Hearing aid comprising a directional microphone system

Abstract

A hearing aid comprises a forward path comprising a) at least two input transducers, each for picking up sound from the environment of the hearing aid and providing respective at least two electric input signals; b) a beamformer filter for filtering said at least two electric input signals or signals originating therefrom and providing a spatially filtered signal; c) a signal processor for processing one or more of said electric input signals or one or more signals originating therefrom, and providing one or more processed signals based thereon; and d) an output transducer for generating stimuli perceivable by the user as sound based on said one or more processed signals. The hearing aid further comprises e) a feedback estimation system for estimating a current feedback from the output transducer to each of the at least two input transducers and providing respective feedback measures indicative thereof; and f) a controller configured to receive said feedback measures from said feedback estimation system and to switch between two modes of operation of the hearing aid, a one-input transducer (e.g. omni-directional) mode of operation, and a multi-input transducer (directional) mode of operation, in dependence of the feedback measures. to. The application further relates to a method of operating a hearing aid. Thereby the gain provided by the hearing aid to the user (without a significant risk of howl) can be maximized.

Claims

1. A hearing aid adapted to be located at or in an ear of a user and to compensate for a hearing loss of the user, the hearing aid comprising a forward path comprising at least two input transducers, each for picking up sound from an environment of the hearing aid and providing respective at least two electric input signals; a beamformer filter for filtering said at least two electric input signals or signals originating therefrom and providing a spatially filtered signal; a signal processor for processing one or more of said electric input signals or one or more signals originating therefrom, and providing one or more processed signals based thereon, and an output transducer for generating stimuli perceivable by the user as sound based on said one or more processed signals; a feedback estimation system for estimating a current feedback from the output transducer to each of the at least two input transducers and providing respective feedback measures indicative thereof; and a controller configured to receive said feedback measures from said feedback estimation system and to switch between two modes of operation of the hearing aid, a one-input transducer mode of operation, and a multi-input transducer mode of operation, in dependence of the feedback measures, wherein the hearing aid comprises an ITE-part adapted for being located at or in an ear canal of the user and the ITE-part comprises said at least two input transducers and said output transducer.

2. A hearing aid according to claim 1 wherein the controller is configured to switch to the one-input transducer mode of operation in case a current feedback path difference measure between two of said feedback measures is larger than a first threshold value, and to select the electric input signal from the input transducer among the at least two input transducers having the smallest feedback measure, or a signal originating therefrom, as the input signal to the signal processor.

3. A hearing aid according to claim 1 wherein the controller is configured to switch to the multi-input transducer mode of operation in case a feedback path difference measure between each of said feedback measures is smaller than a second threshold value, and to select the spatially filtered signal as the input signal to the signal processor.

4. A hearing aid according to claim 1 wherein said feedback measure for a given input transducer comprises an impulse response of the feedback path from the output transducer to the input transducer in question, or a frequency response of the feedback path from the output transducer to the input transducer in question, the latter being measured at a number of frequencies.

5. A hearing aid according to claim 1 wherein the at least two input transducers are asymmetrically located relative to the output transducer.

6. A hearing aid according to claim 1 further comprising: a BTE-part adapted for being located at or behind an ear (pinna) of the user, wherein the BTE-part and the ITE-part are electrically or acoustically connected to each other.

7. A hearing aid according to claim 6 wherein said ITE-part comprises a ventilation channel or other open structure allowing exchange of air between a volume near the ear drum and the environment, when the ITE-part is mounted at or in the ear canal of the user.

8. A hearing aid according to claim 7 wherein the at least two input transducers are asymmetrically located relative to the ventilation channel or to the other open structure.

9. A hearing aid according to claim 1 wherein the beamformer filter is configured to provide said spatially filtered signal as respective frequency sub-band signals.

10. A hearing aid according to claim 9 wherein the beamformer filter is configured to be individually set in an omni-directional or directional mode in the respective frequency sub-bands.

11. A hearing aid according to claim 9 wherein the controller is configured to select the spatially filtered signal or one of the electric input signals, or a signal originating therefrom, as the input signal to the signal processor, individually for different frequency ranges based on said frequency sub-band signals, and a feedback criterion.

12. A hearing aid according to claim 1 wherein said feedback measures are indicative of acoustic feedback or mechanical feedback.

13. A hearing aid according to claim 1 wherein the output transducer comprises a loudspeaker for providing the stimulus as an acoustic signal to the user or a vibrator for providing the stimulus as mechanical vibration of a skull bone to the user.

14. A method of operating a hearing aid adapted to be located at or in an ear of a user and to compensate for a hearing loss of the user, the method comprising providing at least two electric input signals representing sound in the environment of the hearing aid as picked up by respective at least two input transducers; providing a spatially filtered signal based on said at least two electric input signals; processing one or more of said electric input signals or one or more signals originating therefrom, and providing one or more processed signals based thereon; generating stimuli for an output transducer perceivable by the user as sound based on said one or more processed signals; estimating a current feedback from said output transducer to each of the at least two input transducers and providing respective feedback measures indicative thereof; and switching between two modes of operation of the hearing aid, a one-input transducer mode of operation, and a multi-input transducer mode of operation, in dependence of the feedback measures, wherein the hearing aid comprises an ITE-part adapted for being located at or in an ear canal of the user and the ITE-part comprises said at least two input transducers and said output transducer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) 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 signs 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:

(2) FIG. 1 shows a first embodiment of a hearing aid according to the present disclosure,

(3) FIG. 2A shows a second embodiment of a hearing aid according to the present disclosure; and

(4) FIG. 2B shows a third embodiment of a hearing aid according to the present disclosure,

(5) FIG. 3A shows a fourth embodiment of a hearing aid according to the present disclosure; and

(6) FIG. 3B shows a fifth embodiment of a hearing aid according to the present disclosure, and

(7) FIG. 4A schematically shows a mechanical feedback measure (M-FB) versus frequency curve for a hearing aid, illustrating the parameter full-on gain (FOG), and

(8) FIG. 4B schematically illustrates exemplary first and second feedback measures (FBM) versus frequency.

(9) 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.

(10) 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

(11) 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 practiced 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.

(12) 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.

(13) The present application relates to the field of hearing aids.

(14) A well-known problem in hearing aids is feedback. This relates to a) the internal hardware related (mechanical) feedback that set the limit for full-on-gain (FOG) measured in a 711/2 cc coupler (IEC 711 compliant coupler) used in the datasheet as well as b) acoustic feedback typically observed as a howling tone.

(15) There are various ways of handling the feedback problem using digital signal processing for dynamic feedback cancellation as well as tools in the fitting software to reduce gain (at frequencies prone to feedback for the hearing aid or hearing aid style in question).

(16) Whereas for the hardware related feedback, the design options for hearing aids are typically a choice between A) a reduction in the Full-On Gain (FOG)-parameter B) a selection of new transducers and/or C) improvement of mechanical design.

(17) The Full-On Gain (FOG) parameter limitation is an important feature for controlling the stability of digital hearing aids, by limiting the maximum allowable gain in the hearing aid. The full-on gain limitation is a characteristic of the hardware of the hearing aid and represents the maximum gain that can be applied to the hearing aid without causing mechanical feedback. The determination of the full-on gain is typically performed according to a predefined, e.g. standardized, procedure (e.g. ANSI S3.22-2003: Specification of Hearing Aid Characteristics), e.g. with the gain control of the hearing aid set to its full-on position and with an input sound pressure level (SPL) of 50 dB. Alternatively, the measurement conditions may be indicated in a data sheet of the hearing aid together with the limiting Full-On Gain (FOG) value.

(18) FIG. 1 shows an embodiment of a hearing aid according to the present disclosure. The hearing aid (HD) is adapted to be located at or in an ear of a user and to compensate for a hearing loss of the user. The hearing aid comprises a forward path for processing an input signal representing sound in the environment. The forward path comprises at least two input transducers (e.g. microphones (M1, M2)), each for picking up sound from the environment of the hearing aid and providing respective at least two electric input signals (IN1, IN2). The forward path further comprises a beamformer filter (BFU) for filtering the at least two electric input signals or signals originating therefrom and providing a spatially filtered signal (IN.sub.BF). The forward path further comprises a signal processor (HLC) for processing one or more of the electric input signals (IN1, IN2) or one or more signals (e.g. the spatially filtered signal IN.sub.BF) originating therefrom and providing one or more processed signals (OUT) based thereon, and providing one or more processed signals (OUT) based thereon. The forward path further comprises an output transducer (OT, e.g. a loudspeaker) for generating stimuli (STIM, e.g. acoustic stimuli) perceivable by the user as sound based on the one or more processed signals (OUT). The hearing aid (HD) further comprises a feedback estimation system (FE) for estimating a current feedback path (FBP.sub.1, FBP.sub.2) from the output transducer (OT) to each of the at least two input transducers (M.sub.1, M.sub.2) and providing respective feedback measures (FBE1, FBE2) indicative thereof. The microphones (M1, M2) each picks up a sound that is a mixture of an ‘external sound’ from the environment (x.sub.1, x.sub.2) and a sound (v.sub.1, v.sub.2) from the output transducer (OT) leaked back to the microphones via respective acoustic feedback paths (FBP.sub.1, FBP.sub.2) (cf. acoustic sum unit ‘+’ to the left of the respective microphones (M1, M2) in FIG. 1). The hearing aid further comprises a controller (CTR) configured to receive the feedback measures (FBE1, FBE2) from the feedback estimation system (FE) and the electric input signals (IN1, IN2) and the beamformed signal (IN.sub.BF), and possibly a requested gain (or insertion gain, IG) from the signal processor (HLC). The hearing aid may comprise a loop gain estimator for estimating a current loop gain. Using a current estimate of a feedback path from the output transducer to the microphone(s), and knowledge of the currently requested gain to compensate for a hearing impairment of the user, the fulfilment of a specific feedback criterion for entering a critical feedback mode of operation may be checked (e.g. enter critical feedback mode, if LG˜FBE+IG≥0 dB). In the critical feedback mode, the controller (CTR) may be configured to select the electric input signal (IN1; IN2) from the input transducer among the at least two input transducers (M1, M2) having the smallest feedback measure (or gain margin) as the input signal (IN) to the signal processor (HLC), in case a feedback path difference measure determined by comparison of at least two of said feedback measures is larger than a first threshold value FBDM.sub.TH1 (e.g. FBDM.sub.12=FBE1−FBE2>FBDM.sub.TH1). In the critical feedback mode, the controller (CTR) may further be configured to select the spatially filtered signal (IN.sub.BF) as the input signal (IN) to the signal processor (HLC), in case all of the feedback path difference measures determined by comparison of each of said feedback measures is(are) smaller than a second threshold value FBDM.sub.TH2 (e.g. FBDM.sub.12=FBE1−FBE2<FBDM.sub.TH2). In an embodiment, FBDM.sub.TH1=FBDM.sub.TH2. In an embodiment, FBDM.sub.TH1≥FBDM.sub.TH2. The (fully) ‘digital components’ of the hearing aid (e.g. other components than the input and output transducers) are enclosed by the dashed outline and denoted (DSP), cf. e.g. also digital signal processor (DSP) of FIG. 3A.

(19) FIG. 2A shows an embodiment of a hearing aid (HD) according to the present disclosure similar to the embodiment of FIG. 1. In the embodiment of FIG. 2A, however, the hearing aid (HD) is partitioned in a BTE-part and an ITE-part. The BTE-part (BTE) is e.g. adapted to be located at or behind an ear (pinna) of the user. The ITE-part (ITE) is e.g. adapted to be located at or in an ear canal of the user. The hearing aid (HD) may be of a particular style sometimes termed ‘receiver-in-the-ear’ (RITE), because the ITE-part comprises the loudspeaker (OT, often termed ‘receiver’ in the field of hearing aids). The embodiment of FIG. 2A comprises three input transducers, two microphones (M.sub.BTE1, M.sub.BTE2) located in the BTE-part and one further input transducer (IT.sub.ITE, e.g. a microphone, an accelerometer, or the like to pick up vibrations) located in the ITE-part. The BTE and ITE-parts are electrically connected by conductors for connecting the signal processor (HLC) to the output transducer (OT) and input transducer (IT.sub.ITE) to the beamformer filter (BFU), and for providing power (at least) to the input transducer. The third input transducer (IT.sub.ITE) located in the ITE-part receives an external sound (or vibration) x.sub.3 mixed with a feedback signal v.sub.3 from the output transducer (OT) via feedback path FB.sub.3. The BTE-part comprises, in addition to the two microphones (M.sub.BTE1, M.sub.BTE2) and the electric input from the input transducer (IT.sub.ITE) located in the ITE-part, the beamformer filter (BFU), the feedback estimation system (FE), the controller (CTR) and the signal processor (HLC) as described in connection with FIG. 1. The three functional units, BFU, CTR, and FE, are shown as one unit (enclosed in box denoted BFU-CTR-FE) in FIG. 2A. Additionally, each of the three (time domain) inputs (IN.sub.BTE1, IN.sub.BTE2, IN.sub.ITE) from the respective input transducers (M.sub.BTE1, M.sub.BTE2, IT.sub.ITE) to the beamformer filter (BFU) comprises respective analysis filter banks (t/f) for providing the time domain signals as frequency sub-band signals for being individually processed in the forward path of the hearing aid (here the BTE-part) Similarly, the output path (OUT) comprises a synthesis filter bank (f/t) for converting frequency sub-band signals to a time-domain signal (OUT), which is forwarded to the output transducer (OT, e.g. a loudspeaker, in the ITE-part) via an electric cable of a connecting element. The presence of three input transducers provides an improved possibility of making an appropriate beamforming e.g. including directing a beam towards the user's mouth (e.g. in a telephone situation or the like). The different location of the three input transducers provides an improved possibility to identify an input transducer with a relatively low feedback path (high gain margin) in many acoustic situations. In an embodiment, a directional signal (IN′) based on the two BTE-microphone signals IN.sub.BTE1 and IN.sub.BTE2, or feedback corrected versions (ERR1 and ERR2) thereof, may be used as a first microphone signal and the input signal IN.sub.ITE from the ITE-microphone (IT.sub.ITE), or feedback corrected version (ERR3) thereof, may be used as a second microphone signal. The scheme according to the present disclosure may be used to—in a specific critical feedback mode of operation—select between the beamformed signal (IN′) based on the BTE-microphone signals and the beamformed signal (IN) based on all three input signals in dependence of a predetermined feedback criterion.

(20) FIG. 2B shows an embodiment of a hearing aid (HD) according to the present disclosure similar to the embodiment illustrated in FIGS. 1 and 2A. A difference is that the embodiment of FIG. 2B further comprises a feedback control system (denoted FBC in FIG. 2B (curved solid line enclosure)) comprising respective adaptive filters (FBE1, FBE2, FBE3) and combination units (‘+’) (and here also including the beamformer control unit (BFU-CTR); the latter may in other embodiments be excluded from the feedback control system). The three adaptive filters (FBE1, FBE2, FBE3, respectively) are configured to adaptively estimate the three feedback paths (FBP1, FBP2, FBP3, respectively) from the output transducer (OT) to the three input transducers (IT.sub.BTE1, IT.sub.BTE2, IT.sub.ITE, respectively). The three subtraction units (‘+’) are configured to subtract the three feedback path estimates (FB1est, FB2est, FB3est, respectively) from the electric input signals (IN.sub.BTE1, IN.sub.BTE2, IN.sub.ITE, respectively) and to provide respective feedback corrected input signals (ERR1, ERR2, ERR3). The feedback corrected input signals (ERR1, ERR2, ERR3) are fed to the beamformer-control unit (BFU-CTR). The feedback path estimates (FB1est, FB2est, FB3est) are fed to a feedback path difference measure unit (FBPD) configured to determine respective feedback path difference measures (here e.g. FBDM.sub.12=FB1est−FB2est, FBDM.sub.13=FB1est−FB3est, and FBDM.sub.23=FB2est−FB3est) and to provide a selection-control signal SMctr in dependence thereof (e.g. according to a predefined criterion). The selection control signal SMctr is fed to the beamformer-control unit (BFU-CTR) (possibly together with requested gain (IG) from the signal processor (HLC)) for selecting one of the feedback corrected input signals (ERR1, ERR2, ERR3) or a beamformed signal provided as a combination of the three feedback corrected input signals (cf. e.g. IN.sub.BF in FIG. 1). Based thereon, the beamformer-control unit (BFU-CTR) provides a resulting signal (IN) for further processing (e.g. according to the hearing aid user's needs) in the processor (HLC), and presentation to the user. The beamformer filtering unit may e.g. comprise a beamformer algorithm of a generalized sidelobe canceller (GSC) type, e.g. a minimum variance distortionless response (MVDR) type beamformer algorithm. The beamformer filtering unit may e.g. provide a non-linear combination of the input signals, e.g. implemented by a trained neural network.

(21) FIG. 3A shows an embodiment of a BTE-style hearing aid according to the present disclosure. The hearing aid is partitioned in a BTE-part adapted to be located at or behind the ear ((Ear (pinna)) and an ITE-part adapted to be located at or in the ear canal (Ear canal) of the user, as described in connection with FIG. 2A, 2B. As appears from FIG. 3A, the BTE-part comprises two microphones (M.sub.BTE1, and M.sub.BTE2) and the ITE-part comprises one microphone (M.sub.ITE). The ITE-part comprises an ear mould (MOULD) constituting a housing, wherein the microphone (MITE) and the loudspeaker (SPK) are located. The ear mould is e.g. adapted to the user's ear canal to minimize leakage of sound from the loudspeaker (SPK) of the hearing aid to the environment (and from the environment to the ear drum). The ear mould may comprise a vent to allow pressure to be aligned between the environment and the residual volume between the mould and the ear drum (to minimize occlusion). The ear mould (MOULD) may comprise a sensor (SITE) located near the surface of the housing allowing a contact or interaction with tissue of the ear canal. The sensor may e.g. be an electric potential sensor (e.g. to pick up signals from the brain (e.g. EEG) or and/from the eye balls (e.g. EOG) or from muscle contractions (e.g. jaw movements), or a movement sensor, e.g. to pick up vibrations of the skin or bone (e.g. to detect when the user speaks (‘own voice’)), or an EPF-sensor to pick up light reflections from the ear canal, or a temperature sensor for estimating a temperature, or a photoplethysmogram (PPG) sensor for estimating various properties of the user's body (e.g. heart rate), etc.

(22) The three microphone signals (IN.sub.BTE1, IN.sub.BTE2, IN.sub.ITE, cf. FIG. 2A, 2B) are routed to a beamformer filter (BFU) and used for providing one or more beamformed signals Y.sub.BF for further processing in the signal processor (DSP) comprising a controller (CTR) and processor (HLC) according to the present disclosure as e.g. described in connection with FIG. 1, 2A, 2B. The signal(s) from one or more sensors SITE is/are routed to the signal processor (DSP) for being considered there, (e.g. for being processed and/or transmitted to another device, e.g. to a user interface for processing and/or presentation there). One or more other sensors connected to the hearing aid may be located in the BTE-part or elsewhere at or around the ear of the user (or implanted in the head or body of the user).

(23) The hearing aid (HD), e.g. the BTE-part and/or the ITE-part, may comprise a (wireless or wired) programming interface and possibly a (wireless or wired) user communication interface. The programming interface (allowing connection to a programming device, e.g. a fitting system) and the user communication interface may be implemented using one or both wireless transceivers (WLR1, WLR2) shown in FIG. 3A to be located in the BTE-part. Alternatively, the interfaces may be implemented as wired connections, e.g. via a connector.

(24) The connecting element (IC) between the BTE-part and the ITE-part is shown as a cable comprising electric conductors for electrically connecting electronic components (and battery (BAT)) of the BTE- and ITE-parts. The connecting element comprises a connector to the BTE-part allowing the ITE-part (and the connecting element) to be easily detached and attached to the BTE-part (and e.g. to be exchanged with another one, e.g. comprising a different loudspeaker or a different sensor or sensors, or no microphone or more than one microphone, etc.). The connecting element (IC) between the BTE-part and the ITE-part may comprise an acoustic tube, in case the loudspeaker is located in the BTE-part instead of in the ITE-part.

(25) The BTE-part comprises a substrate (SUB) comprising electronic components (memory (MEM), a FrontEnd-IC (FE), and a digital signal processor IC/DSP) and appropriate wiring (Wx) for mutually connecting the electronic components on the substrate and to the battery (BAT), to the wireless transceivers (WLR.sub.1, WLR.sub.2), to the microphones (M.sub.BTE1, M.sub.BTE2, M.sub.ITE) to the sensor(s) (SITE), to the loudspeaker (SPK), and to possible other components of the BTE- and ITE-parts. The memory (MEM) may store appropriate settings for the hearing aid, e.g. different hearing aid programs and customized parameters. The FrontEnd IC (FE) is an integrated circuit handling interfaces to mainly analogue components, such as microphones and loudspeaker, and possibly sensors, etc. The digital signal processor (DSP) comprises digital components of the hearing aid, including the beamformer filter (BFU), the controller (CTR), processor (HLC), etc., as described in connection with FIG. 1, 2A, 2B.

(26) The microphones of the hearing aid are configured to pick up respective sound elements (S.sub.BTE at the BTE-microphones (M.sub.BTE1, M.sub.BTE2) and SITE at the ITE-microphone (M.sub.ITE)) of a sound field (S) around the hearing aid (HD) (i.e. around a user wearing the hearing aid). A sound field (S.sub.ED) at the ear drum (Ear drum) of the user wearing the hearing aid is a result of the sound produced by the loudspeaker (SPK) and sound leaked into the ear canal from the environment (e.g. through a vent or other openings) of the ITE-part of the hearing aid. The sound delivered by the loudspeaker is determined according to the present disclosure based on the user's hearing ability (e.g. hearing loss, i.e. corresponding to an appropriate gain applied by the hearing aid), the sound fields (S.sub.BTE, SITE) picked up by the microphones, and the current feedback estimates from the loudspeaker (SPK) to the respective microphones (M.sub.BTE1, M.sub.BTE2, and M.sub.ITE).

(27) FIG. 3B shows a further embodiment of a hearing aid (HD) according to the present disclosure. FIG. 3B schematically illustrates an ITE-style hearing aid according to an embodiment of the present disclosure. The hearing aid (HD) comprises or consists of an ITE-part comprising a housing (Housing), which may be a standard housing aimed at fitting a group of users, or it may be customized to a user's ear (e.g. as an ear mould, e.g. to provide an appropriate fitting to the outer ear and/or the ear canal). The housing schematically illustrated in FIG. 3B has a symmetric form, e.g. around a longitudinal axis from the environment towards the ear drum (Eardrum) of the user (when mounted), but this need not be the case. It may be customized to the form of a particular user's ear canal. The hearing aid may be configured to be located in the outer part of the ear canal, e.g. partially visible from the outside, or it may be configured to be located completely in the ear canal, possibly deep in the ear canal, e.g. fully or partially in the bony part of the ear canal.

(28) To minimize leakage of sound (played by the hearing aid towards the ear drum of the user) from the ear canal, a good mechanical contact between the housing of the hearing aid and the Skin/tissue of the ear canal is aimed at. In an attempt to minimize such leakage, the housing of the ITE-part may be customized to the ear of a particular user.

(29) The hearing aid (HD) comprises a number Q of microphones M.sub.q, i=1, . . . , Q, here two (Q=2). The two microphones (M.sub.1, M.sub.2) are located in the housing with a predefined distance d between them, e.g. 8-10 mm, e.g. on a part of the surface of the housing that faces the environment when the hearing aid is operationally mounted in or at the ear of the user. The microphones (M.sub.1, M.sub.2) are e.g. located on the housing to have their microphone axis (an axis through the centre of the two microphones) point in a forward direction relative to the user, e.g. a look direction of the user (as e.g. defined by the nose of the user, e.g. substantially in a horizontal plane), when the hearing aid is mounted in or at the ear of the user. Thereby the two microphones are well suited to create a directional signal towards the front (and or back) of the user. The microphones are configured to convert sound (S.sub.1, S.sub.2) received from a sound field S around the user at their respective locations to respective (analogue) electric signals (s.sub.1, s.sub.2) representing the sound. The microphones are coupled to respective analogue to digital converters (AD) to provide the respective (analogue) electric signals (s1, s2) as digitized signals (s1, s2). The digitized signals may further be coupled to respective filter banks to provide each of the electric input signals (time domain signals) as frequency sub-band signals (frequency domain signals). The (digitized) electric input signals (s.sub.1, s.sub.2) are fed to a digital signal processor (DSP) for processing the audio signals (s.sub.1, s.sub.2), e.g. including one or more of spatial filtering (beamforming), (e.g. single channel) noise reduction, compression (frequency and level dependent amplification/attenuation according to a user's needs, e.g. hearing impairment), spatial cue preservation/restoration, etc. The digital signal processor (DSP) may e.g. comprise the appropriate filter banks (e.g. analysis as well as synthesis filter banks) to allow processing in the frequency domain (individual processing of frequency sub-band signals). The digital signal processor (DSP) is configured to provide a processed signal s.sub.out comprising a representation of the sound field S (e.g. including an estimate of a target signal therein). The processed signal s.sub.out is fed to an output transducer (here a loudspeaker (SPK), e.g. via a digital to analogue converter (DA), for conversion of a processed (digital electric) signal s.sub.out (or analogue version s.sub.out) to a sound signal S.sub.out. In a mode of operation according to the present disclosure (in dependence of the current feedback path estimates), the hearing aid is configured to use A) either a spatially filtered signal (from a beamformer filter, cf. e.g. IN.sub.BF and BFU in FIG. 1), or B) a specific one of the electric input signals (s.sub.1, s.sub.2) (or a processed, e.g. feedback corrected, version thereof), to be processed by the processor (e.g. according to the user's needs) and presented to the user via the loudspeaker (SPK) (possibly via the DA-converter (DA)).

(30) The hearing aid (HD) may e.g. comprise a venting channel (Vent) configured to minimize the effect of occlusion (when the user speaks). In addition to allowing an (un-intended) acoustic propagation path S.sub.leak from a residual volume (cf. Res. Vol in FIG. 3B) between a hearing aid housing and the ear drum to be established, the venting channel also provides a direct acoustic propagation path of sound from the environment to the residual volume. The directly propagated sound San reaching the residual volume is mixed with the acoustic output of the hearing aid (HD) to create a resulting sound S.sub.ED at the ear drum. In a mode of operation, active noise suppression (ANS) is activated in an attempt to cancel out the directly propagated sound San.

(31) The hearing aid (HD) comprises a forward path comprising two (or more transducer(s)), here two microphone(s) (M.sub.1, M.sub.2), appropriate AD-converters (AD), the digital signal processor (DSP), e.g. comprising appropriate analysis and synthesis filter banks, as the case may be, and one or more processing algorithms for enhancing the input audio signal(s) (s.sub.1, s.sub.2) to provide a processed signal s.sub.out, possibly a digital to analogue converter (DA), and the output transducer, here loudspeaker (SPK). The forward path is configured to pick up external sound, process the sound and provide a processed version of the sound (S.sub.out) to the user, e.g. the user's ear drum. In addition to the external sound (S.sub.1, S.sub.2), the microphones (M.sub.1, M.sub.2) also receive (and pick up) sound (S.sub.leak1, S.sub.leak2) leaked from the output transducer (SPK) of the hearing aid e.g. via the vent (Vent) and/or other leakage paths (denoted ‘Direct-path’ in FIG. 3B) from the residual volume (Res. vol) at the ear drum to the respective microphones (M.sub.1, M.sub.2). The leakage paths represented by leaked sound (S.sub.leak1, S.sub.leak2) are estimated by the hearing aid via a feedback estimation unit (FE), cf. e.g. FIG. 1, and the resulting estimates (cf. e.g. FBE1, FBE2) are used to control which of the input signals (s.sub.1 or s.sub.2) or the beamformed signal formed as a combination of the electric input signals (s.sub.1, s.sub.2) according to the present disclosure, as e.g. described in connection with FIG. 1, is further processed and presented to the user at a given point in time. The ventilation channel (Vent) is asymmetrically located in the hearing aid housing (Housing). Such asymmetric location may be a result of a design constraint due to components of the hearing aid, e.g. a battery. Thereby the first and second microphones (M.sub.1, M.sub.2) have different feedback paths from the loudspeaker (SPK). The first microphone (M.sub.1) is located closer to the ventilation channel than the second microphone (M.sub.2). Other things being equal, the feedback measure (FBM1) of the first microphone is larger than the feedback measure (FBM2) of the second microphone, at least above a minimum frequency, see e.g. FIG. 4B. The scheme according to the present disclosure for controlling (e.g. to switch, such as fade, between) the use of either a beamformed signal or the signal from a single one of the input transducers in the forward path of the hearing aid may be applied to the ITE-hearing aid of FIG. 3B to allow more flexibility as regards the location of the input transducers and the ventilation channel relative to each other without compromising (decreasing) the full-on gain value of the hearing aid. When the microphone system of the hearing aid is in a DIR-mode (where the beamformed signal is used for amplification and presentation to the user) and when feedback to one of the microphones (or a feedback path difference measure for the two microphones) increases above a threshold level, the mode of the microphone system is changed to an OMNI-mode. In the OMNI-mode, the signal from the (single) microphone having the lowest feedback is used for amplification and presentation to the user. Thereby feedback howl at the current level of feedback can be avoided.

(32) The hearing aid comprises an energy source, e.g. a battery (BAT), e.g. a rechargeable battery, for energizing the components of the device.

(33) FIG. 4A shows a mechanical feedback measure (M-FB) versus frequency curve for a hearing aid, illustrating the parameter full-on gain (FOG), and FIG. 4B schematically illustrates exemplary first and second feedback measures (FBM) versus frequency.

(34) FIG. 4A illustrates how a (mechanical) feedback measure, M-FB [dB], varies over frequency, f [Hz], (possibly on a logarithmic scale) at full-on gain conditions (e.g. ANSI S3.22-2003: Specification of Hearing Aid Characteristics) and that a specific frequency range (between first and second threshold frequencies f.sub.TH1, f.sub.TH2) determine the maximum full-on gain (FOG). The maximum full-on gain for a super- or ultra-power, BTE-type hearing aid (e.g. FIG. 3A) may e.g. be in a range between 60 dB and 90 dB, e.g. ≤87 dB, and between 40 dB and 70 dB for a corresponding ITE-type hearing aid (e.g. FIG. 3B). The specific frequency range determining maximum allowable FOG (i.e. exhibits maximum mechanical feedback) is dependent on the specific hardware construction, but may for a typical BTE-super-power hearing aid lie in a range between 800-1000 Hz, e.g. having a maximum feedback at 900 Hz, and for a corresponding ITE hearing aid around 3 kHz (as indicated in FIG. 4A by ‘f.sub.max’). FIG. 4A illustrates exemplary modes of operation (cf. reference ‘Modes’ and three arrows pointing towards three frequency ranges, and three different modes of operation) of a hearing aid according to the present disclosure (e.g. as indicated in FIG. 3B). At low frequencies (below Gm), the directional system (cf. e.g. BFU in FIG. 1) of the hearing aid is in an omni-directional mode (denoted ‘Enhanced omni in FIG. 4A, e.g. implemented by a delay and sum beamformer (or the like)), so in the frequency bands covering this range, the resulting beamformed signal is used for further processing (amplification, etc.) in the processor (HLC, in FIG. 1). At high frequencies (above f.sub.TH2), the directional system of the hearing aid is in a directional mode, e.g. implemented by a delay and subtract beamformer (or the like), so in the frequency bands covering this range, the resulting beamformed signal is used for further processing in the processor (HLC, in FIG. 1). In the frequency bands covering the intermediate frequency range (above f.sub.TH1 and below f.sub.TH2), one of the input signals (e.g. IN1 or IN2 in FIG. 1, or s.sub.1 or s.sub.2 in FIG. 3B) is selected for further processing in the processor (so the beamformed signal is not used in the intermediate range).

(35) FIG. 4B illustrates an example of different (acoustic) feedback paths from the output transducer to the respective (first and second) input transducers, as e.g. illustrated by M.sub.1 and M.sub.2 of FIG. 3B. The feedback path is represented by feedback gain (attenuation, e.g. expressed by negative gain values in dB), FBG [dB], versus frequency, f [Hz] (e.g. in a logarithmic scale, or as FBG-values at preselected discrete frequencies). The feedback gain for a hearing aid depends of the style, including the relative positions of microphones and loudspeaker. In a (very) general sense feedback typically decreases with increasing frequency from around 1 kHz to 10 kHz. A number of large peaks and valleys providing local deviations from this trend may, however, be experienced in this frequency range. The schematic course of the two FBG-curves of FIG. 4B indicate this general trend.

(36) The first feedback measure (FBM.sub.1), here feedback gain FBG, for the first microphone (M.sub.1) is generally larger (less negative) than the second feedback measure (FBM.sub.2) for the second microphone (M.sub.2). A feedback path difference measure FBDM.sub.12 may be defined as a difference between the first and second feedback measures (e.g. feedback path estimates), FBDM.sub.12=FBM.sub.1−FBM.sub.2. The feedback path difference measure FBDM.sub.12 may be defined at a number of specific frequencies, e.g. at centre frequencies of all (or selected) frequency bands, or in limited number of frequency bands, e.g. 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz. A distance measure, FBDM, defined by values at one or more of these frequencies may—in a specific critical feedback mode of operation, e.g. where a specific feedback criterion (e.g. loop gain≤LG.sub.max) is fulfilled—be used to control (determine a selection of) the input signals to the hearing aid processor according to the present disclosure. In the example of FIG. 4B, the smallest gain margin GM (GM.sub.1, GM.sub.2) (e.g. of the order of 10-20 dB) for the two microphones (M.sub.1, M.sub.2) are indicated at around frequency f.sub.1, e.g. corresponding to maximum feedback gains of −12 dB and −20 dB, respectively.

(37) As discussed in connection with FIG. 4A, the hearing aid may be in different modes of operation in different frequency bands (or ranges) depending on the value of the feedback path difference measure(s) in each frequency band (or range). The (resulting) feedback path difference measure (FBDM(Δf)) of a given frequency range Δf may e.g. be determined as an average (e.g. a weighted average) of individual feedback path difference measures at frequencies of the range in question. The first and second feedback measures or the (resulting) feedback path difference measure may (e.g. furthermore) be averaged over a certain time, e.g. of the order of seconds.

(38) 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.

(39) 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 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.

(40) 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.

(41) 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.

(42) Accordingly, the scope should be judged in terms of the claims that follow.

REFERENCES

(43) EP3185589A1 (Oticon) 28 Jun. 2017. [Brandstein & Ward; 2001] M. Brandstein and D. Ward, “Microphone Arrays”, Springer 2001. EP3229490A1 (Oticon) 11 Oct. 2017. EP3185588A1 (Oticon) 28 Jun. 2017.