-axis, the
  signal on the X output will have polarity
  reversed with respect to the W signal

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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

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A-format to B-format

• The A-format signals are converted to the
  B-format signals by matrixing
• W' FLUFRDBLDBRU
• X' FLUFRD-BLD-BRU
• Y' FLU-FRDBLD-BRU
• Z' FLU-FRD-BLDBRU
• and then applying proper filtering

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Recording
Recording
Processing
Decoding and Playback
Encoding
X Y Z W
Directional components velocity
Omnidirectional component pressure
B-FORMAT
Soundfield Microphone
Polar Diagram
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Encoding (synthetic B-format)
Recording
Processing
Decoding and Playback
Encoding
0 W
1 X
1 Y
1 Z
0,707
s(t)
cos(A)cos(E)
s(t)
sin(A)cos(E)
s(t)
s(t)
sin(E)
s(t)
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Processing
Recording
Processing
Decoding and Playback
Encoding
Rotation
Tilt
Tumble
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Decoding Playback
Recording
Processing
Decoding and Playback
Encoding
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
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Software for Ambisonics decoding
Audiomulch VST host Gerzonic bPlayer Gerzonic
Emigrator
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Software for Ambisonics processing
Visual Virtual Microphone by David McGriffy
(freeware)
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Rooms for Ambisonics playback
ASK (UNIPR) Reggio Emilia
University of Ferrara
University of Bologna
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Rooms for Ambisonics playback
University of Parma (Casa della Musica)
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BRAHMA 4-channels recorder

• A Zoom H2 digital sound recorder is modified in
  India, allowing 4 independent inputs with phantom
  power supply

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BRAHMA 4-channels recorder

• The standard microphone system is usually a
  terahedrical probe equipped with 4 cardioid
  electrect microphones

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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 [phone] www.AquarianAudio.com
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Underwater probe for Brahma

• For underwater recordings, a special setup of 4
  screw-mounted hydrophones is available

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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
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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

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BRAHMA 4-channels underwater recorder

• The system is aligned vertically by means of a
  bubble scope, and horizontally by means of a
  magnetic compass

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BRAHMA 4-channels underwater recorder

• Once placed on the sea bed, the system is usually
  well accepted (and ignored) by the marine life

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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

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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 (_at_ 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

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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
a
Tetrahedrical hydrophonic probe
a azimuth - q elevation
x
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Trajectory from multiple recording buoys

• Employing several buoys, the complete trajectory
  can be triangulated

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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

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Sound sources

• CITYMAP manages 4 types of sound sources
• Roads
• Railways
• Wide-area industrial plants
• point sources
• CITYMAP contains an comprehensive data-base of
  noise emission of Italian vehicles (cars, trucks,
  motorbikes, trains, etc.)

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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

Time profile of the pass-by of a car - d7.5 m
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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

Velocity ranges C1 - 0ltVlt25 km/h acceler. C2 -
25ltVlt50 km/h acceler. C3 - 0ltVlt25 km/h
deceler. C4 - 25ltVlt50 km/h deceler. C5 -
50ltVlt70 km/h C6 - 70ltVlt90 km/h C7 -
90ltVlt110 km/h C8 - V gt 110 km/h.
Vehicle Type V1 - cars V2 small trucks, bus V3
heavy trucks, double-decker bus V4 - TIR V5 -
motorbykes.
Type of rolling surface A1 standard bitume
slope negligible A2 standard bitume, slope gt
5 A3 standard bitume, slope lt -5 A4 - pavé,
slope negligible A5 sound absorbing road
pavement, slope negligible.
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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

Speed ranges C1 - 0ltVlt60 km/h C2 -
60ltVlt90 km/h C3 - 90ltVlt120 km/h C4 - V gt 120
km/h.
Vehicle type V1 freight train V2 passenger
(regional) V3 passenger (intercity)
Type of rails A1 Continuous Welded Rail on
concrete sleepers and ballast A2 Short rails
with open joints on wood sleepers and ballast.
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Computation formulas

• First of all, we get the Leq at 7.5m from axis of
  the road

• Or from the axis of the track (railways)

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Propagation at distant receivers

• The total sound power emitted by each segment of
  linear source is regrouped at its center

• Then the sound level at a distance d is computed
  as if it was a point source

• At each receiver, the contribuition of all
  segments of roads and railways are energetically
  summed

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Effects of screens

• CITYMAP computes a simplified screening effect
  due to obstacles, such as building or noise
  barriers

d B C -A
C
B
A
Frequency f is assumed equal to 340 Hz
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CITYMAP software architecture
CITYMAP reads the geometry from a DXF file, the
traffic flow data are inserted, the emission
value of each vehicle is read from the data-base,
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
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Geometry definition in AutoCAD

• Relevant entities are 3DPOLY on layers named as
  STRADE, BINARI, CASE, BARRIERE

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Import of DXF file in Citymap

• It is possible to select what entities are to be
  imported, and if they have to be appended

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Traffic flow data for roads and railways

• Clicking on an entity, a new window appears,
  making it easy to assign traffic data.

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Single-point computation

• It is very fast to compute the sound pressure
  level in selected points (entity CIRCLE on layer
  PUNTI)

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Computation on a grid of receivers

• It is also possible to define a regular grid of
  receivers, for charting SPL maps

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Post-processing with Surfer

• Surfer converts the GRD file created by Citymap
  in a countor map chart

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From Surfer back to AutoCAD

• Finally the contour map is imported back over the
  original plan, for showing the noise map

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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

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Example of usage of Underwater Citymap

• Mapping of underwater sound pressure level due to
  a boat along a trajectory

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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 )

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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

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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)