Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND SYSTEM FOR CALIBRATING A SOUND SIGNAL IN A
PLAYBACK AUDIO SYSTEM
TECHNICAL FIELD
The present invention relates to the field of methods and system for
calibrating sound level
in a playback audio system, and more particularly for calibrating coherent
sound pressure
level.
BACKGROUND
In order to calibrate sound signal, some sound systems apply equalization
filter on the
channels of the signal while discarding the inter-channel wave cancellation
that might
occur. This results in an expected frequency response when played through only
one
channel but in an unexpected frequency response when played through multiple-
channels
due to interferences.
Some sound systems have been developed to account for these interferences
experimentally
and very quickly. However, such sound systems must be recalibrated every time
the
frequency distribution changes and are subject to inter-model interferences
when multiple
models play the same signals.
Therefore, there is a need for an improved method and system for calibrating a
sound
signal.
SUMMARY
According to a first broad aspect, there is provided a computer-implemented
method for
calibrating a sound signal, comprising: receiving an initial sound signal, a
recorded
background sound signal, a recorded initial sound signal and a target sound
signal;
subtracting the recorded background sound signal from the recorded initial
sound signal,
thereby obtaining a denoised sound signal; dividing the target sound signal by
the denoised
sound signal, thereby obtaining a compensation factor; dividing the initial
sound signal by
the compensation factor, thereby obtaining a calibrated sound signal; and
outputting the
calibrated sound signal.
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In one embodiment, the initial sound signal, the recorded background sound
signal, the
recorded initial sound signal and the target sound signal are expressed in a
logarithmic
scale, the method further comprising converting the initial sound signal and
the recorded
background sound signal from the logarithmic scale into linear Pascal (Pa)
scale before said
subtracting the recorded background sound signal from the recorded initial
sound signal
and converting the denoised sound signal from Pa into the logarithmic scale,
said dividing
the target sound signal by the denoised sound signal comprises subtracting the
denoised
sound signal from the target sound signal and said dividing the initial sound
signal by the
compensation factor comprises subtracting the compensation factor from the
initial sound
signal.
In one embodiment, the method further comprises recording background noise,
thereby
obtaining the recorded background sound signal.
In one embodiment, the method further comprises playing back the initial sound
signal.
In one embodiment, the method further comprises recording the played back
initial sound
signal, thereby obtaining the recorded initial sound signal.
In one embodiment, the initial sound signal comprises a white noise signal.
In one embodiment, the noise signal comprises a random noise signal.
In another embodiment, the noise signal comprises a predetermined noise
signal.
In one embodiment, the method further comprises: receiving an identification;
and
retrieving said initial sound signal from a database based on said
identification.
In one embodiment, the identification comprises a given flight phase.
In one embodiment, the method further comprises: receiving an identification;
and
retrieving said target sound signal from a database based on said
identification.
In one embodiment, the identification comprises a given flight phase.
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In one embodiment, said outputting the calibrated sound signal comprises at
least one of
storing the calibrated sound signal and playing back the calibrated signal
In one embodiment, the method further comprises playing back and muting the
predefined
audio signal while said recording the background sound signal.
According to another broad aspect, there is provided a computer program
product for
calibrating a predefined sound signal, the computer program product comprising
a
computer readable memory storing computer executable instructions thereon that
when
executed by a computer perform the steps of the above-described method.
According to another broad aspect, there is provided a system for calibrating
a predefined
sound signal, the system comprising a communication unit for at least one of
receiving and
transmitting data, a memory and processing unit configured for executing the
steps of the
above-described method.
According to still another broad aspect, there is provided a system for
calibrating a
predefined sound signal, the system comprising: a playback module for playing
back an
initial sound signal, the playback module comprising at least one loudspeaker;
a recording
module for recording background noise to obtain a background sound signal and
recording
the played back initial sound signal to obtain a recorded initial signal, the
recording module
comprising a microphone; a denoising module for subtracting the recorded
background
sound signal from the recorded initial sound signal to obtain a denoised sound
signal; a
compensation module for receiving a target sound signal and dividing the
target sound
signal by the denoised sound signal to obtain a compensation factor; and a
calibration
module for: dividing the initial sound signal by the compensation factor to
obtain a
calibrated sound signal; and outputting the calibrated sound signal
In one embodiment, the initial sound signal, the recorded background sound
signal, the
recorded initial sound signal and the target sound signal are expressed in a
logarithmic
scale, the denoising module is further configured for converting the initial
sound signal and
the recorded background sound signal from the logarithmic scale into Pascal
(Pa) before
subtracting the recorded background sound signal from the recorded initial
sound signal
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and converting the denoised sound signal from Pa into the logarithmic scale,
the
compensation module is configured for subtracting the denoised sound signal
from the
target sound signal and the calibration module is configured for subtracting
the
compensation factor from the initial sound signal.
In one embodiment, the initial sound signal comprises a white noise signal.
In one embodiment, the noise signal comprises a random noise signal.
In one embodiment, the noise signal comprises a predetermined noise signal.
In one embodiment, the playback module is further configured for: receiving an
identification; and retrieving said initial sound signal from a database based
on said
identification.
In one embodiment, the identification comprises a given flight phase.
In one embodiment, the compensation module is further configured for:
receiving an
identification; and retrieving said target sound signal from a database based
on said
identification.
In one embodiment, the identification comprises a given flight phase.
For the purpose of the present disclosure, a sound signal should be understood
as the
amplitude of a sound for a given frequency range. Therefore, a sound signal
comprises no
phase component.
In one embodiment, the recorded initial signal and background signal are
converted from
time domain to frequency domain by the recording module.
In one embodiment, the calibrated sound signal is converted from frequency
domain to time
by the calibration module.
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BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will become apparent
from the
following detailed description, taken in combination with the appended
drawings, in which:
Figure 1 is a flow chart illustrating a method for calibrating a predefined
sound signal, in
accordance with an embodiment;
Figure 2 is an exemplary graph illustrating the amplitude as a function of
frequency for a
recorded initial sound signal, a target sound signal to be achieved and a
recorded
background sound signal;
Figure 3 is a block diagram illustrating a system for calibrating an initial
sound signal, in
accordance with an embodiment; and
Figure 4 is a block diagram of a processing module adapted to execute at least
some of the
steps of the method of Figure 1, in accordance with an embodiment.
It will be noted that throughout the appended drawings, like features are
identified by like
reference numerals.
DETAILED DESCRIPTION
In the following there is described a method and system for calibrating the
sound level of a
sound system used for playing back sound signals. The sound signals to be
played back by
the sound system may be sound signals generated by a computer or sound signals
that have
been previously recorded.
In order to calibrate the sound level for the playback of an initial sound
signal, the
background noise is first recorded within the given area where the initial
sound signal is to
be played back to obtain a background sound signal. Then, the initial sound
signal is played
back and recorded within the given area to obtain a recorded initial sound
signal. The
recorded background sound signal is then subtracted from the recorded initial
sound signal
to obtain a denoised sound signal. The ratio between the denoised sound signal
and a target
sound signal is then calculated. The calculated ratio is then applied to the
initial sound
signal to obtain a calibrated sound signal. When played back by the sound
system, the
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calibrated sound signal substantially corresponds to the target sound signal.
The calibrated
sound signal is then outputted. For example, the calibrated sound signal may
be stored in
memory or sent to the sound system to be played back.
In one embodiment, the present method and system may be used in a simulator
such an
aircraft simulator, a tank simulator, a ship simulator, or the like. Because
the specific
environment of a simulator may affect the way a user of the simulator
perceives a played
back sound that is supposed to replicate the sound heard in a real system that
the simulator
simulates, calibration of the sound signal to be played back in the simulator
may be desired
to improve the experience of the user and render the simulation more
realistic. For example,
it may be of value to consider the background noise generated by pieces of
equipment that
are specific to the simulator, i.e. pieces of equipment of the simulator which
are not present
in the real system that the simulator simulates. For example, an air
conditioning (AC)
system may be present in the simulator for the comfort of the user of the
simulator while
the real system may comprise no AC system. In this case, the sound generated
by the
components of the AC system such as fans will affect the way the user
perceives a sound
signal played back by the simulator. The sound generated by the AC system then
corresponds to background noise. Compensating for the background noise so that
it does
not affect the user perception of a sound signal played back by the simulator
will improve
the user experience.
Furthermore, the environment of the simulator such as the walls of the
simulator may affect
the user perception of a sound signal played back by the simulator. While
playing back a
sound signal, it is expected that the user will hear the sound as if he was
present in the real
system. Usually, the sound heard in the real system that the simulator
simulates is recorded
and then played back into the simulator expecting that the perception of the
user within the
simulator would be identical to the perception he would have in the real
system. However,
since the environment of the simulator is usually different from that of the
real system, the
sound perceived by the user in the simulator may be different from the sound
he would
perceive in the real system even if the sound played back in the simulator has
been recorded
in a real system. For example, the sound played back in the simulator may be
distorted due
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to the simulator environment. The present method and system allows for at
least partially
compensating for these drawback effects and improve the user experience.
In same or another embodiment, multiple sounds may be played back during a
same
simulation to reproduce different sources of sound present in the real system
being
simulated. For example, a simulator may generate a first sound for reproducing
the wind
noise and a second sound for reproducing the sound generated by turbines.
During a given
portion of the simulation, the first sound corresponding to the wind noise
will affect the
way the user perceives a second sound corresponding to the turbine noise. The
second
sound then corresponds to background noise. Compensating for the background
noise so
that it does not affect the user perception of a second sound played back by
the simulator
may improve the user experience.
Figure 1 illustrates one embodiment of a method 10 for calibrating an initial
sound signal.
The initial sound signal is to be played back by a playback system and
modified so as to
improve the user perception of the initial sound signal while played back. In
one
embodiment, the initial sound signal may correspond to a sound signal that was
previously
recorded in a given environment. In another embodiment, the initial sound
signal may be a
sound signal generated by a computer machine.
For example, the initial sound signal may be used to reproduce the sound
perceived by a
pilot while flying in a real aircraft. In this case, the initial sound signal
may correspond to
the sound signal recorded in the cockpit of a real aircraft while in
operation. In another
example, the initial sound signal may have been previously designed and
generated by a
computer machine to mimic the sound heard in the real system.
It should be understood that the method 10 is to be executed by a computer or
computer
machine comprising at least a communication unit for receiving and
transmitting data, a
memory for storing data and a processing unit. The memory has stored thereon
statements
that when executed by the processing unit perform the method 10.
At step 12, an initial sound signal, a target sound signal, a recorded initial
sound signal and
a recorded background sound signal, all expressed in Pa, are received. Each
one of these
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sound signals comprise a respective sound amplitude value for a plurality of
frequencies
contained in a given range of frequencies. As described above, the initial
sound signal is the
signal to be played back. The recorded initial sound signal corresponds to the
sound signal
that was previously recorded while the initial sound signal was played back in
a given area.
The recorded background sound signal corresponds to the background noise that
is present
in the area where the initial sound signal is to be played back and that was
previously
recorded while the initial sound signal is not played back.
In an embodiment in which the method 10 is used in an aircraft simulator, the
initial sound
signal may correspond to the sound heard in the cockpit of the aircraft during
a respective
operation of the aircraft. In this case, the initial sound signal may
correspond to the
recording of the sound present in the cockpit. In another example, the initial
sound signal
may be generated by a computer.
At step 14, the recorded background sound signal is subtracted from the
recorded initial
sound signal, i.e. the amplitude of the recorded background sound signal for
each frequency
is subtracted from the amplitude of the recorded initial sound signal for the
same frequency,
thereby obtaining a denoised sound signal.
In one embodiment, the recorded initial sound signal and the recorded
background sound
signal are expressed in a logarithmic scale such as in Decibels (dB). For
example, the sound
signals may be expressed in dB SPL to correspond to sound pressure levels. In
this case, a
sound signal p expressed in Pa may be converted into a sound pressure level Lp
using the
following equation: Lp = ln(p/p0) where Po is a reference sound pressure. As
known in the
art, po is equal to 20 ttPa when the logarithm scale is in dB SPL.
When the recorded initial sound signal and the recorded background sound
signal are
expressed in a logarithmic scale such as in DB SPL, the method 10 further
comprises a step
of converting the recorded initial sound signal and the recorded background
sound signal
into Pascal before subtracting the recorded background sound signal expressed
in Pa from
the recorded initial sound signal expressed in Pa to obtain a denoised sound
signal also
expressed in Pa. The method further comprises a step of converting the
obtained denoised
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signal expressed in Pa into the same logarithmic scale as that of he recorded
initial sound
signal and the recorded background sound signal, such as in dB SPL.
At step 16, the target sound signal is divided by the denoised sound signal
obtained at step
14, thereby obtaining a compensation factor. It should be understood that at
step 16, the
amplitude of the target sound signal for each frequency is divided by the
amplitude of the
denoised sound signal for the same frequency.
In one embodiment, the denoised sound signal and the target sound signal may
be
expressed in a logarithmic scale. For example, the denoised sound signal and
the target
sound signal can be expressed in dB SPL. In this case, the person skilled in
the art will
understand step 16 consists in subtracting the denoised sound signal expressed
in the
logarithmic scale from the target sound signal expressed in the logarithmic
scale to obtain
the compensation factor expressed in the logarithmic scale.
At step 18, the initial sound signal is divided the compensation factor
obtained at step 16,
thereby obtaining a calibrated sound signal. It should be understood that at
step 18, the
amplitude of the initial sound signal for each frequency is divided by the
amplitude of the
compensation factor for the same frequency.
In one embodiment, the initial sound signal and the compensation sound signal
may be both
expressed in a logarithmic scale. For example, the initial sound signal and
the
compensation sound signal can be expressed in dB SPL. In this case, the person
skilled in
the art will understand step 18 consists in subtracting the compensation
factor expressed in
the logarithmic scale from the initial sound signal expressed in the
logarithmic scale to
obtain the calibrated sound signal expressed in the logarithmic scale.
Finally, the calibrated sound signal is outputted at step 20. In one
embodiment, the
calibrated sound signal is stored in memory. In the same or another
embodiment, the
calibrated sound signal is played back.
In one embodiment, the target sound signal corresponds to a sound signal that
has been
previously recorded. In another embodiment, the target sound signal is
generated by a
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computer. In this case, the method 10 may further comprise the step of
generating the target
sound signal.
In one embodiment, the method 10 further comprises recording the background
noise
present in the area in which the initial sound signal is to be played back,
thereby obtaining
the recorded background sound signal. In one embodiment, the background noise
is
recorded while no sound signal is played back to obtain the recorded
background sound
signal. In another embodiment, the background noise is recorded while the
initial sound
signal is played back while muted, to obtain the recorded background sound
signal.
In one embodiment, the method 10 further comprises recording the initial sound
signal
while it is being played back, thereby obtaining the recorded initial sound
signal. In one
embodiment, the method 10 further comprises playing back the initial sound
signal.
In one embodiment, the above-described method 10 may be used to calibrate a
sound signal
to be played back into a simulator such as an aircraft simulator. In this
case, the target
sound signal may be previously recorded into the cockpit of a real aircraft
that the simulator
simulates while the aircraft is in use.
In one embodiment, the initial sound signal may be a random sound signal, i.e.
a sound
signal for which the amplitude of each frequency is randomly chosen. For
example, the
initial sound signal may correspond to white noise. In one embodiment, the
method 10 may
further comprise generating the initial sound signal.
In another embodiment, the initial sound signal may be selected from a
database of
predefined initial sound signals. In this case, the method 10 may further
comprise a step of
receiving an identification of a given predefined target sound signal and a
step of retrieving
the given predefined target sound signal.
For example, the database may comprise an initial sound signal for different
flight phases
such as a first initial sound signal for cruise, a second initial sound signal
for the takeoff
phase, a third initial sound signal for the landing phase, a fourth initial
sound signal for the
opening of wing flaps, etc. In this case, the method 10 may further comprise a
step of
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receiving an identification of a flight phase and retrieving from the database
the initial
sound signal that corresponds to the received flight phase. Similarly, the
database may
comprise a respective target sound signal for different flight phases and the
method 10 may
further comprise a step of receiving an identification of a flight phase and
retrieving the
target sound signal that corresponds to the received flight phase.
As described below, the initial sound signal may be first played back while
being muted,
i.e. the volume of the playback is set to zero, and the background noise is
recorded within
the simulator concurrently to the muted playback of the initial sound signal
to obtained the
background sound signal 30 illustrated in Figure 2. It should be understood
that the
amplitude or sound level of the sound signals illustrated in Figure 2 are
expressed in scaled
dB SPL.
Then the initial sound signal is played back at a non-zero volume and the
played back
initial sound signal is recorded within the simulator to obtain the recorded
initial sound
signal 32 illustrated in Figure 2. In one embodiment, the volume is set to
maximum during
the playback of the initial sound signal.
Then both the recorded background sound signal 30 and the recorded initial
sound signal 32
are converted from dB SPL into Pa and the recorded background sound signal
expressed in
Pa is subtracted from the recorded background sound signal also expressed in
Pa to obtain
the denoised sound signal which is converted into dB SPL. The denoised sound
signal
expressed in dB SPL is then subtracted from the target sound signal 34,
thereby obtaining a
compensation factor. The compensation factor is then subtracted from the
initial sound
signal to obtain a calibrated sound signal. The obtained calibrated sound
signal may then be
played back and the played back calibrated sound signal substantially
corresponds to the
target sound signal so that the sound environment of user of the simulator
corresponds to
the sound environment of the cockpit of the real aircraft that the simulator
simulates, which
improves the experience of the user.
The above-described method may be embodied as a computer program product for
calibrating a predefined sound signal. The computer program product comprises
a computer
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readable memory storing computer executable instructions thereon that when
executed by a
computer perform the steps of the above-described method.
Figure 3 illustrates one embodiment of a system 50 for calibrating a sound
signal which
may be used in a simulator. The system 50 comprises a playback module 52, a
recording
module 54, a denoising module 56, a compensation module 58, a calibration
module 60 and
a database 62. The database 62 stores at least one initial sound signal and a
target sound
signal.
The playback module 52 comprises at least one speaker and is adapted to
playback the
initial sound signal. In one embodiment, the playback module 52 further
comprises a
processing unit, a memory and communication means, and is further adapted to
receive the
predefined sound signal and the additional sound signal from the database 62
and combine
them together.
In one embodiment, the playback module 52 may adjust the volume of the
playback of the
initial sound signal. For example, the initial sound signal may be played back
while muted.
The recording module 54 comprises a microphone for recording sound and is
adapted to
record the background sound to generate a recorded background sound signal and
a
recorded initial sound signal. The recorded background sound signal and the
recorded
initial sound signal are transmitted to the denoising module 56. In one
embodiment, the
denoising module 56 is adapted to subtract the recorded background sound
signal from the
recorded initial sound signal to obtain a denoised sound signal.
Alternatively, if the sound
signals are expressed in a logarithmic scale such as in dB SPL, the denoising
module 56 is
further configured for converting the recorded background sound signal and the
recorded
initial sound signal from the logarithmic scale into Pa before subtracting the
recorded
background sound signal expressed in Pa from the recorded initial sound signal
also
expressed in Pa to obtain a denoised sound signal expressed in Pa. The
denoising module
56 is further configured for converting the denoised sound signal expressed in
Pa into the
logarithmic scale. The denoised sound signal is then transmitted to the
compensation
module 58.
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The compensation module 58 receives the target sound signal from the database
62. In one
embodiment, the compensation module 58 is configured for dividing the target
sound signal
by the received denoised sound signal to obtain a compensation factor.
Alternatively, if the
target sound signal and the denoised sound signal are expressed in a
logarithmic scale, the
compensation module 58 is configured for subtracting the denoised sound signal
from the
target sound signal to obtain the compensation factor. The compensation factor
is then
transmitted to the calibration module 60.
The calibration module 60 then retrieves the initial sound signal from the
database 62, and
received the compensation factor from the compensation module 58. In one
embodiment,
the calibration module 60 is configured for dividing the initial sound signal
by the
compensation factor to obtain a calibrated sound signal. Alternatively, if the
initial sound
signal and the compensation factor are expressed in a logarithmic scale, the
calibration
module 60 is configured for subtracting the received compensation factor from
the initial
sound signal to obtain the calibrated sound signal. The compensation module 60
then
outputs the calibrated sound signal. For example, the calibrated sound signal
may be stored
in memory. In the same or another embodiment, the compensation module 60
transmits the
calibrated sound signal to the playback module 52 to be played back.
It should be understood that at least some of the steps of the method 10 may
be performed
by a computer machine provided with at least one processing unit, a memory or
storing
unit, and communication means. The memory comprises statements and
instructions stored
thereon that, when executed by the processing unit, performs at least some of
the steps of
the method 10.
In one embodiment, each one of the modules 52-60 is provided with a respective
processing unit such as a microprocessor, a respective memory and respective
communication means. In another embodiment, at least two of the modules 52-60
may
share a same processing unit, a same memory and/or same communication means.
For
example, the system 50 may comprise a single processing unit used by each
module 52-60,
a single memory on which the database 62 is stored and a single communication
unit.
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Figure 4 is a block diagram illustrating an exemplary processing module 80 for
executing
the steps 12 to 20 of the method 10, in accordance with some embodiments. The
processing
module 80 typically includes one or more Computer Processing Units (CPUs)
and/or
Graphic Processing Units (GPUs) 82 for executing modules or programs and/or
instructions
stored in memory 84 and thereby performing processing operations, memory 84,
and one or
more communication buses 86 for interconnecting these components. The
communication
buses 86 optionally include circuitry (sometimes called a chipset) that
interconnects and
controls communications between system components. The memory 84 includes high-
speed random access memory, such as DRAM, SRAM, DDR RAM or other random access
solid state memory devices, and may include non-volatile memory, such as one
or more
magnetic disk storage devices, optical disk storage devices, flash memory
devices, or other
non-volatile solid state storage devices. The memory 84 optionally includes
one or more
storage devices remotely located from the CPU(s) 82. The memory 84, or
alternately the
non-volatile memory device(s) within the memory 84, comprises a non-transitory
computer
readable storage medium. In some embodiments, the memory 84, or the computer
readable
storage medium of the memory 84 stores the following programs, modules, and
data
structures, or a subset thereof:
a playback module 90 for playing back an initial sound signal;
a recording module 92 for recording a background sound signal and the
played back initial sound signal;
a denoising module 94 subtracting the recorded background signal from the
recorded initial sound signal to obtain a denoised sound signal;
a compensation module 96 for one of dividing the target sound signal by the
denoised sound signal or subtracting the denoised sound signal from the target
sound signal
to obtain a compensation factor; and
a calibration module 98 for one of dividing the initial sound signal by the
compensation factor in linear Pascal scale or subtracting the compensation
factor from the
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initial sound signal in logarithm scale to obtain a calibrated sound signal,
and outputting the
calibrated sound signal.
Each of the above identified elements may be stored in one or more of the
previously
mentioned memory devices, and corresponds to a set of instructions for
performing a
function described above. The above identified modules or programs (i.e., sets
of
instructions) need not be implemented as separate software programs,
procedures or
modules, and thus various subsets of these modules may be combined or
otherwise re-
arranged in various embodiments. In some embodiments, the memory 84 may store
a
subset of the modules and data structures identified above. Furthermore, the
memory 84
may store additional modules and data structures not described above.
Although it shows a processing module 80, Figure 4 is intended more as
functional
description of the various features which may be present in a management
module than as a
structural schematic of the embodiments described herein. In practice, and as
recognized by
those of ordinary skill in the art, items shown separately could be combined
and some items
could be separated.
The embodiments of the invention described above are intended to be exemplary
only. The
scope of the invention is therefore intended to be limited solely by the scope
of the
appended claims.
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