Method and apperatus for communcation operator privacy

Method and apperatus for communcation operator privacy
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US 20030152240A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2003/0152240 A1
Resnick
(43) Pub. Date:
(54)
METHOD AND APPERATUS FOR
COMMUNCATION OPERATOR PRIVACY
(75)
Inventor:
Andrew M. Resnick, Bethesda, MD
Aug. 14, 2003
Publication Classi?cation
(51)
Int. Cl.7 .
(52)
US. Cl. ......................... .. 381/731; 381/92; 381/941
................................ .. H04R 3/02
(Us)
Correspondence Address:
ANDREW M. RESNICK
4815 GRANTHAM AVE
CHEVY CHASE’ MD 20815 (Us)
(57)
_
ABSTRACT
_
_
_
_
_
_
Disclosed is a device for use With communications equip
ment to provide privacy for the operator and reduce acoustic
noise from the operator’s voice in the area. The device uses
(73) Assignee; MI; Andrew Resnick, Bethesda, MD
(Us)
active acoustic cancellation to silence the voice of the
operator once past, and captured by the microphone.
Embodiments include the all types of microphones for any
(21) Appl, N()_j
09/683,741
(22)
Feb. 8, 2002
type of telephone, transmitting radio, intercom or other
communication devices Where a operator speaks out loud to
Filed:
20
communicate With another location.
Patent Application Publication Aug. 14, 2003 Sheet 1 0f 9
US 2003/0152240 A1
Figure 1
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Sound
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Level
2
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9
Patent Application Publication Aug. 14, 2003 Sheet 2 0f 9
US 2003/0152240 A1
20
Figure 3
11
21
Pre Amp
12
22\
V
23}
Sig. Processor -—> Amp —
> To Comm. Circuits
Patent Application Publication Aug. 14, 2003 Sheet 3 0f 9
Figure 4
26
Pre Amp J21
23/
K25
l
Band Pass
Filter
ND DIA
i
j_______
Comm.
Silencing
Device
Routine
Signal
Equaiize
Routine
Routine
K28
-->To Digital Comm. Device
Transmission Circuits
US 2003/0152240 A1
Patent Application Publication Aug. 14, 2003 Sheet 4 0f 9
US 2003/0152240 A1
Figure 5
Pre Amp
26
/21
23/
/ 25 \
l
Band Pass
Filter
> AID BIA
1
Silencing
Signai
Equalize
Routine
Routine
30V
—->-To Analogue Comm. Device
Transmission Circuits
Figure 6
Pre Amp _/ 21
iv
K125
23/
Amp
1
Filter
Silencing
Equalization
Circuit
Circuit
Circuit
130 \127
K128
To Comm. Device Transmission Circuits
Patent Application Publication Aug. 14, 2003 Sheet 5 0f 9
Pre Amp
-
V
US 2003/0152240 A1
Sig. Processor
To Communication Device til- .C©\36
Patent Application Publication Aug. 14, 2003 Sheet 6 0f 9
US 2003/0152240 A1
55
Figure 10
5'
(M “3
52
633
Pre Amp ——-> Sig. Processor —> Amp
Patent Application Publication Aug. 14, 2003 Sheet 7 0f 9
Microphone
Signal
Figure 1 1
US 2003/0152240 A1
Silencing
Signal
l
Noise L Comm.
Silencing}. Equalize
Device
Signal
k106 t\117\118> K>119
Cancel
-—-—>' To Comm. Device
Transmission Circuits
Microphone
Signal
ll
Feedback
Figure 12
Comm.
Recluctionn~+ Device
Silencing
Signal
.
Silencing
Signal
Equalize
->
K116 K117K118
\-/119
‘——>- To Comm. Device
Transmission Circuits
Patent Application Publication Aug. 14, 2003 Sheet 8 0f 9
US 2003/0152240 A1
Figure 13
Microphone
Signal
113 (
115
Silencin
112 Signal 9
Time &
b Equalize
Calibration
:---------i
‘-------------|
v
l‘
1
Feedback
Reduction
Comm.
Device
K116
Silencin
signal
l
7
Equaiiz
117K11S
\s’119
‘—-—->- To Comm. Device
Transmission Circuits
Figure 14
I
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121
re mp
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(122
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Adjustments
Silencin
Signal 9
qua we
'- ----- --"|
v
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2553" ———--> Signal
\118
i
Equaliz
,
1
K>119
Patent Application Publication Aug. 14, 2003 Sheet 9 0f 9
Microphone
Signal
Figure 15
124
(
US 2003/0152240 A1
Silencing
Signal
Masking
‘‘
White
~
lhloise
1
Comm.
Silencing Equalize
1_> Deviice
Signal
->
117 \118
\-'—119
= To Comm. Device
Transmission Circuits
Microphone
Signal
Figure 16
125
(
Silencing
Sign
Analysis &
‘i
‘ Masking
‘
Noise
l
Comm.
: Deviice
Silencing Equalize
Signal
117 K118
->
\‘419
> To Comm. Device
Transmission Circuits
Aug. 14, 2003
US 2003/0152240 A1
METHOD AND APPERATUS FOR
COMMUNCATION OPERATOR PRIVACY
BACKGROUND OF INVENTION
[0001]
This invention relates to the active acoustic silenc
ing of conversations being conducted by communications
equipment such as telephones, transmitting radios and other
electronic apparatus.
[0002] Remote communication betWeen people operating
telephones, radios or other devices is common place to the
point Where conversations often take place While either or
both operators’ speech is unintentionally overheard by other
people. Examples include cellular telephones used in public,
telephones used in multi-occupant rooms such as office
cubicle spaces, open sided public pay phones, 2-Way radio
transmissions, and anyWhere the operator of a communica
tions device can be overheard. The result is that the operator
equipment such as all types of telephones, transmitting
radios, intercoms, and the like. The invention also reduces
distracting noise from the operator’s speech for the people in
the adjacent area. The invention attaches to or integrates
With the communications equipment With no impact on the
equipment’s convenience or sanitation, and little impact on
maintenance or siZe greatly improving on prior efforts to
obtain such privacy.
[0009] The invention applies active acoustic silencing to
the problem of speech privacy for the operator of commu
nications equipment. The active acoustic silencing of the
operator’s voice While using communications equipment
results in both privacy of the operator’s communications and
reduction in distraction for other people in the vicinity.
[0010]
The invention may be embodied as an attachment
to eXisting communication equipment, With or Without elec
can not have a private conversation. In addition to the
trical connections, or embodied as an integral part of a
operator’s loss of privacy, people overhearing intelligible
communications device.
conversation are signi?cantly distracted resulting in loss of
[0011] The preferred embodiments of the invention add
concentration and efficiency.
[0003]
Prior art is from tWo areas: communications opera
tors’ privacy and active acoustic silencing.
[0004] Privacy for the operators speaking on communica
tions devices has previously only used passive devices such
one or more loudspeakers behind the microphone of a
communication device’s handset or headset, and some addi
tional circuitry inside the communication device. Other
embodiments of the invention vary in their degree of inte
gration With the communications device. A second embodi
ment of the invention replaces the communications device’s
as US. Pat. No. 5,182,883 to Amberson a telephone enclo
sure or the “Hush-a-Phone” type handsets that enclosed the
operator’s mouth such as US. Pat. No. 271,903 to Nichols.
handset or headset apparatus and connects electrically to the
These devices use passive acoustical dampening to quiet the
connections and uses a separate microphone, placed adja
sound or sealed off the operator’s voice to prevent it from
cent to the communications device microphone.
propagating. The sealing devices either required putting a
sealed container around the operator (e.g. telephone booths
With closing doors) or for the device to seal to the operator,
i.e. around the operator’s mouth, With a host of maintenance
and sanitary issues that many patents tried to addressed.
Both types are rarely used any longer.
[0005]
There is a notable lack of devices applying active
acoustic silencing or active acoustic canceling (synonymous
terms) to communications operator privacy. Active acoustic
silencing Was ?rst patented in the Lueg US. Pat. No.
2,043,416. Active acoustic silencing has seen application in
reducing noise in con?ned spaces like ducts and exhausts, as
in US. Pat. No. 4,815,139 to Eriksson, et al. and in reducing
background noise for operators listening to acoustic signals
on headsets, as in US. Pat. No. 5,675,658 to Brittian.
Methods and devices for applying it to speci?c noise sources
have been patented several times such as US. Pat. No.
communications device. Another embodiment physically
attaches to the communications device With no electrical
[0012]
The generaliZe function of the invention is illus
trated in FIG. 1 and summariZed as folloWs. Aunidirectional
microphone (1) captures the operator’s speech (4) just in
front of the operator’s mouth (10). The electrical signal from
the microphone goes to a electrical or electronic circuit (6)
Which processes the signal to: ampli?ed it, split off the signal
to be sent by communication equipment, modify the signal
to produce the silencing signal, amplify the signal to the
needed volume for the cancellation, and send the signal to
the loudspeaker (2) placed in front of the operator’s mouth
and further aWay than the microphone
[0013] In FIG. 1, the acoustic silencing takes place in the
air betWeen the element of the microphone (1) and the
loudspeaker
The operator’s speech modulates the sound
pressure level verses position (7) commonly called sound
Waves. The silencing loudspeaker (2) produces the mirror
5,872,853 to Marquiss for reduce noise from highWays and
sound pressure level
US. Pat. No. 5,889,869 to Botros et al. for reduce noise from
(8) the both sounds are reduced by active acoustic cancel
lation.
adjacent Workspaces.
Where the tWo sound Waves meet
privacy involve passive mechanical arrangements Which
[0014] Applications of the invention include embodiments
for all types of communications devices including: cellar
have several problems including: inconvenient to use,
telephones, cordless telephones, Wired telephones, inter
unsanitary, high maintenance, and siZe.
coms or 2-Way radios. The invention is applicable any Where
a communications device operator’s speech may be over
heard to preserve privacy or to avoid disturbing others.
[0006]
[0007]
Efforts up to noW to provide such conversational
The need for privacy for telecommunication opera
tors has increased With cellular telephones and of?ce cubicle
telephones providing no privacy for the operator and causing
BRIEF DESCRIPTION OF DRAWINGS
a signi?cant distraction for other people in the area.
SUMMARY OF INVENTION
[0008]
This invention utiliZes active acoustic silencing to
provide speech privacy for the operator of communications
[0015]
FIG. 1 illustrates the principles of the invention.
[0016] FIG. 2 illustrates a preferred embodiment of the
invention.
Aug. 14, 2003
US 2003/0152240 A1
[0017] FIG. 3 illustrates a block diagram and signal path
of the invention for the preferred embodiment.
[0018] FIG. 4 illustrates the signal processing in a digital
embodiment of the invention With a digital communications
device.
[0019] FIG. 5 illustrates the signal processing in a digital
embodiment of the invention With a analogue communica
tions device.
[0020] FIG. 6 illustrates the steps in a analogue signal
processing embodiment of the invention.
[0021] FIG. 7 illustrates a second embodiment of the
invention.
[0033] In FIG. 1, the acoustic silencing takes place in the
air betWeen the element of the microphone (1) and the
loudspeaker
The operator’s speech modulates the sound
pressure level verses position (7) commonly called sound
Waves. The silencing loudspeaker (2) produces the mirror
sound pressure level
the volume and intelligibility of the speech.
[0034] The invention requires the distance betWeen the
loudspeaker face and the microphone face (labeled S in FIG.
1) to be greater than the signal processing time divided by
the velocity of sound in air, i.e.:
S>T/V
[0035]
[0022] FIG. 8 illustrates a block diagram and signal path
of the invention for the second embodiment.
[0023]
tion.
FIG. 9 illustrates a third embodiment of the inven
[0024] FIG. 10 illustrates a block diagram and signal path
of the invention for the third embodiment.
[0025] FIG. 11 illustrates the enhancement of using a
noise cancellation process.
[0026] FIG. 12 illustrates the enhancement of using a
feedback reduction process.
[0027]
FIG. 13 illustrates the enhancement of using a
calibration process.
[0028] FIG. 14 illustrates the enhancement of using adap
tive processing.
[0029]
FIG. 15 illustrates the enhancement of using a
masking noise.
[0030]
FIG. 16 illustrates the enhancement of using a
frequency complement masking noise.
Where the tWo sound Waves meet
(8) the sound pressure levels cancel, measurably reducing
(Equation 1)
S=distance betWeen the invention’s micro
phone face and loudspeaker face.
[0036] T=Time betWeen the microphone receiving
and the loudspeaker broadcasting the signal.
[0037] V=Velocity of sound in air.
[0038] For best sound cancellation performance the dis
tance betWeen the operator’s mouth reference point (3) and
the microphone (1) face, labeled M in FIG. 1, is minimiZed.
[0039] A preferred embodiment is With the invention
integrated into the communications device as illustrated in
FIG. 2. The integration in this embodiment uses one micro
phone (11) and shared signal processing circuitry (14) and
shared poWer supply (not shoWn) for the communications
device and for the invention. The preferred embodiment’s
housing places both the microphone (11) and the silencing
loudspeaker (12) in the handset (20) (or headset) both
positioned to aim at, the operator’s mouth (10). The micro
phone and silencing loudspeaker are each connected by
Wires to the processing circuit (14) Which may be located
anyWhere in the communications device such as in the
handset or in the separate housing of a Wired communica
tions device such as a land line telephone (not shoWn). The
design must satisfy the relationship of Equation (1) above.
DETAILED DESCRIPTION
[0031]
The generaliZe function of the invention is illus
trated in FIG. 1 and summariZed as folloWs. A microphone
(1) or acoustic sensor captures the operator’s speech (4) just
in front of the operator’s mouth (10). The electrical signal
[0040] The handset (20) (or headset) includes a micro
phone (11) that converts the acoustic signal to an electrical
signal for both the communications device and the acoustic
silencing. The microphone (11) is shielded from the acoustic
silencing sound by a acoustic damping material barrier (13)
from the microphone goes to a electrical or electronic circuit
Which supports the microphone in the hand or head set and
(6) Which processes the signal to: ampli?ed it, split off the
signal to be sent by communication equipment, modify the
to be unidirectional and may be of a variety of designs to be
signal by mirroring, inverting, or phase shifting to produce
the silencing signal, amplify the signal to the needed volume
for the cancellation, and send the signal to the loudspeaker
(2) or transducer placed in front of the operator’s mouth and
further aWay than the microphone
[0032] The microphone (1) may comprise any device or
combination of devices for turning acoustical signals into
electrical signals over the frequency range of human speech,
preferentially unidirectional. The loudspeaker (2) may com
prise any device or combination of devices for turning
electrical signals into acoustic signals over the frequency
range of human speech, preferentially focusing the produced
acoustic signals toWard a point to create a complement to the
dispersion pattern of the human mouth The loudspeaker
requires a means of reducing audible emissions from the
back of the speaker, such as a sealed back.
isolates it from vibrations. The microphone (11) is preferred
compatible With the electrical, space, and frequency require
ments.
[0041] The silencing loudspeaker (12) is behind the micro
phone (11) mounted to satisfy equation 1. The loudspeaker
(12) may be made of one or more electrical to acoustic
transducers. The loudspeaker’s (12) design preferably focus
the sound Waves toWard the operator’s mouth (10) to create
a complement to the dispersion pattern of the human mouth.
The loudspeaker (12) has a means of preventing audible
acoustic emissions from the backside of the loudspeaker,
eg a sealed back. The loudspeaker (12) may be a variety of
designs to produce a sound pressure level ?eld that cancels
the operator’s voice and meet the electrical, space and
frequency requirements.
[0042] Ablock diagram of the signal path for a preferred
embodiment is illustrated in FIG. 3. The acoustic signal
Aug. 14, 2003
US 2003/0152240 A1
from the operator’s voice converted to an electrical signal by
the microphone (11). The microphone sends the signal on to
operator’s mouth (10). The microphone and silencing loud
the pre-ampli?er (21) to strengthen the signal. The pre
ampli?er sends the signal on to the signal processor (22).
(34) Which is located in the handset (38) (or headset) or in
the connector housing at the communications device (37).
The handset’s communications loudspeaker (36) is mounted
The signal processor circuit sends the transmission signal to
the communication device’s circuitry then modi?es the
signal to create the silencing signal and then sends the
silencing signal to the ampli?er (23). The silencing signal
goes through the ampli?er (23) and to the loudspeaker (12)
Where it is transformed into the acoustic silencing signal.
[0043] In FIG. 4 the steps to be performed by the signal
processing circuitry are shoWn using a digital signal pro
cessor (DSP) (29) integrated to a digital communications
device. The steps are: analogue ?ltering to pass only the
frequency range of speech from 100 HZ to 8 kHZ (25);
convert the analogue signal to digital
(26); in the DSP
(29) the signal is copied to the communications device
softWare routine (24) and the silencing softWare routine
(27); softWare on the DSP performs the operations to modify
the signal into a silencing signal by inverting, mirroring, or
shifting phase of the signal (27); softWare on the DSP
equaliZes the signal for pre-calibrated microphone and loud
speaker distortions and to match the sound pressure level of
the operator’s voice in the incoming signal (28); convert the
signal from digital to analogue (D/A)(26); and output the
silencing signal to the ampli?er (23).
[0044] In FIG. 5 the steps to be performed by the signal
processing circuitry are shoWn using a digital signal pro
cessor (DSP) (29) integrated to a analogue communications
device. The steps are the same as that described above for
integration to a digital communications device shoWn in
FIG. 4. The connection to the communication device moves
to the analogue signal split to the communications device
circuitry (30) from the Band Pass Filter (25).
[0045]
In FIG. 6 the steps to be performed are shoWn
using analogue signal processing circuitry, Which is inte
grated to either a digital or analogue communications device
by the same connection (130). The steps are: receive the
microphone signal from the pre-ampli?er (21); analogue
?ltering to pass only the frequency range of speech from 100
HZ to 8 kHZ (125); the signal is split to the communications
device (130) and to the silencing circuitry (127); the silenc
ing circuitry (127) mirrors, inverts, or phase shifts the signal
to create the silencing signal; circuitry equaliZes the signal
for pre-calibrated microphone and loudspeaker distortions
and to match the sound pressure level of the operator’s voice
in the incoming signal (128); and output the silencing signal
to the ampli?er (23).
[0046] In a second embodiment, illustrated in FIG. 7, the
invention takes the form of a handset (38) (or headset)
plugging into the communications device (37) as a replace
ment or add-on such as is common for communications
speaker are each connected by Wires to the processing circuit
in the handset and connected to the communications device
(37) by Wires. The design must satisfy the requirements of
equation 1, above. The second embodiment may be poWered
from batteries, from the Wall electrical outlet, or from the
communications device.
[0047] In this second embodiment the handset (38) (or
headset or microphone) includes a microphone (31) that
converts the acoustic signal to an electrical signal for both
the communications device and the acoustic silencing. The
microphone (31) is shielded from the acoustic silencing
sound by an acoustic damping material barrier (33) Which
supports the microphone in the handset (38) (or headset) and
isolates it from vibrations. The microphone (31) is preferred
to be unidirectional and may be variety of designs to be
compatible With the electrical, space, and frequency require
ments.
[0048]
In the second embodiment the silencing loud
speaker (32) is behind the microphone (31) mounted in the
handset (38) (or headset) to satisfy equation 1. The loud
speaker’s (32) may be comprised of one or more electrical
to acoustic transducers. The loudspeaker’s (32) design pref
erably focuses the sound Waves toWard the operator’s mouth
(10) to create a complement to the dispersion pattern from
the human mouth. The loudspeaker has a means of prevent
ing audible acoustic emissions from the backside of the
loudspeaker, eg a sealed back. The loudspeaker (32) may
be a variety of designs to produce a sound pressure level
?eld that cancels the operator’s voice and meet the electrical,
space and frequency requirements.
[0049] A block diagram of the signal path for the second
embodiment is illustrated in FIG. 8. The acoustic signal
from the operator’s voice converted to an electrical signal by
the microphone (31). The microphone sends the signal on to
the pre-ampli?er (41) to strengthen the signal. The pre
ampli?er sends the signal on to the signal processor (42).
The signal processor circuit then modi?es the signal and
sends the transmission signal to the communication device
and the silencing signal to the ampli?er (43). The silencing
signal goes through the ampli?er (43) and to the loudspeaker
(32) Where it is transformed into the acoustic silencing
signal. The handset also receives the incoming signal from
the communications device and sends it directly to the
communications loudspeaker (36).
[0050] The signal processor for the second embodiment
may be either digital or analogue design and folloWs the
steps for the preferred embodiment as illustrated in FIGS. 4,
5 and 6 and described above.
accessories for eXample “hands free headsets”. The com
[0051]
munications device may be any type including: cellular
rate, self contained package that attaches to the microphone
telephone, cordless telephone, Wired telephone, intercom,
housing of a remote communications device illustrated in
FIG. 9. In this embodiment there is no electrical connection
betWeen the communications device and the invention. The
invention attaches to the communications device’s handset
announcing system or transmitting or 2-Way radio. This
embodiment uses one shared microphone (31), partially
shared signal processing circuitry (34), and either shared or
separate poWer supply depending on the communications
device’s design. This second embodiment’s housing places
both the microphone (31) and the silencing loudspeaker (32)
in the handset (38) (or headset) both positioned to aim at the
A third embodiment of the invention is as a sepa
(55) (or headset or microphone). The communications
device may be any type including: cellular telephone hand
set, cordless telephone, Wired telephone, intercom or trans
mitting radio.
Aug. 14, 2003
US 2003/0152240 A1
The third embodiment uses a separate microphone
including handsets, headsets, hand microphones, stand
(51), signal processing circuitry (54) and poWer supply (56)
microphones or microphones integrated into a console or
device.
[0052]
for the invention. The attachment (57) by has a means of
angular adjustment so that the invention’s microphone and
silencing loudspeaker may both be positioned by the opera
tor to aimed at, the operator’s mouth (10). The invention’s
microphone (51) and silencing loudspeaker (52) are each
[0058] An enhancement improves the invention by reduc
ing background noise, picked up by the microphone, in the
silencing signal. An embodiment of this enhancement in the
signal processing, described above, is illustrated in FIG. 11.
connected by Wires to the processing circuit (54) Which may
be located With the loudspeaker (52) or in a separate housing
at the body of the communications device connected by
background noise from the microphone signals (eg in
Wires to the handset attachment (not shoWn). The design
must satisfy the requirements of Equation 1 above for both
US. Pat. No. 5,680,393 to Bourmeyster). As shoWn in FIG.
the invention’s microphone and the communications micro
phone. The device may be poWered from batteries (56) or
from a Wall electrical outlet (not shoWn).
[0053] The third embodiment includes a microphone (51)
that converts the acoustic signal to an electrical signal for the
The embodiment applies prior art noise reduction to ?lter
analogue US. Pat. No. 4,723,294 to Taguchi, and in digital
11 the microphone signal has the background noise removed
by noise cancel (106); the signal is copied the communica
tions device processing (117) and the silencing processing
(118); the signal is modi?ed into a silencing signal by
inverting, mirroring, or shifting phase of the signal (118); the
signal is equaliZed for pre-calibrated microphone and loud
acoustic silencing. The microphone is preferred to be uni
speaker distortions and to match the sound pressure level of
directional and mounted With an acoustic damping material
the operator’s voice in the incoming signal (119). This
barrier (53) to isolate it from vibrations. The microphone
(51) may be variety of designs to be compatible With the
enhancement may be applies to all embodiments.
electrical, space, and frequency requirements.
[0054] The silencing loudspeaker (52) is behind the micro
phone (51) and the communications microphone (58) to
satisfy equation 1 With both microphones. The loudspeak
[0059]
er’s (52) design preferably focuses the sound Waves toWard
the operator’s mouth (10) to create a complement to the
dispersion pattern from the human mouth. The loudspeaker
has means of preventing audible acoustic emissions from the
backside of the loudspeaker, eg a sealed back. The loud
speaker (52) may be a variety of designs to produce a sound
pressure level ?eld that cancels the operator’s voice and
Another enhancement of the invention Will control
acoustic feedback by removing the silencing signal from the
incoming signal. Embodiments for this enhancement use
prior art for feedback suppression (eg in analogue US. Pat.
No. 4,164,715 to Thurmond, and in digital US. Pat. No.
5,091,952 to Williamson) in the invention’s signal process
ing circuitry, a block diagram of Which is shoWn in FIG. 12.
As shoWn in FIG. 12 the microphone signal has the feed
back removed by the feedback reduction (116); the signal is
copied the communications device processing (117) and the
Silencing processing (118); the signal is modi?ed into a
meet the electrical, space and frequency requirements.
silencing signal by inverting, mirroring, or shifting phase of
the signal (118); the signal is equaliZed for pre-calibrated
[0055] A block diagram of the signal path for the third
microphone and loudspeaker distortions and to match the
sound pressure level of the operator’s voice in the incoming
embodiment is illustrated in FIG. 10. The acoustic signal
from the operator’s voice converted to an electrical signal by
the microphone (51). The microphone sends the signal on to
the pre-ampli?er (61) to strengthen the signal. The pre
ampli?er sends the signal on to the signal processor (62).
The signal processor circuit then modi?es the signal and
sends the silencing signal to the ampli?er (63). The silencing
signal goes through the ampli?er (63) and to the loudspeaker
(52) Where it is transformed into the acoustic silencing
signal and travels as a sound Wave toWard the operator’s
mouth. The communications device’s signal operates inde
pendently of the invention.
[0056] The signal processor for the third embodiment may
be either digital or analogue design and folloWs the steps for
the preferred embodiment illustrated in FIGS. 4, 5 and 6 and
described above eXcept With the deletion of the connection
to the communications device (24) in FIG. 4, (30) in FIG.
5 and (130) in FIG. 6.
[0057] Many variations on these embodiments are fea
sible. Each of the described embodiments may be varied in
housing location, housing style, circuitry, number of ele
ments such as multiple loudspeakers or microphones, use of
digital, analogue or a miXture of circuitry, source of poWer
or inclusion of the enhancements. All the embodiments of
the invention can be used With any kind of communications
device such as all types of telephones, transmitting or 2-Way
radios, intercoms, and announcement devices. The invention
can Work With all types of microphone con?gurations
signal (119). The silencing signal is sent to both the ampli?er
and the feedback reduction (116) This enhancement may be
applies to all embodiments.
[0060] In another enhancement the signal processing cir
cuitry periodically calibrates the distance and signal trans
formation of the microphone and loudspeaker. The recali
bration reduces dependency on the physical condition and
spacing betWeen the microphone and loudspeaker and
improves silencing performance When the physical charac
teristics of the microphone and loudspeaker change. The
enhancement may be embodied in the signal processing
circuit as a self calibration using prior art for adaptive ?lters.
As illustrated in FIG. 13 the signal processing circuitry
includes a time and equaliZation calibration part (115) that
sends a knoWn signal (112), covering the frequency range of
speech, out through the ampli?er and loudspeaker, then
receives the signal in from the microphone (113), and
computes the delay and transform coef?cients from the tWo
signals. The coef?cients are then used in the signal proces
sor’s for equaliZation (119) and feedback reduction (116) if
included. This enhancement may be applies to all embodi
ments.
[0061] Another enhancement improves the acoustic
silencing of the device by adjusting the ?ltering and equal
iZation of the silencing signal in the processing circuit.
Illustrated in FIG. 14 this embodiment uses additional
microphone(s) (120) to measure the residual speech sound
Aug. 14, 2003
US 2003/0152240 A1
also termed in prior art the silencing error. The error signal
cancellation of said operator originated acoustic signals
from the microphone (120) is ampli?ed in a pre-amp (121)
beyond a front face of said microphone.
2. The device according to claim 1, having a communi
cation circuit and Wherein said signal processing circuit also
and then send to the processing circuitry. The error signal is
then used for adaptive control of the coef?cients for the
?ltering and equalization (122) of the silencing signal to
minimiZe silencing error using prior art such as US. Pat. No.
4,473,906 to Warmaka. The coef?cients are then applied in
the silencing signal (118) and equalization (119) processing.
The enhancement can be embodied in either analogue or
digital circuitry. This enhancement may be applies to all
embodiments.
[0062] Another enhancement is to provide further privacy
by adding a masking noise to the silencing signal. The
preferred masking noise is a Gaussian signal covering the
frequency range of speech, With a signal level equal to the
estimated level of the residual speech signal. As shoW in
FIG. 15, the masking noise is generated in the signal
processing circuitry (124) using prior art and added to the
silencing signal after the equaliZation (119).
copies the microphone signal to said communication circuit.
3. The device according to claim 1, Wherein said signal
processing circuit adjusts the volume of said acoustic silenc
ing signals to match the strength of an operator’s speech.
4. The device according to claim 1, Wherein said signal
processing circuit performs noise reduction on the signal
from the microphone to reduce background noise.
5. The device according to claim 1, having means to
reduce feedback of the silencing signals into the microphone
by means of ?ltering the acoustic silencing signals from the
microphone signal.
6. The apparatus according to claim 1, having means to
reduce feedback of the silencing signals into the microphone
comprised of an acoustic barrier made of acoustically damp
ing material positioned betWeen the microphone and the
loudspeaker or transducer to reduce the sound from the
[0063]
A further enchantment to the masking is to use the
signal processing circuit to analyZe the speech signal to
create a combined residual signal that is White noise (as
shoWn in FIG. 16). This is done by an analysis and masking
noise circuit or routine (125) periodically computing the
frequency spectrum of the speech signal using a fast Fourier
transform. Then computing the residual signal spectrum by
reducing the speech signal spectrum by a measured, preset
amount. Then the masking signal spectrum is found by
subtracting the residual signal spectrum from a Gaussian
spectrum of a preset level. The masking signal is then
computed from the masking signal spectrum using an
inverse fast Fourier transform. The resulting masking signal
is the frequency complement to the residual speech signal.
The masking signal is added to the silencing signal after
equaliZation (119) and sent to the ampli?er. The acoustic
sum of the masking signal and the residual speech signal is
a Gaussian signal. This enhancement may be applied to all
embodiments.
[0064] While certain preferred embodiments of this inven
tion have been described, it is understood that many varia
tions are possible Without departing from the principles of
this invention as de?ned in the claims Which folloW.
loudspeaker or transducer entering the microphone.
7. The device according to claim 1 in Which said loud
speaker or transducer is physically positioned to satisfy the
relationship:
Where
S=distance betWeen front faces of said microphone and
loudspeaker or transducer facing the operator,
T=time betWeen the microphone receiving a signal and
the loudspeaker or transducer broadcasting its signal,
and
V=velocity of sound in air.
8. The device according to claim 1, having means to
improve silencing by equaliZation or ?ltering of the silenc
ing signals to correct for signal distortion of the microphone
and loudspeaker by means of the signal processing circuit
applying a frequency dependent, amplitude correction to the
silencing signals.
9. The device according to claim 8 having means to
further improve silencing by calibrating the said equaliZa
tion or ?ltering of the silencing signals by means of said
What is claimed is:
1. An active acoustic silencing apparatus that Works as or
With the microphone of telephonic or transmitting commu
nications equipment to maintain the privacy of the trans
mitting operator’s speech and reduce noise in the area from
an operator’s speech comprising:
signal processing circuit periodically folloWing a preset
algorithm to send a knoWn signal through the ampli?er,
loudspeaker or transducer, microphone, and a preampli?er
and adjusting the equaliZation or ?ltering coef?cients based
on the distortion of the silencing signals.
10. The apparatus according to claim 8, having means to
a) a device having a microphone to receive operator
further improve silencing comprising a second microphone
originated acoustic signals composed of speech origi
measuring the silencing error and an algorithm in the signal
processing circuit to adjust the equaliZation or ?ltering
nating from an operator of said apparatus and produc
ing a microphone signal, a signal processing circuit for
coef?cients to minimiZe the error.
amplifying and processing the microphone signal, cre
ating electrical silencing signals, and amplifying said
11. The apparatus according to claim 1, Wherein the said
signal processing circuit includes means for masking White
electrical silencing signals, and a loudspeaker or trans
noise in the frequency range of human conversation to the
silencing signals sent to the loudspeaker or transducer.
12. The apparatus according to claim 11, Wherein the said
masking White noise is adapted to better mask the operator’s
ducer for receiving the ampli?ed electrical silencing
signals from said signal processing circuit;
b) said loudspeaker or transducer converting said electri
cal silencing signals to acoustic silencing signals; and
c) said loudspeaker or transducer being positioned With
respect to said microphone so as to result in substantial
speech and reduce noise by means of the signal processing
circuit continually analyZing the microphone signal and
calculating the frequency domain, spectral complement,
White noise for use as the masking White noise.
Aug. 14, 2003
US 2003/0152240 A1
13. The method of maintaining privacy of speech directed
into a microphone comprising the steps of:
a) positioning a microphone in front of a mouth of a
speaker to receive speech originating from said mouth
of said speaker, said microphone producing an electri
cal signal from said speech;
b) placing a loudspeaker in front of the mouth of said
19. A communications set incorporating acoustic silenc
ing for maintaining privacy of speech so that other persons
in the vicinity Will hear less of any conversation by a user of
said set comprising:
a) a microphone mounted in said set for producing an
electrical signal from speech directed by said user at
said microphone;
speaker behind said microphone facing said speaker at
b) processing circuitry in said set for amplifying and
a distance further aWay from said mouth than said
processing the electrical signal to create an electrical
microphone;
c) amplifying and processing said electrical signal to
create an electrical silencing signal; and
d) sending said electrical silencing signal to said loud
speaker for generating from said electrical silencing
signal an acoustic silencing signal to provide speech
privacy for said speaker, said distance being such as to
result in substantial cancellation of said operator origi
nated acoustic signal beyond a front face of said
microphone.
14. The method of claim 13 in Which said electrical signal
produced by said microphone is also used in a communica
tions device.
15. The method of claim 14 in Which said communica
tions device is a telecommunications handset or headset and
a second loudspeaker is mounted in said handset or headset
for reception by said speaker.
16. The method of claim 14 in Which said communication
device is a telecommunications handset or headset, said
silencing signal; and
c) a loudspeaker mounted in said set behind said micro
phone facing in the same direction as said microphone
and further aWay from said user than said microphone,
the distance betWeen a front face of said microphone
and a front face of said loudspeaker being sufficient to
result in substantial cancellation of said speech beyond
the front face of said microphone.
20. The communications set of claim 19 having means
isolating said microphone against vibrations and providing
an acoustic silencing barrier for said microphone in said set.
21. The communications set of claim 19 in Which said
microphone and loudspeaker are formed into a separate, self
contained package, said package being attached to said
communications set.
22. The communications set of claim 19 in Which said
distance betWeen the front face of said microphone and the
front face of said loudspeaker is de?ned by the folloWing
relationship:
microphone and loudspeaker being formed as a separate, self
contained package, said package being attached to said
handset or headset.
17. The method of claim 14 in Which said microphone is
shielded from the acoustic silencing signal by an acoustic
damping material barrier Which supports the microphone in
said communications device and isolates said microphone
from vibrations.
18. The method of claim 17 in Which said loudspeaker is
behind said microphone, and focuses said acoustic silencing
signal from said loudspeaker toWard the mouth of said
operator.
Where
S=distance betWeen the invention’s microphone face
and loudspeaker face,
T=time betWeen the microphone receiving a signal and
the loudspeaker broadcasting its signal, and
V=velocity of sound in air.
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