EP2506603B1 - Hearing aid system with a directional microphone system and method for operating such a hearing aid system with said directional microphone system - Google Patents

Description

The invention relates to a hearing aid device system comprising two hearing aid devices, each with a directional microphone system according to the preamble of claim 1. Furthermore, the invention relates to a method for operating such a hearing aid system according to the preamble of claim 8.

A hearing aid device according to the invention is understood to mean any device which provides or helps to provide an output signal perceptible by a user as an audible signal, and which has means which help or compensate for an individual hearing loss of the user. In particular, these are hearing aids which can be worn on the body or on the head, in particular on or in the ear, and which can be implanted in whole or in part. However, such devices are also included, whose primary purpose is not to compensate for hearing loss, such as consumer electronics (TVs, hi-fi systems, MP3 players, etc.), or communication devices (mobile phones, PDAs, headsets etc), but over Have means to compensate for an individual hearing loss.

For the binaural supply of a user, a hearing aid system consisting of two hearing aid devices that can be worn on or in the ear, in particular hearing aids, is generally used. In addition to at least one hearing aid device that can be worn on or in the ear, a hearing aid device system can also comprise at least one further device, for example an external processor unit that can be worn on the user's body. The external processor unit can serve, for example, for the remote control of the hearing aid device or hearing aid device system, but also other functions, such as an analysis of the acoustic listening environment.

A hearing aid generally includes an input transducer for receiving an input signal. The input transducer is designed for example as a microphone, which receives an acoustic signal and converts it into an electrical signal. As input transducers but also come into consideration, which have a coil or an antenna and receive an electromagnetic signal and convert it into an electrical signal. Furthermore, a hearing aid usually includes a signal processing unit for processing and frequency-dependent amplification of the electrical signal. For signal processing in the hearing aid, a preferably digital signal processor (DSP) is used, whose operation can be influenced by means of programs or parameters which can be transmitted to the hearing aid. As a result, the mode of operation of the signal processing unit can be adapted both to the individual hearing loss of a hearing aid wearer and to the current hearing situation in which the hearing aid is currently being operated. The thus changed electrical signal is finally fed to an output transducer. This is usually designed as a handset, which converts the electrical output signal into an acoustic signal. However, other embodiments are also possible here, e.g. an implantable output transducer that connects directly to an auditory ossicle and causes it to vibrate.

A hearing aid with a classifier, which analyzes an incoming microphone signal in the hearing aid and automatically detects the hearing situation in which the hearing aid is currently located, is from the published patent application EP 0 064 042 A1 known. Depending on the detected hearing situation, the parameters relating to the signal processing in the hearing aid device are set automatically.

A modern hearing aid generally comprises a directional microphone system, by which in particular the speech intelligibility in various listening situations are improved can, for. As in a conversation in an environment with noise. Usually, a directional microphone system comprises at least two microphones, the outputs of which are interconnected and whose output signals are linked together in order to obtain a directivity. Depending on the interconnection of the microphones, in particular an internal signal delay between the two microphone signals, different directional characteristics are adjustable. As a measure of the directivity usually serves the AI-DI (articulation index directivity index). To achieve the desired directivity in a directional microphone system, an internal base time delay between the microphone signals must be carefully set for each new hearing aid. This is usually done in so-called KEMAR measurements for a specific carrying position of the respective hearing aid device, wherein a reference signal is presented from the frontal direction. The basic time delay is usually adjusted so that a sound signal incident from the front (with respect to the viewing direction) is optimally received and a sound signal incident from the opposite direction (from the rear) is maximally suppressed.

A hearing aid with a directional microphone system with two electrically interconnected microphones, in which different directional characteristics are adjustable as a function of a signal delay between the generated microphone signals, for example, from the patent US 5,757,933 known.

First, the basic time delay is highly dependent on the effective distance of the two microphones with respect to a sound source, and secondly, the effective base time delay is also due to the frequency dependent diffraction and reflection of the sound frequency dependent. The frequency-dependent base time delay is normally determined by KEMAR measurements, but is highly dependent on the reflection characteristics of the listening environment of the Hearing aid from.

The first problem is highly relevant for universally fitting (instant fit) hearing aids with fixed hose or cable lengths between the respective hearing aid and an associated earmold. Due to the given hose or cable lengths, the positions of the individually worn hearing aid devices vary more than in a conventional adaptation, because in the latter the acoustician can manually adjust the hose length to the individual ear of the respective user, thereby achieving the ideal position. The more an angle α between a connecting line of the microphone openings and the horizontal plane in a user-carried hearing aid device deviates from the angle α determined during the development process on the KEMAR for the optimum wearing position, the more ineffective the directivity of the directional microphone system, i. h., the AI-DI is sinking.

The second problem occurs regardless of the wearing position. Individual factors such as the hairstyle or shape of the head and pinna affect the frequency-dependent group delay, thereby impairing the performance of the directional microphone system.

The US 2002/0 041 696 A1 discloses a hearing aid with a directional microphone system and a method for operating such a hearing aid. According to US 2002/0 041 696 A1 the microphone signals of the directional microphone system are correlated with each other.

The. US Pat. No. 7,340,068 B2 discloses an apparatus and method for determining wind noise in which a first time dependent correlation signal consisting of values of a cross correlation function between a first and a second microphone signal and a second time dependent correlation signal are generated from values of an auto cross correlation function of either the first or the second second microphone signal.

Object of the present invention is to achieve a high performance of a directional microphone system in a hearing aid, regardless of the individual carrying position of the hearing aid.

This object is achieved by a hearing aid system with the features according to claim 1. Furthermore, the object is achieved by a method for operating a hearing aid system with the method steps specified in claim 8.

The basic idea of the invention is to determine, by means of a cross-correlation analysis, the time delay with which an acoustic signal arrives at the microphones, in particular the microphone opening assigned to the respective microphone in the housing of the hearing aid. The internal time delay in at least one microphone signal generated by one of the two microphones then takes place as a function of the external delay determined by means of the correlation analysis.

The invention makes it possible to adapt the internal delay to the individual, dependent on the wear position external delay. Thus, an optimized with respect to the individual carrying position directivity can be adjusted. Even with a deviation of the individual wearing position from the ideal wearing position, a high performance of the respective directional microphone system, in particular a high AI-DI, is achieved.

In addition, the hearing aid according to the invention comprises a classifier for determining the hearing situation in which the hearing aid is currently located, wherein the adjustment of the time delay in dependence on the hearing situation. The determination of the effective distance of the microphones of the respective directional microphone system is namely particularly then useful if the position of the acoustic sound source, from which an acoustic signal emanates and is detected by the microphones, is known in relation to the microphones. This can be assumed in certain listening situations. For example, it is assumed in the hearing situation "conversation at rest" that the hearing aid wearer faces the interlocutor. This is therefore an ideal time to determine the effective distance between the microphones. In addition to the listening situation "conversation in peace", however, this also applies to other listening situations, for example "television".

The determination of the time delay with which an acoustic signal arrives at the microphones takes place by means of a cross-correlation function. This is commonly used in signal analysis to describe the correlation of two signals x (t) and y (t) at different time shifts τ between the two signals. It shows, for example, maxima in the case of time shifts which correspond to the signal propagation time from the measuring location of the signal x (t) to the measuring location of the signal y (t). Also, runtime differences from one signal source to both measurement locations can be determined in this way. The cross-correlation function of the microphone signals has a maximum at a time delay τ which corresponds to the transit time of the acoustic signal between the two microphones (that is, between the two microphone openings in the housing of the hearing aid). This time delay is referred to as the effective time delay τ _eff . Thus, based on the cross-correlation function, the effective external transit time of an acoustic signal between the two microphones arriving from the user's point of view from the frontal direction into the hearing aid device carried in the individual position can be determined in a simple manner.

Advantageously, the internal time delay between the microphone signals does not become due to a single determination of the cross-correlation function of the two microphone signals and thus a one-time calculation of the effective time delay τ _eff set. Rather, it is advantageously carried out within a certain period of time a repeated determination of the cross-correlation function and thus the effective time delay τ _eff . Preferably, by means of a histogram analysis, a resulting effective time delay τ _{eff, res is} determined therefrom. This results in stable results. For histogram analysis, the time shift τ is divided into specific time ranges and the frequency with which the effective time delay τ _eff falls within this time range is determined for each time range. From the time range in which the determined effective time delays τ _{eff are} most frequent, the resulting effective time delay τ _{eff, res} results.

In a behind the ear portable hearing aid with a directional microphone system with a front and a rear microphone is advantageously the internal (base) time delay of the microphone signal generated by the rear microphone equal to the determined in the manner described above effective time delay τ _eff or resulting effective time delay τ _{eff, res} set. This is the basic time delay, which largely extinguishes an acoustic signal coming from behind the hearing aid wearer (cardioid characteristic). However, to vary the direction of maximum signal suppression, a time delay different from the base time delay may also be set. Thus, with a directional microphone system with two microphones, for example, a super-cardioid, a hyper-cardioid or even an "eight" characteristic can be set.

As already mentioned, the external time delay due to diffraction and reflection effects is frequency-dependent. Therefore, a preferred embodiment of the invention provides to determine an also time-dependent internal time delay. This can be achieved in a simple manner in that the microphone signals emanating from the microphone signals are first each supplied to a filter bank. Done by this a splitting of the microphone signals into frequency bands. The internal time delay is then determined separately for the respective frequency band. As a result, the influence of diffraction and reflection phenomena can be largely suppressed.

In order to avoid systematic errors in the calculation of the effective time delay and thus the setting of the internal time delay, according to the invention, the calculated effective time delay or possibly the resulting effective time delay is first subjected to a plausibility check before the internal time delay is adjusted. In particular, in the case of a reverberant environment or in the case of an incorrect spatial orientation of the relevant hearing aid devices, erroneous values with regard to the effective time delay can be determined. In order to prevent erroneous setting of the internal time delay, for example, threshold values can be set for the calculated effective time delay, beyond which no adjustment of the internal time delay takes place. According to the invention, a comparison of the effective time delays determined in both hearing aid devices is carried out in a hearing aid device system with two hearing aids worn on the head. If these time delays differ too much from one another, this indicates a hearing situation which is not suitable for the setting according to the invention.

In a preferred embodiment of the invention, there is no abrupt switching from the previously used internal time delay to the newly calculated internal time delay, but rather a gradual transition between the two time delays (fading). This avoids switching artifacts.

1. 1. Durch die Anwendung statistischer Methoden (Histogramm-Analyse) wird eine individuell angepasste und damit effektivere Richtwirkung erreicht.
2. 2. Frequenzabhängige Beugungs- und Reflexionserscheinungen werden berücksichtigt und damit eine hohe Richtwirkung über den gesamten relevanten Frequenzbereich erreicht.
3. 3. Durch ein erfindungsgemäß eingestelltes Hörhilfegerät wird das Sprachverstehen in wechselnden Hörumgebungen deutlich verbessert.

Overall, the invention offers the following advantages:

1. 1. The application of statistical methods (histogram analysis) becomes an individualized and thus more effective Directional effect achieved.
2. 2. Frequency-dependent diffraction and reflection phenomena are taken into account, thus achieving a high directivity over the entire relevant frequency range.
3. 3. A hearing aid set according to the invention significantly improves speech understanding in changing listening environments.

Figur 1

ein hinter dem Ohr tragbares Hörhilfegerät in stark vereinfachter, schematischer Darstellung nach dem Stand der Technik,

Figur 2

die elektrische Verschaltung zweier Mikrofone zu einem Richtmikrofonsystem gemäß dem Stand der Technik,

Figur 3

die Position zweier Mikrofone in Bezug auf eine Schallquelle, und

Figur 4

ein Hörhilfegerätesystem mit zwei Hörhilfegeräten, bei denen eine optimierte Signalverzögerung zwischen jeweils zwei zu einem Richtmikrofonsystem verschalteten Mikrofonen ermittelbar ist.

The invention will be explained in more detail with reference to exemplary embodiments. Showing:

FIG. 1

a behind the ear portable hearing aid in a highly simplified, schematic representation of the prior art,

FIG. 2

the electrical connection of two microphones to a directional microphone system according to the prior art,

FIG. 3

the position of two microphones with respect to a sound source, and

FIG. 4

a hearing aid device system with two hearing aids, in which an optimized signal delay between each two connected to a directional microphone microphones can be determined.

FIG. 1 shows a simplified, schematic representation of the construction of a hearing aid, in particular a portable behind the ear hearing aid HA, according to the prior art. Hearing aids comprise in principle as essential components at least one input transducer, an amplifier and an output transducer. The input transducer is usually a sound receiver, z. As a microphone, and / or an electromagnetic receiver, for. B. an induction coil. The output transducer is usually used as an electroacoustic transducer, z. B. miniature speaker or handset, or as an electromechanical transducer, z. B. bone conduction, realized. The amplifier is usually integrated in a signal processing unit. In the embodiment according to FIG. 1 are in a provided for supporting behind the ear hearing aid housing a front microphone F and a rear microphone B for receiving the sound from the environment built. A signal processing unit SP, which is also located in the housing of the hearing aid HA, processes the microphone signals and amplifies them. The output of the signal processing unit SP is transmitted to a loudspeaker or listener R, which outputs an acoustic signal. The sound is optionally transmitted via a sound tube (not shown), which is fixed with an earmold in the ear canal, to the eardrum of the user. The power supply of the hearing aid device and in particular that of the signal processing unit SP is effected by a likewise arranged in the hearing aid HA voltage source VS, for example a battery.

As a special feature includes the signal processing unit of the known hearing aid according to FIG. 1 a classifier K, which can determine from an analysis of the microphone signals generated by the microphones F and B, the listening environment or the hearing situation in which the hearing aid HA is currently located. Such auditory situations are, for example, "conversation at rest", "conversation in noise", "television" etc. Depending on the detected hearing situation, the signal processing in the signal processing unit parameters are adjusted automatically to adapt the signal processing to the detected hearing situation.

Out FIG. 2 is the usual structure of a directional microphone system used in hearing aids with two microphones F (front) and B (back) visible. The microphones F and B usually have a distance between 5 mm and 15 mm and are equally sensitive in all directions (omnidirectional). To achieve a directional sensitivity, the Microphones F and B electrically interconnected and thereby linked together the microphone signals generated by them. Usually, the microphone signal SB generated by the rear microphone B is delayed in a delay element T by an internal time delay T _i and subtracted from the microphone signal SF, which is generated by the front microphone F. The subtraction is usually realized by an inverter I in conjunction with a summation element S. As a result, the microphone signal SB originating from the rear microphone B is inverted and added to the microphone signal SF originating from the front microphone F. This produces the directional microphone signal SD at the output of the summation element S.

If the internal time delay T _i is set to correspond to the propagation time of an acoustic signal between the two microphones F and B (base time delay), the acoustic signal of a signal source on the line connecting the two microphones will be least attenuated when the signal source is located in front of the front microphone F, and maximally attenuated when the signal source is behind the rear microphone B. By varying the internal time delay T _i , the direction of the maximum attenuation can be pivoted in space in a known manner. As a result, directional characteristics such as "cardioid characteristic", "super cardioid characteristic", "hyper cardioid characteristic", "eight characteristic" etc can be set.

The invention is not limited to the shown conventional embodiment of a directional microphone system for a hearing aid. Rather, this analog is also applicable to other interconnections of microphones and directional microphone systems with more than two microphones.

FIG. 3 serves to explain the effects of a relation to an ideal position changed position of a worn on the head of a user hearing aid or its Directional microphone system. First, it is assumed that a sound source in front of the front microphone F is on a straight line through the two microphones F and B. Then the sound first hits the front microphone F and delays the propagation time, which the sound requires for the distance d between the two microphones F and B, at the rear microphone B. The internal delay T _i (cf. FIG. 2 ) is then set to correspond to the duration of the sound to overcome the distance d.

Is now - as in FIG. 3 represented by a non-ideal wearing position of the hearing aid in question, a sound source AS off the line L, the acoustic signal A emitted from the acoustic signal source A corresponding earlier at the rear microphone B, since this is the acoustic signal only the effective distance d _eff must overcome. The effective distance d _eff results from the distance of the projection of the front microphone F and the rear microphone B in a horizontal plane H. With a not correspondingly adapted internal time delay thus not set the desired directional characteristic.

According to the invention, a time delay resulting from the effective distance d _eff is automatically determined and set.

In some hearing aids, it is already assumed in the basic setting that the microphones of the directional microphone system are not in a horizontal plane, but that even with the ideal carrying position a straight line through the microphones includes a predetermined angle α with the horizontal. However, this does not change the procedure according to the invention, since in this case too the ideal carrying position can deviate from the actual individual carrying position and such a deviation is detected according to the invention and its effects are corrected accordingly.

FIG. 4 shows in a hearing aid device system with two hearing aids HA1 and HA2 required for determining an optimized internal time delay for the respective directional microphone system components. In this case, the first hearing aid HA1 a front microphone F1 and a rear microphone B1 and the second hearing aid HA2 a front microphone F2 and a rear microphone B2. The microphone signals SF1, SB1, SF2, SB2 emanating from the microphones are first fed to the filter banks FB11, FB12 or FB21, FB22, in which the microphone signals SF1, SB1, SF2, SB2 are each subdivided into a plurality of frequency bands. The further signal processing then takes place in parallel in the respective frequency bands. The calculation of the internal time delay will be described below for a particular frequency band. It is analogous to the other frequency bands.

The microphone signals SF3, SF4 of the relevant frequency band are first supplied to the hearing aid HA1 to a cross-correlation analysis unit K1. The time dependent on a time delay τ cross correlation function of the microphone signals has a maximum at a time delay τ _eff 1, which corresponds to the duration of the acoustic signal between the two microphones. Advantageously, in the invention within a certain period of time, for example within a minute, several cross-correlation functions of the microphone signals SF3 and SF4 are determined as a function of the time delay τ. The statistical evaluation of the determined cross-correlation functions is then carried out in a histogram analysis unit H1, which is part of a control unit C1. In this case, the relative frequency of the determined effective time delays τ _eff 1 as a function of the time delay τ at which the respective cross-correlation function had its maximum is plotted for the considered period. In a time delay determination unit D1, a resulting effective time delay τ _{eff, res} 1 is then determined therefrom, at which the cross-correlation functions most often had their maximum. This time delay is then called possible internal time delay used. However, before the internal time delay is actually set, a plausibility check of the resulting effective time delay τ _{eff, res} 1 in a plausibility check unit P1 preferably takes place first. Preferably, in the plausibility check unit P1, a comparison of the determined, resulting effective time delay τ _{eff, res} 1 with a predefined setpoint range as well as a comparison with the resulting effective time delay τ _{eff, res} 2 determined in the second hearing aid HA2 in an analogous manner. Strong deviations of the resulting effective time delays τ _{eff, res} 1 and τ _{eff, res} 2 found in both hearing aids HA1 and HA2 indicate unusable results.

In the case of a successful plausibility check, the internal delay T _i 1 is set in the hearing aid HA 1 and the internal delay T _i 2 is set as a function of the respectively determined, resulting effective time delay τ _{eff, res} 1 or τ _{eff, res} 2 in the case of the hearing aid HA 2 , In particular, the internal time delay T _i 1 or T _i 2 is set equal to the resulting effective time delay τ _{eff, res} 1 or τ _{eff, res} 2 determined according to the invention.

In an analogous manner, the determination of the internal time delay T _i 2 by means of a control unit C2, which comprises a cross correlation analysis unit K2, a histogram analysis unit H2, a time delay determination unit D2 and a plausibility check P2 also for the second hearing aid HA2 of a hearing aid device.

In the hearing aids HA1 and HA2 a linking of the microphone signals, for example analogously to the link according to FIG. 2 in which the determined internal time delays T _i 1 and T _i 2 are set in the respective delay units.

Claims (14)

1. Hearing aid device system having a first hearing aid device (HA1), wearable on or in the left ear of a user, and having a second hearing aid device (HA2), wearable on or in the right ear of a user, wherein each of the two hearing aid devices (HA1, HA2) has a respective directional microphone system and wherein the respective directional microphone system comprises at least

   - a first microphone (F; F1, F2), which outputs a first microphone signal (SF; SF1, SF2),

   - a second microphone (B; B1, B2), which outputs a second microphone signal (SB; SB1, SB2),

   - a delay unit (T), wherein a directivity is generated by virtue of the second microphone signal (SB; SB1, SB2) or a fourth microphone signal (SB3, SB4) that results therefrom being delayed by an internal time delay (T_i; T_i1, T_i2) by means of the delay unit (T) and linked to the first microphone signal (SF; SF1, SF2) or a third microphone signal (SF3, SF4) that results therefrom to generate a directional microphone signal (SD),

   - a cross-correlation analysis unit (K1, K2), which receives the first (SF; SF1, SF2) or the third (SF3, SF4) microphone signal and the second (SB; SB1, SB2) or the fourth (SB3, SB4) microphone signal, for determining a value of a cross-correlation of the two microphone signals (SF, SB; SF1, SB1, SF3, SB3, SF2, SB2, SF4, SB4), wherein a cross-correlation function of the two microphone signals (SF, SB; SF3, SB3, SF4, SB4) is determinable in the cross-correlation analysis unit (K1, K2) on the basis of a time delay, and wherein an effective time delay (τ_eff1, τ_eff2) is determinable for which the cross-correlation function has a maximum;

   - a plausibility check unit (P1, P2) for performing a plausibility check for the ascertained effective time delay (τ_eff1, τ_eff2);

   - a control unit (C1, C2) for adjusting the internal time delay (T_i; T_i1, T_i2) on the basis of the value of the cross-correlation of the two microphone signals (SF, SB; SF1, SB1, SF3, SB3, SF2, SB2, SF4, SB4), wherein the adjustable internal time delay (T_i; T_i1, T_i2) is the ascertained value of the effective time delay (τ_eff1, τ_eff2) on the basis of the result of the plausibility check;

   - a classifier (K) to determine a hearing situation that the hearing aid device (HA; HA1, HA2) is currently in, wherein the internal time delay (T_i; T_i1, T_i2) is adjusted in particular hearing situations;
   characterized in that
   the plausibility check is performable on the basis of a comparison of the effective time delays (τ_eff1, τ_eff2) ascertained in the two hearing aid devices (HA1, HA2).
2. Hearing aid device system according to Claim 1, wherein the internal time delay (T_i; T_i1, T_i2) is adjusted in a "quiet conversation" hearing situation.
3. Hearing aid device system according to Claim 1 or 2, wherein a histogram analysis unit (H1, H2) to perform a histogram analysis on the basis of a number of effective time delays (τ_eff1, τ_eff2) ascertained within a particular period is present and a resultant effective time delay (τ_eff, _res1, τ_eff, _res2) is determinable by means of the histogram analysis.
4. Hearing aid device system according to Claim 3, wherein the adjustable internal time delay (T_i; T_i1, T_i2) is the resultant effective time delay (τ_eff, _res1, τ_eff, _res2).
5. Hearing aid device system according to Claim 3 or 4, wherein the plausibility check unit (P1, P2) is configured for performing a plausibility check for the ascertained resultant effective time delay (τ_eff, _res1, τ_eff, _res2), and the ascertained value of the resultant effective time delay (τ_eff, _res1, τ_eff, _res2) is adjustable on the basis of the result of the plausibility check.
6. Hearing aid device system according to one of the preceding claims, wherein a filter bank (FB11, FB12, FB21, FB22) is present for splitting the microphone signals (SF; SF1, SB1, SF2, SB2) into different frequency bands, and the internal time delay (T_i; T₁1, T_i2) is adjusted on the basis of the respective frequency band.
7. Hearing aid device system according to Claim 5 or 6, wherein the plausibility check is performable on the basis of a comparison of the resultant effective time delays (τ_eff, _res1, τ_eff, _res2) ascertained in the two hearing aid devices (HA1, HA2) .
8. Method for operating a Hearing aid device system having a first hearing aid device (HA1), wearable on or in the left ear of a user, and having a second hearing aid device (HA2), wearable on or in the right ear of a user, wherein each of the two hearing aid devices (HA1, HA2) comprises a directional microphone system having at least a first microphone (F; F1, F2), which outputs a first microphone signal (SF; SF1, SF2), and a second microphone (B; B1, B2), which outputs a second microphone signal (SB; SB1, SB2), wherein in the respective hearing aid device (HA1, HA2)

   - a directivity is generated by virtue of the second microphone signal (SB; SB1, SB2) or a fourth microphone signal (SB3, SB4) that results therefrom being delayed by an internal time delay (T_i; T_i1, T_i2) by means of a delay unit (T) and linked to the first microphone signal (SF; SF1, SF2) or a third microphone signal (SF3, SF4) that results therefrom,

   - a value of a cross-correlation of the two microphone signals (SF, SB; SF1, SB1, SF3, SB3, SF2, SB2, SF4, SB4) is determined, wherein a cross-correlation function of the two microphone signals (SF, SB; SF1, SB1, SF3, SB3, SF2, SB2, SF4, SB4) is determined on the basis of a time delay,

   - an effective time delay (τ_eff1, τ_eff2) is determined for which the cross-correlation function has a maximum,

   - the internal time delay (T_i; T_i1, T_i2) is adjusted on the basis of the value of the cross-correlation of the two microphone signals (SF, SB; SF1, SB1, SF3, SB3, SF2, SB2, SF4, SB4), wherein the adjusted internal time delay (T_i; T_i1, T_i2) is the ascertained effective time delay (τ_eff1, τ_eff2),

   - a hearing situation that the hearing aid device (HA; HA1, HA2) is currently in is determined,

   - the internal time delay (T_i; T_i1, T_i2) is adjusted in particular hearing situations,

   - the ascertained value of the effective time delay (τ_eff1, τ_eff2) is subjected to a plausibility check,
   characterized in that
   the plausibility check is performed on the basis of a comparison of the effective time delays (τ_eff1, τ_eff2) ascertained in the respective hearing aid device (HA1, HA2).
9. Method according to Claim 8, wherein the internal time delay (T_i; T_i1, T_i2) is adjusted in a "quiet conversation" hearing situation.
10. Method according to Claim 8 or 9, wherein a histogram analysis on the basis of a number of effective time delays (τ_eff1, τ_eff2) ascertained within a particular period is used to determine a resultant effective time delay (τ_eff, _res1, τ_eff, _res2).
11. Method according to Claim 10, wherein the ascertained value of the resultant effective time delay (τ_eff, _res1, τ_eff, _res2) is subjected to a plausibility check.
12. Method according to Claim 10 or 11, wherein the adjusted internal time delay (T_i; T_i1, T_i2) is the ascertained resultant effective time delay (τ_eff, _res1, τ_eff, _res2).
13. Method according to one Claims 8 to 12, wherein the internal time delay (T_i; T_i1, T_i2) is adjusted on the basis of the frequency of an acoustic input signal that the hearing aid device receives.
14. Method according to one of Claims 10 to 13, wherein the plausibility check is performed on the basis of a comparison of the effective time delay (τ_eff, _res1, τ_eff, _res2) ascertained in the respective hearing aid device (HA1, HA2).

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