(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property
`Organization
`International Bureau
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` ||||||lllllllillIllllllllllllllllllllIlll|llIlllllllllllllllilllllllllllllliIllllllllllllllllll
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`(43) International Publication Date
`1 April 2004 (01.04.2004)
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`(10) International Publication Number
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`WO 2004/028203 A2
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`(51) International Patent Classification7:
`
`H04R 25/00
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`(21) International Application Number:
`PCT/NL2003/000647
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`(22) International Filing Date:
`18 September 2003 (18.09.2003)
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`(25) Filing Language:
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`(26) Publication Language:
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`Dutch
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`English
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`(30) Priority Data:
`1021485
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`18 September 2002 (18.09.2002)
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`NL
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`(71) Applicant (for all designated States except US): STICHT-
`ING VOOR DE TECHNISCHE WETENSCHAPPEN
`[NL/NL]; Van Vollenhovenlaan 661, NL-3527 JP Utrecht
`(NL).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): SIPKEMA, Mar—
`cus, Karel
`[NL/NL];
`lulianastraat 66, NL-6824 KH
`Arnhem (NL). BOONE, Marinus, Marias [NL/NL];
`Voorweg 105, NL—2715 NG Zoetermeer (NL). HUTJES,
`Thomas, Alfred [NL/NL]; Alien Verhoeffstraat 12—A2,
`NL—6811 HH Arnhem (NL).
`
`(74) Agent: VAN WESTENBRUGGE, Andria; Nederland—
`sch Octrooibureau, Scheveningseweg 82 (PO. Box 29720),
`NL-2502 LS The Hague (NL).
`
`(81) Designated States (national): AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CO, CR, CU,
`CZ, DE, DK, DM, DZ, EC, EE, EG, ES, FI, GB, GD, GE,
`GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR,
`KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK,
`MN, MW, MX, MZ, NI, NO, NZ, OM, PG, PH, PL, PT,
`RO, RU, SC, SD, SE, SG, SK, SL, SY, TJ, TM, TN, TR,
`TT, TZ, UA, UG, US, UZ, VC, VN, YU, ZA, ZM, ZW.
`
`(84) Designated States (regional): ARIPO patent (GH, GM,
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZM, ZW),
`Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European patent (AT, BE, BG, CH, CY, CZ, DE, DK, EE,
`ES, FI, FR, GB, GR, HU, IE, IT, LU, MC, NL, PT, RO,
`SE, SI, SK, TR), OAPI patent (BF, BJ, CF, CG, CI, CM,
`GA, GN, GQ, GVV, ML, MR, NE, SN, TD, TG).
`
`Published:
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`without international search report and to be republished
`upon receipt of that report
`
`For two—letter codes and other abbreviations, refer to the "Guid-
`ance Notes on Codes and Abbreviations " appearing at the begin~
`ning of each regular issue of the PCT Gazette.
`
`(54) Title: HEARING AID/SPECTACLES COMBINATION
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`203A2llllllIlllllllllIllllllllllllllllllllvllllIllllllllllIlllllllllllllllllllllllIllllllllllll
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`w (57) Abstract: Hearing aid/spectacles combination (1) having a spectacle frame (1’, 2', 3’) and a first reproduction unit (5; 6),
`N wherein the spectacle frame has a microphone array (2; 3) in a first spectacle arm (2’; 3’), the microphone array (2; 3) is able to pick
`up a sound signal and is able to transmit a processed signal, produced on the basis of said sound signal, to the first reproduction unit (5;
`4/0
`6), wherein the hearing aid/spectacles combination (1) comprises at least four basic modules (B 1, BZ, B3, B4), comprising: a sound
`a registration module (B 1) that comprises the microphone array (2; 3); a beam forming module (B2) for forming a direction—dependent
`processed signal; a reproduction adaptation module (B3) for controlling a reproduction characteristic of the processed sound signal
`produced by the first reproduction unit (5; 6); a reproduction module (B4) that comprises the first reproduction unit (5; 6); and a
`O reproduction control module (BS) for controlling a reproduction characteristic of the processed sound signal produced by the first
`reproduction unit (5; 6), wherein the beam forming module (B2) and the reproduction adaptation module (B3) are based on digital
`B techniques.
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`WO 2004/028203
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`PCT/NL2003/000647
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`Hearing aid/spectacles combination
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`The present invention relates to a hearing aid/spectacles combination according to the
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`precharacterising clause of Claim 1. The present invention also relates to a spectacle arm, a
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`processing unit and a reproduction unit intended for a hearing aid/spectacles combination.
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`Such a hearing aid/spectacles combination is disclosed in International Patent
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`Application WO 99/21400 and can, for example, be used as a hearing aid for a person hard
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`of hearing.
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`WO 99/21400 discloses a combination of two earphones and a pair of spectacles that
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`is provided in the left and right spectacle arm with several microphones positioned some
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`distance apart. In use, these microphones register sound signals from the surroundings. The
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`combination is furthermore so equipped that a direction—dependent version of the sound
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`signal is determined for the sound signals picked up in each microphone in the right and
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`the left spectacle arm, respectively. These direction—dependent sound signals are
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`transmitted to the two earphones, so that for a user who has placed the respective earphones
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`in his or her left and right ears a sound pattern is produced that concentrates on the sound
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`in the direction of View and also describes the direction—dependence of the sound signal,
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`, based on the principles of binaural sound reproduction.
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`However, it is a problem that the combination of the state of the art takes up a fairly
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`substantial volume in order to accomodate the circuits for the functions that are needed
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`for signal processing and reproduction, as well as the power supply for these. The
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`combination is thus relatively uncomfortable for a user, for example a person who is hard
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`of hearing, to wear.
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`One aim of the present invention is to provide a combination that eliminates the
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`abovementioned disadvantages. Said aim is achieved by a hearing aid/spectacles
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`combination of the type mentioned in the preamble, characterised by the characterising
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`measures of Claim 1.
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`By constructing the combination from components that are linked to one another it is
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`possible to achieve a distribution of the modular functionality, that is to say the
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`functionality as is defined in modules, over the combination, which increases the comfort
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`for the user.
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`What is also achieved by the present invention is that the modules can be localised in
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`different components without this resulting in restrictions for the user of the hearing
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`aid/spectacles combination.
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`What can also be achieved in the present invention by means of the use of scenarios
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`for various use situations is that the modular functionality per scenario is distributed over
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`the components in such a way that the power requirement is principally minimised with
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`regard to the power consumption for wireless signal transfer by selecting the shortest, and
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`thus least expensive, link between components for the signal transfer. In this way the power
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`sources for the components can remain relatively restricted in terms of capacity, as a result
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`of which the size of said components can also be relatively smaller than is known from the
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`state of the art.
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`Further embodiments of the hearing aid/spectacles combination according to the
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`present invention are described in the dependent claims.
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`The invention will be explained in more detail below with reference to a few
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`drawings, in which a few illustrative embodiments are shown. The drawings are intended
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`solely for illustrative purposes and do not serve as a restriction of the inventive concept,
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`which is defined by the appended claims.
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`In the drawings:
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`Figure 1 shows a diagram of the filnctional construction of a monaural signal
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`processing chain in a hearing aid according to the present invention;
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`Figure 2 shows a diagrammatic diagram of the hearing aid/spectacles combination;
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`Figure 3 shows a block diagram of a first and second microphone array;
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`Figure 4 shows a block diagram of a processing unit in a first embodiment;
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`Figure 5 shows a block diagram of a first and a second reproduction unit;
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`Figure 6 shows a perspective View of the hearing aid/spectacles combination;
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`Figure 7 shows a side View of a spectacle arm provided with a microphone array .
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`according to the present invention;
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`Figure 8 shows a block diagram of a processing unit in a second embodiment
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`according to the present invention;
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`Figure 9 shows a first and second reproduction unit in a second embodiment
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`according to the present invention;
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`Figure 10 shows a diagrammatic diagram of a further embodiment of the hearing
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`aid/spectacles combination according to the present invention;
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`Figure 11 shows the general principle of a beam former as used in the hearing
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`aid/spectacles combination according to the present invention;
`Figure 12 shows a polar diagram of a directional characteristic for an output signal
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`Sa, formed by end—fire beam forming;
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`Figure 13 shows a beam former according to Figure 10, with which a second signal
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`Sb can be obtained;
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`Figure 14 shows a polar diagram of a directional characteristic for a second output
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`signal Sb, formed by focusing;
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`Figure 15 shows a diagram for further processing of the output signals Sa and Sb;
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`Figure 16 shows a diagram for further processing of the output signals Sa and Sb for
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`use in a communication unit such as a headset for a telephone;
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`Figure 17 shows a polar directional diagram for signal So for a combination of beam
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`forming and speech suppression;
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`Figure 18 shows the sensitivity of a beam former as a function of the direction and
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`location of a sound source;
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`Figure 19 shows the sensitivity of a beam former, set for focusing in the direction of
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`the mouth of a user;
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`and
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`Figure 20 shows the sensitivity of a beam former that is set to receive signal from the
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`forward direction and with which signals from the direction of the mouth are suppressed.
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`Figure 1 shows a diagram of the functional construction of a monaural signal
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`processing chain in a hearing aid according to the present invention.
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`In the construction in Figure 1 signal processing functions of a hearing aid for
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`processing a monaural signal that is fed to one ear of the user are shown in the monaural
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`signal processing chain. The hearing aid comprises the following modules: a sound
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`registration module B 1 , a beam forming module B2, a reproduction adaptation module B3,
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`a reproduction module B4 and a reproduction control module B5 . Arrows in Figure 1
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`indicate transfer of signals between the various components.
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`Following registration of the sound signals in block B1 the signals are converted into
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`digital signals, so that the signals in digital form are processed and transmitted between the
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`various function modules within the hearing aid.
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`The sound registration module B1 serves for registration of a sound signal that arises
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`and is functionally linked to a registration component that comprises a microphone array 2;
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`3 (Figure 2) provided with a number of microphones (Figure 7). In this context a sound
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`signal that arises must be understood to be: sounds that reach the microphone array 2; 3
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`fiom the surroundings during use. The beam forming module B2 serves to form a sound
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`beam from the sound signal registered by the registration component with the aid of the
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`microphone array 2; 3, such that sound from a specific direction can be amplified as
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`desired compared with sound from other directions. Thus, a direction-dependent sound
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`signal can be generated so that a user is able to distinguish sound from a specific direction
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`from sound from other directions. The reproduction adaptation module B3 serves to adapt
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`the reproduction characteristic of the sound beam, such as, for example, the compression
`characteristic and the frequency characteristic, by means of signal processing. The
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`reproduction module B4 serves to reproduce the adapted sound beam in a user’s ear.
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`Finally, the reproduction control module B5 serves to control the reproduction, such as, for
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`example, the volume. The modular construction according to the present invention that has
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`been outlined above makes it possible to construct the components of hearing aid
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`spectacles with a distribution of the functional modules Bl — BS over components of a
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`hearing aid according to the present invention such that is produced, in which as
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`advantageous as possible a choice can be made with regard to the positioning of the
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`modules B1 - B5 over the components of the hearing aid spectacles. In this context this
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`choice relates to lowering the power consumption or- to adaptation of the functionality to a
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`scenario for a given use condition, as will be explained in more detail below.
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`Figure 2 shows a diagrarmnatic diagram of an embodiment of a hearing
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`aid/spectacles combination according to the present invention. The hearing aid/spectacles
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`combination 1 according to Figure 2 is intended for binaural sound transmission to the
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`user. This leads to a diagrammatic construction in which two signal processing chains for
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`each monaural signal are incorporated individually. The hearing aid/spectacles combination
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`1 comprises a first microphone array 2, a second microphone array 3, a processing unit 4, a
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`first reproduction unit 5 and a second reproduction unit 6.
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`First microphone array 2 is accommodated in. a first spectacle arm of a pair of
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`spectacles, for example the right spectacle arm 2’ (Figure 6). Second micr0phone array 3 is
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`accommodated in a second spectacle arm, in this case the left spectacle arm 3’ (Figure 6).
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`‘ The spectacles are furthermore shown diagrammatically by connection 1’ between first and
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`second microphone array.
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`First microphone array 2 has a wireless link to processing unit 4 by means of a
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`wireless link V1. Second microphone array 3 is linked to processing unit 4 by means of a
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`second wireless link V2.
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`First reproduction unit 5 is linked to processing unit 4 by means of a third wireless
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`link V3. Second reproduction unit 6 is linked to processing unit 4 via a fourth wireless link
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`V4.
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`First microphone array 2 and second microphone array 3 serve, in use, to capture first
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`and second sound signals, respectively, and to transmit these via their respective wireless
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`links V1, V2 to processing unit 4.
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`Processing unit 4 is equipped so as, in use, to receive the first and second sound
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`signals via the respective wireless links V1 and V2 fiom the first microphone array 2 and
`the second microphone array 3, to process the signals and to transmit them to the first
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`reproduction unit 5 and the second reproduction unit 6 via their respective wireless links
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`V3, V4.
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`Processing of the signals received in the processing unit 4 will be explained in more
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`detail below.
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`The first reproduction unit 5 and the second reproduction unit 6 are equipped so as, in
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`use, to receive signals from the processing unit 4 via the third wireless link V3 and,
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`respectively, the fourth wireless link 4 and to feed these as audible audio signals to. the
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`right and the left ear, respectively, of the user.
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`The hearing aid/spectacles combination 1 according to the present invention
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`preferably makes use of analogue techniques to pick up the sound signals from the sound
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`source, of digital techniques to process the signals and of analogue techniques to reproduce
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`the signals.
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`In- the View according to Figure 2, the hearing aid/spectacles combination 1
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`comprises a first and a second signal processing chain, the modules B1, B2, B3, B4 and BS
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`for each individual line being distributed over the components 2, 3, 4, 5 and 6 of the
`hearing aid spectacles 1. This embodiment shows a first example of the way in which
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`modules B1 - BS can be distributed over the components of the hearing aid spectacles. This
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`will be explained in more detail below.
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`In the first embodiment, for example, the sound registration module Bl is
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`accommodated in the spectacle fi'ame near the microphone arrays 2 and 3, the beam
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`forming module B2 together with the reproduction adaptation module B3 and the
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`reproduction control module B5 is accommodated in the processing unit 4 and the
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`reproduction module B4 is accommodated in the reproduction unit 5 and 6.
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`Another embodiment is, for example, hearing aid spectacles in which the sound
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`‘ registration module B1 is accommodated, together with the beam forming module B2, in
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`the microphone arrays 2 and 3, the reproduction adaptation module B3 and the
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`reproduction control module B5 are accommodated in the processing unit 4 and the
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`reproduction module B4 is accommodated in the reproduction unit 5 and 6.
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`A further embodiment is hearing aid spectacles in which the sound registration
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`module B1 is accommodated, together with the beam forming module B2, in the
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`microphone arrays 2 and 3, the reproduction adaptation module B3 is accommodated,
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`together with the reproduction module B4, in the reproduction unit 5 and'6 and the
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`reproduction control module B5 is accommodated in the processing unit 4 or on the
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`spectacles frame.
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`In Figure 10 a general embodiment is shown in which the distribution of the modules
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`can be chosen in accordance with further desired use conditions for the hearing
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`aid/spectacles combination. This will be explained in more detail with reference to Figure
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`l 0.
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`Figure 3 shows a block diagram of first and second microphone array 2, 3 in the first
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`embodiment of the hearing aid/spectacles combination according to the present invention.
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`First microphone array 2 comprises a number of, for example four, microphones M1,
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`M2, M3, M4, analogue/digital converters ADCl, ADC2, ADC3, ADC4, a first multiplexer
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`MPXl and a first transmitter TMTRI . Microphone M1 is connected to an input of
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`analogue/digital converter ADCl. Analogue/digital converter ADCl is connected via its
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`output to a first input of the first multiplexer MPXl. Microphone M2 is connected to an
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`input of analogue/digital converter ADCZ. Analogue/digital converter ADCZ is connected
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`via an output to a second input of the first multiplexer MPXl . Microphone M3 is
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`connected to an input of analogue/digital converter ADC3. Analogue/digital converter
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`ADC3 is connected via its output to a third input of first multiplexer MPXl. Fourth
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`microphone M4 is connected to an input of analogue/digital converter ADC4.
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`Analogue/digital converter ADC4 is connected via its output to a fourth input of the first
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`multiplexer MPXl . MPXl is connected via its output to the first transmitter TMTRl. First
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`microphone array 2 furthermore comprises a power source El , shown diagrammatically,
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`. for supplying the power for the circuit of first microphone array 2.
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`The second microphone array 3 is constructed in a similar manner: in this example
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`second microphone array 3 comprises four microphones M5, M6, M7, M8. Each of the
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`microphones M5, M6, M7, M8 is connected to an input of, respectively, fifth
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`analogue/digital converter ADCS, sixth analogue/digital converter ADC6, seventh
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`analogue/digital converter ADC7 and eighth analogue/digital converter ADCB.
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`Fifth analogue/digital converter ADCS, sixth analogue/digital converter ADC6,
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`seventh analogue/digital converter ADC7 and eighth analogue/digital converter ADC8 are
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`connected via their respective outputs to, respectively, a first input, a second input, a third
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`input and a fourth input of second multiplexer MPX2.
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`Second multiplexer MPX2 is connected at its output to a second transmitter TMTRZ.
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`Second microphone array 2 is provided with a power source E2, shown diagrammatically,
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`for supplying power to the circuit of second microphone array 3.
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`The first transmitter TMTRI and the second transmitter TMTRZ are equipped to
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`transmit sound signals that have been picked up by the microphones M1 to M4 and,
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`respectively, M5 to M8 and have then been digitised and multiplexed, as first and,
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`respectively, second digitised sound signals, for example at radio frequency, Via the
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`respective wireless link V1 and V2.
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`All conceivable transmission techniques are available for the transmission of the first
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`and second digital sound signals. However, it is advisable to take-account of the required
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`dynamic of the signal transfer and the possibility of interference by other transmitters.
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`Significant sources of interference can be GSM telephones and other hearing aid/spectacle
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`combinations. In order as far as possible to restrict GSM radiation-induced interference, the
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`analogue/digital converters ADCl to ADC8 are preferably positioned as close as possible
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`to the microphones. The analogue/digital converters are, for example, constructed as so—
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`. called sigma-delta ADCs. For the requisite dynamic the sigma-delta signals in the ADCs
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`are, for example, processed as samples, which in binary representation contain fourteen or
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`sixteen bits, a sampling frequency of 16 kHz (or higher, for example 32 kHz) being used.
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`The sampled signals are then multiplexed in the multiplexers MPXl , MPX2 and fed
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`as first and second digital multiplexed sound signals to the respective transmitters TMTRl ,
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`TMTRZ.
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`The transmission technology of the transmitters TMTRl , TMTR2 must be robust in
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`connection with the interferences mentioned and comprises a transmitter protocol that is
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`recognised by the processing unit 4 via the wireless link V1, V2.
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`The power supply for the first microphone array 2 and the second microphone array 3
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`by means of their respective power sources E1, E2 must be such that an adequately long
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`period of use of the microphone arrays is possible (for example 18 hours for a day or, for
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`example, 126 hours for a week With a use of 18 hours per day, but another period of use is
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`also practicable). Therefore, in the present invention use is preferably made of micro-
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`electronic building blocks which have a very low power consumption in order to make
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`such a long period of use of the hearing aid/spectacles combination possible.
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`Figure 4 shows a block diagram of a first embodiment of the processing unit 4 of the
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`hearing aid/spectacles combination.
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`Processing unit 4 is a digital device and comprises a first receiver RCVRI, a first
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`demultiplexer DMPXl, a first finite impulse response filter FIRI, a second finite impulse
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`response filter F1R2, a third finite impulse response filter FIR3 and a fourth finite impulse
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`response filter FIR4, a first summator SUMl, a first equaliser/compressor EQCMPRI and
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`a third transmitter TMTR3 for, respectively, reception, processing and transmission of the
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`first digitised multiplexed sound signal that is transmitted by the first microphone array 2
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`via the wireless link V1.
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`Processing unit 4 fiuthermore comprises a second receiver RCVRZ, a second
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`demultiplexer DMPXZ, a fifth finite impulse response filter FIRS, a sixth FIR6, a seventh
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`FIR7 and an eighth FIR8, a second summator SUMZ, a second equaliser/compressor
`EQCMPR2 and a fourth transmitter TMTR4 for, respectively, reception, processing and
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`transmission of the second digitised multiplexed sound signal that has been transmitted by
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`the second microphone array 3 Via its wireless link V2 to the processing unit 4.
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`First receiver RCVRl , which is equipped to receive the signal from first microphone
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`array 2 via the wireless link V1, is connected at its output to an input of first demultiplexer
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`DMPXI. For resolving the signal from first receiver RCVRI into the individual
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`microphone signals, first demultiplexer DMPXl is equipped to demultiplex the signal that
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`has been received at its input from the first received RCVRl and to transmit it via its
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`outputs to finite impulse response filters FIRl to FIR4. For this purpose demultiplexer
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`DMPXl is connected at its first output to the input of first finite impulse response filter
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`FIRl, connected at its second output to the input of second finite impulse response filter
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`FIRZ, connected at its third output to third finite impulse response filter FIR3 and
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`connected at its fourth output to fourth finite impulse response filter FlR4.
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`It is pointed out that the number of finite impulse response filters for the first and the
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`second microphone array 2, 3 preferably corresponds to the number of microphones in each
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`of the microphone arrays.
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`First finite impulse response filter FIRI is connected at its output to a first input of
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`first summator SUMl. Second finite impulse response filter FIR2 is connected at its output
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`to a second input of first summator SUM]. Third finite impulse response filter FIR3 is
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`connected at its output to a third input of first summator SUMl. Finally, fourth finite
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`impulse response filter FIR4 is connected at its output to a fourth input of first surnmator
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`SUM].
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`The combination of finite impulse response filters F[RI to FIR4 and first summator
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`SUMI has the function of first beam former BFl for super-resolution beam forming from
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`the first sound signals picked up by the first microphone array.
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`First summator SUMl is connected at its output to an input of first
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`equaliser/compressor EQCMPRl . An output of first equaliser/compressor EQCMPRI is
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`connected to an input of third transmitter TMTR3.
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`Second receiver RCVRZ, which is equipped to receive signals from second
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`microphone array 3 via the Wireless link V2, is connected at its output to second
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`demultiplexer DMPXZ. Second demultiplexer DMPXZ is connected at its output side via a
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`first output to fifth finite impulse response filter FIRS, via its second output to FIR6, via its
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`third output to FIR7 and Via its fourth output to F1R8. The finite impulse response filters-
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`FIRS to F1R8 are connected at their output to a respective input of second summator
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`SUM2.
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`The combination of finite impulse response filters FIRS to FIR8 and second
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`summator SUM2 has the function of second beam former BFZ for super resolution beam
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`forming from the second sound signals picked up by the second microphone array.
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`Second summator SUM2 is connected at its output to an input of second
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`equaliser/compressor EQCMPRZ. An output of second equaliser/compressor EQCMPRZ is
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`connected to an input of fourth transmitter TMTR4.
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`Furthermore, processing unit 4 contains a control unit CTRLl that is equipped to
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`control the third transmitter TMTR3 and the fourth transmitter TMTR4.
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`Control unit CTRLI is connected by a first input to a fitrther output of first
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`equaliser/compressor EQCMPRI and connected by a second input to a filrther output of
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`second equaliser/compressor BQCMPRZ. Control unit CTRLI is connected via a first
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`output to a further input of third transmitter TMTR3. Control unit CTRLl is connected Via
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`a second output to a further input of fourth transmitter TMTR4. Control unit CTRLl is
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`connected via a third output to first beam former BFl and via a fourth output to second
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`beam former BFZ.
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`For the power supply, processing unit 4 is provided with a power source E3 for
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`supplying power to the circuit of processing unit 4.
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`Third transmitter TMTR3 and fourth transmitter TMTR4 are equipped to transmit
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`signals fed in at their input side, preferably at radio frequency, via a respective wireless link
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`V3, V4 to, respectively, first reproduction unit 5 and second reproduction unit 6.
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`The signals from the first microphone array 2 and the second microphone array 3 are
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`thus each processed separately by applying so—called super—resolution beam forming. The
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`processing of received signals in the processing unit 4 will now be described for a signal
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`received via wireless link V1. Signals that are receiVed via second wireless link V2 are
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`processed in a comparable manner.
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`After receiving a digitised multiplexed sound signal from the first microphone array
`2, the first receiver RCVRl feeds the digitised multiplexed sound signal to first
`demultiplexer DMPXl .
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`The signals from the first microphone array 2 and the second microphone array 3 are
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`thus each processed separately by applying so-called super—resolution beam forming. The
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`processing of the signal will now be discussed with reference to the signal from the first
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`microphone array 2.
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`After the signal from the first microphone array 2 has been received in the receiver
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`RCVRl via the first Wireless link V1, the signal is demultiplexed in first demultiplexer
`DMPXl into a number of separate signals that corresponds to the number ofmicrophones
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`in the first microphone array 2. Via its respective outputs the first demultiplexer DMPXl
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`feeds the separate signals to the respective inputs of the first to fourth finite impulse
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`response filters FlRl to FIR4.
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`After application of the finite impulse response filters, the separate signals are fed to
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`the first summator SUMl, the signals being summed and the desired direction-dependent
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`output signal being preduced. This beam forming technique is disclosed in
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`abovementioned Patent Application WO 99/21400. The first summator SUMl feeds the
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`signal via its output to an input of the first equaliser/compressor EQCMPRl .
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`The first equaliser /compressor EQCMPRI serves to compensate for fiequency-
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`dependent hearing losses on the part of the user (equalisation fimction) and to adapt the
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`amplification of the signal to the sound level that arises (compression function). To this
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`end the compressor part of the first equaliser/compressor EQCMPRI preferably comprises
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`a set of optimised response time and decay time constants. It is also possible that the
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`compressor uses multi-channel frequency-dependent compression. Control unit CTRLI
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`serves to supply a control signal to the first and second equaliser/compressor EQCMPRI,
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`EQCMPRZ, which control signal indicates the way in which the equalisation function and
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`compression function have to be carried out. The control unit CTRLl also ensures that the
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`compression functions in EQCMPRl and EQCMPR2 proceed synchronously and no
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`intentional differences between the compression functions in EQCMPRl and EQCMPRZ
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`arise. It is pointed out that the equalisation function in EQCMPR] and EQCMPR2 can be
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`different, for example because of differences in hearing characteristic of the left ear and the
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`right ear of a user, for which compensation is required.
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`The first equaliser/compressor EQCMPRl feeds the equalised and compressed signal
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`via its output to the third transmitter TMTR3, which then transmits the digital signal via
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`third Wireless link V3.
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`The first control unit CTRLl as shown in processing unit 4 (Figure 3) also serves to
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`transmit reproduction control signals via the third and fourth transmitter TMTR3, TMTR4
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`to the respective first and second reproduction unit 5, 6.
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`With the aid of the reproduction control signal at the second input of the third and/or
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`fourth receiver the further processing in the respective first and second reproduction unit 5,
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`6 is influenced, in accordance with the reproduction control signal that was originally
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`generated by the first control unit CTRLl in the processing unit. Such a reproduction
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`control signal can, for example, be the volume of the reproduction units.
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`The third transmitter TMTR3 is equipped to transmit the direction-dependent output
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`signal, preferably at radio frequency, via the third wireless link V3 to the first reproduction
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`unit 5.
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`In a similar manner a signal that is fed from second microphone array 3 Via the
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`second wireless link V2 to the second receiver RCVRZ of the processing unit 4 is
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`processed to give a second direction-dependent output signal that is transmitted via the
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`fourth wireless link by the fourth transmitter TMTR4 to the second reproduction unit 6.
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`It is pointed out that in Figure 3 multiplexing of the sound signals picked up by the
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`microphones M1, M2, M3, M4; M5, M6, M7, M8 takes place and in Figure 4
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`demultiplexing takes place because of the wireless transmission of the sound signals from
`the sound registration module Bl (the microphone array) to the bundle forming module B2
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`in the first and, respectively, second monaural signal processing chain. In an embodiment
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`in which the sound registration module B1 and the beam forming module B2 are positioned
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`next to one another, multiplexing and demultiplexing can be dispensed with, as can the
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`transmission of the multiplexed signal via TMTRl and TMTR2 and reception of the
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`multiplexed signal via RCVRl and RCVR2.
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`Incidentally, in the case of wireless transmission of the sound signals from the sound
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`registration module B1 to the beam forming module B2 it