`US005815582A5582
`5,815,582
`[11] Patent Number:
`United States Patent
`Claybaughetal.
`[45] Date of Patent:
`Sep. 29, 1998
`
`
`515
`
`
`
`[54] ACTIVE PLUS SELECTIVE HEADSET
`[75]
`Inventors: David Claybaugh, Germantown;
`Jeffrey N. Denenberg, Trumbull;
`Ralph Busch, Takoma Park; John
`Hohman, Towson, all of Md.
`
`
`
`
`
`73| Assignee: Noise Cancellation Technologies, Inc.,
`Linthicum, Md.
`
`21]
`591
`
`63]
`
`Appl. No.: 899,090
`Filed:
`Jul. 23, 1997
`
`_o,
`Related U.S. Application Data
`
`Continuation of Ser. No. 347,417, Dec. 2, 1994,
`
`Int. Che eeeceeeeee AGLF 11/06; HO3B 29/00
`ST]
`52] US. Ch. cisssiutenismsinnennes GOLL66; 381/72
`58]
`Field of Search ..........csseeee 381/72, 74, 103,
`381/94.9, 155, 71.1, 71.6, 71.11, 71.12;
`181/206; 379/406, 407, 410, 412, 387,
`388, 390, 395
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`4/1976 Kyle etal. .
`3,952,158
`12/1977 Freifield et al. .
`4,061,875
`12/1977 Williams .
`4,064,362
`3/1987 Chaplin 2... cceesceeeteneee SB1/72
`4,054,871
`6/1987 McCutchen.
`4,677,678
`.
`8/1990 Twineyet al.
`4,953,217
`9/1991 Warnakaetal. .
`5,046,103
`2/1992 Tretler .
`5,091,953
`.
`4/1992. Ziegler, Jn.
`5.105.377
`1/1993 Bourk seeccscssssseecscsssseeesessssneeeees 381/74
`5,182,774
`Primary Examiner—Minsun Oh Harvey
`
`[57]
`
`ABSTRACT
`
`es
`-
`y
`:
`An active plus selective headset system for provision of
`active attenuation of broadband noise as well as speech
`filtering comprising a headset with reference microphones,
`residual microphonesandspeakers on each ofapair of open
`backed muffs and a controller means.
`
`s
`
`20 Claims, 4 Drawing Sheets
`
`REFERENCE
`MICROPHONE
`
`
`
`OPEN
`BACK
`HEADSET
`
`53
`
`53
`
`SPEECH
`+
`NOISE
`
`REFERENCE
`INPUT
`
`
`
`RESIDUAL
`
`
`
`
`ANTI-NOISE
`NOISE
`OUTPUT
`
`~~ 50
`
`seb oo we Ba
`
`60
`
`APPLE 1140
`APPLE 1140
`
`FEEDBACK
`COMPENSATION
`CANCELLATION
`FILTER “A"
`
` 1
`
`||
`
`I
`
`v
`
`;
`l
`
`|!tt||1
`
`1
`
`

`

`U.S. Patent
`
`Sep. 29, 1998
`
`Sheet 1 of 4
`
`5,815,582
`
`SPEAKER
`
`
`
`SPEECH
`WARNING
`a=
`
`
`
`
`RESIDUAL
`ANTI-NOISE
`NOISE
`
`
`OUTPUT
`INPUT
`
`
`REFERENCE
`INPUT
`
`eepelincaras wercpecrecrmmmies a2 cams imenomasmnvescsatpaeasines| scene
`
`N/C
`
`25
`
`
`
`
`I | | | | | |
`
`| |
`
`|
`I
`
`) | L
`
`
`
`FILTER
`
`
`
`
`ADAPTER
`
`24
`
`27
`
`
`
`
`e. eee eR SS RES Se
`
`SB SS Se eS Se SS Sere
`
`FIG.I
`
`2
`
`

`

`U.S. Patent
`
`Sep. 29, 1998
`
`Sheet 2 of4
`
`5,815,582
`
`REFERENCE
`MICROPHONE
`
`53
`
`SPEECH
`+
`NOISE
`
`REFERENCE
`INPUT
`
`53
`
`
`
`RESIDUAL
`
`
`ANTI-NOISE
`OUTPUT
`
`
`
`NOISE
`
`
`FEEDBACK
`COMPENSATION
`
`CANCELLATION
`FILTER “A*
`
`
`
`Sr—
`
`3
`
`

`

`RESIDUAL
`SENSOR
`
`AMPLIFIER &
`GAIN CONTROL
`
`ANTI-ALIASING
`FILTERS
`
`SAMPLE &
`HOLD
`
`A/D
`
`REFERENCE
`SENSOR
`
`AMPLIFIER &
`GAIN CONTROL
`
`ANTI-ALIASING
`FILTERS
`
`SAMPLE &
`HOLD
`
`A/D
`
`~
`
`<
`
`
`
`PROCESSOR
`
`ACTUATOR
`
`AMPLIFIER
`
`RECONSTRUCTION
`FILTER
`
`
`
`D/A
`
`MIXER
`
`FIG.3
`
`OUTPUT y OF SPEECH
`FILTER
`
`quayed*S'0
`8661“67“dag
`pJO€Ways
`
`78S‘°ST8'S
`
`4
`
`

`

`REFERENCE
`SENSOR
`
`
`
` AMPLIFIER &
`
`GAIN CONTROL
`
` ANTI-ALIASING
`
`FILTERS
`
`WEIGHT
`ADAPTION
`
` ACTUATOR
`
`AMPLIFIER
`
`
`
`RECONSTRUCTION
`FILTER
`
`
`
`
`
`
`
`yuazed*S'0
`8661“67“dag
`fbJ0p19Y8
`
`78S‘°ST8'S
`
`SPEECH
`FILTER "S"
`
`F1G.4
`
`5
`
`

`

`5,815,582
`
`1
`ACTIVE PLUS SELECTIVE HEADSET
`
`This application is a continuation, of application Ser. No.
`08/347,417, filed Dec. 2, 1994, now abandoned.
`
`BACKGROUND OF THE INVENTION
`
`This invention relates to a headset for actively canceling
`unwantednoise while selectively allowing necessary speech
`to reach the user’s ear.
`
`In the past, attempts to combine the twoprotections, i.c.,
`high and low frequency attenuation, has resulted in not only
`the noise being attenuated, but also the speech that
`the
`wearer needs to hear. Some systems met only limited
`success with fixed or “near-stationary” noise but not with the
`other noise ofeither (a) varying spectral characteristics or
`(b) brief duration noises with “spikes”. Examples of such a
`systemis found in U.S. Pat. No. 4,025,721, to Graupe et al
`and U.S. Pat. No. 4,185,168 to Graupe et al. Other systems
`like that found in U.S. Pat. No. 4,455,675 to Bose actively
`attenuate all sounds at low frequencies and passively altenu-
`ate all high frequency sounds. These sounds include speech
`and warning signals that want
`to be heard by the person
`wearing the headset.
`SUMMARY OF THE INVENTION
`
`The instant invention solves oftotal attenuation of the
`noise and speech, by providing a solution of an active
`headset that can employ any ofseveral selective algorithms
`such as those disclosed in U.S. Pat. No. 4,654,871 to
`Chaplin, hereby incorporated by reference herein,
`Alternatively, this invention can employ the algorithm dis-
`closed in U.S. Pat. No. 5,105,377 to Ziegler which is also
`incorporated herein by reference. In addition this invention
`can employ other algorithms such as that disclosed in the
`application of Ziegler in U.S. patent application Ser. No,
`07/421 759; which is hereby incorporated by reference.
`In applications for noise canceling headsets, particularly
`in industrial environments, attenuation of low frequency
`noise as well as noise that covers the speech band (300 to
`3300 Hz) passive hearing protection works extremely well at
`higher frequencies (typically above L000 Hz) whereas active
`noise cancellation has been shown to achieve similar levels
`of protection at lower frequencies (50 to 1000 Hz). Passive,
`however, also attenuates speech and warning signals andthe
`protectors are uncomfortable to wear. This invention pro-
`vides a solution that simultaneously provides the protection
`offered by a passive headset
`in a lightweight open back
`headset while using active adaptive feed forward control
`algorithms that attenuate all sounds in the 20 to 3300 Hz
`frequency band. Additionally, adaptive speech filtering or
`in-wire control technology separates speech from noise and
`passes the speech to the user.
`Accordingly it is an objectof this invention to provide an
`active noise canceling headset with selectivity.
`Another object of this invention is the provision of an
`open back muff headset with selective filtering.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`These and other objects of this invention where reference
`is had to the accompanying drawings in which
`FIG.
`1 shows a typical active/passive headset system
`incorporating the instant invention.
`FIG. 2 showsan active plus selective headset system with
`an open back muff that
`incorporates active control and
`adaptive speech filtering to allow speech to pass with the
`“anti-noise” signal.
`
`a)
`
`10
`
`ta an
`
`30
`
`40
`
`50
`
`A an
`
`60
`
`2
`FIG. 3 shows a more detailed description of the active
`control system of FIG. 2.
`FIG. 4 shows a more detailed description ofthe adaptive
`speech filtering technique to be usedin this headset design.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`there is shown an active/passive closed back
`1
`In FIG.
`headset system 10. It consists ofa typical passive headset 11,
`loudspeakers 12 that drive the anti-noise and residual micro-
`phones 13 to sense any remaining noise near the ear and
`reference microphones 14 to send advancedinformation for
`feed forward approaches and a system controller 20 which
`synthesizes the anti-noise signal.
`The headset shown has closed backs 21, 22 for passive
`attenuation without the speakers, microphones and system
`controller, this headset would be a typical passive hearing
`protector.
`The systemis designedto use various algorithms such as
`that of Ziegler in U.S. Pat. No. 5,105,377 or an adaptive feed
`forward approach. Both these algorithms use a reference
`signal as inputs. The digital virtual earth (DVE) algorithm
`develops a reference signal by subtracting an equalized
`version of its own anti-noise signal fromthe residual signal.
`The adaptive feed forwarduses the reference microphone as
`its input and is very effective on complicated noise envi-
`ronments that are broadband and random in character. The
`
`Least Means Square (LMS) adapter 24 shown in FIG. 1 are
`Filtered-X versions which have inherent compensation for
`the effects of the feedback delays aroundthe loop. Box “C”
`at 25 is the impulse response of active cancellation system.
`Feedback compensator 26 and cancellation filter 27 com-
`plete the component portions of the controller.
`DVE is highly effective to use in simple noise environ-
`ments having only a few harmonics even where the noise
`varies tremendously.
`It has also been demonstrated to be
`very effective doing broadband cancellation at low frequen-
`cies (50-700 Hz).
`Speakers 12 ofthe headset are large enoughto be capable
`of producing antinoise at the same level as the noise to be
`canceled. They have little or no distortion and have a
`minimum of input-to-output delay as any delay in the
`feedback loop slows down the system adaptationrate.
`Residual microphones 13 are typically small electret
`microphones mounted on the speaker frame near the ear.
`They must faithfully reproduce the sound that remainsat the
`ear after cancellation so that the controller can make further
`adjustments to the anti-noise signal.
`Reference microphones 14 are small electret microphones
`attachedto the outside of the headset at a distance from the
`ear canal. These referenced microphonesare used to provide
`advanced information about the noise. The higher the fre-
`quency of the noise the more advanced information is
`neededto effectively cancel the noise.
`FIG. 2 showsan active plus selective headset system 50
`with headset 51 having open backed muff positions 52,
`reference microphones 53, speakers 54 and residual micro-
`phones 55. An earplug (not shown) may be substituted for
`the open backed muff.
`The active /passive system 10 previously described can be
`configuredto actively attenuate all sounds in the frequency
`bandfrom 20to 3300 Hz without the needfor a passive mulf
`or earplug. The approach uses an adaptive feed forward
`control algorithmto actively attenuate the damaging noise in
`this band.
`In order to accomplish this it
`is necessary to
`
`6
`
`

`

`5,815,582
`
`3
`minimize the delays ofthe digital signal processing system,
`which include delays introduced by the anti-aliasing and
`reconstructionfilters shown in FIG. 3 and the acoustic delay
`of the speaker and residual microphone physical system, in
`order to effectively attenuate noise at the higher frequencies.
`The controller 60 has adapters 61, 62, feedback compen-
`sation 63, cancellation filter 64 and adaptive speech filter 65.
`Controller 60 uses a parallel adaptive speech filtering tech-
`nique to pass speech to the user. Adaptive speech filtering
`techniques can be employed to work with the particular
`noisy environment. The active controller attenuates noise in
`the band ofinterest and allows speech and warning signals
`to pass via the adaptive speech filtering path which incor-
`porates a warning signal filter as shown in FIG. 2.
`It
`is
`similar to the active/passive system except
`for the open
`backed headset design andthe addition ofa parallel adaptive
`speech filtering path and warning signal filter path as inte-
`gral parts ofthe controller. The input to the speech filter and
`controller are the upstream reference microphones 53.
`This reference microphone contains noise and speech.
`The speech is filtered from the noise and passed with the
`“anti-noise” generated from the adaptive feed forward con-
`troller and sent to the headset loud speaker. Both speech and
`warning signals, which are typically above the speech band
`and of known frequencies, will be heard by the user of the
`lightweight and open back headset.
`With reference to FIG. 2,
`the “anti-noise” and speech
`output signals are mixed and input to the speakers. This
`combined signal output sample, u,, is given by
`Xg=rye-ze
`
`MRA
`
`Ug=Wety,
`
`u, is the output speech and anti-noise value
`where r, is a vector of the most recent examples ofthe
`residual signal
`z, is a vector of the output of the speech filter after it
`passed through the impulse response C,
`A, is a vector of cancellation filter coefficients
`y, is the output anti-noise value
`w, is the output speech value.
`s, is the vector of compensated inputs.
`Inputs to the controller and speech filter are the reference
`signal, v,, and residual signal r, that are picked up via the
`reference sensor andresidual sensor respectively. The adap-
`tive feedforward controller generates an “anti-noise”, y;,,
`and the adaptive speech filter generates a clean speech
`signal, w,, that are mixedto form the output signal u, which
`is sent
`to the speakers. Each ear piece operates indepen-
`dently with separate reference and residual sensors and
`actuator.
`
`It is essential that the output of the speech filter, w,, be
`filtered through the system in pulse response, C,, and
`subtracted from the residual input, r,, so as not to interfere
`with the operation of the adaptive feedforward controller.
`Otherwise, the controller will attempt to adapt to and cancel
`the speechsignal that is output to the speaker.
`Several techniques can be used to minimize the delays of
`the system. First, passive material can effectively act as a
`low passfilter for the input reference and residual sensors.
`This would eliminate the need for anti-aliasing filters and
`thus the delays introduced by these filters would be elimi-
`nated. This technique has been shown to be quite effective
`
`a)
`
`30
`
`40
`
`50
`
`A an
`
`60
`
`4
`in the active control of noise in ducts using the adaptive
`feedforward controller.
`Another technique removesneither the anti-aliasing filters
`nor the reconstruction filters but essentially by-passes the
`delays introduced by these filters by inserting an analog
`zeroth order tap. This is achieved by placing an amplifier
`between the output of the incoming gain control and the
`output of the reconstruction filters shown in FIG, 3.
`A final technique, which will be even more effective as the
`speed of microprocessor technology increases, is to sample
`at a rate of 40 kHz or greater, this eliminates the need for
`anti-aliasing and reconstruction filters because the cut off
`frequency of 20 kHz is at
`the limit of the loudspeaker
`response.
`We claim:
`1. An active plus selective headset system which provides
`active broadbandattenuation of noise as well as adaptive
`speech filtering, said system comprising:
`a headset means adapted to be worn by a user;
`reference sensing means onsaid headset means adapted to
`sense speech and noise signals;
`speaker means on said headset means adapted to convey
`speech signals to a user’s ear; and
`controller means adapted to control the speaker means
`based on input from the reference sensing means to
`provide active broadband attenuation of all random
`inbandnoise as well as adaptive speech filtering sothat
`only the speech reaches the ear, wherein said active
`broadband attenuation is accomplished without syn-
`chronization pulses.
`2. Asystem as in claim 1 wherein said headset means
`includes residual microphone means located on said headset
`means and including a feedback means connected to said
`speaker means.
`3. Asystem as in claim 2 wherein said feedback means
`includes an adaptive speechfilter means and a cancellation
`filler means.
`4. Asystem as in claim 2 wherein said controller means
`is run by an adaptive feedforward algorithm.
`§. A-ssystem as in claim 2 wherein said headset means
`includes an open backed mulf.
`6. Asystem as in claim 2 wherein said reference sensing
`means is an electret microphone.
`7. Asystem as in claim 6 wherein said headset system
`comprises a pair of open backed muffs with the reference
`sensing means located on the outside of said muffs.
`8. An active plus selective headset system which provides
`active broadband attenuation of noise as well as speech
`filtering, said system comprising:
`a headset means adapted to be worn by a user, wherein
`said headset means includes residual microphone
`means located on said headset means andincluding a
`feedback means connected to said speaker meansthat
`includes an adaptive speech filler means adapted to
`filter speech from noise anda cancellation filter means;
`reference sensing meanson said headset means adaptedto
`sense speech, noise and warning signals;
`speaker means on said headset means adapted to convey
`speech and warning signals to a user’s ear; and
`controller means adapted to control the speaker means
`based on input from the reference sensing means to
`provide active broadband attenuation of noise as well
`as speechfiltering so that only the warning signals and
`speech reach the ear.
`9. An active plus selective headset system whichprovides
`active broadband attenuation of noise as well as speech
`filtering, said system comprising:
`
`7
`
`

`

`5,815,582
`
`>
`a headset means adapted to be worn by a user, wherein
`said headset means includes residual microphone
`means located on said headset means and including a
`feedback means connected to said speaker meansthat
`includes an adaptive speech filter means anda cancel-
`lation filter means;
`reference sensing meanson said headset means adaptedto
`sense speech, noise and warning signals:
`speaker means on said headset means adapted to convey
`speech and warning signals to a user’s ear; and
`controller means adapted to control the speaker means
`based on input from the reference sensing means to
`provide active broadband attenuation of noise as well
`as speech filtering so that only the warning signals and
`speech reach the ear;
`wherein an output
`from said adaptive speech filtering
`means is mixed with an output from said controller
`means and a resulting signal passed to said speaker
`means.
`
`10. An active plus selective headset system which pro-
`vides active broadband attenuation of noise as well as
`speech filtering, said system comprising;
`a headset means adapted to be worn by a user, wherein
`said headset means includes residual microphone
`means located on said headset means and including a
`feedback means connected to said speaker means that
`includes an adaptive speech filter means anda cancel-
`lation filter means;
`reference sensing means onsaid headset means adaptedto
`sense speech, noise and warning signals;
`speaker means on said headset means adapted to convey
`speech and warning signals to a user’s ear; and
`controller means adapted to control the speaker means
`based on input from the reference sensing means to
`provide active broadbandattenuation of noise as well
`as speech filtering so that only the warning signals and
`speech reachthe ear,
`wherein an output
`from said adaptive speech filtering
`means is filtered by an impulse response of the can-
`cellation means and subtracted from a signal from the
`residual microphone so as not to interfere with opera-
`tion of said controller means.
`Il. Asystem as in claim | wherein said reference sensing
`means is external of said speaker means on said headset
`means and said controller means is adapted to employ a
`feedforward methodof noise cancellation.
`12. Asystem as in claim 2 wherein said residual micro-
`phone means is
`internal of said speaker means on said
`headset means and said controller means is adapted to
`employ a feedback methodof noise cancellation.
`13. A headset system for providing active broadband
`attenuation of unwanted random inband noise, as well as
`adaptive speech filtering, comprising:
`a pair of muffs, each of said mulls comprising:
`a reference microphone attachedto an outside portion
`ofsaid muff for sensing speech signals and unwanted
`random inband noise signals;
`
`10
`
`_ wn
`
`ta an
`
`30
`
`aoon
`
`40
`
`50
`
`A an
`
`6
`a speaker located on an inside portion ofsaid muff; and
`a controller attachedto said reference microphone such
`that said signals sensed by said reference micro-
`phone act as an input
`to said controller; said con-
`troller producing an anti-noise output at said speaker
`to eliminate said unwanted random inband noise
`
`signals at a user’s ear and removing noise from said
`speech signal by adaptive speechfiltering so that the
`speech signals output
`to the user’s ear is clearer,
`wherein said elimination of said unwanted random
`inband noise signals is accomplished without syn-
`chronization pulses.
`14. A headset system as in claim 13, further comprising a
`residual microphone attachedto said speaker for sensing any
`unwanted random inband noise near the user’s ear and
`
`providing an output to said controller so that the anti-noise
`output can be adjusted to compensate for said unwanted
`random inband noise.
`
`15. A headset system as in claim 13 wherein said con-
`troller includes a feedback compensator connected to said
`speaker.
`16. A headset system for providing active broadband
`attenuation of unwanted noise, as well as speech filtering,
`comprising:
`a pair of muffs, each of said muffs comprising:
`a reference microphone attached to an outside portion
`of said muff for sensing speech signals, warning
`signals, and unwanted noise signals;
`a speaker located on an inside portion of said muff; and
`a controller including a feedback compensator con-
`nected to said speaker andattached to said reference
`microphone such that said signals sensed by said
`reference microphone act as an input
`to said con-
`troller; said controller producing an anti-noise output
`at said speaker to eliminate said unwanted noise
`signal at a user’s ear and removing noise from said
`speech signal so that the speech signals output to the
`user’s ear is clearer.
`
`wherein said feedback compensator includes an adaptive
`speech filter and a cancellation filter.
`17. A headset system as in claim 13 wherein said con-
`troller is operated based on an adaptive feedforward algo-
`rithm.
`
`18. A headset system as in claim 13 wherein said refer-
`ence sensing microphone ts an electret microphone.
`19. Asystem as in claim 1 wherein the reference sensing
`meansis adaptedto additionally sense warning signals, the
`speaker means is adapted to convey speech and warning
`signals to the user, and the controller means is adapted to
`provide active broadband attenuation of noise as well as
`speech filtering so that only the warning signals and speech
`reach the ear.
`
`20. Aheadset system as in claim 13, wherein the reference
`microphone additional senses warning signals.
`*
`Ef
`eo
`*
`a
`
`8
`
`