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Patent No. 4395600 Auditory subliminal message system and method (Lundy, et al., Jul 26, 1983)
Abstract
Ambient audio signals from the customer shopping area within a store are sensed and fed to a signal processing circuit that produces a control signal which varies with variations in the amplitude of the sensed audio signals. A control circuit adjusts the amplitude of an auditory subliminal anti-shoplifting message to increase with increasing amplitudes of sensed audio signals and decrease with decreasing amplitudes of sensed audio signals. This amplitude controlled subliminal message may be mixed with background music and transmitted to the shopping area. To reduce distortion of the subliminal message, its amplitude is controlled to increase at a first rate slower than the rate of increase of the amplitude of ambient audio signals from the area. Also, the amplitude of the subliminal message is controlled to decrease at a second rate faster than the first rate with decreasing ambient audio signal amplitudes to minimize the possibility of the subliminal message becoming supraliminal upon rapid declines in ambient audio signal amplitudes in the area. A masking signal is provided with an amplitude which is also controlled in response to the amplitude of sensed ambient audio signals. This masking signal may be combined with the auditory subliminal message to provide a composite signal fed to, and controlled by, the control circuit.
Notes:
We
claim:
1. An auditory subliminal message system for an area comprising:
ambient audio signal processing circuit means adapted to receive an input representing
ambient audio signals in the area, said ambient signal processing means comprising
means for producing a control signal output which continuously varies with variations
in the received input and thereby with variations in the ambient audio signals
in the area; and
subliminal message control circuit means having a first input adapted to receive
an auditory subliminal message signal, said control circuit means having a second
input coupled to said ambient signal processing means for receiving said control
signal output, and said control circuit means comprising means for continuously
adjusting the amplitude of the received auditory subliminal message signal and
for producing an adjusted output signal comprising the amplitude adjusted auditory
subliminal message signal, the adjusted output signal being adapted for transmission
to the area and having an amplitude which varies in response to said control
signal so as to increase with increases in amplitude of ambient audio signals
in the area and decrease with decreases in amplitude of ambient audio signals
in the area.
2. A system according to claim 1 in which said ambient audio signal processing
circuit means changes said control signal at one rate with increases in amplitude
of ambient audio signals in the area and changes it at a faster rate with decreases
in amplitude of ambient audio signals in the area, said control circuit means
comprising means responsive to said control signal to produce an adjusted auditory
subliminal message output signal which has an amplitude which increases at a
first rate with increases in the amplitude of ambient audio signals in the area
and which decreases at a second rate faster than the first rate with decreases
in the amplitude of ambient audio signals in the area.
3. An auditory subliminal message system for an area comprising:
audio sensor means for sensing ambient audio signals in the area and for producing
an ambient audio output signal representing the volume of the sensed ambient
audio signals;
means having an input coupled to the output of said audio sensor means for producing
a subliminal message output signal with a volume which follows the volume of
the sensed ambient audio signals in the area.
4. A system according to claim 3 in which said last named means includes:
subliminal message source means for providing an auditory subliminal message
output signal; and
volume control circuit means having an input coupled to the output of said audio
sensor means and an input coupled to the output of said subliminal message source
means, said volume control circuit means comprising means for adjusting the
volume of the received subliminal message output signal in response to the received
ambient audio output signal so as to produce a modified subliminal message output
signal which comprises the volume adjusted received subliminal message output
signal.
5. A system according to claim 3 in which said last named means comprises means
for producing a subliminal message output signal at a volume which increases
in response to increases in the volume of sensed ambient audio signals at a
rate slower than the rate of increase of the sensed ambient audio signals.
6. A system according to claim 5 in which said last named means comprises means
for producing a subliminal message output signal at a volume which decreases
in response to decreases in the volume of sensed ambient audio signals at a
rate which is faster than the rate the subliminal message output signal increases
in response to increases in the volume of sensed ambient audio signals.
7. An auditory subliminal message system for an area comprising:
at least one audio sensor means for sensing ambient audio signals in the area
and for producing an ambient audio output signal representing the amplitude
of the sensed ambient audio signals;
subliminal message source means for providing an auditory subliminal message
output signal;
control circuit means coupled to the output of said audio sensor means and to
said subliminal message source means for adjusting the amplitude of the subliminal
message output signal so as to follow the amplitude of the sensed ambient audio
signals; and
masking signal source means for providing and combining a masking signal having
frequency characteristics and an amplitude such that when the masking signal
is combined with the amplitude adjusted subliminal message output signal it
renders the adjusted subliminal message output signal outside of the conscious
recognition range.
8. A system according to claim 7 in which said subliminal message source means
comprises means for producing a repetitive auditory subliminal message output
signal.
9. A system according to claim 7 in which said subliminal message source means
and said masking signal source means comprise means for providing a composite
signal which includes the auditory subliminal message output signal as one component
and which includes the masking signal as another component;
said control circuit means comprising means for adjusting the amplitude of the
composite signal so as to follow the amplitude of the sensed ambient audio signals.
10. A system according to claim 9 including system testing means for selectively
adjusting the amplitude of the composite signal to bring the masking signal
into the conscious recognition range and thereby indicate the system is operating.
11. A system according to claim 7 in which said masking signal source means
provides a masking signal having an amplitude which is in the range of approximately
3 db to 15 db greater than the amplitude of the amplitude adjusted subliminal
message output signal.
12. A system according to claim 11 in which said masking signal source means
provides a masking signal having an amplitude which is approximately 5 db greater
than the amplitude of the amplitude adjusted subliminal message output signal.
13. A system according to claim 7 in which said masking signal source means
comprises a white noise signal generator.
14. A system according to claim 9 in which said means for providing a composite
signal comprises an audio recording playback means for playing back a recording
of the composite signal.
15. A system according to claim 9 in which said means for providing a composite
signal includes voice synthesizer means for providing the auditory subliminal
signal component.
16. A system according to claim 15 in which said means for providing a composite
signal includes white noise signal generator means for providing the masking
signal component and mixer circuit means for combining the output of said voice
synthesizer means and the output of said white noise signal generator means
to provide an output from said mixer circuit means which comprises the composite
signal.
17. A system according to claim 9 including output circuit means having at least
one audio speaker means for transmitting the amplitude adjusted composite signal
to the area.
18. A system according to claim 7 in which said control circuit means is also
coupled to said masking signal source means and comprises means for adjusting
the amplitude of the masking signal so as to follow the amplitude of the sensed
ambient audio signals.
19. An auditory subliminal message system for an area comprising:
at least one audio sensor means for sensing ambient audio signals in the area
and for producing an ambient audio output signal representing the amplitude
of the sensed ambient audio signals;
subliminal message source means for providing an auditory subliminal message
output signal;
masking signal source means for providing and combining a masking signal having
frequency characteristics and an amplitude such that when the masking signal
is combined with the amplitude adjusted subliminal message output signal it
renders the adjusted subliminal message output signal outside of the conscious
recognition range;
ambient audio signal processing circuit means coupled to the output of said
audio sensor means for producing a control signal which varies with variations
in the amplitude of the sensed ambient audio signals;
amplitude control circuit means coupled to said subliminal message source means,
to said masking signal source means and to said ambient audio signal processing
circuit means for controlling the amplitude of said auditory subliminal message
and the amplitude of said masking signal in response to the control signal from
said ambient audio signal processing circuit means such that the amplitudes
of said auditory subliminal signal and of said masking signal increase with
increasing amplitudes of the sensed ambient audio signals and decrease with
decreasing amplitudes of the sensed ambient audio signals; and
output circuit means including speaker means for transmitting the amplitude
controlled auditory subliminal message output signal and the amplitude controlled
masking signal to the area.
20. A system according to claim 19 in which said ambient audio signal processing
circuit means includes an audio channel circuit means associated with each said
sensor means.
21. A system according to claim 20 including plural audio sensor means and plural
audio channel means, each said audio channel means including rectifier circuit
means having an input coupled to the output of its associated audio sensor means
for receiving and producing a rectified output signal representing the amplitude
of the ambient audio signals sensed by the associated audio sensor means, each
said audio channel means also including signal shaping circuit means having
an input coupled to the output of said rectifier means for producing a shaped
output signal which increases at a first rate in response to increases in the
rectified output signal which corresponds to increases in the amplitude of the
ambient audio signals sensed by the associated audio sensor means, the shaped
output signal decreasing at a second rate which is faster than the first rate
in response to decreases in the rectified output signal which corresponds to
decreases in the amplitude of the ambient audio signals sensed by the associated
audio sensor means; and
said system also including averaging circuit means having an input coupled to
the outputs of said signal shaping circuit means for receiving and averaging
the shaped output signals to produce a control signal comprising the average
of the received shaped output signals.
22. A system according to claim 20 including plural audio sensor means and plural
audio channel means, each said audio channel means including rectifier circuit
means having an input coupled to the output of its associated audio sensor means
for receiving and producing a rectified output signal representing the amplitude
of the ambient audio signals sensed by the associated audio sensor means;
said system also including averaging circuit means having an input coupled to
the outputs of said rectifier circuit means for receiving and averaging the
rectified output signals to produce an averaging circuit output signal comprising
the average of the received rectified output signals; and
signal shaping circuit means having an input coupled to the output of said averaging
circuit means for producing a shaped output signal which increases at a first
rate in response to increases in the averaging circuit output signal which corresponds
to increases in the amplitude of the sensed ambient audio signals, the shaped
output signal decreasing at a second rate which is faster than the first rate
in response to decreases in the averaging circuit output signal which correspond
to decreases in the amplitude of the sensed ambient audio signals.
23. A system according to claim 21 or 22 in which the first rate is slower than
the rate of increase of the sensed ambient audio signals.
24. A system according to claim 19 in which said output circuit means includes
means for combining background audio signals, such as music, with the amplitude
controlled auditory subliminal signal prior to transmitting this latter signal
to the area.
25. A system according to claim 21 in which the control signal comprises a control
voltage and in which said amplitude control circuit means comprises a voltage
controlled amplifier circuit.
26. A method of reducing shoplifting in a customer area of a store comprising:
sensing ambient audio signals from the area;
providing an auditory anti-shoplifting subliminal message signal;
adjusting the amplitude of the subliminal message signal to follow the amplitude
of the sensed audio signals; and
transmitting the amplitude adjusted subliminal message signal to the area.
27. A method according to claim 26 in which the step of adjusting the amplitude
comprises the steps of increasing the amplitude at a first rate with increasing
amplitudes of the sensed audio signals and decreasing the amplitude at a second
rate faster than the first rate with decreasing amplitudes of the sensed audio
signals.
28. A method according to claim 26 or 27 including the steps of providing a
masking signal having amplitude and frequency characteristics which when combined
with the auditory subliminal message signal renders the subliminal message signal
below the level of conscious recognition;
adjusting the amplitude of the masking signal to follow the amplitude of the
sensed audio signals; and
transmitting the amplitude adjusted masking signal to the area.
29. A method according to claim 28 in which the step of providing a subliminal
message signal comprises the step of providing a composite signal having the
auditory subliminal message signal as one component and the masking signal as
another component;
the step of adjusting the amplitude comprises the step of adjusting the amplitude
of the composite signal to follow the amplitude of the sensed audio signals;
and
the step of transmitting comprises the step of transmitting the amplitude adjusted
composite signal to the area.
BACKGROUND OF THE INVENTION
The present invention relates to a system and method for providing subliminal
auditory signals to an area such as a customer shopping area within a store.
More particularly, the invention relates to such a system and method in which
the amplitude of the subliminal signal is adjusted in response to the amplitude
of ambient audio signals from the customer shopping area.
It has been established that auditory subliminal signals, that is, those presented
below the conscious recognition level of the listener, can be used to influence
the listener's behavior to some degree. Some early research into visual and
auditory subliminal stimulation effects are exemplified in U.S. Pat. Nos. 3,060,795
of Corrigan, et al. and 3,278,676 of Becker.
In addition, Becker is understood to have experimented with the use of auditory
subliminal messages to deter shoplifting by retail store customers. Although
applicants have not seen or studied Mr. Becker's device, it is believed to combine
an auditory subliminal message with background music. However, during non-peak
shopping and other times when the store area is exceptionally quiet, the background
music signal component in Becker must be much louder than the subliminal signal
as otherwise the subliminal signal would be at a level such that it may be consciously
recognized by a listener. In addition, as a result of this large difference
between the amplitude of the background music and that of the subliminal message
signal, the effectiveness of the Becker subliminal message is reduced. Also,
Becker is understood to maintain his combined background music and subliminal
message at a level sufficiently high enough to enable the music to be heard
even under noisy store conditions. However, when the ambient audio signal level
drops, such as during non-peak store traffic times, the combined background
music and subliminal signal would remain the same and seem overly loud. Thus,
Becker is simply not understood to control the amplitude of a subliminal message
in response to ambient audio signals from an area.
Accordingly, there is a need for an auditory subliminal message system and method
which solves these and other problems.
SUMMARY OF THE INVENTION
The present invention is a method and system for adjusting the amplitude of
an auditory subliminal message in response to the amplitude of ambient audio
signals from an area to which the subliminal message is to be transmitted. In
accordance with one aspect of the invention, an audio signal processing circuit
means receives signals representing the amplitude of audio signals in the area,
such as a retail shopping area of a store. This processing circuit means produces
a control signal for an amplitude adjustment or control circuit means which
adjusts the amplitude or volume of an auditory subliminal signal which is to
be transmitted to the area. The amplitude of the auditory subliminal signal
is adjusted to increase with increasing sensed ambient audio signals and decrease
with decreasing sensed ambient audio signals.
As a more specific aspect of the invention, a masking signal is generated and
fed to the area. This masking signal has frequency and amplitude characteristics
which cover or render the subliminal signal inperceptible to the conscious recognition
level of a listener. In the preferred embodiment, the amplitude of this masking
signal is also controlled in response to the sensed ambient audio signals so
that its amplitude follows the amplitude of the adjusted subliminal message
signal. The masking signal may be combined with the subliminal signal to provide
a composite signal having an amplitude controlled by the control circuit in
response to the control signal.
As a more specific feature of the invention, to reduce distortion of the subliminal
message signal, the processing circuit means produces a control signal which
causes the control circuit means to increase the amplitude of the auditory subliminal
message signal slowly at a rate slower than the rate of change of the ambient
audio signals at times when the ambient audio signals are increasing in magnitude.
In addition, at times when the ambient audio signals are decreasing to minimize
the possibility of conscious perception of the subliminal message signal, the
processing circuit means produces a control signal which causes the control
circuit means to decrease the amplitude of the subliminal signal at a fast rate.
It is accordingly one object of the invention to provide an improved auditory
subliminal message system and method.
Another object of the invention is to provide an auditory subliminal message
having an amplitude which is adjusted in response to ambient noise levels within
an area to which the auditory subliminal message is to be transmitted.
A further object of the invention is to provide a method and system which adjusts
the amplitude of an auditory subliminal message at one rate with increasing
ambient audio signal levels in the area and at another, faster rate with decreasing
ambient audio signal levels.
A still further object of the invention is to provide such a method and system
in which the amplitude of an auditory subliminal signal is adjusted to rise
at a rate slower than the rate of increases in ambient audio signal levels.
Another object of the invention is to provide an auditory subliminal message
which is continuously maintained below the conscious perception level.
A further object of the invention is to provide an auditory subliminal message
which is maintained below the conscious perception level of listeners in an
area and which is adjusted in response to ambient audio signals in the area
so as to remain close to the level of conscious perception.
Still another object of the invention is to provide an auditory masking signal
for an auditory subliminal message, the masking signal having an amplitude which
is adjusted in response to ambient noise levels in an area to which the auditory
subliminal message is to be transmitted.
A more specific object of the invention is to provide an auditory subliminal
message anti-shoplifting system and method.
These and other objects, features and advantages of the invention will become
apparent with reference to the following drawings and description.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing
FIG. 1 is a block diagram of an auditory subliminal message system in accordance
with the present invention;
FIG. 2 is a block diagram illustrating one embodiment of an auditory subliminal
message signal and masking signal source;
FIG. 3 is a block diagram showing another embodiment of an auditory subliminal
message signal and masking signal source;
FIG. 4 is a block diagram showing an alternate ambient audio signal processing
circuit; and
FIG. 5 is a detailed circuit schematic diagram of the ambient audio signal processing
circuit and other portions of the circuit of FIG. 1.
DETAILED DESCRIPTION
General Description of Preferred Embodiment
It has now been discovered that in an environment with constantly changing ambient
audio levels, such as in the shopping area of a store, it is desirable to adjust
the amplitude of an auditory subliminal message signal to follow the amplitude
of the ambient audio signals. That is, by increasing the amplitude of the auditory
subliminal message with increasing ambient audio levels and decreasing the amplitude
of the subliminal signal with decreasing ambient audio levels, the subconscious
perception of the subliminal message by listeners is improved. This in turn
increases the effectiveness of the subliminal message.
Therefore, with reference to FIG. 1, the system includes circuit means for controlling
the amplitude of an auditory subliminal message signal in response to the level
of ambient sounds in an area 26, such as the customer shopping area within a
store, to which the subliminal message signal is to be transmitted. Such circuit
means includes an ambient audio signal processing circuit 10 and a control circuit
12. Control circuit 12 is adapted to receive an auditory subliminal message
signal input at 14 and processing circuit 10 has at least one input 16 for receiving
signals representing the amplitude or volume of ambient audio signals within
the area. Processing circuit 10 and control circuit 12 adjust the amplitude
of the auditory subliminal message signal received at input 14, in response
to the amplitude of ambient audio signals received at input 16, to produce an
auditory subliminal message signal output at 18 having an amplitude which varies
with variations in the level of ambient audio signals in the area.
The output signal at 18 is fed to an output circuit which, in the illustrated
form, includes an output mixer circuit 20 having an input coupled to output
18, a preamplifier and amplifier circuit 22 with an input 21 coupled to the
output of mixer circuit 20, and a speaker 24 for transmitting the amplitude
adjusted auditory subliminal message signal to area 26. The circuit also may
include an optional background auditory signal source 28 which produces music
or other background auditory signals which are fed to an input 29 of the output
mixer circuit 20. These background signals are combined within mixer circuit
20 with the amplitude controlled subliminal message signal and the combined
signal is transmitted by speaker 24 to room 26.
The preferred embodiment of the system also includes at least one audio sensor
means, such as microphone 30 positioned within the area 26. Microphone 30 detects
ambient audio signals within the area and produces an electrical output signal
representing these detected signals. The microphone output is fed to input 16
of ambient audio signal processing circuit 10.
Processing circuit 10 includes an audio channel 32 associated with microphone
30 for modifying the input 16 to produce an audio channel output signal at 34
which varies with variations in the ambient audio signal input at 16, as explained
below. Preferably, plural microphones 30, 30a, 30b, 30c, 30d, etc. are provided
for detecting ambient audio signals in various parts of the area 26. For convenience,
these microphones may be positioned in the ceiling of the shopping area. A respective
audio channel 32a, 32b, 32c and 32d is associated with each of the microphones
30a, 30b, 30c and 30d and produces output signals 34a, 34b, 34c and 34d in the
same manner as the audio channel 32. The output signals 34 are averaged by an
averaging circuit 36 to produce an output control signal at 38 which varies
with variations in the amplitude of ambient audio signals sensed by the microphones
throughout the store area 26.
In the embodiment of FIG. 1, each audio channel 32 includes a preamplifier circuit
40 for amplifying the input signal 16, a rectifier circuit 42 for rectifying
the amplified input signal and a signal shaping circuit 44 for modifying the
rectified ambient audio signal input from microphone 30, as explained below.
In connection with this signal shaping circuit, it has now been discovered that
rapid changes of an amplitude of an auditory subliminal signal can distort it
to such an extent that it becomes unrecognizable to subconscious perception.
Hence, to reduce such distortion and increase the subconscious perceptibility
of the subliminal signal, the signal shaping circuit adjusts the control signal
to cause the amplitude of the auditory subliminal message signal at a rate which
is slower than the rate of increase of ambient audio signals at times when the
amplitude of such ambient signals is increasing. However, with sudden drops
in the level of ambient audio signals, a slow drop in the amplitude of the subliminal
message could lead to conscious perception of this message. This can be extremely
disadvantageous in situations wherein it is desired to keep the existence of
the subliminal message a secret. Therefore, the signal shaping circuit adjusts
the control signal to cause the volume of the auditory subliminal message to
drop at a faster rate upon a decrease in the volume of ambient audio signals.
Hence, with this form of signal shaping circuit 44, the control signal output
at 38 of the averaging circuit 36 varies at one rate with increasing ambient
audio signals and at another faster rate with decreasing ambient audio signals.
Furthermore, control circuit 12 is responsive to this varying control signal
to produce an amplitude adjusted auditory subliminal message output at 18 which
increases at a first rate with increases in ambient audio signals and decreases
at a second rate, faster than the first rate, with decreases in ambient audio
signals. In addition, to prevent distortion of the subliminal message, the first
rate is slower than the rate of increase of the ambient audio signals.
It has also now been discovered that time lags are introduced into an auditory
subliminal system. Such time lags are primarily due to the amount of time required
by ambient audio signals is travel to microphones and the time required by an
amplitude controlled subliminal message to travel from speakers to a listener.
Thus, no matter how quickly the system reduces the amplitude of the auditory
subliminal message in response to declining ambient sound levels, a reduction
in the amplitude of the subliminal message would lag the reduction in volume
of ambient sound. Thus, a rapid drop in ambient sound level could momentarily
leave the subliminal message signal at a level sufficiently high to be perceived
by a listener. In certain applications this would prove extremely disadvantageous.
For example, if an anti-shoplifting subliminal system is used to deter shoplifting
in a store, customers may be extremely reluctant to patronize the store if they
consciously perceive a normally anti-shoplifting message and hence realize that
such a system is in use. Thus, although a store may realize savings due to a
reduction in shoplifting, its overall profits may suffer because of customer
reluctance to patronize a store wherein such a system is in use. Hence, in such
applications it is desirable to maintain the subliminal signal continuously
below the conscious perception range of listeners. On the other hand, in other
applications such as in connection with a weight loss class in which the listeners
realize that an auditory subliminal weight loss message is being transmitted,
it is not as critical to continuously maintain the subliminal message below
conscious perception levels.
To solve this problem, the preferred embodiment of the system includes means
for producing a masking signal which screens the auditory subliminal message
and blocks its conscious perception, particularly during times when the volume
of ambient noise drops quickly. Thus, as illustrated in FIG. 1, the system includes
a subliminal message and masking signal source means 48 which produces the auditory
subliminal message signal fed to input 14 of control circuit 12. In addition,
source 48 includes means for providing a masking signal with amplitude and frequency
characteristics which block conscious perception of the auditory subliminal
message. The masking signal may bypass control circuit 12 and be fed directly
to room 26. However, it is preferable that the amplitude of the masking signal
also be controlled in response to the amplitude of ambient audio signals. Otherwise,
when the room becomes very quiet, the masking signal could be so loud that it
is readily perceived and annoying. Also, if the masking signal amplitude remained
constant while the subliminal signal amplitude dropped in response to drops
in ambient sound levels, the amplitude of the masking signal would become so
large relative to that of the subliminal message, that subconscious perception
of the subliminal message is impaired.
Although a separate control circuit may be provided for controlling the amplitude
of the masking signals, preferably the masking signal is combined with the auditory
subliminal message signal and the resulting composite signal is fed to input
14 of control circuit 12. As illustrated in FIG. 1, control circuit 12 may include
a voltage control amplifier circuit 39 for adjusting the output 18 in response
to the control signal input 38.
As shown in FIG. 2, subliminal message and masking signal source 48 may comprise
a means such as a tape recorder for playing back a recording of a composite
auditory subliminal message and masking signal. In an alternate form illustrated
in FIG. 3, the subliminal message and masking signal source 48 may comprise
a voice synthesizer circuit 50 which produces an auditory subliminal component
of the composite subliminal and masking signals. One suitable voice synthesizer
circuit 50 comprises a commercially available "Digitalker" kit produced
by National Semiconductor Company. This kit includes a sixteen kilobite, eight
bit memory chip No. MM52116 and a speech processor chip designated SPC. In addition,
a masking signal circuit 52 is provided for producing the masking signal. This
circuit may take various forms and comprise a white noise signal generator circuit
such as a random noise oscillator with an internal shift register. One suitable
generator is available from Radio Shack and designated random events generator
chip No. S2688/MM5837. The masking signal circuit and voice synthesizer circuit
outputs are fed to a commercially available mixer amplifier circuit 54, in which
they are combined. The mixer circuit output comprises the composite auditory
signal which is fed to input 14 of the control circuit 12.
As previously mentioned, the masking signal has frequency and amplitude components
which make the auditory subliminal message signal incapable of conscious recognition
by a listener. More specifically, the masking signal has frequency components
which overlay the frequency components of the auditory subliminal message signal.
In addition, the amplitude of the masking signal is slightly higher than the
amplitude of the auditory subliminal message signal. More specifically, it has
now been discovered that preferred results are obtained when the amplitude of
the masking signal is continuously maintained approximately within the range
of 3 db to 15 db above the amplitude of the subliminal message signal. Furthermore,
that the best results occur when the masking signal is approximately 5 db above
the amplitude of the auditory subliminal message signal. That is, with such
relative amplitudes of the masking signal to the auditory subliminal message
signal, a temporary screen is provided for the subliminal message at times,
such as during rapid declines in ambient noise levels, when the subliminal message
may otherwise become supraliminal. Also, with such relative amplitudes, the
masking signal provides a satisfactory screen for the subliminal message without
impairing satisfactory subconscious perception of the auditory subliminal message.
It should be noted that with such relative amplitudes of the masking signal
and subliminal message signal, the masking signal typically may not block conscious
perception of the subliminal signal in a situation where the composite subliminal
message and masking signal are at a high amplitude in relation to the volume
of ambient audio signals. However, such conditions are prevented by controlling
the amplitude of the composite signal in response to ambient audio signals,
as explained above.
FIG. 4 illustrates an alternate ambient audio signal processing circuit. Components
of this circuit which are similar to those of the FIG. 1 form of processing
circuit have numbers incremented by two hundred over the corresponding numbers
in FIG. 1. Hence, these components will not be described in detail. Unlike the
FIG. 1 form of processing circuit, the audio channels of the FIG. 4 embodiment
do not include the signal shaping circuit. Instead, the output of the respective
rectifier circuits are averaged by an averaging circuit 236 prior to signal
shaping by a signal shaping circuit 244 in the manner explained above.
DETAILED CIRCUIT DESCRIPTION
With reference to FIG. 5, a four-channel audio signal processing circuit is
illustrated. Since each of the illustrated channels is identical, only the upper
channel will be described in detail.
The audio channel includes series connected preamplifier circuit 40, rectifier
circuit 42, and signal shaping circuit 44. The input 16 to the channel is obtained
from the microphone 30 (FIG. 1) and thus fluctuates in response to changes in
ambient audio signals detected by the microphone. Input 16 and hence the microphone
output is fed to preamplifier circuit 40. More specifically, this input is coupled
by a 0.1 microfarad capacitor 58 through a one kilohm gain establishing resistor
60 to the inverting input of an operational amplifier 62. The output of amplifier
62 is connected through a one megohm feedback resistor 64 to its inverting input.
The gain of amplifier 62 is established by the ratio of resistors 64 and 60
and, with these particular resistors is set at approximately one thousand. Also,
a positive biasing voltage V is fed through a two megohm biasing resistor 66
to the noninverting input of amplifier 62. With the circuit components utilized
in the FIG. 5 circuit, the positive biasing voltage is six volts and a negative
biasing voltage is at negative six volts. One suitable amplifier 62 comprises
one amplifier section of an LM3900 quad Norton operational amplifier. When connected
as described above, amplifier 62 inverts and amplifies the input signal at 16.
To convert the input at 16 to a direct current signal, 0.1 microfarad capacitor
68 couples the output of amplifier 62 to the inverting input of an amplifier
70 connected as an amplifying, inverting, precision rectifier. Rectifier circuit
42 produces an output signal comprising a positive half-cycle inverted and amplified
version of the input signal. More specifically, the output of amplifier 70 is
connected to the anode of a diode 74 having its cathode connected through a
one megohm feedback resistor 76 to the inverting input of amplifier 70. Thus,
the positive half-cycles of the output signal from amplifier 70 are coupled
through diode 74 and resistor 76 to the inverting input of amplifier 70. In
contrast, the negative half-cycle output signals from amplifier 70 are blocked
by diode 74. However, because the output of amplifier 70 is connected to the
cathode of a diode 72 having its anode coupled to the inverting input of amplifier
70, these negative going half cycles are coupled through diode 72 to the inverting
input of amplifier 70. The output of rectifier 42 is taken at the cathode of
diode 74 and comprises a positive representation of the input signal 16 and
hence of the amplitude of ambient audio signals detected by microphone 30. A
suitable amplifier for accomplishing this rectification comprises one amplifier
section of a type 324 quad operational amplifier.
The rectified output signal from rectifier circuit 42 is fed to signal shaping
circuit 44. That is, the output of the rectifier circuit is fed to a resistor-capacitor
network. This network comprises a ten kilohm resistor 78 coupled between the
output of rectifier 42 and the noninverting input of an operational amplifier
80, a one microfarad capacitor 88 which couples the noninverting input of amplifier
80 to ground, and a one hundred kilohm resistor 86 in parallel with capacitor
88. This network has a charging time constant of approximately 0.01 seconds
and discharging time constant of approximately 0.1 seconds. Amplifier 80 may
comprise one amplifier section of a type 324 quad operational amplifier and
has its output coupled directly through a feedback loop to its noninverting
input so that the amplifier acts as a voltage follower. The output of amplifier
80 drives another resistor-capacitor network including a five hundred kilohm
resistor 82 and a ten microfarad capacitor 90. The time constant of this latter
resistor-capacitor is approximately five seconds. Also, a diode 84, having a
turn-on voltage of approximately 0.7 volts, has its anode connected to the contact
between resistor 82 and capacitor 90 and its cathode connected to the noninverting
input of amplifier 80. The positive side of capacitor 90 is coupled through
a one hundred kilohm resistor 92 to the output 34 of the audio channel. This
output 34 is then fed to averaging circuit 36 as explained below.
For reasons explained above, signal shaping circuit 44 operates in the following
manner to produce an output on line 34 which increases at one rate with increasing
sensed ambient audio signals and which decreases at a rate faster than said
one rate with decreases in the sensed audio signals. Furthermore, because of
the delays within the signal shaping circuit 44 resulting from charging time
of the resistor-capacitor networks, the output signal on line 34 will increase
at a slower rate than the rate of increase of ambient noise signals. This slows
the rate of change of the audio subliminal signal and thereby minimizes rapid
amplitude fluctuations therein and resulting distortions. That is, as the amplitude
of ambient audio signals increases, the signal reaching capacitor 90 also increases.
However, because of the relatively long charging time constant of the resistor-capacitor
network including capacitor 90, capacitor 90 charges slowly. Hence, under those
conditions the output on line 34 comprises a slowly rising DC signal. Furthermore,
because the voltage at the anode of diode 84 is greater than or equal to the
voltage at its cathode, diode 84 is nonconducting. In contrast, upon a sudden
decrease in the amplitude of the sensed ambient audio signals, the input to
operational amplifier 80 quickly decreases. As a result, the voltage at the
cathode of diode 84 drops below the voltage at the anode of this diode sufficiently
to cause the diode to conduct. While conducting, diode 84 establishes a short
circuit between the positive side of capacitor 90, through resistor 86 and to
ground so that capacitor 90 rapidly discharges. Therefore, the output signal
at 34 drops rapidly and at a rate much faster than the rate at which the output
34 rose with increases of the amplitude of the ambient audio signals. Of course,
by adjusting the time constants of the resistor-capacitor circuits within shaping
circuit 44, the rate of change of the output 34 in response to changes in ambient
audio signals can be adjusted as desired.
The outputs of the audio channels are fed to averaging circuit 36. More specifically,
resistor 92 and a similar resistor in each of the other audio channels couple
the DC outputs from these channels to the inverting input of an operational
amplifier 94 connected to average the signals received at its inverting input.
Amplifier 94 may comprise a type 741 operational amplifier. The noninverting
input of this amplifier is grounded and a twenty-five kilohm feedback resistor
96 couples the output of amplifier 94 to its inverting input. In addition, a
ten kilohm current limiting resistor 98 couples the output of amplifier 94,
which comprises the control signal 38, to control circuit 12. More specifically,
with this particular circuit, control signal 38 comprises a varying direct current
signal. Resistor 96 is set at one-quarter the value of the input resistors 92
so that the gain of the averaging amplifier 94 is established at 0.25. In the
event only one microphone is used to detect ambient audio signals, then averaging,
of course, is not performed.
Control circuit 12 controls the amplitude of the composite auditory subliminal
message and masking signal received at its input 14 in response to the control
signal on line 38 and thereby in response to changes in ambient sound levels
within room 26. More specifically, the control signal on line 38 is used as
a gain control for an amplifier 102 of circuit 39. Amplifier 102 may comrise
a type CA3080A operational transconductance amplifier connected as a voltage
controlled amplifier. The control signal on line 38 is fed to the control signal
input .sup.I ABC of amplifier 102. Amplifier 102 is conducted in a conventional
manner as a single supply operational amplifier. Also, the positive reference
voltage is fed through a voltage divider network including a forty-seven kilohm
resistor 106 and forty-seven kilohm resistor 110 to ground. The three-volt signal
available from this divider is supplied to the noninverting input of amplifier
102. A ten microfarad capacitor 108 couples this latter input to ground to remove
stray alternating current signals at this input. In addition, the composite
subliminal auditory message signal and masking signal is fed to input 14 of
voltage control amplifier circuit 39. That is, these signals are coupled through
a ten microfarad capacitor 104 to the inverting input of amplifier 102. The
output of amplifier 102 is fed to one side of a ten kilohm potentiometer 112
having its other side coupled to ground through resistor 110. The output of
circuit 39 is taken from potentiometer 112 and, as explained above, comprises
a composite auditory subliminal message signal and masking signal having an
amplitude adjusted in response to ambient audio signals within area 26. The
wiper arm of potentiometer 112 also permits adjustment of the amplitude of the
voltage controlled composite auditory subliminal signal and masking signal.
Hence, this amplitude can be selectively adjusted to make the masking signal
component more clearly consciously perceptible to provide an indication that
the system is operational.
The gain controlled output signal of circuit 39 is connected through a one hundred
kilohm resistor 114 to the inverting input of an operational amplifier 116 within
output mixer circuit 20. Amplifier 116 may comprise a type 741 operational amplifier
connected as an inverting mixer. Any optional background audio signals, such
as music, may be fed to input 29 of output mixer circuit 20. This input is coupled
by a ten microfarad coupling capacitor 124 in series with a one hundred kilohm
input resistor 122 to the inverting input of amplifier 116. A one hundred kilohm
feedback resistor is also coupled between the output of amplifier 116 and its
inverting input. Since resistors 114, 118 and 122 are all equal, the gain of
the amplifier 116 is established at one. The output of amplifier 116 is coupled
through a ten microfarad coupling capacitor 120 to preamplifier and amplifier
circuit 22 (FIG. 1) and hence to the speaker 24 located in the area 26.
In a specific anti-shoplifting application, an auditory subliminal message signal
designed to encourage honesty is provided. One such signal comprises the phrase
"I am honest, I will not steal".
This auditory subliminal message signal is combined with a white noise masking
signal to provide a composite signal input to the control circuit 12. The amplitude
of this composite signal is then adjusted within control circuit 12, as explained
above, in response to changes in the amplitude of ambient audio signals detected
within the shopping area of a store. The amplitude controlled composite signal
is then transmitted to the shopping area so that the subliminal message is subconsciously
perceived by individuals within the store.
It has now been experimentally determined that, although shoplifting and theft
are not completely eliminated, significant reductions in these losses have resulted
in such an application of the system of this invention.
Having illustrated and described the principles of our invention with reference
to several preferred embodiments, it should be apparent to those persons skilled
in the art that such embodiments may be modified in arrangement and detail without
departing from such principles. We claim as our invention all such modifications
as come within the true spirit and scope of the following claims.