Convergence Instruments ACAM 64 User manual
ACAM_64
User’s Manual
December 18 2021
Bruno Paillard
ACAM_64
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1INTRODUCTION _____________________________________________ 3
2WARNINGS _________________________________________________ 3
3THEORY OF OPERATION______________________________________ 3
3.1 Frequency, Aperture Size, and Image Resolution ____________________________________ 4
3.2 Spatial Sampling and Upper Frequency Limit _______________________________________ 4
3.3 Field of View (FOV)_____________________________________________________________ 5
3.4 Audio Beamformer _____________________________________________________________ 5
4FEATURES__________________________________________________ 5
5ACAM_64 APPLICATIONS _____________________________________ 6
6GETTING STARTED __________________________________________ 6
6.1 Software Installation ____________________________________________________________ 6
6.2 Hardware Installation ___________________________________________________________ 6
6.3 Initial Test and Configuration ____________________________________________________ 6
7INSTRUMENT_MANAGER APPLICATION_________________________ 7
7.1 Starting the Application _________________________________________________________ 7
7.2 Main Functions ________________________________________________________________ 8
7.2.1 Image Field ________________________________________________________________ 8
7.2.2 Cursors____________________________________________________________________ 8
7.2.3 Instrument Information Fields __________________________________________________ 8
7.2.4 Frequency Response _________________________________________________________ 8
7.2.5 Frequency Response Controls __________________________________________________ 8
7.2.6 Trace of Past Levels _________________________________________________________ 8
7.2.7 Persistance Control __________________________________________________________ 9
7.2.8 Lin/Log Button _____________________________________________________________ 9
7.2.9 Interpolation Button__________________________________________________________ 9
7.2.10 Palette Button ______________________________________________________________ 9
7.2.11 AutoTrack Button ___________________________________________________________ 9
7.2.12 FOV Button ________________________________________________________________ 9
7.2.13 Record Button ______________________________________________________________ 9
7.2.14 Playback Button_____________________________________________________________ 9
7.2.15 Pause Button _______________________________________________________________ 9
7.2.16 Scrubber bar________________________________________________________________ 9
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1Introduction
ACAM_64 is a USB-connected acoustic camera and beamforming acoustic array. Its 64-microphone
array allows it to produce 32x32-pixel (128x128-pixel interpolated) real-time images showing sound
sources in its field of view.
2Warnings
•Never blow air at or near the microphones.
•Do not store or operate the instrument in environments where liquids could be projected onto
the microphone array. Ingestion of droplets of liquids (however small) into the pressure ports of
the microphones will damage them.
•Do not store or operate the instrument in dusty environments. Ingestion of dust particles, even
a few microns in size, into the pressure ports of the microphones will damage them.
•Do not store or operate the instrument at temperatures exceeding the following limits: -20 °C to
80 °C (-4 °F to 176 °F)
•Do not expose the microphones to sound pressures in excess of 160 dBSPL.
3Theory of Operation
An acoustic camera produces an image where the intensity of each pixel represents the amplitude of
acoustic waves coming from the corresponding direction. This is akin to an optical camera producing an
image where each pixel represents the intensity of light coming from the corresponding direction.
For an optical camera, the lens focuses light coming from a certain direction to the corresponding pixel
on the sensor or film. Each pixel in the image represents the intensity of light coming from a specific
azimuth (angle in the horizontal plane) and elevation (angle in the vertical plane). The lens does this by
slowing and delaying the light waves hitting the lens by precisely the right amount, so that all waves
coming from a certain direction arrive in phase in the focal plane, at the position of the corresponding
pixel.
An acoustic camera does much the same thing, except that the work of the lens is replaced by a digital
computational engine that processes signals captured by an array of microphones (see Figure 1).
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Figure 1
An array of microphones captures the sound waves hitting the array from many different directions. For
every pixel, a massively parallel digital processing engine applies specific delays, and sums the acoustic
signals from every microphone, so that the signals from a specific angle of incidence (azimuth and
elevation) arrive in phase. Figure 1shows that process for a single pixel. Note that a different and
precisely adjusted delay must be applied to every path, from every microphone in array to every pixel in
the image. In the simplest implementation, the intensity of every pixel is calculated as the energy of that
sum signal, averaged over a specific length of time.
3.1 Frequency, Aperture Size, and Image Resolution
For an optical camera, as well as for an acoustic camera, the image resolution is a proportional to the
ratio of aperture size to wavelength.
For an optical camera the aperture size of the camera (the size of the lens or more generally the light
collector) is always very large relative to the wavelengths of interest. This is true even for very small
lenses, such as those found in camera phones, where the size of the lens is a few mm, while the
wavelengths of interest are in the hundreds of nm (more than 10000 times smaller). For an optical
camera, resolution is rarely limited by the size of the aperture.
For an acoustic camera on the other hand, the frequencies of interest often extend to quite low
frequencies (long wavelengths). For instance, the wavelength at 100 Hz is 3.4 m. To have a reasonable
resolution at such low frequency would require an array of at least 8 to 10 times as large (25 to 30 m
wide). This is usually not practical. Therefore, for acoustic cameras the resolution is typically poor at lower
frequencies and improves only as the frequency of interest increases.
3.2 Spatial Sampling and Upper Frequency Limit
For an acoustic camera, the maximum frequency is limited by the spatial separation between two
adjacent microphones. The half wavelength of the maximum frequency sampled by the microphones
must be wider than the distance between two microphones. Otherwise, the array is not able to distinguish
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between sources that are within the field of view, and sources that are outside, leading to artifacts such
as phantom images.
For ACAM_64, the distance between microphones is 23 mm, so that frequencies up to 7.5 kHz can be
imaged properly. In practice the array is sampled at 16 kHz, with a Nyquist frequency of 8 kHz. The anti-
aliasing filters in the camera ensure that the signal energy is low above 7.5 kHz.
3.3 Field of View (
FOV
)
The field of view of a camera represents the number of degrees that the camera can see (that are
represented in the image) in the horizontal plane (azimuth) and vertical plane (elevation).
For ACAM_64, the field of view is the same in azimuth and elevation (the image is square). There are
two possible settings:
•90 degrees (-45 degrees to +45 degrees from left to right and from bottom to top)
•60 degrees (-30 degrees to +30 degrees from left to right and from bottom to top)
3.4 Audio Beamformer
The acoustic “sum” signal corresponding to any pixel position is available and can be streamed out
of the processing engine, to be listened to. This process is called “beamforming”. The microphone
array can be digitally steered to the angle of incidence corresponding to any pixel in the field of view
and focus on that source. In addition, since the image shows the azimuth and elevation of the loudest
source in the field of view of the camera, the beamformer can be made to follow that “hot-spot” as it
moves across the field of view.
4Features
•32x32 real-time image of the acoustic environment, displayed as a thermal map.
•Ready to run application provided for Windows.
•The beamformer can capture the audio signal at any specific direction within the field of view of
the camera
•Using the provided application, the audio capture can track the source direction, following the
source as it moves within the field of view of the camera.
•Frequency response can be adjusted by defining lower and upper frequency limits.
•Adjustable field of view: 60 deg or 90 deg.
•Adjustable image persistence from 10ms to 10s
•Massively parallel real-time all-digital design. Can build every pixel of the image from every
sample captured by every microphone in the array.
•Open communication protocol allows applications designed by OEMs
•Editable individual custom ID for easier instrument management.
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ACAM_64
Applications
•Detection, tracking and recording of acoustic sources.
•Soundproofing.
•Mechanical product design for acoustical performance.
6Getting Started
6.1 Software Installation
•On the PC that is used to setup the instrument, run Instrument_Manager_Installer.exe. This
installs the Instrument_Manager application, as well as its USB driver and documentation.
Note: Perform the software installation above BEFORE connecting the instrument to the PC for the
first time. The installer includes the USB driver of the instrument, without which the PC will not recognize
the instrument.
6.2 Hardware Installation
1. Connect the instrument to an available USB port on the PC
2. Verify that the PC properly detects the instrument and wait for the PC to load the driver. In case
of doubt see section Troubleshooting
6.3 Initial Test and Configuration
1. Upon connection to the PC, the LED should light-up red, yellow then green. The LED turning
green means that the instrument has finished its boot procedure, and that the PC has recognized
it.
2. Go into Start\All Programs\Convergence_Instruments\Instrument_Manager and run
Instrument_Manager.exe. The front-panel described in Figure 2appears, and the application
tries to connect to the instrument. If it fails to find the instrument it indicates No Device Found. If
this is the case see section Troubleshooting
3. Otherwise, the application starts communicating with the instrument and the image should
change as the acoustic environment changes.
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7Instrument_Manager Application
Figure 2 Instrument Manager Controls
1. Real-time acoustic image
2. Cursor
3. Instrument information
4. Instrument frequency response
5. Frequency response controls
6. Trace of past levels (in dB)
7. Image persistance control
8. Lin/Log image mapping
9. Image interpolation button
10. Image palette
11. Auto-Track button
12. Field of view button
13. Record button
14. Play-back button
15. Pause button
16. Scrubber bar
7.1 Starting the Application
To control an ACAM_64 using the Instrument_Manager, proceed as follows:
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1. Connect the instrument to an available USB connector on the PC.
2. Make sure that the operation LED turns green. If not, review the installation procedure, or see
section Troubleshooting
3. Go to Start\All-Programs\Convergence_Instruments\Instrument_Manager and run
Instrument_Manager.exe.
4. The front-panel described in Figure 2appears, and the application tries to connect to the
instrument. If it fails to find the instrument it indicates No Device Found. If this is the case, see
section Troubleshooting
5. Otherwise, the application immediately starts communicating with the ACAM_64 and presents
the acoustic image on the screen.
7.2 Main Functions
The front-panel of the application has several fields:
7.2.1 Image Field
The image field displays the real-time acoustic image captured by the instrument. The image is auto
scaled in contrast and brightness.
7.2.2 Cursors
In Tracking mode, the cursor follows the highest pixel in the image. That is also where the beamformer
is pointing.
In No-Track mode, the cursor can be grabbed and moved manually to steer the beamformer to a specific
location. The yellow curve in the trace of past levels shows the level measured at the position of the
cursor.
7.2.3 Instrument Information Fields
These fields present information about the instrument. The User_ID can be set to any alphanumeric
string (limited to 32 characters). This is used to identify the instrument to something pertinent to the user.
7.2.4 Frequency Response
This shows the frequency response of the camera.
7.2.5 Frequency Response Controls
This pair of controls select the lowest and highest frequencies processed by the acoustic imager. Note
that the resolution of the camera is dependent on the frequencies that it is imaging. Lower frequencies
produce images that have a very low resolution, while higher frequencies can show finer details. The two
controls allow the response of the imager to be selected between a very wide frequency range (the
default) to a very narrow one. By choosing a very narrow band and changing this band different images
can be produced to show the effects of various frequency components in a source.
7.2.6 Trace of Past Levels
This white curve presents the highest level in the image (in dB-SPL), as a function of time. The yellow
curve shows the level at the location of the cursor. The blue curve presents the lowest level in the image.
These levels represent the contribution of the corresponding source to the measured level at the location
of the camera.
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7.2.7 Persistance Control
This control adjusts the persistence of the image. This is the equivalent of the exposure time for an optical
camera. A persistence of a 200 to 300 ms is recommended for most applications. A longer persistence
will allow the averaging of the image over longer time periods, and therefore present images with less
noise. But events occurring at short intervals will blur from one to the next. A shorter persistence will allow
the tracking of more dynamic events, at the expense of noisier images.
7.2.8 Lin/Log Button
In Lin mode, the brightness of the pixel is proportional to the pressure-squared received from the
corresponding direction. In Log mode, the brightness of the pixel is proportional to the level in dB received
from the corresponding direction. Log mode allows the representation of a wider dynamic range of levels,
but it also tends to produce images with less sharp details.
7.2.9 Interpolation Button
When this button is pressed, the 32x32-pixel image is interpolated to 128x128 pixels. When not pressed,
the window shows the raw 32x32 image. The interpolation is performed by the PC, so on some low-end
PCs the interpolation process can slow-down the image presentation.
7.2.10 Palette Button
This control selects a monochrome or polychrome palette. On some images, a polychrome palette allows
more details to be visible in the low-level part of the dynamic range.
7.2.11 AutoTrack Button
When this button is pressed, the audio beamformer will track the highest-intensity pixel in the image. The
audio produced by the camera will automatically follow and focus on the source as it moves across the
field of view. When the mode is not set to AutoTrack, the cursor can be moved manually to any pixel in
the image.
7.2.12 FOV Button
The user can choose between two fields of view: 60 deg or 90 deg. Changes from one field of view to
the other take time, as the camera must be completely reprogramed for the new field of view. The choice
of field of view is persistent across connections/disconnections.
7.2.13 Record Button
A movie can be recorded by pressing this button. The recording starts when the button is pressed and
stops when the button is pressed for a second time. When the recording stops, the application will ask
where to store the recorded file.
7.2.14 Playback Button
A previously recorded movie can be played back by pressing the Play button. The application then asks
to point to the recorded file. The recorded file plays at normal speed. The playback can be paused by
pressing the Pause button at any time. After the complete file has played, the playback system is left in
pause mode at the last image of the file. Pressing the Play button while a file is being played will abort
the playback.
7.2.15 Pause Button
Pressing the Pause button during playback will pause the image. At that time, the scrubber bar can be
moved manually to quickly change locations in the file.
7.2.16 Scrubber bar
While the playback is paused, the scrubber bar can be used to quickly move the playback to a new
position in the file.
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8Troubleshooting
8.1 USB Driver Installation
If the Instrument_Manager application is unable to communicate with the ACAM_64 it may be because
the USB driver failed to install properly. To check the USB driver installation, follow the procedure below:
1. Make sure the Instrument_Manager application has been installed BEFORE the instrument is
connected to the PC for the first time. If not, disconnect the instrument and install
Instrument_Manager.
2. If necessary, take the PC out of stand-by.
3. Connect the instrument to an available USB port on the PC. The first time the instrument is
connected it may take some time for the PC to recognize the instrument and load its USB driver.
Wait until the instrument has been recognized by the PC. If necessary, open the Settings page
of Windows, and observe that the PC has recognized the instrument.
4. Make sure the charge LED lights-up and turns green after 1 to 2 s. If not, make sure that the
PC’s USB port is functional, and that the USB cable is not damaged. If necessary, try on a
different PC, and/or with a different USB cable. If the PC does not recognize the instrument, go
to step 5
5. If the PC does not seem to recognize the instrument, open the Device Manager on the PC. This
is usually found in Control Panel – System and Maintenance.
6. Just after connecting the instrument to the PC, observe that the Device Manager window
refreshes.
7. Verify that the following 3 items are created:
a. Microphone (ACAM-Audio) should be created in the Audio Inputs and Outputs
section.
b. DDCI Platform should be created in the list of devices.
c. USB serial device (COM x) should be created in the Ports section. It is possible that
your PC has more than one of these ports installed, each one corresponding to a
different device.
8. If an unknown item appears, or an item with the above names is found but has an exclamation
mark (indicating a problem) beside it, disconnect the device and try re-installing the driver (see
step 9).
9. For a manual installation of the driver, contact support@convergenceinstruments.com
8.2 Electrostatic Discharges
When the instrument is subjected to electrostatic discharges it can lose communication with the host PC.
If that happens, simply disconnect, and reconnect the USB cable, and restart the application.
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