Note: Descriptions are shown in the official language in which they were submitted.
METHOD AND SYSTEM FOR LIMITING SPATIAL INTERFERENCE
FLUCTUATIONS BETWEEN AUDIO SIGNALS
TECHNICAL FIELD
The present technology relates to the field of sound processing, and more
particularly to
methods and systems for generating sound within a predetermined environment.
BACKGROUND
Vehicle simulators are used for training personnel to operate vehicles to
perform maneuvers.
As an example, aircraft simulators are used by commercial airlines and air
forces to train
their pilots to face various types of situations. A simulator is capable of
artificially recreating
various functionalities of an aircraft and reproducing various operational
conditions of a
flight (e.g., takeoff, landing, hovering, etc.). Thus, in some instances, it
is important for a
vehicle simulator to reproduce the internal and external environment of a
vehicle such as an
aircraft as accurately as possible by providing sensory immersion, which
includes
reproducing visual effects, sound effects (e.g., acceleration of motors, hard
landing, etc.), and
movement sensations, among others.
In the case of sound assessment, the location of a microphone to be used for
sound tests or
calibration is usually important to ensure repeatability such as when running
sound
Qualification Test Guide (QTG) tests. There are also requirements that certain
frequency
bands correspond to a certain amplitude, which must be contained within a
certain tolerance
range. For example, a QTG may require that for a minimum time period of 20
seconds, the
average power in a given frequency band must be equal to a predetermined
quantity.
[0001] If when running sound tests the microphone is positioned at a location
different
from previous positions, there will be a difference in travel distance between
the speakers
and the microphone that may cause a dephasing of the periodic signals which
will cause
different interferences and modify the recorded signal amplitudes so that the
amplitude of the
sound varies spatially within the simulator. The interferences and
modifications in amplitude
cause spatial variation of recorded sounds.
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Therefore, there is a need for a method and system for limiting spatial
interference
fluctuations between audio signals within an environment.
SUMMARY
Developer(s) of the present technology have appreciated that a variation in
the position of a
user within a simulator may result in the user moving from a constructive
interference area
to a destructive interference area and vice versa, which may cause
fluctuations in the sound
heard by the user. If the fluctuations are above an allowed tolerance range,
regulating
authorities may not qualify the simulator, which could cause delay, increase
costs and lead
engineers to follow false trails for solving the problem.
Developer(s) have thus realized that phase modulation of audio signals could
be used, such
that the fluctuations of the spatial average energy inside the cockpit be
minimized.
Thus, it is an object of one or more non-limiting embodiments of the present
technology to
diminish or avoid the effect of spatial sound interferences within a given
environment such
as a simulator environment.
According to a first broad aspect, there is provided a method for generating
sound within a
predetermined environment, the method comprising: emitting a first audio
signal from a first
location; and concurrently emitting a second audio signal from a second
location, wherein:
the first location and second location are distinct within the environment;
the first audio signal
and second audio signal have the same frequency; and the first audio signal
and second audio
signal have a phase difference that varies as a function of time to limit the
time-averaged
interference fluctuation across the environment.
In one embodiment, an amplitude of the first audio signal is identical to an
amplitude of the
second audio signal.
In one embodiment, the phase difference varies continuously as a function of
time.
In one embodiment, a variation rate of the phase difference is constant in
time. In another
embodiment, the variation rate of the phase difference varies as a function of
time.
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In one embodiment, the phase difference is comprised between zero and 2n.
In one embodiment, the second audio signal is identical to the first audio
signal prior to the
phase difference being added to the second audio signal.
In one embodiment, the second audio signal is generated before being emitted
by receiving
.. the first audio signal and adding the phase difference to the received
first audio signal.
According to another broad aspect, there is provided a system for generating
sound within a
predetermined environment, the system comprising: a first sound emitter for
emitting a first
audio signal from a first location; and a second sound emitter for emitting a
second audio
signal from a second location; wherein: the first location and second location
are distinct
within the environment; the first audio signal and second audio signal have
the same
frequency; and the first audio signal and second audio signal have a phase
difference that
varies as a function of time to limit the time-averaged interference
fluctuation across the
environment.
In one embodiment, an amplitude of the first audio signal is identical to an
amplitude of the
.. second audio signal.
In one embodiment, the system further comprises a controller for transmitting
the first audio
signal to the first audio emitter and the second audio signal to the second
sound emitter.
In one embodiment, the controller is configured to vary the phase difference
continuously as
a function of time.
.. In one embodiment, the controller is configured for varying the phase
difference so that a
variation rate of the phase difference be constant in time. In another
embodiment, the
controller is configured for varying the phase difference so that a variation
rate of the phase
difference varies as a function of time.
In one embodiment, the phase difference is comprised between zero and 2n.
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In one embodiment, the second audio signal is identical to the first audio
signal prior to the
phase difference be added to the second audio signal.
In one embodiment, the controller is further configured to: receive the first
audio signal and
transmit the first audio signal to the first sound emitter; add the phase
difference to the first
audio signal, thereby obtaining the second audio signal; and transmitting the
second audio
signal to the second sound emitter.
According to a further broad aspect, there is provided a non-transitory
computer program
product for generating sound within a predetermined environment, the computer
program
product comprising a computer readable memory storing computer-executable
instructions
thereon that when executed by a computer perform the method steps of:
transmitting a first
audio signal to be emitted from a first location; and concurrently
transmitting a second audio
signal to be emitted from a second location, wherein: the first location and
second location
are distinct within the environment; the first audio signal and second audio
signal have the
same frequency; and the first audio signal and second audio signal have a
phase difference
that varies as a function of time to limit the time-averaged interference
fluctuation across the
environment.
In one embodiment, an amplitude of the first audio signal is identical to an
amplitude of the
second audio signal.
In one embodiment, the phase difference varies continuously as a function of
time.
In one embodiment, a variation rate of the phase difference varies as a
function of time.
In one embodiment, the computer-executable instructions are further configured
to perform
the step of adding the phase difference to the first audio signal to generate
the second audio
signal before said emitting the second audio signal.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present technology will become apparent
from the
following detailed description, taken in combination with the appended
drawings, in which:
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FIG. 1 is a conceptual diagram illustrating a system comprising two sound
emitters and a
controller for emitting two sound signals in accordance with an embodiment of
the present
technology;
FIG. 2 schematically illustrates the mitigation of time-averaged interference
fluctuations at
three different locations within an environment when a constant-phase audio
signal and a
phase-modulated audio signal are emitted;
FIG. 3A illustrates a schematic diagram of a frequency response model in
accordance with
one or more non-limiting embodiments of the present technology;
FIG. 3B illustrates a schematic diagram in accordance with one or more non-
limiting
embodiments of the present technology; and
FIG. 4 illustrates a flow-chart of a method of limiting interference
fluctuations between audio
signals within an environment.
It will be noted that throughout the appended drawings, like features are
identified by like
reference numerals.
.. DETAILED DESCRIPTION
FIG. 1 schematically illustrates a system 10 for emitting sound within a
predetermined
environment 12 such as within the interior space of a simulator. The system 10
comprises a
first sound or audio emitter 14, a second sound or audio emitter 16 and a
controller 18. The
first and second sound emitters 14 and 16 are positioned at different
locations within the
.. environment 12 and oriented so as to propagate sound towards a listening
area 20.
The controller 18 is configured for transmitting a first sound, acoustic or
audio signal to the
first sound emitter 14 and a second sound, acoustic or audio signal to the
second sound
emitter 16, and the first and second audio signals are chosen so as to at
least limit interference
fluctuations between the first and second audio signals within the listening
area 20 of the
.. environment 12. In one embodiment, the spatial interference fluctuations
between the first
and second audio signals may be mitigated within substantially the whole
environment 12.
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In one embodiment, the first and second audio signals may reproduce sounds
that would
normally be heard if the user of the system 10 would be in the device that the
predetermined
environment 12 simulates. For example, when the predetermined environment 12
corresponds to an aircraft simulator, the first and second sound emitters 14
and 16 may be
positioned on the left and right sides of the seat to be occupied by a user of
the aircraft
simulator and the first sound emitter 14 may be used to propagate the sound
generated by a
left engine of an aircraft while the second sound emitter 16 may be used to
propagate the
sound generated by the right engine of the aircraft. The present system 10 may
then improve
the quality of the global sound heard by the user by mitigating interference
fluctuations
between the sounds emitted by the first and second sound emitters 14 and 16
within the
aircraft simulator.
Referring back to FIG. 1, the controller 18 is configured for controlling the
first and second
emitters 14 and 16 so that the first audio signal and the second audio signal
be emitted
concurrently by the first sound emitter 14 and the second sound emitter 16,
respectively, i.e.
so that the first and second audio signals be concurrently heard by a user
positioned within
the listening area 20 of the environment 12.
The first and second audio signals are chosen or generated so as to have the
same frequency
or the same range of frequencies. The first and second audio signals are
further chosen or
generated so as to have a difference of phase (hereinafter referred to as
phase difference) that
.. varies in time so as to limit the time-averaged spatial interference
fluctuation within the
environment 12, or at least within the listening area 20 of the environment
12.
In one embodiment, the amplitude of the first signal emitted by the first
sound emitter 14 is
identical to the amplitude of the second audio signal emitted by the second
sound emitter 16.
In the same or another embodiment, the amplitude of the first signal within
the listening area
20 or at a given position within the listening area 20 is identical to the
amplitude of the second
audio signal within the listening area 20 or at the given position within the
listening area 20.
In one embodiment, the controller 18 is configured for modulating or varying
in time the
phase of only one of the first and second audio signals. In another
embodiment, the controller
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18 is configured for varying the phase in time of each audio signal as long as
the phase
difference between the first and second audio signals still varies as a
function of time.
In one embodiment, the controller 18 is configured for modulating the phase of
at least one
of the first and second audio signals so that the phase difference between the
first and second
audio signals varies continuously as a function of time. For example, the
phase of the first
audio signal is maintained constant in time by the controller 18 while the
phase of the second
audio signal is modulated in time by the controller 18 so that the phase
difference between
the first and second audio signals varies continuously as a function of time.
In another
embodiment, the controller 18 is configured for varying the phase difference
between the
first and second audio signals in a stepwise manner, e.g. the phase difference
between the
first and second audio signals may be constant during a first short period of
time and then
varies as a function of time before being constant during a second short
period of time, etc.
In an embodiment in which the phase difference between the first and second
audio signals
varies continuously as a function of time, the rate of variation for the phase
difference is
constant in time. Alternatively, the rate of variation for the phase
difference between the first
and second audio signals may also vary as a function of time as long as the
first and second
audio signals have a different phase in time.
In one embodiment, the rate of variation of the phase difference is comprised
between about
0.005 Hz and about 50 Hz, which corresponds to a period of variation comprised
between
about 20 ms and 20 sec. The person skilled in the art will understand that a
faster modulation
will lead to more audible artifact, while a slower modulation will increase
time-averaged
interference fluctuations.
It should be understood that any adequate variation function may eb used. For
example, the
variation function may be a sine function. In another example, the variation
function may be
a pseudo-random variation function that is updated periodically such as at
every 10 ms. In
this case, the faster the variation is performed, the lower the range of the
randomness change
can be.
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In one embodiment, the first and second audio signals may be identical except
for their phase
(and optionally their amplitude). In this case, the controller 18 is
configured for generating
an audio signal or retrieving an audio signal from a memory and varying the
phase of the
audio signal such as by adding the phase difference to the audio signal to
obtain a phase
modified audio signal. One of the first and second audio signals then
corresponds to the
unmodified audio signal while the other one of the first and second audio
signals corresponds
to the phase modified audio signal. For example, the unmodified audio signal
may be the first
audio signal to be emitted by the first sound emitter 14 and the phase
modified audio signal
may be the second audio signal to be emitted by the second sound emitter 16.
It will be understood that the sound emitter 14, 16 may be any device adapted
to convert an
electrical audio signal into a corresponding sound, such as a speaker, a
loudspeaker, a
piezoelectric speaker, a flat panel loudspeaker, etc.
In one embodiment, the controller 18 is a digital device that comprises at
least a processor or
processing unit such as digital signal processor (DSP), a microprocessor, a
microcontroller
.. or the like. The processor or processing unit of the controller 18 is
operatively connected to
a non-transitory memory, and a communication unit. In this case, the processor
of the
controller 18 is configured for retrieving the first and second audio signals
from a database
stored on a memory. In this case, the system 10 further comprises a first
digital-to-analog
converter (not shown) connected between the controller 18 and the first sound
emitter 14 for
converting the first audio signal transmitted by the controller 18 from a
digital form into an
analog form to be played back by the first sound emitter 14. The system 10
also comprises a
second digital-to-analog converter (not shown) connected between the
controller 18 and the
second sound emitter 16 for converting the second audio signal transmitted by
the controller
18 from a digital form into an analog form to be played back by the second
sound emitter 16.
In an embodiment in which the controller 18 is digital, the controller 18 is
configured for
generating the first and second audio signals having a phase difference that
varies in time.
In another embodiment in which the controller 18 is digital, the controller 18
is configured
for retrieving the first and second audio signals from a database and
optionally vary the phase
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of at least one of the first and second audio signals to ensure that the first
and second audio
signals have a phase difference that varies in time. For example, the
controller may retrieve
an audio signal from the database and modify the phase in time of the
retrieved audio signal
to obtain a phase-modified audio signal. The unmodified signal is transmitted
to one of the
first and second sound emitter 14 and 16 and the phase-modified audio signal
is transmitted
to the other, via the first and second digital-to-analog converters.
It will be understood that the controller 18 is further configured for
controlling the emission
of the first and second audio signals so that first and second audio signals
be concurrently
emitted by the first and second sound emitters 14 and 16 and/or concurrently
received within
the listening area 20. Since the distance between the sound emitters 14 and 16
and the
listening area 20 is usually in the order of meters, audio signals that are
concurrently emitted
by the sound emitters 14 and 16 are usually concurrently received in the
listening area 20 so
that emitting concurrently sound signals by the sound emitters 14 and 16 is
equivalent to
concurrently receiving the emitted sound signals in the listening area 20.
In another embodiment, the controller 18 is an analog device comprising at
least one phase
modulation device for varying in time the phase of at least one analog audio
signal. For
example, the analog controller 18 may receive the first audio signal in an
analog format and
transmit the first audio signal to the first sound emitter 14, and may receive
the second audio
signal in an analog format, vary the phase of the second audio signal so as to
ensure a phase
difference in time with the first audio signal and transmit the second audio
signal to the
second sound emitter 16. In another example, the analog controller 18 may
receive a single
analog audio signal and transmit the received analog audio signal directly to
the first sound
emitter 14 so that the first audio signal corresponds to the received analog
audio signal. In
this case, the analog controller is further configured for creating a phase
modified copy of
the received audio signal, i.e. the second audio signal, by varying the phase
of the received
analog audio signal and for transmitting the phase modified analog audio
signal to the second
sound emitter 16.
In one embodiment, the analog controller 18 comprises at least one oscillator
for varying the
phase of an audio signal. For example, the analog controller 18 may comprise a
voltage-
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controlled oscillator (VCO) of which the voltage varies slightly around a
desired frequency
since a frequency variation triggers a phase variation. In another example,
the analog
controller 18 may comprise a first VCO and a second VCO connected in series.
The first
VCO is then used a time-varying frequency signal while the second VCO is used
to generate
.. the audio signal. The second VCO receives the time-varying frequency signal
and a DC
signal as inputs to generate an audio signal, the phase of which varies in
time.
In one embodiment, the phase difference in time between the first and second
audio signals
is comprised within the following range: [0; 27c]. In a further embodiment,
the range of
variation of the phase may be arbitrarily chosen. For example, the phase
difference in time
between the first and second audio signals may be comprised within the
following ranges:
[0; 7c/2], [1.23145, 2], etc.
In one embodiment, the range of variation of the phase difference between the
first and
second audio signals is chosen to be small enough to limit the subjective
impact.
The present system 10 uses phase modulation of at least one audio signal to
limit the spatial
fluctuations of time-averaged interferences between the first and second audio
signals. This
is achieved by ensuring that the phase difference between the first and second
audio signals
varies in time.
FIG. 2 schematically illustrates an exemplary limitation of time-averaged
interference
fluctuation across an environment that may be achieved using the present
technology.
.. A system 100 comprises a first sound emitter 112 such as a first speaker, a
second sound
emitter 116 such as a second speaker and a controller or playback system 110
for providing
audio signals to be emitted by the first and second sound emitters 112 and
116. Three
microphones 130, 132 and 134 are located at different locations within an
environment 102
to detect the sound received at the three different locations. In the
illustrated embodiment,
the first, second and third microphones 130, 132 and 134 are located at the
locations 142,
152 and 162, respectively, within the environment 102.
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In one embodiment, the environment 102 is a closed space or a semi-closed
space such as a
vehicle simulator. As non-limiting examples, the vehicle simulator may be a
flight simulator,
a tank simulator, a helicopter simulator, etc.
The first sound emitter 112 is located at a first location 114 within the
environment 102. The
first emitter 112 is operable to emit a first audio signal which propagates
within the
environment 102. A first portion 122 of the first audio propagates up to the
first microphone
130, a second portion 122' of the first audio signal propagates up to the
second microphone
132 and a third portion 122" propagates up to the third microphone 134.
The first location 114 of the first sound emitter 112 is a fixed position
within the environment
.. 102 and does not vary in time. In one embodiment, the position of the first
sound emitter 112
is unknown while being constant in time. In another embodiment, the position
of the first
emitter 112 is known and constant in time.
The second sound emitter 116 is located at a second location 118 within the
environment
102. The second location 118 is distinct from the first location 112 so that
the first and second
sound emitters 112 and 116 are spaced apart. Similarly to the first sound
emitter 112, the
second sound emitter 116 is operable to emit a second audio signal which
propagates within
the environment 102. A first portion 124 of the second audio propagates up to
the first
microphone 130, a second portion 124' of the second audio signal propagates up
to the second
microphone 132 and a third portion 124" propagates up to the third microphone
134.
The second location 118 of the second emitter 116 is a fixed position within
the environment
102 and does not vary in time. In one embodiment, the position of the second
emitter 116 is
unknown while being constant in time. In another embodiment, the position of
the second
emitter 116 is known and constant in time.
The first and second audio signals are chosen so as to have the same
frequency, i.e., at each
point in time, the first and second audio signals have the same frequency. In
one embodiment,
the first and second audio signals have the same amplitude, i.e., at each
point in time, the first
and second audio signals have the same amplitude. In another embodiment, the
first and
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second audio signals have different amplitudes, i.e., for at least some points
in time, the first
and second audio signals have different amplitudes.
The phase difference between the first and second audio signals varies in
time. In the
illustrated embodiment, the phase of the first audio signal emitted by the
first sound emitter
112 is constant in time while the phase of the second audio signal varies in
time to obtain the
time-varying phase difference between the first and second audio signals.
Therefore, the
phase of the second audio signal is modulated as a function of time, i.e. a
time-varying phase
shift is applied to the second audio signal. It will be understood that the
phase of the second
audio signal could be constant in time while the phase of the first audio
signal could vary in
order to reach the time-varying phase difference between the first and second
audio signals.
In another example, a different time-varying phase shift may be applied to
both the first and
second audio signals so as to obtain the time-varying phase difference between
the first and
second audio signals.
As illustrated in FIG. 2, since the distance between the second sound emitter
116 and each
microphone 130, 132, 134 is different, the propagation time of the second
audio signal
between the second sound emitter 116 and each microphone 130, 132, 134 is also
different.
Since the phase of the second audio signal varies as a function of time and
since the
propagation times are different, at each point in time the phase of the second
audio signal is
different at each location 142, 152 and 162 where a respective microphone 130,
132, 134 is
positioned.
As illustrated in FIG. 2 and since the first and second audio signals have the
same frequency,
the first audio signal interferes or combines with the second audio signal to
provide a third
audio signal at each point of the environment 102 where the two audio signals
propagate. At
the location 142 where the first microphone 130 is positioned, the combination
of the first
and second audio signals generates a third sinusoidal audio signal 146. At the
location 152
where the second microphone 132 is positioned, the combination of the first
and second audio
signals generates a fourth sinusoidal audio signal 156. At the location 162
where the third
microphone 134 is positioned, the combination of the first and second audio
signals generates
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a fifth sinusoidal audio signal 166. As illustrated in FIG. 2, the third,
fourth and fifth audio
signals 146, 156 and 166 are different.
The reference element 144 illustrated in FIG. 2 represents the audio signal
that would result
from the combination of the first and second audio signals at the location 142
if the phase of
the second audio signal is not modulated in time. The reference element 154
represents the
audio signal that would result from the combination of the first and second
audio signals at
the location 152 if the phase of the second audio signal is not modulated in
time. The
reference element 164 represents the audio signal that would result from the
combination of
the first and second audio signals at the location 162 if the phase of the
second audio signal
is not modulated in time.
From FIG. 2, the person skilled in the art will understand that the difference
in amplitude
between the audio signals 146, 156 and 166 (which are obtained by modulating
the phase of
the second audio signal) is less than the difference in amplitude between the
audio signals
144, 154 and 164, which are obtained without modulating the phase of the
second audio
signal. As a result, the difference in amplitude over space of the audio
signal resulting from
the combination of the first and second audio signals is reduced in comparison
to the case in
which there is no phase modulation of the second audio signal, therefore
limiting the time-
averaged interference fluctuation across the environment 102, i.e., the
fluctuation of the
spatial average energy within the environment 102 is limited, thereby
improving the sound
rendering within the environment 102.
In one embodiment, the second audio signal is identical to the first audio
signal except for
the phase of the second audio signal which is modulated in time while the
phase of the first
audio signal is constant in time.
In one embodiment, the phase modulation applied to the second audio signal is
random. In
this case, the signal produced by the phase modulation may be expressed as in
equation (1):
s(t) = sin(2n- = f = t + 0(t)) (1)
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where 0(t) is a progressive random number generator such as a spline
interpolation between
two numbers of a distribution such as a uniform distribution [0, fl] expressed
as in
equation (2):
0(t) = fl = spline(rand(tõ t1,1)) (2)
In one embodiment, a spline interpolation is used because a steep variation in
0 may be
audible.
While a spline interpolation is used in the above example, it should be
understood that any
smooth interpolation function can be used. For example, a linear interpolation
function may
be used.
The phase shift may be calculated by calculating 2 7/- f = t(N), where N is
the sample to
retrieve from the vector t, which is calculated in a classic manner (t=(0
:duration)/Fs). To
calculate 0(N), M equally spaced points are generated, a Spline approximation
is applied
such that t and 0 are equal, the two values are summed, and the corresponding
sinus value is
then calculated.
FIG. 3A illustrates a schematic diagram of a frequency response model 200 in
accordance
with one or more non-limiting embodiments of the present technology.
In one embodiment, the frequency response of the present technology may be
represented as
a feed-forward comb filter. It will be appreciated that the feed-forward comb
filter may be
implemented in discrete time or in continuous time. A comb filter is a filter
implemented by
adding a delayed version of a signal to itself, causing constructive and
destructive
interference.
The difference equation representing the frequency response of the system 200
is expressed
as equation (3):
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y[n] = x[n] + a x[n ¨ K] (3)
where K represents the delay length (measured in samples) and a is a scaling
factor applied
to the delayed signal.
FIG. 3B illustrates an exemplary plot 250 of the magnitude of the transfer
function with
respect to the frequency for different values of the scaling factor.
It will be appreciated that the frequency response tends to drop around an
average value (the
variance of the values decreases), as a moves away from 1. Thus, this
information about the
scaling factor can be used for repeatability. Phase modulation can be used as
a modulation
pattern for conditioning communication signals for transmission, where a
message signal is
encoded as variations in the instantaneous phase of a carrier wave. The phase
of a carrier
signal is modulated to follow the changing signal level (amplitude) of the
message signal.
The peak amplitude and the frequency of the carrier signal are maintained
constant, but as
the amplitude of the message signal changes, the phase of the carrier changes
correspondingly.
Thus, it is possible to adjust two parameters to adapt the phase modulation: a
number of
random samples during a recording cycle or recording frequency, and the
interval on which
the uniform distribution is sampled.
With reference to FIG. 4 there is illustrated an embodiment method 300 for
limiting
interference fluctuations between audio signals within an environment when at
least two
audio signals having the same frequency propagate within the environment.
.. At step 302, a first audio signal is emitted from a first location within
the environment, the
first audio signal having a first frequency. As a non-limiting example, a
first sound emitter
such as a speaker may be positioned at a first location within the environment
to emit the first
audio signal.
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At step 304, a second audio signal is emitted from a second location within
the environment
concurrently with the emission of the first audio signal, the second audio
signal having the
same frequency as the first audio signal so that they may interfere with one
another. As a
non-limiting example, a second sound emitter such as a speaker may be
positioned at the
second location within the environment to emit the second audio signal.
The first and second audio signals are chosen so that the phase difference
between the first
and second audio signals varies as a function of time. In one embodiment, the
phase of one
of the first and the second audio signals is constant in time while the phase
of the other is
modulated as a function of time. In another embodiment, the phase of both the
first and
second audio signals may be modulated as a function of time as long as the
phase difference
between the first and second audio signals varies in time.
In one embodiment, the second audio signal is initially identical to the first
audio signal, and
a phase difference is added to the second audio signal before emission
thereof, i.e. the phase
of the second audio signal is modulated in time while the phase of the first
audio signal
remains constant in time.
In one embodiment, the phase difference between the first and second audio
signals varies
continuously as a function of time. In one or more other embodiments, the
phase difference
between the first and second audio signals varies as a function of time in a
step-wise manner.
In one or more alternative embodiments, the phase difference is constant as a
function of
time.
In one embodiment, the phase difference in time between the first and second
audio signals
is comprised within the following range: [0; 27c].
Thus, the first and second audio signals are emitted such that an amplitude
difference across
space of the signal resulting from the combination of the first and second
audio signals is
limited, which results in limited energy fluctuation across space. In one
embodiment, the first
and second audio signals may be emitted such that the fluctuation across space
is within a
predetermined fluctuation range. The fluctuations may be detected for example
via one or
more microphones positioned at different locations within an environment.
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It will be appreciated that the first sound emitter and the second sound
emitter may be
operatively connected to one or more controllers which may be operable to
transmit
commands for generating concurrently the first and second audio signals, and
for controlling
amplitudes, frequencies, and phases of the first audio signal and the second
audio signal. It
is contemplated that a microphone may detect audio signals emitted by the
first sound emitter
and the second sound emitter and provide the audio signals to the one or more
controllers for
processing.
The method 300 is thus executed such that the time-averaged interference
fluctuation across
at least a portion the environment is limited, i.e. the fluctuation of the
spatial average energy
within at least a portion of the environment is limited.
In one embodiment, the method 300 further comprises receiving the first and
second audio
signals by a controller for example before the emission of the first and
second audio signals.
In one embodiment, the first and second audio signals are uploaded from a
database stored
on a non-volatile memory.
In another embodiment, the method 300 further comprises a step of generating
the first audio
signal and/or the second audio signal. In one embodiment, the method 300
comprises
receiving a first audio signal, generating a second audio signal by varying
the phase of the
first audio signal in time, and concurrently emitting the first and second
audios signals from
different locations.
In one embodiment, a non-transitory computer program product may include a
computer
readable memory storing computer executable instructions that when executed by
a processor
cause the processor to execute the method 300. The processor may be included
in a computer
for example, which may load the instructions in a random-access memory for
execution
thereof.
While the technology has been described as involving the emission of two audio
signals
having a time-varying phase difference, it will be understood that more than
two audio signals
may be generated and emitted towards the listening area as long as a time-
varying phase
difference exists between at least two audio signals. In an example in which
three audio
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signals, i.e. audio signals 1, 2 and 3, are emitted, a time-varying phase
difference may exist
between audio signals 1 and 2 and between audio signals 1 and 3, but not
between audio
signals 2 and 3. In another example, a first time-varying phase difference may
exist between
the audio signals 1 and 2, a second time-varying phase difference may exist
between the
audio signals 1 and 3, and a third time-varying phase difference may exist
between the audio
signals 2 and 3.
The one or more embodiments of the technology described above are intended to
be
exemplary only. The scope of the present technology is therefore intended to
be limited solely
by the scope of the appended claims.
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