HEARING AID COMPRISING A DIRECTIONAL MICROPHONE SYSTEM

Abstract

A hearing aid comprises a BTE-part adapted for being located behind an ear (ear) of a user, and comprising a) a multitude M of microphones, which—when located behind the ear of the user—are characterized by respective transfer functions, H.sub.BTEi(θ, φ, r, k), representative of propagation of sound from sound sources S to the respective microphones b) a memory unit comprising complex, frequency dependent constants W.sub.i(k)′, i=1, . . . , M, c) a beamformer filtering unit for providing a beamformed signal Y as a weighted combination of the microphone signals using said complex, frequency dependent constants The frequency dependent constants are determined to provide a resulting transfer function

H.sub.pinna(θ, φ, r, k)=Σ.sub.i=1.sup.M W.sub.i(k).Math.H.sub.BTEi(θ, φ, r, k),

so that a difference between the resulting transfer function H.sub.pinna(θ, φ, r, k) and a transfer function H.sub.ITE(θ, φ, r, k) of a microphone located close to or in the ear canal fulfils a predefined criterion.

Claims

1. A hearing aid (HD) comprising a part, termed a BTE-part (BTE), adapted for being located in an operational position at of behind an ear (Ear) of a user, the BTE-part comprising A multitude M of microphones (M.sub.BTEii−1, . . . , M) for converting an input sound to respective electric input signals (IN.sub.i, i=1, . . . , M), the multitude of microphones of the BTE-part, when located behind the ear of the user being characterized by transfer functions H.sub.BTEi((θ, φ, r, k), i−1, . . . , M, representative of propagation of sound from sound sources S located at (θ, φ, r) around the hearing aid to the respective microphones (M.sub.BTEi, i=1, . . . , M), when the BTE-part is located at its operational position, (θ, φ, r) representing spatial coordinates and k is a frequency index, a memory unit comprising complex, frequency dependent constants W.sub.i(k)′, i=1, . . . , M, a beamformer filtering unit (BFU) for providing a beamformed signal Y as a weighted combination of said multitude of electric input signals using said complex, frequency dependent constants W.sub.i(k)′, i=1, . . . , M: Y(k)=W.sub.1(k)′.Math.IN.sub.1+ . . . W.sub.M(k)′.Math.IN.sub.M, and wherein said frequency dependent constants W.sub.i(k)′, i=1, . . . , M, are determined to provide a resulting transfer function
H.sub.pinna(θ, φ, r, k)=Σ.sub.i=1.sup.M W.sub.i(k).Math.H.sub.BTEi(θ, φ, r, k), so that a difference between the resulting transfer function H.sub.pinna(74 , φ, r, k) and a transfer function H.sub.ITE(θ, φ, r, k) of a microphone located close to or in the ear canal (ITE) fulfils a predefined criterion,

2. A hearing aid according to claim 1 wherein said predefined criterion comprises a minimization of a difference or distance measure between the resulting transfer function H.sub.pinna(θ, φ, r, k) and the transfer function H.sub.ITE(θ, φ, r, k) of the microphone located close to or in the ear canal.

3. A hearing aid according to claim 1 comprising a hearing instrument, a headset, an earphone, an ear protection device or a combination thereof.

4. A method of determining a multitude M of complex, frequency dependent constants W.sub.i(k)′, representing an optimized fixed beam pattern of a fixed beamformer filtering unit providing a beamformed signal as a weighted combination of said multitude of electric input signals IN.sub.i, i=1, . . . , M, to the beamformer filtering unit, where IN.sub.i are electric input signals provided by a multitude of microphones (M.sub.BTEi, i=1, . . . , M) of a hearing aid, the BTE-part being adapted for being located at or behind an ear of a user, the method comprising Determining respective transfer functions H.sub.BTEi(φ, θ, r, k) and H.sub.ITE(φ, θ, r, k) from sound sources S located at spatial coordinates (θ, φ, r) around the hearing aid to the multitude of microphones (M.sub.BTEi, i=1, . . . , M), and to a microphone located close to or in the car canal (ITE), (φ, θ, r) representing spatial coordinates and k being a frequency index, and Determining said frequency dependent constants W.sub.i(k)′, i=1, . . . M, to provide a resulting transfer function
H.sub.pinna(θ, φ, r, k)=Σ.sub.i=1.sup.M W.sub.i(k).Math.H.sub.BTEi(θ, φ, r, k), so that a difference between the resulting transfer function H.sub.pinna(φ, θ, r, k) and the transfer function H.sub.ITE(φ, θ, r, k) of a microphone located close to or in the ear canal (ITE) fulfils a predefined criterion.

5. A method according to claim 4 wherein said predefined criterion comprises a minimization of a difference or distance measure between the resulting transfer function H.sub.pinna(φ, θ, r, k) and the transfer function H.sub.ITE(φ, θ, r, k) of the microphone located close to or in the ear canal.

6. A method according to claim 4 wherein said predefined criterion comprises determining W.sub.i(k), i=1, . . . , M, to minimize a cost function comprising the resulting transfer function H.sub.pinna(φ, θ, r, k) and the transfer function H.sub.ITE(φ, θ, r, k) of a microphone located close to or in the ear canal (ITE).

7. A method according to claim 4 wherein said predefined criterion comprises determining W.sub.i(k)′, i=1, . . . , M, according to one of the following expressions: $\underset{W_i\left(k\right),\forall i}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math..Math.\log .Math..Math.H_{\mathrm{pinna}}\left(\theta ,\varphi ,r,k\right).Math.-\log .Math..Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math..Math.\right),.Math.\underset{W_i\left(k\right),\forall i}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math.{\left(\log .Math..Math.H_{\mathrm{pinna}}\left(\theta ,\varphi ,r,k\right).Math.-\log .Math..Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math.\right)}^2\right),.Math.\underset{W_i\left(k\right),\forall i}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math..Math..Math.H_{\mathrm{pinna}}\left(\theta ,\varphi ,r,k\right).Math.-.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math..Math.\right),.Math.\underset{W_i\left(k\right),\forall i}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math.{.Math..Math.H_{\mathrm{pinna}}\left(\theta ,\varphi ,r,k\right).Math.-.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math..Math.}^2\right),.Math.\underset{W_i\left(k\right),\forall i}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math.{\left({.Math.H_{\mathrm{pinna}}\left(\theta ,\varphi ,r,k\right).Math.}^2-{.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math.}^2\right)}^2\right),.Math.\underset{W_i\left(k\right),\forall i}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math..Math.{.Math.H_{\mathrm{pinna}}\left(\theta ,\varphi ,r,k\right).Math.}^2-{.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math.}^2.Math.\right),$ where ρ(φ, θ, r, k) is a weighting function, and i=1, . . . , M of is a microphone index.

8. A method according to claim 4 wherein M=2 further comprising Generating first and second fixed beamformers BF1 and BF2 as different weighted combinations of the first and second electric input signals IN.sub.1 and IN.sub.2, respectively, each beamformer being defined by frequency dependent complex weighting parameter sets (W.sub.11(k), W.sub.21(k)) and (W.sub.12(k), W.sub.22(k)), respectively, so that
BF1(k)=W.sub.11(k).Math.IN.sub.1+W.sub.21(k).Math.IN.sub.2,
BF2(k)=W.sub.12(k).Math.IN.sub.1+W.sub.22(k).Math.IN.sub.2, and Generating a beamformed signal Y as a combination of said first and second fixed beamformers BF1 and BF2 according to the following expression
Y(k)=BF1(k)−β(k).Math.BF2(k), where β(k) is a frequency dependent parameter controlling the shape of the directional beam pattern of the beamformer filtering unit.

9. A method according to claim 8 wherein said first and second fixed beamformers BF1 and BF2 are a delay and sum beamformer O and a delay and subtract beamformer C, respectively.

10. A method according to claim 4, wherein said predefined criterion comprises determining W.sub.1(k)′ and W.sub.2(k)′ by minimizing an expression for a distance measure between the beamformed signal Y(θ, φ, r, k) and the transfer function H.sub.ITE(θ, φ, r, k) of a microphone located at or in the ear canal (ITE) with respect to the parameter β(k).

11. A method according to claim 10, wherein said predefined criterion comprises determining W.sub.1(k)′ and W.sub.2(k)′ according to one of the following expressions: $\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math..Math.\log .Math..Math.Y\left(\theta ,\varphi ,r,k,\beta \right).Math.-\log .Math..Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math..Math.\right),.Math.\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math.{\left(\log .Math..Math.Y\left(\theta ,\varphi ,r,k,\beta \right).Math.-\log .Math..Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math.\right)}^2\right),.Math..Math.\underset{\beta \left(k\right)}{a.Math.\mathrm{rgmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math..Math..Math.Y\left(\theta ,\varphi ,r,k,\beta \right).Math.-.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math..Math.\right),.Math..Math.\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math.{.Math..Math.Y\left(\theta ,\varphi ,r,k,\beta \right).Math.-.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math..Math.}^2\right),.Math..Math.\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math.{\left({.Math.Y\left(\theta ,\varphi ,r,k,\beta \right).Math.}^2-{.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math.}^2\right)}^2\right),.Math..Math.\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r,k\right).Math..Math.{.Math.Y\left(\theta ,\varphi ,r,k,\beta \right).Math.}^2-{.Math.H_{\mathrm{ITE}}\left(\theta ,\varphi ,r,k\right).Math.}^2.Math.\right).$ where ρ(φ, θ, r, k) is a weighting function.

12. A method according to claim 7 wherein the weighting function ρ(φ, θ, r, k) is configured to compensate for the fact that some directions and/or frequency ranges are more significant than other directions, and/or to compensate for a non-uniform data collection,

13. A method according to claim 7 wherein the weighting function ρ(θ, φ, r, k) is adaptively determined.

14. A method according to claim 4, wherein the impulse response (h.sub.ITE)/transfer function (H.sub.ITE) of the microphone (M.sub.ITE) located at or in the ear canal is/are normalized with respect to the target direction (e.g. H.sub.ITE(θ.sub.target)=1).

15. A method according to claim 4 wherein the predefined criterion comprises minimizing a directional response of the beamformed signal to have a similar directivity index or a similar front-back ratio compared to the directivity index or the front-back ratio, respectively, of a microphone located at or in the ear canal (ITE).

16. A method according to claim 15 wherein the predefined criterion comprises determining W.sub.1(k) and W.sub.2(k) according to one of the following expressions: $\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(.Math.{\mathrm{DI}}_{\mathrm{pinna}}\left(k\right)-{\mathrm{DI}}_{\mathrm{ITE}}\left(k\right).Math.\right),.Math.\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(.Math.{\mathrm{FBR}}_{\mathrm{pinna}}\left(k\right)-{\mathrm{FBR}}_{\mathrm{ITE}}\left(k\right).Math.\right),$ where the directivity index DI is given as the ratio between the response of the target direction θ.sub.0 and the response of all other directions, and the front-back ratio FBR is the ratio between the responses of the front half plane and the responses of the back half plane: $\mathrm{DI}\left(k\right)={\log }_{10}.Math.\frac{{.Math.R\left({\theta }_0,k\right).Math.}^2}{\int {.Math.R\left(\theta ,k\right).Math.}^2.Math.\rho \left(\theta ,k\right).Math.d.Math..Math.\theta }$ $\mathrm{FBR}\left(k\right)={\log }_{10}.Math.\frac{{\int }_{\mathrm{front}}.Math.{.Math.R\left(\theta ,k\right).Math.}^2.Math.{\rho }_{\mathrm{front}}\left(\theta ,k\right).Math.d.Math..Math.\theta }{{\int }_{\mathrm{back}}.Math.{.Math.R\left(\theta ,k\right).Math.}^2.Math.{\rho }_{\mathrm{back}}\left(\theta ,k\right).Math.d.Math..Math.\theta }$ where ρ.sub.x(θ, k) is a direction-dependent weighting function (x=front, back) either compensating for a non-uniform dataset or in order to take into account that some directions are more significant than other directions.

17. A method according to claim 4 wherein at least one of the transfer functions H.sub.BTE1(θ, φ, r, k), H.sub.BTE2(θ, φ, r, k), and H.sub.ITE(θ, φ, r, k) is determined in less than three dimensions of space, e.g. in two dimensions, such as in a polar plane, and/or only in one dimension, such as in a polar plane, e.g. at one radial distance, e.g. r(=3-5 m, or a distance r.sub.∞ corresponding to the acoustic far field.

18. A method according to claim 4 wherein the transfer function H.sub.ITE(Bθ, φ, r, k) of the microphone located close to or in the ear canal, before being used in said predefined criterion, is modified in one or more frequency bands.

19. A method according to claim 4 comprising fading between an adaptively determined beam pattern and the optimized fixed beam pattern.

20. A method according to claim 4 wherein β(k) is adapted so that null directions or attenuation above a certain threshold, e.g. attenuation larger than 10 dB, on the ipsi-lateral side are avoided to mimic the effect of a natural pinna that does not cancel out sounds completely from any direction.

21. A data processing system comprising a processor and program code means for causing the processor to perform the method of claim 4.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0079] The patent or application file contains at least one color drawings. Copies of this patent or patent application publication with color drawings will be provided by the USPTO upon request and payment of the necessary fee.

[0080] The aspects of the disclosure may be best understood from the following detailed description taken in conjunction with the accompanying figures. The figures are schematic and simplified for clarity, and they just show details to improve the understanding of the claims, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts. The individual features of each aspect may each be combined with any or all features of the other aspects. These and other aspects, features and/or technical effect will be apparent from and elucidated with reference to the illustrations described hereinafter in which:

[0081] FIG. 1A shows a geometrical setup for a listening situation, illustrating a microphone of a hearing aid located at the centre (0, 0, 0) of a spherical coordinate system with a sound source located at (θ, φ, r), and

[0082] FIG. 1B shows a hearing aid user wearing left and right hearing aids in a listening situation comprising different sound sources located at different points in space relative to the user,

[0083] FIG. 2A shows a hearing aid comprising a BTE part having two microphones operationally mounted behind an ear of the user, and

[0084] FIG. 2B shows a hearing aid comprising a BTE part having three microphones operationally mounted behind an ear of the user,

[0085] FIG. 3 shows an example of a directional polar response for a given frequency band k for a BTE-microphone (bold solid line), for an optimally located (ear canal) microphone (thin solid line), and for an optimized BTE-microphone (bold dashed line) according to the present disclosure,

[0086] FIG. 4 shows examples of directional polar responses at different frequency bands having center frequencies from from 150 Hz (upper left graph) to 8 kHz (lower right graph) for an omni-directional beamformer (sum of two BTE-microphones), for an optimally located (ear canal, CIC) microphone, and for an optimized BTE-microphone according to the present disclosure,

[0087] FIG. 5A shows a block diagram of a first exemplary 2-microphone beamformer configuration for use in a hearing aid according to the present disclosure, and

[0088] FIG. 5B shows a block diagram of a second exemplary 2-microphone beamformer configuration for use in a hearing aid according to the present disclosure,

[0089] FIG. 6A shows a block diagram of a third exemplary 2-microphone beamformer configuration for use in a hearing aid according to the present disclosure, and

[0090] FIG. 6B shows an equivalent block diagram of the third exemplary 2-microphone beamformer configuration for use in a hearing aid according to the present disclosure,

[0091] FIG. 7A shows a block diagram of a first embodiment of a hearing aid according to the present disclosure, and

[0092] FIG. 7B shows a block diagram of a second embodiment of a hearing aid according to the present disclosure,

[0093] FIG. 8A shows a first embodiment of a hearing aid according to the present disclosure comprising a BTE-part located behind an ear of a user and an ITE part located in an ear canal of the user, and

[0094] FIG. 8B shows a second embodiment of a hearing aid according to the present disclosure comprising a BTE-part located behind an ear of a user and an ITE part located in an ear canal of the user,

[0095] FIG. 9 shows a flow diagram for an embodiment of a method of determining optimized first and second sets of filter coefficients w.sub.1 and w.sub.2 and/or first and second complex, frequency dependent constants W.sub.1(k) and W.sub.2(k) of a fixed beamformer filtering unit. and

[0096] FIG. 10 illustrates a hearing aid comprising a user interface implemented in an auxiliary device according to the present disclosure.

[0097] The figures are schematic and simplified for clarity, and they just show details which are essential to the understanding of the disclosure, while other details are left out. Throughout, the same reference signs are used for identical or corresponding parts.

[0098] Further scope of applicability of the present disclosure will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only. Other embodiments may become apparent to those skilled in the art from the following detailed description.

DETAILED DESCRIPTION OF EMBODIMENTS

[0099] The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practised without these specific details. Several aspects of the apparatus and methods are described by various blocks, functional units, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements”). Depending upon particular application, design constraints or other reasons, these elements may be implemented using electronic hardware, computer program, or any combination thereof.

[0100] The electronic hardware may include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. Computer program shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0101] The present application relates to the field of hearing aids, e.g. hearing instruments configured to augment a hearing sensation of a user, e.g. to compensate for a hearing impairment. The application relates to the capture of sound signals around the user using microphones located on the user's body, e.g. at an ear, such as behind an ear of the user. Specifically when a sound signal is picked up by microphones located in a BTE-part behind an ear of a user, the microphones will have a tendency to (over-) emphasize signals from behind the user compared to signals from a frontal direction (cf. e.g. H.sub.BTE in FIG. 3). The present disclosure provides a scheme for compensating an inherent preference to signals from other directions than a target direction (e.g. the front) in a hearing aid comprising microphones located at non-ideal positions away from the ear canal).

[0102] FIG. 1A shows a geometrical setup for a listening situation, illustrating a microphone (M) of a hearing aid located at the centre (0, 0, 0) of a coordinate system (x, y, z) or (θ, r) with a sound source S.sub.s located at (x.sub.s, y.sub.s, z.sub.s) or (θ.sub.s, φ.sub.s, r.sub.s). FIG. 1A defines coordinates of a spherical coordinate system (θ, φ, r) in an orthogonal coordinate system (x, y, z). A given point in three dimensional space, here illustrated by a location of sound source S.sub.s, is represented by a vector r.sub.s from the center of the coordinate system (0, 0, 0) to the location (x.sub.s, y.sub.s, z.sub.s) of the sound source S.sub.s in the orthogonal coordinate system. The same point is represented by spherical coordinates (θ.sub.s, φ.sub.s, r.sub.s) where r.sub.s is the radial distance to the sound source S.sub.s, φ.sub.s is the (polar) angle from the z-axis of the orthogonal coordinate system (x, y, z) to the vector r.sub.s, and θ.sub.s, is the (azimuth) angle from the x-axis to a projection of the vector r.sub.s in the xy-plane (z=0) of the orthogonal coordinate system.

[0103] FIG. 1B shows a hearing aid user (U) wearing left and right hearing aids (HD.sub.L, HD.sub.R) (forming a binaural hearing aid system) in a listening situation comprising different sound sources (S.sub.1, S.sub.2, S.sub.3) located at different points in space (θ.sub.s, r.sub.s, (φ.sub.s=φ.sub.0), s=1, 2, 3) relative to the user (or the same sound source S located at different positions (1, 2, 3)). Each of the left and right hearing aids (HD.sub.L, HD.sub.R) comprises a part, termed a BTE-part (BTE). Each BTE-part (BTE.sub.L, BTE.sub.R) is adapted for being located behind an ear (Left ear, Right ear) of the user (U). A BTE-part comprises first (‘Front’) and second (‘Rear’) microphones (M.sub.BTE1,L, M.sub.BTE2,L; M.sub.BTE1,R, M.sub.BTE2,R) for converting an input sound to first IN.sub.1 and second IN.sub.2 electric input signals (cf. e.g. FIG. 5A, 5B), respectively. The first and second microphones (M.sub.BTE1, M.sub.BTE2) of a given BTE-part, when located behind the relevant ear of the user (U), are characterized by transfer functions H.sub.BTE1(θ, φ, r, k) and H.sub.BTE2(θ, φ, r, k) representative of propagation of sound from a sound source S located at (θ, φ, r) around the BTE-part to the first and second microphones of the hearing aid (HD.sub.L, HD.sub.R) in question, where k is a frequency index. In the setup of FIG. 1B, the target signal is assumed to be in the frontal direction relative to the user (U) (cf. e.g. LOOK-DIR (Front) in FIG. 1B), i.e., (roughly) in the direction of the nose of the user, and of a microphone axis of the BTE-parts (cf. e.g. reference directions REF-DIR.sub.L, REF-DIR.sub.R, of the left and right BTE-parts (BTE.sub.L, BTE.sub.R) in FIG. 1B). The sound source(s) (S.sub.1, S.sub.2, S.sub.3) are located around the user as defined by spatial coordinates, here spherical coordinates (θ.sub.s, φ.sub.s, r.sub.s), s=1, 2, 3, defined relative to the reference directions REF-DIR.sub.L for the left hearing aid (HD.sub.L) (and correspondingly to REF-DIR.sub.R for the right hearing aid, HD.sub.R).

[0104] The sound source(s) (S.sub.1, S.sub.2, S.sub.3) are intended to schematically illustrate a measurement of transfer functions of sound from all relevant directions (defined by azimuth angle θ.sub.s) and distances (r.sub.5) around the user (U). The directions for the left hearing aid HD.sub.L to the sound sources S.sub.s are indicated in FIG. 1B by DIR.sub.Ss,L, s=1, 2, 3. The first and second microphones of a given BTE-part are located at predefined distance ΔL.sub.M apart (often referred to as microphone distance d). The two BTE-parts (BTE.sub.L, BTE.sub.R) and thus the respective microphones of the left and right BTE-parts, are located a distance a apart, when mounted on the user's head in an operational mode. The view in FIG. 1B is a planar view in a horizontal plane through the microphones of the first and second hearing aids (perpendicular to a vertical direction, indicated by out-of-plane arrow VERT-DIR in FIG. 1B) and corresponding to plane z=0(φ=90°) in FIG. 1A. In a simplified model, it is assumed that the sound sources (S.sub.i) are located in a horizontal plane (e.g. the one shown in FIG. 1B).

[0105] FIG. 2A shows an exemplary use case of a hearing aid (HD) according to the present disclosure. The hearing aid (HD) comprises a BTE part (BTE) comprising two microphones (M1, M2, denoted BTE microphones, M.sub.BTE1, M.sub.BTE2 in FIG. 2A) is mounted in an operational position behind an ear (Ear) of the user. In addition to the BTE-part containing two microphones, the hearing aid may comprise further parts, e.g. an ITE-part adapted for being located at or in the ear canal. The ITE-part may e.g. comprise a loudspeaker for presenting sound to the user (cf. e.g. FIG. 8). Alternatively or additionally, the hearing aid may comprise a fully or partially implanted part for electrically stimulating the cochlear nerve or a vibrator for transferring vibrations representing sound to bones of the skull. Since the BTE-part comprising the BTE microphones is placed at, and typically behind, the ear (pinna, Ear in FIG. 2A), even if located in an upper section of the BTE-part (as shown in FIG. 2A), the spatial perception of sound direction becomes disturbed (due to the shadowing effect of pinna towards sound from the front (and other directions of the frontal half plane, and from certain angles of the rear half-plane as well). The most natural spatial perception can be obtained by having a microphone placed close to the eardrum, e.g. at or in the ear canal (cf. indication Ideal microphone position, (ITE (test) microphone) in FIG. 2A). When the BTE-part is properly mounted at the ear of the user, the BTE-microphones (M.sub.BTE1, M.sub.BTE2) are preferably located horizontally so that a line through the two microphones defines front and rear directions relative to the user (cf. dotted arrow denoted Front and Back in FIG. 2A). In an embodiment, the only microphones of the hearing aid are the BTE-microphones, e.g. two BTE-microphones as illustrated in FIG. 2A. In an embodiment, the hearing aid comprises more than two microphones, e.g. three or more. In an embodiment, the hearing aid optionally comprises a microphone (termed an ITE-microphone) located near the ideal microphone position, e.g. at or in the ear canal (cf. e.g. FIG. 8). In an embodiment, the ITE-microphone is used to pick up sound from the environment in a first mode of operation, whereas the BTE-microphones are used to pick up sound from the environment in a second mode of operation (e.g. if feedback from the output transducer (e.g. a loudspeaker) to the ITE-microphone is of concern). In a further mode of operation, a combination of the BTE-microphones and the ITE-microphones is used to generate a beamformed signal (e.g. if a large directivity is intended).

[0106] FIG. 2B shows a hearing aid comprising a BTE part having three (instead of two as in FIG. 2A) microphones operationally mounted behind an ear of the user. The embodiment of FIG. 2B resembles the embodiment of FIG. 2B but the BTE-part comprises three microphones. In this embodiment, the BTE-microphones (M.sub.BTE1, M.sub.BTE2, M.sub.BTE3) are not located in the same horizontal plane (the first and second microphones M.sub.BTE1 and M.sub.BTE2 are located in a horizontal plane, whereas the third microphone M.sub.BTE3 is not). Preferably in a triangle, where two of the microphones are located in the horizontal plane. This has the advantage of increasing the opportunities of forming a directional pattern, e.g. that the directional pattern can be adapted not only to the directional ITE response in the horizontal plane, but the directional pattern towards the directional ITE response measured at other elevation angles can also be optimized.

[0107] FIG. 3 shows an example of a directional polar response for a given frequency band (k) for a BTE-microphone (bold solid line), for an optimally located (ear canal) microphone (thin solid line), and for an optimized BTE-microphone (bold dashed line) according to the present disclosure. The BTE-microphone may e.g. be one of the BTE-microphones (M.sub.BTE1, M.sub.BTE2) as shown in FIG. 1B or FIG. 2A. The optimally located (ear canal) microphone may e.g. be an ITE-microphone as illustrated in FIG. 2A (ITE (test) microphone) or ITE-microphone (M.sub.ITE) of FIG. 8. The polar response for the optimized BTE-microphone may e.g. represent the polar response of beamformed signal Yin FIG. 5A, 5B or FIG. 6A, 6B or FIG. 7A, 7B.

[0108] FIG. 3 illustrates and example showing the directional polar response for a given frequency band, e.g. above 1.5 kHz for a scenario as illustrated by left hearing aid (HD.sub.L) in FIG. 1B. The directional response is shown for the horizontal plane only (e.g. z=0 (φ=90°) in FIG. 1A, 1B), but it is easy to imagine that also the response from other elevation angles (φ≠90°) are included (spherical response). Due to the head location and the shadowing effect of the head (cf. e.g. dashed part of path r.sub.2 from source S.sub.2 to the (front) BTE-microphone M.sub.BTE1,L of left hearing aid (HD.sub.L) in FIG. 1B), the response (of the left ear) has an asymmetric left-right response (cf. e.g. point H.sub.BTE(2 π-θ.sub.2,k) for location of source S.sub.2 in FIG. 3). Due to the position behind the ear (cf. e.g. FIG. 1B), the directional response of the BTE microphone(s) has significantly more gain towards the back (cf. e.g. point H.sub.BTE(π−θ.sub.3,k) for location of source S.sub.3 in FIG. 3) compared to an optimal microphone position closer to the eardrum (cf. thin line polar plot denoted Optimal microphone location in FIG. 3). Signals from the front of the user are attenuated by the ear (pinna), ‘behind’ which the BTE-part comprising the BTE-microphones is situated (cf. e.g. point H.sub.BTE(θ.sub.1,k) for location of source S.sub.1 in FIG. 3). The (unmodified) directional BTE response (cf. polar plot denoted BTE microphone in FIG. 3) is thus likely to introduce front-back localization confusions. The ‘data points’ (three shaded circles) of the transfer function for a BTE-microphone (located at the left ear), corresponding to directions defined by angles θ.sub.1, θ.sub.2, θ.sub.3, illustrate that the response H.sub.BTE(π−θ.sub.3,k) from the rear (S.sub.3) is larger than a response from the front H.sub.BTE(θ.sub.1,k) (S.sub.1), which again is larger than a response H.sub.BTE(2 π−θ.sub.2,k) from the right (S.sub.2) (cf. indications 1, 2, 3, 4, on the dashed circles having their center at the left ear microphone(s)). It is assumed that the sound sources S.sub.1, S.sub.2, S.sub.3 are located at substantially the same distance r from the left ear of the user (r.sub.1=r.sub.2=r.sub.3).

[0109] By combining the directional response of the two (or more) BTE microphones (providing polar plot denoted Optimized BTE response in FIG. 3), it is possible to obtain a directional response of the BTE hearing instrument, which is closer to the response at the ear canal (cf. polar plot denoted Optimal microphone location in FIG. 3).

[0110] It is possible to obtain a dataset consisting of recorded measured (or simulated or both) hearing aid microphone responses h.sub.BTE1(θ, φ, r), h.sub.BTE2 (θ, φ, r) from different locations. h.sub.BTE1(θ, φ, r) and h.sub.BTE2 (θ, φ, r) are vectors formulated in the time domain, but could as well consist of (complex) numbers formulated in the frequency domain H.sub.BTE1(θ, φ, r, k) and H.sub.BTE2 (θ, φ, T, k), where k is a frequency (band) index. Further a similar recorded (or simulated or both) microphone response close to or in the ear canal (ITE), h.sub.ITE (θ, φ, r) or H.sub.ITE (θ, φ, r, k) (Containing the correct pinna reflections) may be obtained. θ indicates the azimuth angle, φ is the elevation angle, and r is the source distance from the microphone in question. By combining the recorded BTE microphone signals (1 and 2) it is possible to obtain a different directional transfer function which is better at mimicking the pinna (here formulated in the time-domain), i.e.

h.sub.pinna(θ, φ, r)=w.sub.1*h.sub.BTE1(θ, φ, r)+w.sub.2* h.sub.BTE2(θ, φ, r),

where w.sub.1 and w.sub.2 are filters applied to the first and the second microphone signals, respectively, and * denotes the convolution operator. Our objective is thus to find w.sub.1 and w.sub.2 (optimized sets, w.sub.1′ and w.sub.2′, of filter coefficients) such that a difference measure, e.g. the (magnitude) response difference, between the BTE pinna response and the ideal directional response is minimized, i.e. fulfills the following expression

[00006]$\underset{w_1,w_2}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r\right).Math.{\left(\log .Math..Math.h_{\mathrm{pinna}}\left(\theta ,\varphi ,r\right).Math.-\log .Math..Math.h_{\mathrm{ITE}}\left(\theta ,\varphi ,r\right).Math.\right)}^2\right),$

where ρ(θ, φ, r) is a weighting function.

[0111] One could as well imagine other cost functions or distance measures:

[00007]$\underset{w_1,w_2}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r\right).Math..Math.\log .Math..Math.h_{\mathrm{pinna}}\left(\theta ,\varphi ,r\right).Math.-\log .Math..Math.h_{\mathrm{ITE}}\left(\theta ,\varphi ,r\right).Math..Math.\right),.Math.\underset{w_1,w_2}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r\right).Math..Math..Math.h_{\mathrm{pinna}}\left(\theta ,\varphi ,r\right).Math.-.Math.h_{\mathrm{ITE}}\left(\theta ,\varphi ,r\right).Math..Math.\right),.Math.\underset{w_1,w_2}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r\right).Math.{.Math..Math.h_{\mathrm{pinna}}\left(\theta ,\varphi ,r\right).Math.-.Math.h_{\mathrm{ITE}}\left(\theta ,\varphi ,r\right).Math..Math.}^2\right),.Math.\underset{w_1,w_2}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r\right).Math.{\left({.Math.h_{\mathrm{pinna}}\left(\theta ,\varphi ,r\right).Math.}^2-{.Math.h_{\mathrm{ITE}}\left(\theta ,\varphi ,r\right).Math.}^2\right)}^2\right),.Math.\underset{w_1,w_2}{\mathrm{argmin}}\left(\underset{\theta ,\varphi ,r}{.Math.}.Math..Math.\rho \left(\theta ,\varphi ,r\right).Math..Math.{.Math.h_{\mathrm{pinna}}\left(\theta ,\varphi ,r\right).Math.}^2-{.Math.h_{\mathrm{ITE}}\left(\theta ,\varphi ,r\right).Math.}^2.Math.\right),$

[0112] The cost function can easily be expanded to include more than two microphones.

[0113] The criteria may alternatively be expressed in the time-frequency domain to provide optimized complex, frequency dependent parameters W.sub.1(k)′ and W.sub.2(k)′, based on transfer functions H.sub.x(θ, φ, r, k) (where x=pinna, ITE, and k is a frequency index).

[0114] The weighting function ρ(θ, φ, r) can be used to compensate e.g. if the data are not uniformly recorded (e.g. conversion to spherical coordinates), or for emphasizing perceptual significant directions in the optimization, or to introduce a dependence of a current direction to the target (or dominating) signal.

[0115] FIG. 3 illustrates the principle of the proposed scheme. In this case, we solely consider the directional response in the horizontal plane (φ=90°, cf. FIG. 1A), e.g. for a predetermined distance or range of distances r between sound source S.sub.s (s=1, 2, 3 in FIG. 3) and hearing aid microphones (M in FIG. 1A), e.g. in the acoustic far field. In this case, for a given frequency band (k), we have found the optimal combination of the BTE microphones in order to achieve a response similar to an in-the-ear microphone response, i.e.

[00008]$\underset{W_i\left(k\right),W_2\left(k\right)}{\mathrm{argmin}}\left(\underset{\theta }{.Math.}.Math..Math.{\left(\log .Math..Math.H_{\mathrm{pinna}}\left(\theta ,k\right).Math.-\log .Math..Math.H_{\mathrm{ITE}}\left(\theta ,k\right).Math.\right)}^2\right),$

where k denotes the frequency band index.

[0116] Often the response of the BTE microphones is constrained such that the response at a certain direction (and/or frequency) has a response similar to the response at the ideal microphone location for the same direction. This may e.g. be achieved by combining the microphones such that the combined response Y(k) is given by

Y(k)=O(k)−β(k)C(k),

where O(k) is an omnidirectional delay and sum beamformer having a desired response in the target direction θ.sub.0 and C (k) is a target cancelling beamformer having a null response towards the target direction, cf. e.g. EP2701145A1. β(k) is a, possibly complex numbered, parameter controlling the shape of the directional beam pattern. As β is applied to the target cancelling beamformer, the response towards the target direction is independent of β. We thus only have a single parameter to optimize, i.e.

[00009]$\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(\underset{\theta }{.Math.}.Math..Math.{\left(\log .Math..Math.Y\left(\theta ,k,\beta \right).Math.-\log .Math..Math.H_{\mathrm{ITE}}\left(\theta ,k\right).Math.\right)}^2\right),$

[0117] The minimization of the expression above may e.g. be found by an exhaustive search across a range of β-values. Other methods, e.g. minimization algorithms, may be used.

[0118] Contrary to minimizing the difference between the in-the-ear transfer functions and the hearing instrument transfer functions one could also imagine a cost function based on other measures, such as optimizing towards having a directional response with a similar directivity index (DI) or a similar front-back ratio (FBR) compared to the in-the-ear recordings, i.e.

[00010]$\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(.Math.{\mathrm{DI}}_{\mathrm{pinna}}\left(k\right)-{\mathrm{DI}}_{\mathrm{ITE}}\left(k\right).Math.\right),.Math.\underset{\beta \left(k\right)}{\mathrm{argmin}}\left(.Math.{\mathrm{FBR}}_{\mathrm{pinna}}\left(k\right)-{\mathrm{FBR}}_{\mathrm{ITE}}\left(k\right).Math.\right),$

where the DI is given as the ratio between the response of the target direction θ.sub.0 and the response of all other directions, and the FBR is the ratio between the responses of the front half plane and the responses of the back half plane:

[00011]$\mathrm{DI}={\log }_{10}.Math.\frac{{.Math.R\left({\theta }_0\right).Math.}^2}{\int {.Math.R\left(\theta \right).Math.}^2.Math.\rho \left(\theta \right).Math.d.Math..Math.\theta }$$\mathrm{FBR}={\log }_{10}.Math.\frac{{\int }_{\mathrm{front}}.Math.{.Math.R\left(\theta \right).Math.}^2.Math.{\rho }_{\mathrm{front}}\left(\theta \right).Math.d.Math..Math.\theta }{{\int }_{\mathrm{back}}.Math.{.Math.R\left(\theta \right).Math.}^2.Math.{\rho }_{\mathrm{back}}\left(\theta \right).Math.d.Math..Math.\theta }$

[0119] where ρ(θ) is a direction-dependent weighting function either compensating for a non-uniform dataset or in order to take into account that some directions are more significant than other directions. The dependence on a front-back ratio (FBR) in the above expressions may alternatively be substituted by a ratio between any two appropriately selected ranges of directions.

[0120] FIG. 4 shows examples of directional polar responses at different frequencies from 150 Hz (upper left graphs) to 8 kHz (lower right graphs) for an omni beamformer (sum of two BTE-microphones, denoted Omni response (EO) in FIG. 4), for an optimally located microphone (denoted CIC response (ITE) in FIG. 4), and for an optimized BTE-microphone response according to the present disclosure (denoted Optimized pinna response (OPT) in FIG. 4). FIG. 4 is intended to (schematically) illustrate the frequency dependence of the polar response of microphones (which is at least partially due to the different propagation and reflection properties of the human body and the different resonance properties of the ear (pinna) at different frequencies). It further illustrates that the resemblance of the optimized response of two BTE-microphones to that of the optimally located microphone is different at different frequencies. The optimized response generally depends on the predefined criterion used to determine sets of filter constants w.sub.1′, w.sub.2′of the fixed optimized beamformer (or equivalently the complex, frequency dependent parameters W.sub.1(k)′, W.sub.2(k)′). A close to perfect fit is observed at relatively low frequencies (reflecting that the response of the BTE- and optimally located microphone are nearly equal at frequencies below 1.5 kHz). It is typically not possible to get a ‘perfect fit’ of the two responses over all frequencies, which is clearly reflected in the example of FIG. 4 by comparison of responses at approximately 8.3 kHz (lower right graphs) and 3.7 kHz (lower left graphs). At 3.7 kHz, the optimized response (OPT) is close to the response (ITE) for the optimally located microphone. At 8.3 kHz, all three responses are different, and the optimized response (OPT) is relatively far from the response (ITE) for the optimally located microphone. The weighting function ρ(θ, φ, r) may be used to manage the occurrence of such differences, e.g. to emphasize the importance of certain frequencies (e.g. where speech content is predominant, e.g. below 4 kHz). The measured transfer function H.sub.ITE at 8.3 kHz actually exhibits a higher gain in a backward direction (front direction is indicated by arrow denoted Front in FIG. 4). To avoid this bias, the transfer function H.sub.ITE at relatively high frequencies (e.g. the highest frequency band) may be modified (before it is used in the optimization procedure for determining complex weights W.sub.i(k)′ or filter coefficients w, or adaptation parameter β(k).

[0121] FIG. 5A shows a block diagram of a first exemplary two-microphone beamformer configuration for use in a hearing aid according to the present disclosure. The hearing aid comprises first and second microphones (M.sub.BTE1, M.sub.BTE2) for converting an input sound (Sound) to first IN.sub.1 and second IN.sub.2 electric input signals, respectively. A front direction and the direction from the target signal to the hearing aid is e.g. defined by the microphone axis and indicated in FIG. 5A (and 5B) by arrows denoted Front and Target sound, respectively (cf. REF-DIR in FIG. 1B). The first and second microphones (when located behind the ear of the user) are characterized by time-domain impulse responses h.sub.BTE1(θ, φ, r) and h.sub.BTE2(θ, φ, r) (or transfer functions H.sub.BTE1(θ, φ, r, k) and H.sub.BTE2(θ, φ, r, k) in the time-frequency domain) representative of propagation of sound from sound source S located at (θ, φ, r) around the hearing aid to the first and second microphones (M.sub.BTE1, M.sub.BTE2). The hearing aid comprises a memory unit (MEM) comprising filter coefficients w.sub.1′(w.sub.10, w.sub.11, w.sub.12, . . . ) and w.sub.2′ (w.sub.20, w.sub.21, w.sub.22, . . . ). The hearing aid further comprises a beamformer filtering unit (BFU) for providing a beamformed signal Y (denoted Pinna BF) as a weighted combination of the first and second electric input signals using said filter coefficients w.sub.1 and w.sub.2: Y=w.sub.1′*IN.sub.1+w.sub.2′*IN.sub.2, where * denotes the convolution operator. In FIG. 5A the convolution operator “*” is represented by filters (e.g. FIR filters, applying filter coefficients w.sub.1′ and w.sub.2′, respectively), whereas ‘+’ represent a summation unit. The filter coefficients w.sub.1′ and w.sub.2′ are determined (in advance of use of the hearing aid and stored in the memory unit MEM) to provide a resulting impulse response

h.sub.pinna(θ, φ, r)=w.sub.1*h.sub.BTE1(θ, φ, r)+w.sub.2* h.sub.BTE2(θ, φ, r),

so that a difference between the resulting impulse response h.sub.pinna(θ, φ, r, k) and an impulse response h.sub.ITE(θ, φ, r) of a microphone located close to or in the ear canal (ITE) fulfils a predefined criterion.

[0122] FIG. 5B shows a block diagram of a second exemplary two-microphone beamformer configuration for use in a hearing according to the present disclosure. The beamformer configuration of FIG. 5B is equal to that of FIG. 5A, except that the beamformer configuration of FIG. 5B is configured to operate in the time-frequency domain. The beamformer configuration FIG. 5B comprises first and second microphones (M.sub.BTE1, M.sub.BTE2) for converting an input sound to first IN.sub.1 and second IN.sub.2 electric input signals, respectively.

[0123] First and second analysis filter bank units (FBA1 and FBA2) convert first and second time domain signals IN.sub.1 and IN.sub.2 to time-frequency domain signals IN.sub.i(k), i=1, 2, and k=1, 2, . . . , K, where K is the number of frequency bands. The memory unit (MEM) contains first and second complex constants W.sub.1(k)′, W.sub.2(k)′ (for each frequency band i=1, 2, . . . , K).

[0124] The beamformer filtering unit (BFU) is configured to provide beamformed signal Y as a weighted combination of the first and second electric input signals using the complex, frequency dependent constants W.sub.1(k)′ and W.sub.2(k)'stored in the memory unit (MEM): Y(k)=W.sub.1(k)′.Math.IN.sub.1+W.sub.2(k)′.Math.IN.sub.2, k=1, 2, . . . , K (denoted Pinna BF). In FIG. 5B units ‘x’ represent multiplication units for multiplying complex constants W.sub.1(k)′ and W.sub.2(k)′ onto respective band signals IN.sub.1(k) and IN.sub.2(k), respectively, k=1, 2, . . . , K, whereas ‘+’ represent summation units. The complex constants W.sub.1(k)′ and W.sub.2(k)′ are determined (optimized) (in advance of use of the hearing aid and stored in the memory unit MEM) to provide a resulting transfer function:

H.sub.pinna(θ, φ, r, k)=W.sub.1(k).Math.H.sub.BTE1(θ, φ, r, k)+W.sub.2(k).Math.H.sub.BTE2(θ, φ, r, k),

so that a difference between the resulting transfer function H.sub.pinna (θ, φ, r, k) and a transfer function H.sub.ITE(θ, φ, r, k) of a microphone located close to or in the ear canal (ITE) fulfils a predefined criterion.

[0125] FIG. 6A shows a block diagram of a third exemplary two-microphone beamformer configuration for use in a hearing aid according to the present disclosure. The beamformer configuration of FIG. 6A comprises first and second microphones (M.sub.BTE1, M.sub.BTE2) for converting an input sound to first IN.sub.1 and second IN.sub.2 electric input signals, respectively. A direction from the target signal to the hearing aid is e.g. defined by the microphone axis and indicated in FIG. 6A (and 6B) by arrow denoted Target sound. The beamformer unit (BFU) comprises first and second fixed beamformers BF1 and BF2 in the form of different, weighted combinations of the first and second electric input signals IN.sub.1 and IN.sub.2, respectively. The first beamformer BF1 may represent a delay and sum beamformer providing (enhanced) omni-directional signal O. The second beamformer BF2 may represent a delay and subtract beamformer providing target-cancelling signal C. Each beamformer BF1, BF2 may be defined by frequency dependent complex weighting parameter sets (W.sub.11(k)=W.sub.1o(k), W.sub.21(k)=W.sub.2o(k)) and (W.sub.12(k)=W.sub.1c(k), W.sub.22(k)=W.sub.2c(k)), respectively, so that the fixed beamformers are given by

O=BF1(k)=W.sub.1o(k).Math.IN.sub.1+W.sub.2o(k).Math.IN.sub.2,

C=BF2(k)=W.sub.1c(k).Math.IN.sub.1+W.sub.2c(k).Math.IN.sub.2,

[0126] In the embodiment of FIG. 6A, each of the first and second beamformers BF1, BF2 are implemented in the time-frequency domain (appropriate filter banks being implied) by two multiplication units ‘x’ and a sum unit ‘+’. The beamformer unit (BFU) comprises a further beamformer (implemented by further multiplication ‘x’ and summation units ‘+’) for generating beamformed signal Y as a combination of said first and second fixed beamformers BF1 and BF2 (or beamformed signals) according to the following expression

Y(k)=BF1(k)−β(k).Math.BF2(k),

Y=O−βC

where β(k) is a frequency dependent parameter controlling the final shape of the directional beam pattern (of signal Y) of the beamformer filtering unit (BFU). In an embodiment, β represents the optimized beamformer based on a predefined criterion to minimize a difference between the polar response of the second (target cancelling) beamformer and the polar response of a microphone located at the ideal position at or in the ear canal. Since β(k) is only multiplied to the target cancelling beamformer (C), the response towards the target direction will (ideally) be unaffected when β(k) changes. The complex weighting parameter sets (W.sub.1o(k), W.sub.2o(k)), (W.sub.1c(k), W.sub.2c(k)), and β(k) are preferably stored in the memory unit MEM of the beamformer unit (BFU) or elsewhere in the hearing aid (e.g. implemented in firmware of hardware).

[0127] FIG. 6B shows an equivalent block diagram of the exemplary two-microphone beamformer configuration shown in FIG. 6A. By insertion of the complex constants in the logic diagram of FIG. 6A, and re-arranging the elements, the following expression for Y appears:

Y(k)=(W.sub.1o(k)−β(k).Math.W.sub.1c(k)).Math.IN.sub.1+(W.sub.2o(k)−β(k).Math.W.sub.2c(k)).Math.IN.sub.2,

[0128] Hence the beamformer unit (BFU) of FIG. 6A may be implemented as the beamformer unit (BFU) of FIG. 6B where optimized complex constants W.sub.1=W.sub.1o(k)−β(k).Math.W.sub.1c(k) and W.sub.2=W.sub.2o(k)−β(k).Math.W.sub.2c(k) are stored in memory unit (MEM). The optimized constants W.sub.1(k)′ and W.sub.2(k)′ are determined by minimizing an expression for a distance measure (for each frequency band k) between the beamformed signal Y(θ, φ, r, k) and the transfer function H.sub.ITE(θ, φ, r, k) of a microphone located at or in the ear canal (ITE) with respect to the parameter β(k). This configuration has the advantage that a single parameter β (for each frequency band, k) can be used to optimize the predefined criterion. This comes at the cost of requiring that a signal from the target direction in principle is unaltered (cannot be attenuated).

[0129] FIG. 7A shows a block diagram of a first embodiment of a hearing aid according to the present disclosure. The hearing aid of FIG. 7A comprises a 2-microphone beamformer configuration as shown in FIG. 5A and a signal processing unit (SPU) for (further) processing the beamformed signal Y and providing a processed signal OUT. A direction from the target signal to the hearing aid is e.g. defined by the microphone axis and indicated in FIG. 7A (and 7B) by arrow denoted Target sound. The signal processing unit may be configured to apply a level and frequency dependent shaping of the beamformed signal, e.g. to compensate for a user's hearing impairment, and/or to compensate for the microphone location effect (MLE), and/or to compensate for an ear canal being blocked by an ear mould. The processed signal (OUT) is fed to an output unit for presentation to a user as a signal perceivable as sound. In the embodiment of FIG. 7A, the output unit comprises a loudspeaker (SPK) for presenting the processed signal (OUT) to the user as sound. The forward path from the microphones to the loudspeaker of the hearing aid may be operated in the time domain.

[0130] FIG. 7B shows a block diagram of a second embodiment of a hearing aid according to the present disclosure. The hearing aid of FIG. 7B comprises a 2-microphone beamformer configuration as shown in FIG. 5B and a signal processing unit (SPU) for (further) processing the beamformed signal Y(k) in a number (K) of frequency bands and providing a processed signal OU(k), k=1, 2, . . . , K. The signal processing unit may be configured to apply a level and frequency dependent shaping of the beamformed signal, e.g. to compensate for a user's hearing impairment. The processed frequency band signals OU(k) are fed to a synthesis filter bank FBS for converting the frequency band signals OU(k) to a single time-domain processed (output) signal OUT, which is fed to an output unit for presentation to a user as a signal perceivable as sound. In the embodiment of FIG. 7B, the output unit comprises a loudspeaker (SPK) for presenting the processed signal (OUT) to the user as sound. The forward path from the microphones (M.sub.BTE1, M.sub.BTE2) to the loudspeaker (SPK) of the hearing aid is (mainly) operated in the time-frequency domain (in K frequency bands).

[0131] FIG. 8A illustrates an exemplary hearing aid (HD) formed as a receiver in the ear (RITE) type hearing aid comprising a BTE-part (BTE) adapted for being located behind pinna and a part (ITE) comprising an output transducer (OT, e.g. a loudspeaker/receiver) adapted for being located in an ear canal (Ear canal) of the user (e.g. exemplifying a hearing aid (HD) as shown in FIG. 7A, 7B). The BTE-part (BTE) and the ITE-part (ITE) are connected (e.g. electrically connected) by a connecting element (IC). In the embodiment of a hearing aid of FIG. 8A, the BTE part (BTE) comprises two input transducers (here microphones, M=2) (M.sub.BTE1, M.sub.BTE2) each for providing an electric input audio signal representative of an input sound signal (S.sub.BTE) from the environment (in the scenario of FIG. 8A, from sound source S).

[0132] The hearing device of FIG. 8A further comprises two wireless receivers (WLR.sub.1, WLR.sub.2) for providing respective directly received auxiliary audio and/or information signals. The hearing aid (HD) further comprises a substrate (SUB) whereon a number of electronic components are mounted, functionally partitioned according to the application in question (analogue, digital, passive components, etc.), but including a configurable signal processing unit (SPU), a beamformer filtering unit (BFU), and a memory unit (MEM) coupled to each other and to input and output units via electrical conductors Wx. The configurable signal processing unit (SPU) provides an enhanced audio signal (cf. signal OUT in FIG. 7A, 7B), which is intended to be presented to a user. In the embodiment of a hearing aid device in FIG. 8A, the ITE part (ITE) comprises an output unit in the form of a loudspeaker (receiver) (SPK) for converting the electric signal (OUT) to an acoustic signal (providing, or contributing to, acoustic signal S.sub.ED at the ear drum (Ear drum). In an embodiment, the hearing aid comprises more than two microphones. In an embodiment, the BTE-part comprises more than two microphones (M>2, cf. e.g. FIG. 8B for M=3). In an embodiment, the ITE-part further comprises an input unit comprising an input transducer (e.g. a microphone) (M.sub.ITE) for providing an electric input audio signal representative of an input sound signal S.sub.ITE from the environment at or in the ear canal. In another embodiment, the hearing aid may comprise only the BTE-microphones, e.g. two (M.sub.BTE1, M.sub.BTE2) or three (M.sub.BTE1, M.sub.BTE2, M.sub.BTE3, cf. FIG. 8B) microphones. In yet another embodiment, the hearing aid may comprise an input unit (IT.sub.3) located elsewhere than at the ear canal in combination with one or more input units located in the BTE-part. The ITE-part further comprises a guiding element, e.g. a dome, (DO) for guiding and positioning the ITE-part in the ear canal of the user.

[0133] FIG. 8B shows a second embodiment of a hearing aid according to the present disclosure comprising a BTE-part located behind an ear of a user and an ITE part located in an ear canal of the user. The embodiment of FIG. 8B resembles the embodiment of FIG. 8B but has no microphone in the ITE-part. Further, the BTE-part comprises three microphones (M=3). In this embodiment, the BTE-microphones (M.sub.BTE1, M.sub.BTE2, M.sub.BTE3) are not located in the horizontal plane. Preferably in a triangle, where two of the microphones are located in the horizontal plane. This has the advantage that the directional pattern can be adapted not only to the directional ITE response in the horizontal plane, but the directional pattern towards the directional ITE response measured at other elevation angles can also be optimized.

[0134] The hearing aid (HD) exemplified in FIG. 8A, 8B is a portable device and further comprises a battery (BAT) for energizing electronic components of the BTE- and ITE-parts.

[0135] The hearing aid (HD) comprises a directional microphone system (beamformer filtering unit (BFU)) adapted to enhance a target acoustic source among a multitude of acoustic sources in the local environment of the user wearing the hearing aid device. In an embodiment, the directional system is adapted to detect (such as adaptively detect) from which direction a particular part of the microphone signal (e.g. a target part and/or a noise part) originates. The memory unit (MEM) comprises predefined complex, frequency dependent constants W.sub.1(k)′, W.sub.2(k)′ (FIG. 8A) or W.sub.1(k)′, W.sub.2(k)′, W.sub.3(k)′ (FIG. 8B) defining an optimized (fixed) beamformer according to the present disclosure, together defining the beamformed signal Y.

[0136] The hearing aid of FIG. 8A, 8B may constitute or form part of a hearing aid and/or a binaural hearing aid system according to the present disclosure.

[0137] FIG. 9 shows a flow diagram for an embodiment of a method of determining optimized first and second sets of filter coefficients w.sub.1′ and w.sub.2′ and/or optimized first and second complex, frequency dependent constants W.sub.1(k)′ and W.sub.2(k)′ of a fixed beamformer filtering unit.

[0138] The method aims at (e.g. in an off-line procedure, before the hearing aid is taken into normal use by a user) determining optimized first and second sets of filter coefficients w.sub.1′ and w.sub.2′ and/or optimized first and second complex, frequency dependent constants W.sub.1(k)′ and W.sub.2(k)′ of a fixed beamformer filtering unit (BFU, cf. e.g. FIG. 5A, 5B, 6A, 6B) providing a beamformed signal. The a beamformed signal Y reflects a resulting beam pattern of the beamformer filtering unit (BFU), and is provided a) as a combination (e.g. a sum) of filtered versions or the first and second electric input signals (IN.sub.1 and IN.sub.2) (time domain) using first and second sets of filter coefficients w.sub.1′ and w.sub.2′, or b) as a weighted combination (e.g. a sum) of first and second electric input signals (IN.sub.1 and IN.sub.2) (frequency domain) using first and second complex, frequency dependent constants W.sub.1(k)′ and W.sub.2(k)′. IN.sub.1 and IN.sub.2 are electric input signals provided by first and second microphones (M.sub.BTE1, M.sub.BTE2), respectively, to the beamformer filtering unit (BFU). The first and second microphones may e.g. form part of a BTE-part of a hearing aid, the BTE-part being adapted for being located at or behind an ear of a user.

[0139] In an embodiment, the method provides fading between an adaptively determined beam pattern and the pinna omni-pattern (optimized fixed beam pattern) according to the present disclosure, such fading being e.g. described in our co-pending European patent application titled “A hearing device comprising a beamformer filtering unit” referred to above.

[0140] The method may e.g. be carried out during manufacture of the hearing aid or during fitting of the hearing aid to the needs of a particular user.

[0141] The method comprises

[0142] S1. Determine impulse responses h.sub.M1, h.sub.M2 and/or transfer functions H.sub.M1, H.sub.M2 from sound sources S(θ, φ, r) around a user to first and second microphones (M.sub.1, M.sub.2) of a hearing aid worn by a user (or a model of the user), or determine said impulse responses h.sub.M1, h.sub.M2 and/or transfer functions H.sub.M1, H.sub.M2 using an acoustic simulation model.

[0143] S2. Determine an impulse response h.sub.ITE and/or a transfer function H.sub.ITE from sound sources S(θ, φ, r) around a user to a microphone (M.sub.ITE) located at or in an ear canal of the user (or a model of the user), or determine said impulse response h.sub.ITE and/or a transfer function H.sub.ITE using an acoustic simulation model.

[0144] S3. Determine a resulting impulse response h.sub.12 and/or a resulting transfer function H.sub.12 based on impulse responses h.sub.M1, h.sub.M2 and/or transfer functions H.sub.M1, H.sub.M2 by convolution with respective first and second sets of filter coefficients w.sub.1, w.sub.2 and multiplication with respective first and second frequency dependent constants W.sub.1(k), W.sub.2(k), respectively.

[0145] S4. Determine optimized sets of filter coefficients w.sub.1′, w.sub.2′ or optimized frequency dependent constants W.sub.1(k)′, W.sub.2(k)′ that fulfil a predefined criterion between the impulse responses h.sub.12 and h.sub.ITE or between transfer functions H.sub.12 and H.sub.ITE, respectively.

[0146] S5. Store optimized sets of filter coefficients w.sub.1′, w.sub.2′ and/or optimized frequency dependent constants W.sub.1(k)′, W.sub.2(k)′ in a memory unit of the hearing aid.

[0147] (θ, φ, r) denote spatial coordinates of the sound source S.

[0148] The resulting impulse response h.sub.12 may be defined by the following expression

h.sub.12(θ, φ, r)=w.sub.1*h.sub.M1(θ, φ, r)+w.sub.2*h.sub.M2(θ, φ, r)

where * denotes the convolution operator.

[0149] The resulting transfer function H.sub.12 may be defined by the following expression

H.sub.12(θ, φ, r, k)=W.sub.1(k) .Math.H.sub.M1(θ, φ, r, k)+W.sub.2(k).Math.H.sub.M2(θ, φ, r, k)

where .Math. denotes multiplication.

[0150] In an embodiment, the predefined criterion comprises a minimization of a difference or distance measure between the resulting transfer function H.sub.12(θ, φ, r, k) and the transfer function H.sub.ITE(θ, φ, r, k) of the microphone located close to or in the ear canal. Correspondingly, the predefined criterion may comprise a minimization of a difference or distance measure between the resulting impulse response h.sub.12(θ, φ, r, k) and the impulse response H.sub.ITE(θ, φ, r, k) of the microphone located close to or in the ear canal.

[0151] The specific predefined criterion may e.g. comprise one or more of the criteria mentioned in previous parts of the present disclosure.

[0152] It is intended that the structural features of the devices described above, either in the detailed description and/or in the claims, may be combined with steps of the method, when appropriately substituted by a corresponding process.

[0153] The concept of the present disclosure is illustrated by examples where the microphones of the hearing aid are located in a BTE-part and a scheme for amending a directional response of the BTE-microphones to reflect a response of a microphone located at or in the ear canal more closely. Other (non-ideal) locations of the microphones than behind the ear may be envisage as well (e.g. in a front facing part of pinna, e.g. in concha). The method can also be used to optimize towards directional patterns, which listens more towards the front direction compared to the natural directivity of a pinna. In that case another target directional pattern should be included than h.sub.ITE(θ, k), or the desired directivity index or the desired front back ratio should be increased compared to the directivity of the natural pinna. This could e.g. be relevant for people who have lost most of their audibility at the high frequencies. In that case, directional cues could be introduced at lower frequencies. The method can also include a modification of the impulse response h.sub.ITE and/or a transfer function H.sub.ITE of a microphone (M.sub.ITE) located at or in an ear canal of the user in one or more frequency bands, e.g. to remove a possible bias towards a rear direction (over a front direction), i.e. e.g. in case gain of the ITE microphone response is larger in a rear direction than in a front direction.

[0154] Alternatively, the modification could be made in order to further bias the gain of the ITE microphone response towards the front direction (target signal).

[0155] FIG. 10 illustrates a hearing aid (HD) as shown in FIG. 8A comprising a user interface (UI) implemented in an auxiliary device (AD) according to the present disclosure.

[0156] The hearing aid (HD) according to the present disclosure (e.g. as shown in FIG. 8A or FIG. 8B) may comprise a user interface (UI) implemented in an auxiliary device (AUX), e.g. a remote control, e.g. implemented as an APP in a smartphone or other portable (or stationary) electronic device. In the embodiment of FIG. 10, the screen of the user interface (UI) illustrates a Sound source weighting APP. The user interface (UI) is adapted to allow a user (as shown in the central part of the screen, here wearing left and right hearing aids, HD.sub.l, HD.sub.r) to emphasize a direction to and/or a frequency range of interest of a current sound source S in the environment of the user, thereby determining or influencing a weighting function ρ(θ, φ, r, k) for a current sound source of interest to the user. A direction to the present sound source (S) of interest may be selected from the user interface, e.g. by dragging the sound source symbol to a currently relevant direction relative to the user. The currently selected target direction is to the right side of the user, as indicated by the bold arrow to the sound source S. The lower part of the screen allows the user to emphasize a particular current frequency range of interest (Emphasize frequency bands) A choice between ‘All frequencies’ (e.g. 0-10 kHz), ‘Below 4 kHz’, and ‘Above 4 kHz’ is offered the user by ticking the relevant box to the left of each option (other relevant ranges may be selectable according to the practical application). In the illustrated example, the frequency range below 4 kHz has been chosen (as indicated by the black filled tick box and the bold face highlight of the text ‘Below 4 kHz’). A low frequency range may be emphasized in certain situations, e.g. in a telephone mode of operation or during transportation in a car, etc. A choice of ‘All frequencies’ may be implemented as a default. In an embodiment, the user interface is adapted to allow a user to qualify (e.g. accept or reject or modify) an adaptively determined weighting function for emphasizing a direction to or a frequency range of interest of a current sound source in the environment of the user and/or a specific frequency range of interest.

[0157] The auxiliary device and the hearing aid are adapted to allow communication of data representative of the currently selected direction (if deviating from a predetermined direction (already stored in the hearing aid)) to the hearing aid via a, e.g. wireless, communication link (cf. dashed arrow WL2 in FIG. 10). The communication link WL2 may e.g. be based on far field communication, e.g. Bluetooth or Bluetooth Low Energy (or similar technology), implemented by appropriate antenna and transceiver circuitry in the hearing aid (HD) and the auxiliary device (AUX), indicated by transceiver unit WLR.sub.2 in the hearing aid.

[0158] As used, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well (i.e. to have the meaning “at least one”), unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element but an intervening elements may also be present, unless expressly stated otherwise. Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The steps of any disclosed method is not limited to the exact order stated herein, unless expressly stated otherwise.

[0159] It should be appreciated that reference throughout this specification to “one embodiment” or “an embodiment” or “an aspect” or features included as “may” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the disclosure. The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects.

[0160] The claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more.

[0161] Accordingly, the scope should be judged in terms of the claims that follow.