NANA
`
`US 20030228015
`
`as) United States
`a2) Patent Application Publication 0) Pub. No.: US 2003/0228019 Al
`(43) Pub. Date: Dec. 11, 2003
`
`Kichleret al.
`
`(54) METHOD AND SYSTEM FOR REDUCING
`NOISE
`
`(52) U.S. Ch wow. SB8I/7L8; 381/711; 381/57
`
`(75)
`
`Inventors: Uzi Eichler, Haifa (IL); Lior Barak,
`Haifa (IL); Avner Paz, Reut (IL)
`
`(57)
`
`ABSTRACT
`
`Correspondence Address:
`TESTA, HURWITZ & THIBEAULT, LLP
`HIGH STREET TOWER
`125 HIGH STREET
`
`BOSTON, MA 02110 (US)
`
`(73) Assignee: Elbit Systems Ltd., Haifa (IL)
`
`(21) Appl. No.:
`
`10/167,066
`
`(22)
`
`Filed:
`
`Jun. 11, 2002
`
`Publication Classification
`
`(51)
`
`Int. Ch? woo. AGLF 11/06; GIOK 11/16;
`HO3B 29/00
`
`Systemfor producing a substantially noise-free signal of an
`acoustic sound, and for producing a sound,
`the sound
`including a desired soundandan anti-phase noise sound, the
`anti-phase noise sound being in anti-phase relative to a
`noise, the system including an acoustoelectric transducer, a
`reference-acoustoelectric transducer and an audio controller
`
`coupled with the reference-acoustoelectric transducer and
`the acoustoelectric transducer, wherein the acoustoelectric
`transducer produces a noise bearing soundsignal by detect-
`ing the acoustic sound and the noise, wherein the reference-
`acoustoelectric transducer produces the reference noise sig-
`nal by detecting the noise in a noisy environment and
`wherein the audio controller produces the substantially
`noise-free signal, according tothe reference noise signal and
`the noise bearing soundsignal.
`
`ff
`
`NOISE
`
`ACOUSTIC
`SOUND AND
`NOISE
`
`‘126
`
`102
`
`AUDIO CONTROLLER
`
`{22
`118
`
`
`ADAPTIVE
`FILTER
`
` 104
` 116
`
`1
`
`APPLE 1136
`APPLE1136
`
`1
`
`

`

`e 100
`
`ACOUSTIC
`SOUND AND
`NOISE
`
`NOISE
`
`104
`
`102
`CONTROLLER 110
`
` AUDIO
`
`
`
`
`
`
`
`€1J91aysECNOTTT2Uuonvayqnguonesyddyjuajeg
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`IV6LO8zc0/E007SN
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`FIG. 1A
`
`2
`
`

`

`NOISE
`
`fr 100
`
`ACOUSTIC
`SOUND AND
`
`102
`
`
`
`
`
`€1J97PISCONTTLC=woHRIGngUONRayddyjude
`
`NOISE 104
`FILTER 116
`
`
`AUDIO CONTROLLER
` 122
`118
`‘126
`
`
`ADAPTIVE
`
`
`FIG. 1B
`
`IV6LO8zc0/E007SN
`
`3
`
`

`

`AMBIENT
`NOISE
`
`150
`
`VOICE WITH
`AMBIENT NOISE
`
`as
`
`
`
`
`102
`
`
`AUDIO
`
` CONTROLLER
`
`
`
`
`
`Cj
`
`FIG. 1C
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`elJOEHIYSENTTTPC
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`4
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`192
`
`186
`
`
`
`
`
`ELJOPPISCONTTTAwoHRoGngUoNRayddyjuseg
`
`IV6LO8zc0/E007SN
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`FIG. 2A
`
`194
`
`198
`
`
`
`a ANALOGANR
`
`
`
`
`
`
`
`5
`
`

`

`192
`
`PORTION 186
`
`DIGITAL
`
`FIG. 2B
`
`
`
`€1J9SPIYSENOTTTCwoHRaygnguonesyddyjudeq
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`
`
`
`
`IV6LO8zc0/E007SN
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`6
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`

`

`€1J99WAYSCOOTELC=UoNRoygnguoNRayddyuse
`
`214
`
`
` ANR
`
`
`
`
`CONTROLLER 222
`
`
`
`L 170
`
`AMBIENT
`NOISE
`
`AMBIENT
`NOISE
`
`238
`
`
`
`FIG. 2C
`
`IV6LO8zc0/E007SN
`
`7
`
`

`

` NOISE
`CONTROLLER
`
`
` AUDIO
`
`Ls|
`
`
`
`
`
`€1J9LP9YSCOOTTELC=uoONRoygnguoNRayddyuse
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`IV6LO8zc0/E007SN
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`AMBIENT
`
`NOISE
`
`266
`
`VOICE WITH
`NOISE
`
`268
`
`272
`
`258
`
`FIG. 3A
`
`8
`
`

`

`
`
`€1J98HIYSCOOTTLC=uoNRoyqnguoNRayddyjus
`
`NOISE CONTROLLER
`
`
`
`
`
`ik
`
`
` AMBIENT
`
`308
`
`NOISE
`
`FIG. 3B
`
`IV6LO8zc0/E007SN
`
`9
`
`

`

`
`
`
`
`uoneayqngwoueojddy1u9}eg
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`e007“TT9d
`€1496PINS
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`FIG. 4A
`
`AMBIENT NOISE
`
`332 354
`
`en so ee Sa a en et ——)
`348
`350
`FEEDBACK,
`
`10
`
`10
`
`

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`€EJ9OLPANSE007TTPd
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`354
`
`FIG. 4B
`
`AMBIENT
`NOISE
`
`
`
`ELEMENT
`
`332 FEEDFORWARD
`
`
`
`330
`
`FROM
`FEEDBACK
`ELEMENT
`
`TO
`FEEDBACK
`ELEMENT
`
`11
`
`11
`
`

`

`
`
`€1J91PaysCONTTTC=voNnRsyqnguonRayddyjudeg
`
`
`ELEMENT FEEDBACK
` 354
`
`FROM
`FEEDFORWARD
`
`
`
`
`
`ELEMENT
`
`IV6LO8zc0/E007SN
`
`TO
`FEEDFORWARD
`ELEMENT
`
`FIG. 4C
`
`12
`
`12
`
`

`

`Patent Application Publication Dec. 11,2003 Sheet 12 of 13
`
`US 2003/0228019 Al
`
`400
`
`402
`
`
`
`PRODUCING A REFERENCE
`PRODUCING A NOISE BEARING
`
`
`
`SOUND SIGNAL BY DETECTING
`NOISE SIGNAL BY DETECTING
`
`
`NOISE
`ACOUSTIC SOUND AND NOISE
`
`
`
`
` 406
`
`DETERMINING A CORRECTION SIGNAL ACCORDING TO THE
`REFERENCE NOISE SIGNAL
`
`404
`
`PRODUCING A NOISE-FREE SOUND SIGNAL, ACCORDING TO THE
`CORRECTION SIGNAL AND THE NOISE BEARING SOUND SIGNAL
`
`408
`
`410
`
`
`
`
`
`412
`
`FIG. 5A
`
`
`
`
`
`PRODUCING A REFERENCE NOISE SIGNAL BY DETECTING NOISE
`
`DETERMINING A NOISE-CANCELING SIGNAL, ACCORDING TO THE
`REFERENCE NOISE SIGNAL
`
`PRODUCING A NOISE-CANCELING SOUND ACCORDING TO THE
`DETERMINED NOISE-CANCELING SIGNAL
`
`FIG. 5B
`
`13
`
`13
`
`

`

`uoneayqngwoueojddy1u9}eg
`
`
`
`€LJOELPaYSCONTTLOd
`IV6LO8zc0/E007SN
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`420
`
`422
`
`PRODUCING A
`NOISY VOICE
`SIGNAL BY
`DETECTING VOICE
`
`PRODUCING A
`REFERENCE
`NOISE SIGNAL BY
`DETECTING
`NOISE
`
`424
`
`AND NOISE
`SIGNAL
`
`DETERMINING A CORRECTION SIGNAL
`ACCORDING TO THE REFERENCE NOISE
`
`426
`
`
`
`PRODUCING A NOISE-FREE VOICE SIGNAL
`
`
`ACCORDING TO THE CORRECTION SIGNAL
`AND THE NOISY VOICE SIGNAL
`
`428
`RECEIVING AN
`AUDIO SIGNAL
`
`77430
`PRODUCING AN ERROR
`SIGNAL BY DETECTING
`SOUNDIN THE VICINITY
`
`OF THE EAR OF A USER
`AND THE ERROR SIGNAL
`
`
`
`
`
`
`
`432
`
`DETERMINING AN AUDIO-AND-
`NOISE-CANCELING SIGNAL, ACCORDING TO TH
`REFERENCE NOISE SIGNAL, THE AUDIO SIGNAL,
`
`434
`
`PRODUGING AN AUDIO-AND-NOISE-CANCELING
`SOUND ACCORDING TO THE DETERMINED
`AUDIO-AND-NOISE-CANCELING SIGNAL
`
`FIG. 6
`
`14
`
`14
`
`

`

`US 2003/0228019 Al
`
`Dec. 11, 2003
`
`METHOD AND SYSTEM FOR REDUCING NOISE
`
`FIELD OF THE DISCLOSED TECHNIQUE
`
`[0001] The disclosed technique relates to audio systems in
`general, and to methods and systems for reducing back-
`ground noise, in particular.
`
`BACKGROUND OF THE DISCLOSED
`TECHNIQUE
`
`[0002] Ambient noise from various sources creates a noisy
`environment that often amountsto a disturbance to a person
`or an acoustic receiver. The noise may considerably interfere
`with sounds that are required to be captured by an acoustic
`sensor, or distract a person whois required to concentrate on
`specific tasks. Tasks that require listening to sounds by a
`human ear or their capturing via a microphone, are particu-
`larly vulnerable to disruption by noise. In this context, the
`noise is an objectionable acoustic pressure impinging upon
`the eardrumsofa person or upon the receiving means of an
`acoustic sensor.
`
`[0003] Devices and methods in the prior art were designed
`to provide active attenuation of noise. U.S. Pat. No. 4,985,
`925 issued to Langberg et al., provides an active noise
`reduction based on a negative feedback electro-acoustical
`system. The electro-acoustical system consists of an elec-
`tronic earplug seated in the concha fossa. The system
`combines active and passive noise reduction in the quiet
`zone of the ear, a bilateral
`transducer circuit,
`a shunt
`feedback controlfilter network, and a combinedinput noise-
`filter/feedback system. Thebilateral transducer circuit drives
`a speaker as an acoustical velocity source. The shunt feed-
`back control filter network improves stability and increases
`noise reduction.
`
`[0004] U.S. Pat. No. 5,600,729issued to Darlington et al.,
`teaches the application of Active Noise Reduction (ANR) in
`an ear defender. The ear defender includes detector means
`
`in the
`(c.g., a microphone) for detecting the sound level
`proximity ofthe ear of the person. The ear defender further
`includes output means (¢.g., a speaker) for generation of
`noise reduction signal within the ear shell. The ear defender
`also includes a digital feedback controller for generating a
`feedback signal derived from the output of the detector
`means andapplying it to the output means. The ear defender
`also features estimation means for providing estimation of
`the ear shell transfer function andsubtracting from the input
`to the feedback controller, a signal representing the esti-
`mated electroacoustic transfer function of the system. A
`second, analog or digital feedback controller provides an
`active noise control on the basis of an average configuration
`for the system.
`
`[0005] U.S. Pat. No. 6,078,672 issued to Saunders et al.,
`provides a personal noise attenuation system for attenuating
`both tonal and broadband sound in a noisy environment
`immediately adjacent
`to a user. The system includes a
`spatially adjustable acousto-electric sensor adapted to sense
`ambient noise,
`including certain preselected sounds, The
`system also has attenuation means including both feedback
`and feed forward components so as to provide a heterono-
`mous attenuation and more complete active noise altenua-
`tion. The adjustable acoustoelectric sensor
`is spatially
`moved soas to adapt to the changing physical characteristics
`of spatial zones in different noise fields adjacent to the user,
`
`[0006] U.S. Pat. No. 6,278,786 issued to McIntosh, pro-
`vides an active noise cancellation aircraft headset system. A
`speaker is mounted within each earcup of a headset
`for
`receiving and acoustically transducing a composite noise
`cancellation signal. A microphone is also mounted within
`each earcup for transducing acoustic pressure within the
`earcup to a corresponding analog error signal. An analog
`filter receives the analog error signal and inverts it
`to
`generate an analog broadband noise cancellation signal. The
`analog error signal is also provided to an analog todigital
`converter, which receives the analog microphoneerror sig-
`nal and converts it
`to a digital error signal.
`
`[0007] A digital signal processor (DSP) takes the digital
`error signal and using an adaptive digital feedback filter,
`generates a digital tonal noise cancellation signal. A digital
`to analog converter then converts the digital
`tonal noise
`cancellation signal
`to an analog tonal noise cancellation
`signal so that it can be summed with the analog broadband
`noise cancellation signal to form a composite cancellation
`signal. The composite cancellation signal is providedto the
`speakers in the earcups to cancel noise within the earcups.
`The broadband analog cancellation is effective to reduce
`overall noise within the earcup. The DSP provides active
`control of the analog cancellation loop gain to maximize the
`effectiveness ofthe broadbandanalog cancellation. The DSP
`also uses the adaptive feedback filter/algorithm to substan-
`tially reduce at least the loudest tonal noises penetrating the
`earcup. The tonal noses include engine and propeller noises,
`as well as harmonic vibrations of components ofthe fuse-
`lage ofthe aircraft.
`
`SUMMARY OFTHE DISCLOSED TECHNIQUE
`
`It is an object of the disclosed technique to provide
`[0008]
`a novel methodand system for producing a noise-free sound
`signal of the voice of a person talking in a noisy environ-
`ment, which overcomes the disadvantages ofthe prior art.
`
`In accordance with the disclosed technique,there is
`[0009]
`thus provided a system for producing a substantially noise-
`free signal of an acoustic sound(e.g., the voice of a pilot
`transmitting to an air traffic controller). The system further-
`more produces a sound which includes a desired sound(e.g.,
`the voice ofan air traffic controller transmitted to the pilot)
`and an anti-phase noise sound, the anti-phase noise sound
`being in anti-phase relative to a noise. The system includes
`an acoustoelectric transducer, a reference-acoustoelectric
`transducer and an audio controller coupled with the refer-
`ence-acoustoclectric transducer
`and the acoustoelectric
`transducer.
`
`[0010] The acoustoelectric transducer produces a noise
`bearing sound signal by detecting the acoustic sound andthe
`noise, and the reference-acoustoelectric transducer produces
`the reference noise signal by detecting the noise in a noisy
`environment. The audio controller produces the substan-
`tially noise-free signal, according to the reference noise
`signal and the noise bearing sound signal.
`
`includes an electroacoustic
`[0011] The system further
`transducer for producing the sound and an active noise
`reduction controller coupled with the electroacoustic trans-
`ducer and the reference-acoustoelectric transducer. The
`
`active noise reduction controller produces a soundsignal
`according to the reference noise signal and according to a
`
`15
`
`15
`
`

`

`US 2003/0228019 Al
`
`Dec. 11, 2003
`
`desired sound signal respective of the desired sound. The
`electroacoustic transducer produces the sound according to
`the soundsignal.
`
`In accordance with another aspect ofthe disclosed
`[0012]
`technique, there is thus provided a system for producing a
`sound. The sound includes a desired sound(e.g., the voice
`of an air traffic controller transmitted to a pilot) and an
`anti-phase noise sound, the anti-phase noise soundbeing in
`anti-phase relative to a noise. The system includes an
`electroacoustic transducer, a reference-acoustoelectric trans-
`ducer and an active noise reduction controller coupled with
`electroacoustic transducer and the reference-acoustoelectric
`transducer.
`
`[0013] The electroacoustic transducer produces the sound
`and the reference-acoustoelectric transducer produces a ref-
`erence noise signal by detecting the noise in a noisy envi-
`ronment. The active noise reduction controller produces a
`sound signal according to the reference noise signal and
`according to a desired soundsignal respective of the desired
`sound, and the electroacoustic transducer produces the
`sound according to the soundsignal.
`
`In accordance with a further aspect ofthe disclosed
`[0014]
`technique, there is thus provided a system for producing an
`anti-phase noise sound. The system includes an electroa-
`coustic transducer, a reference-acoustoelectric transducer
`for producing a reference noise signal by detecting noise in
`a noisy environment anda digital active noise reduction
`controller coupled with the electroacoustic transducer and
`the reference-acoustoelectric transducer.
`
`[0015] The digital active noise reduction controller pro-
`duces an anti-phase noise signal according to the reference
`noise signal, wherein the anti-phase noise signal
`is
`in
`anti-phase relative to the reference noise signal. The elec-
`troacoustic transducer produces the anti-phase noise sound
`according to the anti-phase noise signal.
`
`In accordance with another aspect ofthe disclosed
`[0016]
`technique, there is thus provided a system for producing
`sound, the sound including a desired sound(e.g., the voice
`of an air traffic controller transmitted to a pilot) and an
`anti-phase noise sound, the anti-phase noise soundbeing in
`anti-phase relative to a noise. The system includes an
`electroacoustic transducer, a reference-acoustoelectric trans-
`ducer, an error-acoustoelectric transducer, a feedforward
`element and a
`feedback element. The system further
`includes a first summing element, a second summing ele-
`ment,
`a
`third summing element, a
`first estimated plant
`response element and a second estimated plant response
`element.
`
`‘The reference-acoustoelectric transducer produces
`[0017]
`a reference noise signal by detecting the noise in a noisy
`environment. The feedforward element is coupled with the
`reference-acoustoelectric transducer. The feedback element
`is coupled with the feedforward element. The first summing
`element is coupled with the feedforward element, the feed-
`back clement and with the electroacoustic transducer. The
`second summing element
`is coupled with the feedback
`element, the feedforward clement and with the error-acous-
`toelectric transducer. The third summing element is coupled
`with the feedback element and with the second summing
`element. The first estimated plant
`response element
`is
`coupled with the second summing element and the second
`
`estimated plant response element is coupled with the third
`summing element and with the electroacoustic transducer.
`
`[0018] The first summing element produces a summation
`signal, by adding a
`feedback signal
`received from the
`feedback element, a feedforward signal received from the
`feedforward element, and a soundsignal respective of the
`desired sound. The electroacoustic transducer produces the
`sound according to the summation signal. The first estimated
`plant response element produces a first estimated desired
`soundsignal, respective ofthe desired soundas produced by
`the electroacoustic transducer.
`
`[0019] The error-acoustoelectric transducer produces an
`error signal by detecting the sound. The second summing
`element producesa first difference signal, by subtracting the
`first estimated desired sound signal from the error signal.
`The second estimated plant response element produces an
`estimated difference signal, according to the summation
`signal. The third summing element produces a seconddif-
`ference signal, by subtracting the estimated difference signal
`from the first difference signal. The feedback element pro-
`duces the feedback signal according to the first difference
`signal and the seconddifference signal and the feedforward
`element produces the feedforward signal, according to the
`reference noise signal andthe first difference signal.
`
`In accordance with a further aspect of the disclosed
`[0020]
`technique, there is thus provided a method for producing a
`noise-free soundsignal. The methodincludes the procedures
`of producing a noise bearing sound signal by detecting
`acoustic soundandnoise, producing a reference noise signal
`by detecting noise, determining a correction signal accord-
`ing to the reference noise signal and producing the noise-
`free sound signal, according to the noise bearing sound
`signal and the correction signal.
`
`In accordance with another aspect ofthe disclosed
`[0021]
`technique, there is thus provided a method for producing a
`noise-canceling sound. The methodincludes the procedures
`of producing a reference noise signal by detecting noise,
`determining a noise-canceling signal according to the ref-
`erence noise signal and producing the noise-canceling sound
`according to the determined noise-canceling signal.
`
`In accordance with a further aspect ofthe disclosed
`[0022]
`technique, there is thus provided a methodfor producing an
`audio-and-noise-canceling sound. The method includes the
`procedures of producing a reference noise signal by detect-
`ing noise, receiving an audio signal, determining an audio-
`and-noise-canceling signal according to the reference noise
`signal and the audio signal, and producing the audio-and-
`noise-canceling sound according to the determined audio-
`and-noise-canceling signal.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0023] The disclosed technique will be understood and
`appreciated more fully from the following detailed descrip-
`tion taken in conjunction with the drawings in which:
`
`[0024] FIG. 1A is a schematicillustration of a system for
`producing a noise-free sound signal, constructed and opera-
`live in accordance with an embodiment of the disclosed
`technique;
`
`[0025] FIG. LB is a schematic illustration ofa detail ofthe
`audio controller of the system of FIG. 1A;
`
`16
`
`16
`
`

`

`US 2003/0228019 Al
`
`Dec. 11, 2003
`
`[0026] FIG. 1C is a schematic illustration ofthe systemof
`FIG. 1A incorporated with a head-mounted device;
`
`[0027] FIG. 2A is a schematic illustration of a noise-
`canceling system, constructed and operative in accordance
`with another embodiment ofthe disclosed technique;
`
`[0028] FIG. 2B is a schematicillustration ofa detail ofthe
`analog ANR controller of the ANR controller of the system
`of FIG. 2A;
`
`[0029] FIG. 2C is a schematic illustration ofthe system of
`FIG. 2A, incorporated with a head-mounted device;
`[0030] FIG. 3A is a schematic illustration of a noise
`reduction system, constructed and operative in accordance
`with a further embodiment ofthe disclosed technique;
`
`[0031] FIG. 3B is a schematicillustration ofthe system of
`FIG. 3A, incorporated with a head-mounted device;
`
`[0032] FIG. 4A is a schematic illustration of a digital
`noise reduction system, constructed and operative in accor-
`dance with another embodiment ofthe disclosed technique;
`[0033] FIG. 4Bis a schematic illustration of the feedfor-
`ward portion of the system of FIG. 4A;
`
`[0034] FIG. 4C is a schematic illustration ofthe feedback
`portion of the system of FIG. 4A;
`
`[0035] FIG. 5A is a schematicillustration of a method for
`operating the system of FIG, 1A, operative in accordance
`with a further embodiment of the disclosed technique;
`
`
`
`[0036] FIG. 5B is a schematicillustration of a method for
`operating a noise-canceling system, operative in accordance
`with another embodiment of the disclosed technique; and
`[0037] FIG. 6 is a schematic illustration of a methodfor
`operating the system of FIG, 3A, operative in accordance
`with a further embodiment ofthe disclosed technique.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS
`
`[0038] The disclosed technique processes a background
`noise signal
`together with a signal containing the back-
`ground noise and a desired sound, and produces a signal of
`the desired sound, substantially free of the background
`noise. The disclosed technique producesa noise-[ree signal
`from the voice of a person speaking in a noisy environment.
`The disclosed technique allows a person located in a noisy
`environment, to hear the desired sound, substantially free
`from noise.
`
`transducer” herein
`term “acoustoelectric
`[0039] The
`below, refers to a device which converts acoustical signals
`to electrical signals (e.g., a microphone). The term “elec-
`troacoustic transducer” herein below, refers to a device
`which converts electrical signals to acoustical signals (e¢.g.,
`a loudspeaker). An acoustoelectric transducer can operate
`based on principles of electrodynamics, electrostatics,
`piezoelectricity, magnetostriction, fiber-optics, stimulation
`of carbon particles, and the like. An electroacoustic trans-
`ducer can operate based on principles of electrodynamics,
`magnetism, piezoelectricity, magnetostriction, hydraulic,
`andthe like. The term “electric” herein includesall electro-
`magnetic signals, such as electric, optic, radio, and the like,
`that can be transmitted by wire or other communication
`channels, or wirelessly.
`
`17
`
`[0040] The term “quiet zone” herein below, refers to a
`region in the vicinity of the ear-drum, the car, or within the
`outer canal thereof, at which a soundat approximately 180
`degrees out-of-phase relative to the ambient noise (anti-
`phase, or out-of-phase by a radians), cancels the ambient
`noise and as a result, the person does not hear the ambient
`noise. The locations “close to the ear” herein below, are
`approximate and refer to the quiet zone. The term “tonal
`noise” herein below, refers to a noise which is confined to
`substantially limited frequency range or ranges, suchas the
`noise generated by the rotors of a helicopter.
`
`[0041] Reference is now made to FIGS, 1A, 1B and 1C,
`FIG,1A is a schematic illustration of a systemfor producing
`a noise-free sound signal, generally referenced 100, con-
`structed and operative in accordance with an embodiment of
`the disclosed technique. FIG. 1B is a schematic illustration
`of a detail of the audio controller of the system of FIG, LA.
`FIG. 1C is a schematic illustration ofthe system of FIG. 1A
`incorporated with a head-mounted device, generally refer-
`enced 150.
`
`[0042] With reference to FIG, LA, system 100 includes
`acoustoelectric transducers 102 and 104 and an audio con-
`troller 106. Audio controller 106 is coupled with acousto-
`electric transducers 102 and 104.
`
`[0043] Audio controller 106 is a digital processor, which
`simultaneously samples two input signals at the same sam-
`pling rate and determines a transfer function for these two
`input signals, according to an adaptive filtering method.
`Audiocontroller 106 applies the transfer function on one of
`the input signals and subtracts the result from the other input
`signal. Audio controller 106, then produces an output signal
`respective ofthe result of the subtraction.
`
`[0044] Acoustoelectric transducer 102 detects acoustic
`sound. This acoustic sound can be a human voice, machine
`generated voice, and the like. If the acoustic soundis the
`voice of a person (not shown), then acoustoelectric trans-
`ducer 102 is located close to the mouth (not shown) ofthe
`person. Acoustoelectric transducer L102 detects the desired
`sound(i.¢., the voice) as well as the noise (i.c., an undesired
`sound) which is present in the environment surrounding the
`person. The noise is generated for example, by other persons
`anddevices, such as engines, turbines, motors, and mechani-
`cal devices, hydraulic or pneumatic devices (e.g., tubing,
`actuators), electromechanical devices (e.g., electric motor),
`loud-speakers which surround the speaker, firing of ammu-
`nition, by environmental sources, such as wind, rain, ocean
`waves, thunderstorm, by animals, andthelike.
`
`[0045] Acoustoelectric transducer 104 and acoustoelectric
`transducer 102 detect different sounds, due to either a sound
`absorbing material (not shown), located between acousto-
`electric transducers 102 and 104, or
`the mere distance
`between acoustoelectric transducers 102 and 104. Thus,
`acoustoelectric transducer 104 detects the noise and sub-
`stantially none of the desired sound, while acoustoelectric
`transducer 102 detects the desired sound and noise.
`
`[0046] Audio controller 106 receives signals 108 and 110
`from acoustoelectric transducers 102 and 104, respectively.
`Each ofsignals 108 and 110 is in analog format. An analog
`to digital converter (not shown) and herein belowreferred to
`as ADC, which converts an analog signaltoa digital signal,
`is coupled with acoustoelectric transducer 102 and audio
`
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`controller 106. Another ADC(not shown) is coupled with
`acoustoelectric transducer 104 and audio controller 106.
`Thus, audio controller 106 receives signals 108 and 110
`which are in digital format,
`
`[0047] Signal 108 includes information respective of a
`desired sound and noise. Signal 110 includes information
`respective of noise. Audio controller 106 determines a new
`reduced-intensity sound pressure level (SPL) for signal 110,
`by employing an SPL converter (not shown). The SPL
`converter can be in form of a hardwired look-up table, a
`software look-up table,
`a hardwired transfer function, a
`software transfer function, an adaptive filter, and the like.
`Audio controller 106 subtracts the new determined SPL
`from the SPLofsignal 108, which corresponds to signal 110.
`The noise detected by acoustoclectric transducer 102 is
`different from the noise detected by acoustoelectric trans-
`ducer 104, namely—it is usually at a reducedintensity and
`with a retarded phase (due to an acoustic insulation or
`acoustic insulating distance between acoustoelectric trans-
`ducers 102 and 104). Thus, the new determined SPL corre-
`sponds to a reduced and retarded function of the SPL of
`signal 110. Audio controller 106 produces a signal 112
`respective of the result of the above subtraction operation.
`Thus, signal 112 includes information respective of the
`desired sound, substantially excluding the noise.
`
`[0048] The form andthe parameters of the SPL converter
`are determined in accordance with certain physical param-
`eters, such as the hearing characteristics of a person,
`the
`voice characteristics of a person, the sound absorbing char-
`acteristics of a headset worn by a person, the dimensions of
`the headset, the relative distances between acoustoelectric
`transducer 102 and acoustoelectric transducer 104,
`the
`acoustic properties of the environment which surround
`acoustoelectric transducer 102 and acoustoelectric trans-
`ducer 104, the acoustic properties of the sound absorbing
`material located between acoustoelectric transducer 102 and
`acoustoelectric transducer 104, andthe like.
`
`[0049] With reference to FIG. 1B, system 100 includes
`acoustoelectric transducers 102 and 104, audio controller
`106 and analog to digital converters 114 and 116. Audio
`controller 106 includes an adaptive filter 118 and a summing
`element 120. ADC 114 is coupled with acoustoelectric
`transducer 102 and summing element 120. ADC 116 is
`coupled with acoustoelectric transducer 104 and adaptive
`filter 118. Alternatively, ADC 114 is integrated with either
`acoustoelectric transducer 102 or audio controller 106. Simi-
`larly, ADC 116 can be integrated with acoustoelectric trans-
`ducer 104 or audio controller 106.
`
`[0050] Acoustoelectric transducer 102 produces an analog
`signal 122 and sends analog signal 122 to ADC 114. ADC
`114 converts analog signal 122 toa digital signal 124, sends
`digital signal 124 to summing element 120 and adaptive
`filter 118 produces a signal 130 according to signal 128.
`Signal 130 is respective of the ambient noise detected by
`acoustoelectric transducer 104 at a reduced SPL (i.e., the
`SPL ofthe ambient noise close to acoustoelectric transducer
`102). Summing element 120 produces signal L112 by sub-
`tracting signal 130 from signal 124. Signal 112 is further
`provided to an interface (not shown) for further processing
`or transmission. Acoustoelectric transducer 104 produces an
`analog signal 126 and sends analog signal 126 to ADC 116.
`ADC116 converts analog signal 126 to a digital signal 128
`
`andsends digital signal 128 to adaptive filter 118, Signal 112
`from summing clement 120is fed back to adaptivefilter 18,
`in a feedback loop 132. If signal 112 includes any residual
`noise, then adaptive filter 118 detects this residual noise and
`adjusts signal 130 accordingly. Summing element 120 then
`subtracts this residual noise from signal 124.
`[0051] With reference to FIG. 1C, acoustoelectric trans-
`ducer 102 is incorporated with head-mounted device 150.
`Audio controller 106 is coupled with acoustoelectric trans-
`ducers 102 and 104. Head-mounted device 150is in form of
`a helmet, a headset, andthe like. Acoustoelectric transducer
`102 is located at
`the mouth (not shown) of the user (not
`shown). Acoustoelectric transducer 104 is located external
`to head-mounted device 150 or externally mountedthereon,
`but acoustically insulated or remote from the mouth of the
`user.
`
`[0052] Head-mounted device 150 can include a visual
`device (not shown), such as a head-up display, visor, liquid
`crystal display (LCD), field emission display (FED), mirror,
`and the like. Additionally, head-mounted device 150 can
`include one or more electroacoustic transducers.
`
`If head-mounteddevice 150is in form ofa helmet,
`[0053]
`it can include sound absorbing material, such as mineral
`wool, fiberglass, and the like. In this case, acoustoelectric
`transducer 102 detects the voice of the user, while also
`detecting the background noise—but at a reduced SPL.
`[0054]
`In case head-mounted device 150 is in form ofa
`headset, due to the physical distance of acoustoelectric
`transducer 104 from the mouth of the user, acoustoelectric
`transducer 104 detects the ambient noise and substantially
`none of the voice of the user. However, acoustoclectric
`transducer 102 detects the voice of the user and the ambient
`noise.
`It
`is noted that even ambient air can effectively
`acoustically insulate, such as
`insulating acoustoelectric
`transducer 104 from the mouth ofthe user.
`
`In case head-mounted device 150is a helmet worn
`[0055]
`by a pilot (not shown), the ambient noise can be the noise
`generated by the engine (i.c., power-plant) ofthe aircraft, by
`the engines ofother aircraft flying closeby, the voices ofthe
`aircraft crew, the soundofthunder, the sound of ice particles
`striking the windshield, the soundoffiring ammunition, and
`the like. Acoustoelectric transducer 102 is attached to the
`inner portion of head-mounted device 150, close to the
`mouth of the pilot and acoustoelectric transducer 104 is
`attached to the outer portion of head-mounted device 150.
`[0056] Head-mounted device 150 includes sound absorb-
`ing material, and acoustoelectric transducer 104 is farther
`away from the mouth of the pilot
`than acoustoelectric
`transducer 102. Hence, acoustoelectric transducer 104
`detects mostly the ambient noise and substantially none of
`the voice of the pilot. However, since the sound absorbing
`material of head-mounted device 150 absorbs only a portion
`of the sound, acoustoelectric transducer 102 detects the
`voice of the pilot,
`in addition to the ambient noise at a
`reduced SPL. Thus, signal 108 includes information respec-
`tive of the voice ofthe pilot and an attenuated level of the
`ambient noise, while signal 110 includes information respec-
`tive of the ambient noise at an SPL higher than that detected
`by acoustoelectric transducer 102, The attenuation level of
`the ambient noise may depend on frequency.
`[0057] The parameters of the SPL converter can be deter-
`mined empirically, by measuring the SPL values ofsignals
`
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`
`108 and 110 in a selected frequency range, in response to
`sound corresponding to the SPL values andin the frequency
`range of the expected ambient noise. It is noted that these
`measurements are performed without the voice of the pilot
`in the same location within the aircraft, in which system LOO
`is employed. These measurements can be performed before
`flight as “pre-calibrations” or during speech pauses at flight
`time. In addition, audio controler 106 calibrates system 100,
`at the beginning ofevery flight. Alternatively, the parameters
`of the SPL converter can be determined analytically, by
`computing the estimated attenuation of SPL values of the
`ambient noise in a selected frequency range.
`
`It is further notedthat the attenuated SPLvalue of
`[0058]
`the ambient noise detected by acoustoelectric transducer
`102, depends also on the physical distan