Umted States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,721,783
`
`Anderson
`
`[45] Date of Patent:
`
`Feb. 24, 1998
`
`USO0S721783A
`
`[54] HEARING AID WITH WIRELESS REMOTE
`PROCESSOR
`
`OTHER PUBLICATIONS
`
`[76]
`
`Inventor:
`
`James C. Anderson, 40 Aran Rd.,
`Westwood, Mass. 02090
`
`[21] Appl. No.: 479,629
`_
`22
`F11 d'
`7 1995
`J““'
`° '
`9
`1
`[
`Int. Cl.‘ ..................................................... H04R 25/00
`[51]
`
`[52] U.S. Cl.
`381/686; 381/68; 381/68.2;
`
`[53] Field of Search ........................... 381/68, 632,634,
`381/68.6; 342/42-51, 2; 340/6, 325.54,
`505
`
`[56]
`
`References Cited
`ETEI H.
`In IENI.
`S
`DOC
`US’ P
`2,774,060 12/1956 Richardson ................................. 325/9
`3,384,892
`5/1968 Posunann
`343/65
`
`34g/2255/3
`------
`'3
`“Se”
`179/82
`8/1971 Spracklen
`3,601,550
`.. 340/280
`.
`1/1973 Martens .
`3,711,848
`3/1973 Fearon .................................... 340/230
`3,754,226
`9/1977 Strong et al. .
`4,051,331
`4,063,229 12/1977 Vaughan et al. .
`4,334,315
`6/1982 Ono et a1.
`-
`-
`4v791=672 12/1933 N““1°Y 6* 31-
`................................. 381/68
`
`8/1990 Tophofin .
`4’947’432
`6,1991 Williamson CH1 _
`5:027:410
`5/1992 Knoll et al.
`......................... 310/313 R
`5,115,160
`4/1993 Topholm ................................ 381/68.6
`5,202,927
`5/1993 Martin et a1.
`.
`5,210,803
`7/1993 Platt ....................................... 381/58
`5,226,086
`9/1993 Janning ................................... 340/573
`5,241,923
`Ea“ V‘°°“h;‘1"°"-
`381/682
`gviggalgé
`2/1995 A‘dfl1h/man‘°t
`' """"""""""""
`'
`51390,3354
`' etal
`381/682
`5479522 12/1995 Lind
`
`‘ """""""""
`5613495
`3/1997 Mms at al.
`128/69'6
`5:636:285
`6/1997 Sauer ..................................... 381/68.2
`FOREIGN PATENT DOCUMENTS
`
`2651634
`
`3/1991
`
`France .
`
`“Q & A about Biological Effects and Potential Hazards of
`RF Rfidiafi0I1”. OET Bllllfitill 55. FCC, Wfishiflgmlls D-C-9
`1311- 1989: PP- 1'3-
`“How to Buy a Hearing Aid”, Consumer Reports Magazine,
`Nov. 1992. 1111- 716-712-
`T. Tanji, “A digital Radio Hearing Aid”, I—P—14, Program
`and Abstracts of First Biennial Conference on Advancing
`gumgm Efiimlinumcafilonazgn Ifwrdiscilpllénfiry afirlnltrlglmtcgn
`“H113
`650310 an
`eve Opmen ,
`a on
`s
`s
`Of Health, Bethesda, MD,
`SHS WHG1?“ R00” C°mm““1°a‘1°11S Data 500°‘ F1011
`E-A-R 111°» 1011- 1990-
`CROS Product Data Sheets From Telex Communications,
`Inc.; Jan. 1989.
`H. Levitt, A. Neuman, R. Mills and T. Schwander, “Digital
`Master Hearing Aid” Journal of Rehabilitation Research and
`Development, vol. 23, No. 1, 1986, pp. 79-87, May 1986.
`
`Primary Examiner—-Curtis Kuntz
`Assistant Examiner—Rexford N. Barnie
`A
`,A ,
`F‘ RihdF.B
`Sfizféney
`gent or
`”m— C at
`
`[57]
`
`ABSTRACT
`
`enway
`
`;Marti M.
`11
`
`A hearing aid or audio communication system includes an
`earpiece (10) that can be hidden in the ear canal, and which
`communicates wirelessly with a remote processor unit, or
`RPU (16), that enhances audio Signals and can be concealed
`under clothing. Sounds _from the environment are picked up
`by a microphone (12) 111 the earpiece and sent with other
`iI1f°1'mfi0“ W01 0 ‘W<*W0Y Wireless 11111417) 1° 1110 RPU
`(1_6)_- The Wireless link (17) uses microwavcs for 6011190110111
`rmmaturization. Furthermore, use of radar technology to
`implement the wireless link (17), with an RPU (16) inter-
`rogatof and cafpigcc
`transponder, Igduocs carpiccc sizs
`and power, as no microwave oscillator is needed in the
`earpiece (10). Optional secondary wireless link circuitry
`(19) can be used between the RPU (16) and a cellular
`telephone system or other sources of information. Electronic
`V_01'00 1000801000 11110 1051101150 01111 0011001 System 011010-
`U011.
`
`71 Claims, 9 Drawing Sheets
`
`Secondary
`Wireless Link '29
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`U.S. Patent
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`Feb. 24, 1998
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`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet 5 of 9
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`5,721,783
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`U.S. Patent
`
`Feb. 24, 1998
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`Sheet 6 of 9
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`U.S. Patent
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`Feb. 24, 1993
`
`Sheet 8 of 9
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`Feb. 24, 1998
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`

`5,721,783
`
`1
`HEARING AID WITH WIRELESS REMOTE
`PROCESSOR
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention is directed to hearing aids, and in
`particular to a hearing aid having an earpiece housing worn
`in or at tl1e ear and a remote processor unit (RPU) worn by
`or located near the user that wirelessly receives signals from
`and transmits signals to the earpiece. The present invention
`is also directed to the use of hearing aid systems as wireless
`communication devices for hands—free cellular telephone
`and mobile radio communication “handsets,” covert opera-
`tion andcontrol of hearing aids, hearing protection and noise
`cancellation simultaneous with binanral hearing aid
`functions, hearing test equipment, location of misplaced
`hearing aid system components and wireless cochlear
`implants.
`2. Brief Description of the Related Art
`In the prior art, a basic hearing aid without remote control
`is a self-contained earpiece comprising a microphone,
`speaker and associated processor electronics. In such hear-
`ing aids, the earpiece microphone converts acoustic waves
`into electrical representations of the acoustic waves,
`the
`electrical signals are amplified by the earpiece processor
`electronics and converted back into acoustic waves by the
`earpiece speaker. A remote control (see, e.g., U.S. Pat. No.
`4,918,736) that controls earpiece amplification functions
`(e.g., volume) via a one-way wireless link from the remote
`control to the earpiece is sometimes used in the prior art, but
`the path taken by the electrical signals that represent the
`acoustic waves (known in the art as the “audio path”) is the
`same whether or not a remote control is used; i.e., the audio
`path is from the microphone to the speaker via the earpiece
`electronics.
`
`Wireless hearing aids using a one—way radio frequency
`(RF) transmission path, comprising a wireless microphone
`transmitter (not normally worn at the ear) and a wireless
`receiver (normally worn at the ear) are well lmown in the
`prior art. Such devices commonly use the “auditory assis-
`tance device” RF bands near 73 MHZ (see the U.S. Code of
`Federal Regulations, 47 CFR Ch. 1, Para. 15.237) and have
`proven eflective as teaching aids for hearing-impaired stu-
`dents in a classroom setting. Thus, in the prior art, RF
`transmissions are sent from a hand-held wireless micro-
`phone (not a microphone located in an earpiece) to a
`wireless receiver in or near an earpiece, providing a one-way
`radio transmitter and receiver system for the audio path.
`The present invention uses an audio path that is different
`from the audio path used by devices in the prior art. The
`present invention uses a primary two-way wireless link (not
`a one-way link as in the prior art) between an earpiece worn
`in or at the user’s ear and an RPU worn by or located near
`the user. In the present invention, audio signals from the
`environment are picked up by a microphone in the earpiece
`(not a hand-held microphone as used by wireless hearing
`aids in the prior art) and transmitted over the primary
`two-way wireless link to the RPU (instead of going to
`processor electronics contained in the earpiece, as in basic
`hearing aids known in the prior art), where the audio signals
`are enhanced according to the user’s needs before transmis-
`sion over the primary wireless link to the earpiece. Signal
`processing is performed in the RPU rather than the earpiece
`to take advantage of relaxed size and power constraints. This
`new approach eliminates the need for most physically large
`and power-consuming electronics in the earpiece, eliminates
`
`2
`the need for conventional remote controls, and provides a
`variety of optional features (e.g., telephone communication
`capability via a secondary two-way wireless link) not avail-
`able in the prior art. Note that the present invention also
`maintains all capabilities (e.g., acoustic feedback reduction
`and adaptive volume control) of prior art devices.
`Although cordless and cellular telephone handsets (as
`well as wireless communication headsets) well known in the
`art contain a microphone, radio transceiver (transmitter and
`receiver) and speaker, such devices are not used for the
`reception, enhancement and subsequent reproduction of
`audio signals from the ambient environment as required for
`a hearing aid application. Such devices do not act as hearing
`aids because they do not provide the user with enhanced
`sounds from the user’s immediate surroundings, but only
`provide sounds from another user.
`
`SUMMARY OF THE INVENTION
`
`It is an object of the present invention to provide a new
`and useful auditory aid for hearing-impaired persons (i.e.,
`those having certain residual hearing) by removing audio
`signal enhancement functions from the earpiece and placing
`them in an RPU. Use of an RPU provides several advantages
`over systems that attempt to place all system capabilities
`within the earpiece. The RPU approach allows a simple
`earpiece design comprising a miniature low—power wireless
`transceiver, microphone and speaker. Note that the speaker
`is also known in the hearing aid art as a “receiver,” but the
`term “speaker” is used here to avoid confusion (similarly,
`the term “talker,” not “speaker,” is used to describe a human
`producing vocal sounds). The resulting earpiece is
`extremely small, can be hidden from view in the ear canal
`if desired, and allows complete fleedom of movement when
`a primary two-way wireless link to the RPU is used.
`Processing for all major system capabilities, such as a.mpl.i—
`fication and other forms of signal enhancement, takes place
`in the RPU where size and power constraints are relaxed,
`leading to a cost-eflective design.
`Another object of this invention is to provide supplemen-
`tal audio information (e.g. a verbal warning from the RPU
`that an earpiece battery is low) and communication services
`(e.g., cellular telephone and paging services) to the user via
`the hearing aid system. Such services are accessed in a
`manner that can be made imperceptible to a casual observer
`if desired. The RPU (which contains a digital signal pro-
`cessor or other computer) acts as one source of information,
`e.g., by using a synthesized voice message to provide the
`time of day, and the RPU can also be used to access a
`secondary wireless link to the general subscriber telephone
`network or voice paging services. User control of hearing
`aid parameters and requests for information are accom-
`plished using pushbuttons located on the RPU (including
`pushbuttons suitable for data entry in a covert manner) or
`voice recognition. Many sensors and peripheral devices can
`reside in or be attached to the RPU by wired or Wireless
`means, and can provide a variety of information for diiferent
`applications (e.g., heart pulse rate) as audio in the user’s
`earpiece.
`A further object of this invention is to provide some
`degree of protection for the residual hearing capability of a
`hearing-impaired user (or a non—impaired user who wishes
`to avoid impairment) in a wireless hearing aid system having
`the simultaneous capabilities of noise cancellation and bin-
`aural processing (e.g., directionality). Other objects of the
`invention are to provide a convenient means for testing a
`user’s hearing capability without the need for additional
`
`10
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`

`

`5,721,783
`
`3
`equipment, to assist users in the location of misplaced
`hearing aid system components, and to provide profoundly
`deaf cochlear implant patients with a wireless system allow-
`ing improved freedom of movement compared to existing
`wire-connected systems.
`
`DESCRIPTION OF THE DRAWINGS
`
`These and other objects, features and advantages of the
`invention will best be understood with the aid of the fol-
`lowing detailed description in conjunction with the accom-
`panying drawings in which:
`FIG. 1 is a block diagram system overview illustrating
`how an earpiece (comprising a microphone, RF transceiver,
`dual-use antenna/extractor and speaker) is worn in the ear,
`communicates via a primary two-way RF linkwith an RPU,
`and also communicates via an optional secondary wireless
`link to a telephone system.
`FIG. 2 is a block diagram illustrating a limited-feature
`preferred embodiment of the invention that uses commercial
`off-the-shelf system elements.
`FIG. 3 is a relative spectral magnitude plot showing the
`frequency domain characteristics of a wireless link used in
`a full-featured preferred embodiment of the invention.
`FIG. 4 is a simplified schematic of the earpiece transpon-
`der (transmitter responder) RF circuitry used to illustrate
`operation of a full-featured preferred embodiment of the
`invention.
`
`FIG. 5 is a waveform timing diagram showing character-
`istics of a typical interrogation from an RPU interrogator
`followed by a corresponding typical reply from an earpiece
`transponder.
`FIG. 6 is a bird’ s-eye view used to describe the RF mutual
`interference geometry occuning when many users of the
`invention are in close proximity.
`FIG. 7 is a drawing showing the front view of a typical
`RPU for a full-featured preferred embodiment of the inven-
`tion.
`
`FIG. 8 is a block diagram showing details of an earpiece
`for a full-featured preferred embodiment of the invention.
`FIG. 9 is a block diagram showing details of an RPU for
`a full-featured preferred embodiment of the invention.
`FIG. 10 is a block diagram showing details of a wireless
`cochlear implant system.
`FIG. 11 is a block diagram showing details of a wireless
`cochlear implant electrode driver unit.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`One preferred embodiment of the invention herein
`described is shown in block diagram form in FIG. 1. In this
`figure. the earpiece 10 shown worn in the ear 11 uses a
`standard completely-in-the-canal (CIC) housing, well
`known in the art, although many other earpiece housing
`types known in the art (e.g., behind-the-ear, or BTE) can be
`used. The earpiece shown in FIG. 1 comprises a microphone
`12, RF transceiver 13 with an antenna that doubles as an
`earpiece extractor 14, and speaker 15. Although the dual-use
`antenna/extractor arrangement shown in FIG. 1 is often
`desirable, a separate antenna or antennae can be used in
`conjunction with many different types of earpiece extractors
`as appropriate for a particular application. Antennae and
`extractors can be disguised as ear hair or jewelry (e.g.,
`earrings), or conductive filaments can be permanently
`implanted in the ear cartilage to act as antennae using a
`
`4
`process similar to ear piercing. The earpiece 10 communi-
`cates with a remote processor unit (RPU) 16 via a primary
`two-way RF link 17, although many other wireless link
`media (e.g., ultrasonic or infrared) may be used instead. The
`RPU is typically worn under clothing (e.g., carried in a
`pocket or purse), but may also be worn in plain sight (e.g.,
`on a belt) if desired. The RPU 16 may be connected (via
`wired or wireless means 18) to optional secondary wireless
`link circuitry 19 that allows wireless communication
`between the RPU and other sources of information (e.g., the
`general subscriber telephone network) via a secondary wire-
`less link. Note that the optional secondary wireless link
`circuitry 19 may or may not be contained within the RPU
`case 70 of FIG. 7.
`
`It will be apparent to those skilled in the art that many
`variations of the system shown in FIG. 1 are possible, and
`two embodiments of the invention are described here in
`detafl. The first preferred embodiment is a limited-feature
`embodiment, assembled using commercial off-the-shelf sys-
`tem elements, that demonstrates the basic features of a
`hearing aid with wireless remote processor as well as
`communication capability via a secondary wireless link. The
`second preferred embodiment is a considerably more com-
`plex full-featured embodiment for general application.
`1. Limited-feature embodiment
`The limited-feature hearing aid embodiment shown in
`FIG. 2 can be fabricated using low-cost commercial off-the-
`shelf RF system elements operating in the standard 88 MHz
`to 108 MHZ FM (frequency modulation) broadcast band.
`Although the system described here is monaural, it will be
`clear to those skilled in the art that a binaural (stereo) system
`can be constructed based on the same principles as the
`monaural system. Note that the earpiece 22 of FIG. 2 is
`physically different from the earpiece 10 of FIG. 1, but the
`two earpieces are functionally similar. An FM wireless
`microphone 20 transmitter, e.g. Radio Shack (R) model
`33-1076, is mounted on an FM headset 21 receiver, e.g.
`Radio Shack (R) model 12-103, to form an earpiece 22
`which is not necessarily hidden from view. ‘The earpiece
`wireless microphone 20 transmitter is tuned to a fixed
`frequency F1 free of local interference, e.g. F1=l 06 MHz.
`while the earpiece headset 21 receiver is tuned to a different
`frequency F2 free of local interference, e.g., F2=9O MHz.
`The RPU 23 includes an FM receiver 24, e.g. Radio Shack
`(R) model l2-210, tuned to the earpiece wireless micro-
`phone 20 transmitter frequency F1 (106 MHz in this
`example) and operating in monaural mode (see instructions
`for the Radio Shack (R) model 12-210 FM receiver regard-
`ing details of operation). The FM receiver 24 speakers are
`removed, and a wire is installed in place of one of the
`speakers to connect
`the FM receiver 24 output
`to the
`double-pole double-throw (DPDT) switch 25 as shown in
`FIG. 2. When the DPUF switch 25 is in the lower position
`as shown in FIG. 2, a direct connection is provided between
`the output of the FM receiver 24 and the input of a signal
`enhancer 26 signal processing device. The signal enhancer
`26 may be, for example, an OKI Semiconductor MSM6322
`“pitch control LSI for the speech signal” which has been
`conveniently packaged for battery-powered operation as in
`the Questech International Inc. Transition 2001 telephone
`voice changing accessory (see the instruction sheets for
`these devices regarding details of operation). ‘The output of
`the signal enhancer 26 is connected to the input of the RPU
`FM transmitter 27, which is tuned to the earpiece headset 2]
`receiver frequency F2 (90 MHz in this example). The RPU
`FM transmitter 27 may be a wireless microphone of the
`same type used in the earpiece. but which has been modified
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`by disconnecting the microphone transducer and connecting
`the signal enhancer 26 in its place.
`During normal operation, speech signals from a nearby
`talker (and other signals in the ambient audio environment)
`are picked up by the earpiece wireless microphone 20 and
`transmitted to the RPU FM receiver 24. The RPU FM
`receiver 24 output level may be adjusted using the RPU FM
`receiver 24 volume control. The resulting electrical wave-
`form representing signals from the nearby talker travels
`through the DPDT switch 25, which is set to the lower
`position as shown in FIG. 2, to the signal enhancer 26. The
`signal enhancer 26 may be, for example, a voice changer
`device that varies tl1e pitch of a received speech signal
`according to the setting of pushbutton controls located on
`the RPU signal enhancer 26. The speech signals pitch can
`then be raised or lowered as desired to help compensate for
`a user’s hearing loss relative to a particular talker’s voice
`characteristics. The modified speech signal travels from the
`RPU signal enhancer 26 to the RPU FM transmitter 27, and
`finally to the earpiece headset 21 receiver where the signal
`is converted to acoustic waves heard by the user.
`No user adjustments need to be made to the earpiece 22
`components, and all necessary user adjustments are made
`using controls located at the RPU 23 (e.g., the volume is
`adjusted for a comfortable listening level using the RPU FM
`receiver 24 volume control, not the earpiece headset 21
`volume control). Since no earpiece 22 user adjustments are
`required, the commercial wireless microphone 20 transmit-
`ter and headset 21 receiver designs used for the earpiece 22
`can be modified by eliminating the unnecessary earpiece
`adjustment controls to achieve significant size reduction.
`Such miniaturization techniques are well known in the art,
`and schematics are available from Radio Shack (R) for the
`designs used in this example (see service manuals for the
`Radio Shack (R) model 33-1076 wireless microphone and
`model 12-103 headset). A set of fixed-value components can
`be used to replace the bulky variable components in the
`earpiece 22 (e.g., the volume control on the earpiece headset
`21 and frequency controls on both the earpiece headset 21
`and earpiece wireless microphone 20). Any resulting fre-
`quency drift effects in earpiece 22 components can be
`minimized by placing temperature-sensitive devices in a
`position where their temperature is regulated by that of the
`human body, which is a relatively constant 37 C (98.6 F).
`Such components can be bonded to the earpiece headset 21
`speaker to provide the required thermal mass. A miniature
`speaker of the type commonly used in hearing aids can be
`used in place of the speaker commercially supplied with the
`earpiece headset 2], and a miniature microphone of the type
`commonly used in hearing aids can be used in place of the
`microphone transducer commercially supplied with the ear-
`piece wireless microphone 20. Both the earpiece headset 21
`and earpiece wireless microphone 20 can operate from the
`same 1.5V battery, and the entire earpiece 22 can be pack-
`aged in a standard BTE hearing aid housing if desired. Such
`miniaturization provides an earpiece which can be hidden
`from the view of a casual observer in many cases (e.g. if the
`user has long hair). especially when miniature ferrite anten-
`nae are used. The RPU 23 may be hidden from View when
`carried and operated in a pocket or purse.
`The RPU 23 shown in FIG. 2 also includes, as an optional
`feature, a telephone handset 28 which may be a cordless
`handset (e.g. Panasonic model IQ{-T37l0H), cellular hand-
`set (e.g., NEC model P120), or a cordless or cellular handset
`with voice-dialing capability, or any of a variety of other
`devices (e.g. a “wallcie-talkie”) capable of communication
`via any type of secondary wireless link 29 (e.g., RF or
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`infrared). In this application, the handset 28 is not held in the
`user’s hand, but instead forms a part of the RPU 23 carried
`on or located near the user’s body. The handset 28 push-
`buttons and other handset 28 controls are available at the
`surface of the RPU 23, and operated in the usual fashion.
`When communication via the secondary wireless link 29 is
`desired, the DPDT switch 25 is placed in the upper position
`(i.e., the alternate position from that shown in FIG. 2). The
`user’s voice (and other signals in the ambient audio
`environment) is picked up by the earpiece wireless micro-
`phone 20, transmitted to the RPU 23 FM receiver 24, sent
`through the DPDT switch 25 to the microphone input of the
`handset 28 (the handset’s microphone transducer may be
`removed) and transmitted on the secondary wireless link 29
`to, e.g., the general subscriber telephone network. Signals
`from the secondary wireless link 29 are received by the
`handset 28, sent from the speaker output of the handset 28
`(the handset’s speaker may be removed) via the DPDT
`switch 25 to the signal enhancer 26, FM transmitter 27 and
`finally to the earpiece headset 21 receiver where the signals
`are converted to acoustic waves heard by the user. Note that
`the RPU 23 may also include straight-forward connections
`to a “personal digital assistant” computer, or voice-operated
`devices connected to the FM receiver 24 output and not
`shown in FIG. 2.
`RF output power of the earpiece wireless microphone 20
`and RPU FM transmitter 27 may be limited by FCC regu-
`lations to a level of -47 dBm, or -47 decibels relative to a
`power level of one rnilliwatt (see 47 CFR Ch. 1, Para
`15.239, for field strength limits, and the relationship
`between field strength and transmitter power is discussed
`later with regard to the full-featured embodiment) in the 88
`MHz to 108 MHz band, which is low compared to the RF
`power output from commercial broadcast radio stations that
`operate in the same band. As a result, “clear" operating
`frequencies for the earpiece 22 and RPU 23 (i.e., operating
`frequencies with suitably low interference levels) must be
`chosen (depending on location of use) in advance of opera-
`tion to avoid interference from commercial broadcast radio
`stations, and also to allow operation of many units in close
`proximity without mutual interference. Interference prob-
`lems and RF transmitter power limitations can be alleviated
`by operating the system in the “auditory assistance device”
`frequency bands near 73 MHz, where RF transmitter power
`can be as much as +2.8 dBm (see 47 CFR Ch. 1, Para.
`15.237).
`2. Full-featured embodiment
`Desirable features: Many features are considered desir-
`able for a full-featured preferred embodiment of the inven-
`tion. For widespread application, it is preferred that the
`system allow operation of many units in close proximity
`without mutual interference. Occasional interference from
`natural or man-made sources is acceptable as long as such
`interference does not result in significant degradation of
`audio quality. Earpiece power consumption is preferably
`minimized to extend battery life, and use of a rechargeable
`battery is desirable. The earpiece is preferably smaller than
`the head of a cotton swab so as to be hidden from view for
`the majority of users. FIG. 1 depicts an earpiece 10 that
`provides the desired CIC form factor. The preferred embodi-
`ment should be able to operate when the earpiece 10 and
`RPU 16 are separated by 0.6 meter (two feet), and greater
`range is desirable. To allow lip reading, total delay between
`the arrival of an ambient acoustic signal at the earpiece
`microphone 12 and production of a corresponding processed
`acoustic signal at the earpiece speaker 15 is preferably less
`than 50 milliseconds. To tell where sounds are coming from
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`localization) random left/right earpiece timing
`(binaural
`variations are preferably less than 20 microseconds. Note
`that larger. fixed left/right timing variations are tolerable.
`Microphones are preferably mounted in the earpieces (rather
`than body-worn) to allow stand-alone earpiece operation in
`the event that the primary communication link 17 between
`the earpiece 10 and RPU 16 is disrupted, and to preserve the
`user’s natural direction-finding capabilities with head
`motion while reducing wind and clothing noise from the
`critical audio path. Note that auxiliary body-wom micro-
`phones (eg.. in the RPU 16) may be used to measure
`background noise for the purpose of automatically setting
`hearing aid parameters. The system’s audio bandwidth (i.e.,
`the audio signal bandwidth preserved throughout all pro-
`cessing and available at the speaker 15 of each earpiece 10)
`is preferably more than 6 KHz so that all essential speech
`information is preserved. See the use of articulation index in
`“Reference Data for Radio Engineers” to evaluate the con-
`sequences of using less than a 6 KHZ bandwidth.
`Choice of wireless medium: A wide variety of wireless
`media can be used in this invention, e.g., RF, optical
`(including infrared), acoustic waves (including ultrasonic),
`induction loop and capacitive coupling. It is possible to use
`any of these forms of wireless communication, as well as
`others not discussed in detail here (e.g., acousto-magneto
`resonance techniques), in the implementation of the present
`invention. Since induction loop and capacitive coupling
`wireless communication technologies are typically more
`suited to one-way rather than two-way communication
`systems, these techniques are not discussed further in ref-
`erence to the present description of the preferred embodi-
`ment. Similarly. optical and acoustic wave approaches are
`not considered further due to the difficulties involved in
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`providing a system which can effectively penetrate clothing.
`An RF approach is therefore the only approach detailed for
`the full—featured preferred embodiment, and one RP
`approach has already been described as a limited-feature ‘
`embodiment.
`Choice of radio frequency: Operating frequencies in the
`900 MHZ to 6 GHZ range have long been used for electronic
`article surveillance (EAS) anti-theft systems and RF iden-
`tification tags (see the Hewlett Packard “Communications
`Components Catalog" for a description of such systems and
`the associated components). EAS technology has a proven
`ability to penetrate clothing and provide a short-range wire-
`less communication link. Operation of the full—featured
`preferred embodiment of the invention within this frequency
`range is desirable due to the availability of low—cost com-
`ponents. In EAS and other systems, a simple approach to RF
`antenna design is to provide a conductor which is one-
`quarter of the wavelength at the RF operating frequency (see
`the discussion of antenna fundamentals in ‘The ARRL
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`Handbook for the Radio Amateur” for a description of the
`Marconi antenna). Since a quarter-wavelength antenna at 6
`GHz is 1.27 cm (one-half inch) long, an antenna at this
`frequency can easily be disguised as an ear hair and can also
`serve as a hearing aid earpiece extractor 14 (although it is
`not required that the antenna or antennae act as an extractor
`nor be disguised as an ear hair). Note that frequencies lower
`than 6 GHz can be used (e.g., as previously described for the
`limited-feature embodiment), but components and antennae
`generally become larger. Similarly, frequencies higher than
`6 GHz can also be used for the present
`invention but
`components are not as readily available. The range of
`frequencies near 6 GHZ is therefore chosen for the present
`description of the preferred embodiment due to the fact that
`6 GHZ is the lowest frequency for which the antenna length
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`is the same as that of a typical extractor or ear hair, and
`miniature components that operate in the vicinity of 6 GHZ
`are readily available.
`RF path effects: The path between the earpiece and RPU
`is preferably, but not necessarily, line-of-sight. To illustrate
`that a line-of-sight path is possible, assume the RPU is
`located near the user’s navel. A telescoping pointer having
`0.6 meter (two feet) length when fully extended can then be
`used to physically demonstrate that a direct line-of-sight
`path exists between the RPU and both earpieces for all head
`and body positions by placing one end of the pointer at the
`navel and the other end at t