EP2373063B1 - Hearing device and method for setting the same for acoustic feedback-free operation - Google Patents

Description

The invention relates to a method for adjusting a hearing device in order to enable a feedback-reduced operation of the hearing device. The invention also relates to a hearing device in which such a feedback reduced operation can be made possible. In the case of the hearing device, at least one directional parameter for defining a directional characteristic of a microphone arrangement of the hearing device can be set. The term hearing device is understood in particular to mean a hearing device. In addition, however, the term includes other portable acoustic devices such as headsets, headphones and the like.

Hearing aids are portable hearing aids that are used to care for the hearing impaired. In order to meet the numerous individual needs, different types of hearing aids such as behind-the-ear hearing aids (BTE), hearing aid with external receiver (RIC: receiver in the canal) and in-the-ear hearing aids (IDO), e.g. Concha hearing aids or canal hearing aids (ITE, CIC). The hearing aids listed by way of example are worn on the outer ear or in the ear canal. In addition, bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. The stimulation of the damaged hearing takes place either mechanically or electrically.

Hearing aids have in principle as essential components an 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. As miniature speaker, or as an electromechanical transducer, z. B. bone conduction, realized. The amplifier is standard integrated into a signal processing unit. This basic structure is in FIG. 1 shown using the example of a behind-the-ear hearing aid. In a hearing aid housing 1 for carrying behind the ear, one or more microphones 2 for receiving the sound from the environment are installed. A signal processing unit 3, which is also integrated in the hearing aid housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker or earpiece 4, which outputs an acoustic signal. The sound is optionally transmitted via a sound tube, which is fixed with an earmold in the ear canal, to the eardrum of the device carrier. The power supply of the hearing device and in particular the signal processing unit 3 is effected by a likewise integrated into the hearing aid housing 1 battery. 5

In a hearing device, in particular a hearing aid, it may happen that the sound generated by the listener passes out of the ear canal of the device wearer and back to a microphone of the hearing device. The possible ways in which the sound can be transmitted acoustically together form an acoustic feedback path from the listener to the microphone. For example, in the case of an earpiece for fixing a sound tube in an auditory canal, a passage opening for aerating the auditory canal, a so-called vent, may be provided. Through such openings but then the sound of the listener can escape from the ear canal. Accordingly, a feedback path can thus result, which leads through this vent. A feedback path may also pass through portions of the skull of the implement carrier if these areas are e.g. be excited by the sound waves of the listener to vibrations and the sound signal propagates as structure-borne noise. In the case of bone-assisted hearing aids, the listener already produces a structure-borne noise, which may be fed back under certain circumstances.

If the sound signal of the listener is detected by a microphone, it can be amplified in the hearing device and back from the listener be radiated. In such a case, the acoustic feedback path and the signal processing of the hearing aid together constitute a feedback loop. In the context of illustrating the invention, the transmission of a signal along a feedback loop is referred to as a feedback effect.

The feedback effect is critical when there is an overall gain in the feedback loop greater than unity. If, for example, an earmold of the hearing device has not been inserted into the auditory canal in the intended manner, so that an air gap remains between the earmold and the skin of the device wearer, a feedback path may result, which leads mainly through this gap. An attenuation of the feedback sound is then particularly low. At the microphone, the fed-back sound has a correspondingly high volume. If the received microphone signal is then amplified and converted again into a sound by the listener, this can lead to the listener producing an ever louder sound. A feedback loop having a gain greater than one may result in self-excitation of the hearing device resulting in a whistling sound referred to as feedback or feedback in the context of the illustration of the invention. Such a whistling sound is usually disturbed by the equipment wearer and by persons in his vicinity.

Another way to describe a hearing device and areas in its environment through which the feedback paths pass is when the hearing device and its environment are considered together as a system. This system is said to be unstable when it is capable of being excited by feedback from an environment incident on the hearing device. Vice versa, in a stable system, a feedback-reduced operation of the hearing device is always possible. A mathematical description Such a system is referred to herein as the overall transfer function of the system.

The probability of a feedback increases, in particular, when the microphone unit signals are amplified very strongly in some frequency ranges by the signal processing unit of the hearing device in order to compensate for a hearing loss of the equipment wearer. A gain that triggers feedback also means critical amplification.

Another influence on the occurrence of a feedback has the directional characteristic of a microphone or a microphone arrangement of the hearing device. The directional characteristic describes how strongly a sound signal is attenuated by the signal processing of the hearing device as a function of which direction the sound strikes the hearing device. If it is found that a sound fed back from the listener from one direction strikes the microphones, for which a particularly strong attenuation results according to the directional characteristic, this may possibly prevent feedback. If, on the other hand, a feedback sound from one direction reaches the microphones, for which, according to the directional characteristic, a particularly low attenuation results, this can even encourage feedback.

In the case of a microphone arrangement comprising a plurality of microphones, the directional characteristic can be set by means of a directional parameter. Then, in the hearing apparatus, it may be possible to control the value of the directional parameter, for example, depending on environmental parameters, so that in different situations, e.g. in a conversation or during a concert, in each case a directional characteristic is provided by which a device carrier can perceive its environment particularly well.

From the publication DE 103 13 330 A1 a method and a hearing aid with a directional microphone system is known which has at least two microphones. By weighting the microphone signals in different frequency bands, a direction-dependent sensitivity of the directional microphone is determined. With the method, at least one acoustic interference signal can thus be effectively suppressed.

From the publication DE 198 44 748.A1 shows a method for providing a directional characteristic and a hearing aid, which has a high noise suppression under constantly changing listening situations. By using mixers and adaptive correction units, different directional characteristics can be achieved. Furthermore, weight signals, which are calculated as gain values, can also support a pronounced directional characteristic.

Further, in the document DE 10 2005 019 149 B3 a hearing aid device is described which compensates for acoustic and electromagnetic feedback signals by means of an adaptive compensation device. The hearing aid device in this case has a weighting device with which the signal of the microphone and / or the electromagnetic receiver is weighted.

In the document WO 2005/091675 A1 a hearing aid is described, which has both a multi-microphone arrangement with a processing unit for generating a directional characteristic and a unit for feedback suppression. A step size of the feedback suppression is always changed in the hearing device when a directional parameter is within a medium interval between the two possible extreme values 0 and 1. This is to be preempted possible feedback whistles. The feedback suppression unit is capable of attenuating an actually occurring feedback whistle with the aid of a tone detector. These are parameters of a FIR filter the feedback suppression unit changed until the whistle disappears.

The object of the present invention is to enable a hearing device in which a directional characteristic of a microphone arrangement depends on a value of a directional parameter, a feedback-reduced operation of the hearing device.

The object is achieved by a method according to claim 1. The object is also achieved by a method according to claim 6 and by a hearing device according to claim 7. Advantageous developments of the method according to the invention and the hearing device according to the invention are given by the subclaims.

By means of the method according to the invention, a hearing device can be operated. The first of these procedures concerns while a hearing device with a microphone arrangement, in which a directional parameter for setting a directional characteristic of the microphone arrangement is adjustable. Such adjustable microphone arrangements are known in principle from the prior art in many embodiments.

According to the first method according to the invention, a stability condition for a feedback-reduced operation of the hearing device is specified. Such a stability condition can for example be based on a calculation rule by means of which it can be determined whether the system is stable in the sense described above. It is always given a stability condition in which it depends on the value of the directional parameter, whether it is satisfied or not. Based on the stability condition, those values of the directional parameter for which the stability condition is fulfilled are then determined according to the method. In a further step, the values for the directional parameter which are possible during operation of the hearing device are then limited to the determined values. In other words, such settings of the directional characteristic are prevented, by which a feedback is favored. This is achieved by the exclusive admission of the determined values.

Which of the permitted values is actually set can thereby be determined by another method. Such a method may be, for example, the already mentioned method for optimizing the directional characteristic as a function of environmental parameters. As a result of the limitation to the determined stability values, it is then always ensured in an advantageous manner that the operation of the hearing device remains reduced in terms of feedback.

For example, a stability condition may be that an overall gain resulting from one sweep of a feedback loop is less than one. The overall gain is a dependent on the directional characteristic of the microphone array size. That the overall gain is less than one, but need not always be the condition for a stable, so essentially feedback-free, operation. If, for example, an algorithm for feedback suppression is also provided in the hearing device, then a stability condition can be that only such feedback is prevented, which can no longer be suppressed by the algorithm in a time period acceptable to the device carrier.

However, as a stability condition, it can also be specified that the overall gain of the feedback loop must be significantly less than unity. This can be useful, for example, if changes in the transfer function are to be expected and also for such changed transfer functions a substantially feedback-free operation should still be guaranteed. A transfer function can change, for example, in that the hearing device slips on an ear of the device carrier.

Finally, a stability condition can also include the criterion that a measured value of a physical variable or a value of a control parameter lies within a correspondingly predetermined interval.

In a preferred embodiment of the first method according to the invention, a term of a denominator of a total transfer function is specified, the term comprising at least the directional parameter and a transfer function of a feedback path. Those values are determined for the directional parameter for which the stability condition is satisfied, that the term fulfills a predetermined criterion. The term preferably determines a position of one pole of the total transfer function in the complex number plane.

It is particularly advantageous that the overall transfer function also includes a transfer function of a feedback path. This also becomes an influence of an environment the hearing device on the feedback behavior taken into account. Since the total transfer function also includes the directivity parameter itself, an analytical calculation of the stability value or an interval of stability values is advantageously possible. Preferably, a corresponding transfer function is determined for each microphone.

The method according to the invention is also advantageously developed if the values are determined as a function of a frequency of a signal. Then, for example, different stability values can be provided for individual channels of a filter bank. As a result, a different stability condition can be specified for each channel, without having to unnecessarily restrict a directional characteristic in another channel in order to fulfill a stability condition in one channel.

• eine Übertragungsfunktion F₁ eines ersten Rückkopplungspfads und eine Übertragungsfunktion F₂ eines zweiten Rückkopplungspfads,
• eine Verstärkungsfunktion H_c der Hörvorrichtung,
• eine Frequenz ω eines Signals,
• eine Verzögerungszeit τ_i und ein Gewichtungsfaktor a als der Richtparameter, durch welche beiden die Richtcharakteristik der Mikrofonanordnung festgelegt ist, und
• eine Laufzeit τ_e eines Schalls zwischen zwei Mikrofonen der Mikrofonanordnung umfasst. Die Laufzeit τ_e ergibt sich als τ_e=d/c*cos(α), wobei d ein Abstand der beiden Mikrofone und c die Schallgeschwindigkeit in Luft ist. Der Faktor cos(α) ist der Kosinus des Einfallswinkels α des Schalls bezüglich der Hörvorrichtung. Die Verstärkungsfunktion H_c umfasst insbesondere einen Frequenzgang, durch welchen ein Hörverlust eines Geräteträgers ausgeglichen wird. Für die Frequenz des Umgebungssignals gilt: ω=2πf , wobei f eine Frequenz gemessen in Hertz ist. Auch die übrigen Größen in der Gesamtübertragungsfunktion können frequenzabhängig sein.

In a further advantageous embodiment of the inventive method, the overall transfer function is formed as the quotient A / B, where A = [1-exp (- j ω (τ _s + τ _i))] H _c and B = 1-H _c [F ₁ (1 + a exp (- j ω τ _i)) F ₂ (a + exp (- j ωτ _i))] is used. Here are of the total transfer function:

• a transfer function F _{1 of} a first feedback path and a transfer function F _{2 of} a second feedback path,
• an amplification function H _{c of} the hearing device,
• a frequency ω of a signal,
• a delay time τ _i and a weighting factor a as the directional parameter, by which both the directivity of the microphone array is fixed, and
• a transit time τ _{e of} a sound between two microphones of the microphone assembly comprises. The transit time τ _e results as τ _e = d / c * cos (α), where d is a distance between the two microphones and c is the speed of sound in air. The factor cos (α) is the cosine of the angle of incidence α of the sound with respect to the hearing device. In particular, the amplification function H _c comprises a frequency response by which a hearing loss of a device carrier is compensated. For the frequency of the ambient signal ω = 2πf, where f is a frequency measured in Hertz. The remaining variables in the overall transfer function may also be frequency-dependent.

The overall transfer function A / B allows, for the first time, an analytical calculation of values for stable operation. The directional parameter here is preferably the weighting factor a. The development of the first method according to the invention is based on the knowledge that a feedback-reduced or substantially feedback-free operation is often possible for entire intervals a <a ₀ . Accordingly, then only the limit a _{0 of} the interval must be determined in an advantageous manner. For each value from this interval, there is the certainty that a feedback reduced operation is possible. By accurately calculating values for the weighting factor, it is advantageously ensured that a predetermined stability condition is maintained and yet the weighting factor is not unnecessarily severely restricted.

Based on the total transfer function can be checked according to an advantageous development of the method according to the invention for determining the values, for which values of the weighting factor a, an amount of a term H _{c [F 1} (1 + a exp (- j ω τ _i)) - F ₂ ( a + exp - is less than a stability limit)] (j ωτ _1). The term can be used to easily calculate an interval of possible stability values for the weighting factor a.

In addition, a measure of a strength of the feedback effect can be provided by the term. This measure allows, for example, to determine how robust the hearing device is for a given value of the weighting factor a against feedback. A hearing device is all the more robust, the more the transfer function F ₁ and F ₂ and other variables contained in the term can change, without this leading to an unforeseen feedback comes. As the stability limit, the value of one is preferably used.

The second method according to the invention relates to the operation of a hearing device in which a directional parameter for determining a directional characteristic of a microphone arrangement can be set as a first parameter and a control parameter for controlling a device for feedback suppression as a second parameter. The method provides a measure of a feedback effect. An example of such a measure is the overall transfer function already described or the mathematical term above. From the term, a strength of the feedback effect, e.g. the feedback gain can be determined. Based on a current value of the directional parameter, a value for the dimension is determined. Depending on the determined value, at least one of the parameters is set.

As a measure of the feedback effect, a distance measure to a stability limit as a function of the directional parameter is specified. As parameter, a step size for an adaptation algorithm of the unit for feedback suppression is set. In this case, an adaptation speed of the adaptation algorithm is then increased if the hearing device is operated near the stability limit.

In addition or as an alternative to the distance measure, a measure of the feedback effect is analyzed as to whether there is feedback, and in the setting step the instantaneous value of the directional parameter is changed until a feedback effect falls below a predefined threshold. Such a threshold is determined in particular by the fact that for the feedback loop, a gain is less than one, so that an existing feedback decays independently.

With the method, the directional characteristic can advantageously be used to avoid or suppress feedback or the feedback suppression are set. It is only known from the prior art to reduce the gain of the receiver signal.

The adaptation algorithm may for example be part of a feedback suppression unit as already described. The step size thereby controls the adaptation speed of the algorithm. According to the second method, if it is found from the value of the directional parameter that the hearing device is operated near a stability limit, the adaptation speed is increased. By controlling the step size as a function of the value for the directional parameter, there is the advantage that the adaptation speed is always particularly high, even if the risk for feedback is high.

A further aspect of the invention relates to a hearing apparatus in which a directional parameter for determining a directional characteristic of a microphone arrangement can be set as a first parameter and a control parameter for controlling a device for feedback suppression can be set as a second parameter. Furthermore, a control device is provided in the hearing device according to the invention, which is designed to operate the hearing device according to at least one of the two methods according to the invention or one of the described developments thereof.

The hearing device according to the invention is thus advantageously able to independently ensure a feedback-reduced operation by means of the control device.

In a microphone arrangement, a directional characteristic can be made possible, for example, by superimposing a cardioid directional characteristic and an anti-cardioid directional characteristic. It can be provided be that a proportion of the anti-Kardioid directional characteristic of the overall directional characteristic of the microphone array is determined by a weighting factor a. Then the overall directional characteristic is adjustable by means of the weighting factor a.

FIG 1

eine schematische Darstellung eines Aufbaus eines Hin- ter-dem-Ohr-Hörgeräts ohne Schallschlauch und Ohrstück;

FIG 2

einen Signalflussgraphen zu einem System, welches eine Ausführungsform der erfindungsgemäßen Hörvorrichtung umfasst; und

FIG 3

ein Blockschaltbild zur prinzipiellen Funktionsweise einer Ausführungsform einer erfindungsgemäßen Hörvor- richtung.

The invention will be explained in more detail below with reference to exemplary embodiments. This shows:

FIG. 1

a schematic representation of a construction of a behind-the-ear hearing aid without sound tube and earpiece;

FIG. 2

a signal flow graph to a system, which comprises an embodiment of the hearing device according to the invention; and

FIG. 3

a block diagram of the basic operation of an embodiment of a hearing device according to the invention.

The examples illustrate preferred embodiments of the invention.

In FIG. 2 a hearing aid 12 with a microphone assembly 14 of two microphones 16, 18 is shown. The hearing aid 12 may be, for example, a behind-the-ear hearing aid, of which a in FIG. 2 not further illustrated housing with the microphone assembly 14 is located behind an ear of a device carrier.

The hearing device 12 may also include, for example, a sound tube and an earmold. The earmold can be used in an ear canal of the equipment wearer. By a receiver 20 of the hearing aid 12, a sound is generated, which is passed through the sound tube and earmold in the ear canal. Instead of an earmold, another type of earmold can also be provided.

An air surrounding the hearing device 12 and the ear of the equipment wearer form an environment of the hearing device 12, which together with the hearing aid 12 form a system 10, in which it can come to a feedback. Through the environment feedback paths 22, 24 are formed, via which a sound Y of the listener 20 can get to the microphone assembly 14. The feedback paths 22, 24 include, for example, an acoustic propagation path which passes through a vent opening of the earmold. Upon propagation of the sound signal Y along the feedback path 22, the sound signal Y is changed according to a transfer function F ₁ , which in FIG. 2 designated by the reference numeral 26. For the feedback path 24 results in a transfer function F ₂ , which in FIG. 2 designated by the reference numeral 28.

Through the microphone 16, a sound X is received by a sound source, which is located in a vicinity of the equipment carrier. The sound X also hits the microphone 18 with a time delay τ _e. The time delay τ _e depends on a distance d of the microphones 16, 18 and on an angle α between the direction of propagation of the sound X and an axis of the microphone arrangement 14 in the one described Way off. The sound X and the sound Y passed through the feedback paths 22, 24 are superimposed on the microphones 16, 18. This is in FIG. 2 indicated by sum symbols 30, 30 '.

The hearing device 12 has a device 32 for generating a directivity of the microphone arrangement 14. The microphones 16 and 18 themselves can each have an omnidirectional directivity, ie each of the microphones 16, 18 detects a sound in this case, without direction. The device 32 comprises delay elements 34, by means of which a microphone signal can be delayed by a delay time τ _i . Such a delay may be effected, for example, by varying a phase of a spectral component of the microphone signal. The device 32 also includes summers 36, 38, 40, by means of which two signals can be superimposed, ie added, in each case. It is in the summers 36, 38 inverts one of the input signals before the superposition. This is in FIG. 2 indicated by a minus sign. The unit 32 further comprises a multiplier 42, by which a signal with a weighting factor a can be weighted, ie multiplied.

By means 32, a cardioid branch 44 and an anti-cardioid branch 46 are provided as signal paths. In the case of a signal which reaches the summer 40 via the cardioid branch 44, signal components are attenuated in accordance with a cardioid directional characteristic of the microphone arrangement 14. A signal is sent to the summer 40 via the anti-cardioid branch 46, in which signal portions are damped in accordance with an anti-cardioid directional characteristic of the microphone arrangement 14. A portion of the signal of the branch 46 on a sum signal at the output 48 of the unit 32 is determined by the weighting factor a. The weighting factor a is a directional parameter of the device 32.

The output 48 of the unit 32 is coupled to an amplifier 50 of the hearing aid 12. Through the amplifier 50, a signal may be amplified in response to a hearing curve of the equipment wearer to compensate for hearing loss.

A signal path consisting of the feedback path 22 and the electrical path from the microphone 16 to the listener 20 forms a first feedback loop. The feedback path 24 and the electrical signal path from the microphone 18 to the handset 20 together form a second feedback loop. The two feedback loops give a feedback effect. Of a gain along the feedback loops depends on whether a signal to a feedback in the sense already described, i. an audible whistle, leads.

For the in FIG. 2 shown system 10 from the hearing aid 12 and its environment results in a total transfer function Y / X = A / B, where A and B in the manner already described are defined. In connection with the quantities A and B, it should be mentioned that exp () is the exponential function and j is the imaginary unit for which j * j = -1.

Based on the total transfer function Y / X, a stability limit of the system 10 can be calculated in dependence on values for the transfer functions F ₁ and F ₂ . Is a stability condition for the system 10 that the amount of the term H _{c [F i} (1 + a exp (- j ωτ _i) -F ₂ (a + exp (- j ωτ _i))] is less than or equal to 1. Then, the sound X does not generate feedback, that is, a sound Y of the listener 20 passing through the feedback paths 22 and 24 to the microphone assembly 14 generates a feedback effect so that a microphone signal in the hearing aid 12 can again be caused by it However, the signal is always attenuated along the feedback loop to such an extent that it automatically decays over time.

On the other hand, if the value for the term is greater than one, because, for example, the weighting factor a was chosen to be too large, this can lead to a feedback, i. an audible whistle.

Parts of the specified term can also be examined individually. The factor C ₁ = H _c (1 + a exp (- j ωτ _i) for R ₁ and the factor C ₂ = H _c (a + exp (- j ωτ _i)) for R ₂ may, for example, are analyzed in each case, whether it is greater or less than 1. If at least one of these factors is greater than 1, the stability limit, in the system 10 reached earlier than in a system with a single, omnidirectional microphone. If the two transfer functions F ₁ and F ₂ of the feedback paths 22 and Of course, both have a significant effect on the stability limit.

By contrast, if the summands C ₁ and C ₂ are less than 1, the system 10 is more stable than a system with a single omnidirectional microphone. Then, a larger amplification of the signal by the amplifier 50 is possible than in a Hearing aid with a single microphone. Both summands C ₁ and C ₂ depend on the weighting factor a for the anti-cardioid branch 46 and on the frequency ω. Depending on the weighting factor a, the critical gain value is greater than in a hearing aid with a single omnidirectional microphone. In such a case, a correspondingly greater amplification can be provided by the hearing device 12 without a feedback being triggered in the process.

By the overall transfer function, a calculation of a maximum weighting factor a for the anti-cardioid branch 46 is possible, up to which a substantially feedback-free operation of the hearing aid 12 is possible. This calculation requires a measurement of the transfer functions F ₁ and F _{2 of} the feedback paths 22, 24. Transfer functions F ₁ and F ₂ and further transfer functions for the individual feedback paths can be determined, for example, by a device carrier carrying a hearing device intended for it in the intended manner and test measurements, for example by a hearing care professional. On the basis of the transfer functions of the feedback paths thus determined, it is then possible to determine, for example, an interval a <a ₀ of values for which a reduced-feedback operation results.

In operation, the weighting factor a can then be limited to the maximum value a ₀ , ie to the upper limit of the determined interval. A device carrier then perceives such a limitation as reduced directivity in those situations in which feedback is expected.

By calculating a distance of the weighting factor a from the maximum allowable value a ₀ , an algorithm for feedback suppression can also be controlled. If the weighting factor a is set to a value close to the maximum permissible value a ₀ at a certain point in time, a relatively small change in the weighting factor a lead to an unstable system. Similarly, the instability may be caused by a slight change in the transfer functions F ₁ or F ₂ . If the system 10 is close to such a stability limit, then an adaptation rate of the feedback suppression algorithm can be increased. If it actually comes to a feedback, this is suppressed by the algorithm very quickly.

In a feedback suppression algorithm, detection or detection may also be provided for feedback. On the basis of such recognition, an adaptive limitation of the weighting factor a can be made possible. If a feedback is detected, then a limit for the weighting factor a can be reduced. As a result, the instantaneous value of the weighting factor a itself is also reduced until the system is stable again. Then the feedback sounds self-contained. If no further feedback is subsequently detected for a predetermined period of time, the limit for the weighting factor a can be raised again. In such an adaptive limitation, it can be ensured by specifying appropriate time constants that no cyclic repetition of feedbacks is caused. The adaptive adaptation of the weighting factor a for the anti-cardioid branch 46 using the algorithm for feedback suppression results in the advantage that a hearing aid always allows a correspondingly maximum possible value for the weighting factor a even when the environment changes.

A particular aspect of the invention is the ability to mathematically determine a stability limit for a system based on the directivity parameter a and the transfer functions F ₁ , F ₂ for feedback paths. This makes it possible to limit the weighting factor a, so that a stable system is always ensured. In this case, the predetermined for example by a hearing curve of a device carrier gain of the microphone signals are taken into account.

Further, in conjunction with an algorithm for feedback suppression, there are possibilities to adaptively adapt the limitation during operation of the hearing device when a sound is critically amplified. By aligning notches of the directional characteristic in a corresponding manner, a particularly high gain, as is possible for hearing aids with only a single omnidirectional microphone, can also be achieved for a hearing aid with directivity. A notch of a directional characteristic is such a detection direction, for which results in a comparatively strong attenuation.

In FIG. 3 For example, a control device 52, a directional microphone device 54 and a device for suppressing a feedback, ie a feedback suppression 56, are shown. The three devices 52, 54, 56 may be provided as programs on a signal processing processor of a hearing device. The directional microphone device 54 can process signals of a microphone arrangement, for example in the manner explained in connection with the device 32, in order to generate a directional characteristic for the microphone arrangement. For example, the feedback suppression 56 may be configured to estimate transfer functions of feedback paths to generate a compensation signal from the estimated transfer functions to attenuate a signal of acoustic feedback.

The directional microphone device 54 and the feedback suppression 56 are each coupled to the controller 52. By the control device 52, a directional parameter of the directional microphone device 54 is adjustable. Furthermore, a step size for an adaptation algorithm of the feedback suppression 56 can be set by the control device 52. Conversely, instantaneous values of these parameters can also be read from the directional microphone device 54 and the feedback suppression 56. additionally For example, the estimated transfer functions for the feedback paths from the feedback suppression 56 can also be read out.

The control device 52 is designed to use these values to determine the directional parameter or the step size in connection with FIG. 2 to control described manner. Thus, it is possible in the hearing device to control the directional microphone device 54 and / or the feedback suppression 56 to prevent or suppress an acoustic feedback accordingly. In particular, it can be made possible to flexibly set the directional characteristic in accordance with the needs of a wearer of the hearing device, while correspondingly controlling the step size of the feedback suppression adaptation algorithm 56 in order to suppress possible feedback. In the same way, however, it is also possible to effectively avoid feedback or to suppress a feedback that has occurred since the directional characteristic is set by a corresponding control of the directional microphone device 54.

Claims (8)

1. Method for operating a hearing device (12), in which a directional parameter for fixing a directional characteristic of a microphone array (14) of the hearing device (12) can be set,
   comprising the steps of:

   - prescribing a stability condition, depending on the directional parameter, for feedback-reduced operation of the hearing device (12);

   - establishing those values of the directional parameter that satisfy the stability condition;

   - restricting the possible values for the directional parameter during operation of the hearing device to the established values.
2. Method according to Claim 1,
   wherein a term of a denominator of an overall transfer function is prescribed and, here, the term comprises at least the directional parameter (a) and a transfer function (26, 28) of a feedback path (22, 24),
   and wherein those values for the directional parameter (a) are established that satisfy as a stability condition that the term satisfies a predetermined criterion.
3. Method according to Claim 1 or 2, wherein
   the values are established as a function of a frequency of a signal.
4. Method according to one of Claims 2 or 3, in which the overall transfer function is formed as a fraction A/B, with A= [1-exp (-j ω(τ_e+τ_i))] H_c and
   B=1-H_c[F₁(1+a exp (-j ωτ_i)) -F2 (a+exp (-j ωτ _i))], and this comprising:

   - a transfer function F₁ of a first feedback path and a transfer function F₂ of a second feedback path,

   - a gain function H_c of the hearing device,

   - a frequency ω of a signal,

   - a delay time τ_i and a weighting factor a as the directional parameter, by means of which two factors the directional characteristic of the microphone array is fixed, and

   - a run time τ_e of sound between two microphones of the microphone array.
5. Method according to one of the preceding claims, wherein, in order to establish the values for the weighting factor a, a check is carried out as to whether a value of the term H_c[F₁(1+a exp(-j ωτ_i))-F₂(a+exp(-j ωτ_i))] is less than a stability threshold, more particularly whether it is less than one.
6. Method for operating a hearing device (12), in which a directional parameter for fixing a directional characteristic of a microphone array (14) can be set as a first parameter and a control parameter for controlling an apparatus (56) for the purpose of feedback suppression can be set as a second parameter,
   comprising the steps of:

   - prescribing a measure for a feedback effect;

   - establishing a value for the measure on the basis of a current value of the directional parameter;

   - setting at least one of the parameters as a function of the established value,

   characterized in that

   a) a distance measure from a stability threshold, dependent on the directional parameter, is prescribed as a measure for the feedback effect and
   an increment for an adaptation algorithm of the unit for the purpose of feedback suppression is set as parameter and, here, an adaptation speed of the adaptation algorithm is increased if the hearing device is operated in the vicinity of the stability threshold, and/or

   b) as a measure for the feedback effect, there is analysis relating to whether there is feedback and,
   in the step of setting, the current value of the directional parameter is changed until a feedback effect drops below a prescribed threshold.
7. Hearing device (12), with
   a microphone array and an apparatus (56) for the purpose of feedback suppression, wherein
   a directional parameter for fixing a directional characteristic of a microphone array (14) can be set as a first parameter and a control parameter for controlling the apparatus (56) for the purpose of feedback suppression can be set as a second parameter,
   characterized by
   a control apparatus (52) that is designed to operate the hearing device as per a method according to one of the preceding claims.
8. Hearing device according to Claim 7, wherein
   the directional characteristic of the microphone array (14) can be generated by a superposition of a cardioid directional characteristic (44) and an anti-cardioid directional characteristic (46) and an anti-cardioid directional characteristic (46) component is determined by the directional parameter.

Images