EP2988529B1 - Adaptive separation frequency in hearing aids - Google Patents

Description

The invention relates to a method for suppressing acoustic feedback in a hearing aid, wherein a pitch frequency between a first frequency range with feedback suppression and a second frequency range is adapted without feedback suppression, and an apparatus and a system for carrying out the method.

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 (ITE), 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 an acoustoelectric transducer, 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 usually integrated in a signal processing device. The power is usually supplied by a battery or a rechargeable battery.

Because of the large spatial proximity between the microphone and the electro-acoustic output transducer there is always the danger that an acoustic signal as sound through the air, whether through a vent, a gap between the wall of the ear canal and the hearing aid or an earpiece of the hearing aid or is transmitted in the interior of the hearing aid or as structure-borne noise on the hearing aid itself. If the overall gain of a feedback loop, which results from the signal processing in the hearing aid and the attenuation between the output transducer and microphone, is greater than 1, this can occur with a suitable phase shift of a signal, in particular if the phase shift is 0 or integral multiples of 2 * Pi along this feedback loop give an oscillation which is manifested to the wearer as an unpleasant whistle.

For the suppression of feedback noise in hearing aids different measures are known from the prior art. One possibility is to use adaptive filters to estimate the feedback signal and thus the impulse response between the listener and the microphone (also called the feedback path). By means of this estimated impulse response, a signal inverse in phase with the feedback signal can be generated, which is added to the microphone signal and thus eliminates the feedback component. Since this estimation is error-prone and mispredictions can lead to disturbing artifacts, it is advantageous to apply the filter adaptation and thus the estimate of the feedback component only above a division frequency (English Split-Band Frequency, SFB).

It is known from the prior art that a frequency shift or a time-variable phase shift (eg a phase modulation) of the receiver signal has an advantageous effect on the quality of the estimated feedback pulse response. However, a superimposition of signal components which are unchanged in frequency and / or phase and of frequency-shifted or phase-modulated signal components to disturbing artifacts. A superimposition of these two signal components comes about for two reasons: 1. Signal components emitted directly from the sound source are superimposed acoustically in front of the eardrum with signal components emitted by the listener. 2. Due to the finite edge steepness of the filters, which realize the pitch frequency, above which the signal is frequency-shifted and / or phase-modulated, signal components are superimposed electrically.

From the publication US 2010/0272289 A1 It is known to place the pitch frequency in a frequency range which has a low signal energy, since in this way it is also ensured that artifacts, which have a simultaneous occurrence of phase-shifted and unchanged signals, by electrical interference, also have low energy and less disturbing.

In the EP 2 003 928 A1 For a hearing aid, it is proposed to continuously determine the gain of the closed feedback loop and, if the same exceeds a critical value, to adjust the active forward gain in the hearing aid to avoid feedback.

In the WO 2008/000842 A2 the frequency bandwise determination of gain limits for feedback is described. In this case, the limit values are explicitly determined only in those frequency bands for which the exact knowledge of the limit value is assumed to be particularly important, and for the remaining frequency bands the limit values are interpolated on the basis of the exactly measured values, for example using corresponding tables.

I'm in the DE 39 27 765 A1 said approach, the signal of a hearing aid is filtered by means of a high pass filter with a variable cutoff frequency. To determine the cutoff frequency is proposed to sample the amplitudes of low-frequency components of the filtered signal, and increase the cut-off frequency correspondingly at high amplitude contributions.

It is therefore an object of the present invention to provide an improved method for feedback suppression as well as a hearing aid with improved feedback suppression.

According to the invention this object is achieved by a method according to claim 1, and a system according to claim 6.

The inventive method relates to a method for suppressing an acoustic feedback in a hearing aid. The hearing aid has an acousto-electric input transducer, signal processing and an electro-acoustic output transducer. The method according to the invention has the following steps.

In one step, an acoustic frequency range transmitted by the hearing aid is divided into a first frequency range above a first division frequency and a second frequency range below the first division frequency. It is conceivable that in the real implementation of the frequency division by filters due to finite edge steepness an overlap region is given, for example, 10 Hz, 50 Hz, 100 Hz or 200Hz may be and in which an amplitude of a signal from the respective adjacent frequency range, for example by 6 dB, 12 dB or 18 dB is attenuated.

In a further step, a first transfer function of a feedback loop via the electro-acoustic output transducer, an acoustic feedback path, the acousto-electric input transducer and the signal processing in the first frequency range is estimated. The estimated first transfer function is an illustration of a real transfer function resulting for the feedback loop from the acoustic environment (i.e., the estimated feedback impulse response) and the hearing aid. In order to facilitate the estimation of correlated signals, it is conceivable that a frequency shift and / or phase modulation is also carried out in a predetermined frequency range below the division frequency, for example at a fixed distance of 50 Hz, 100 Hz or 200 Hz or in a predetermined dependence of the pitch frequency.

In another step, the first transfer function is evaluated as to whether the behavior of the first transfer function in the vicinity of the first division frequency is to be expected to exceed a predetermined limit value by the real transfer function. Various ways to evaluate the first transfer function are given in the dependent claims.

If, in the vicinity of the first division frequency, the predetermined transfer value is not expected to be exceeded by the real transfer function, the first division frequency is increased to a second division frequency such that all values of a gain of the first transfer function of the feedback loop become smaller for frequencies smaller than the increased second division frequency as the predetermined limit are. In other words, the second division frequency is increased at most to a value below a cutoff frequency at which the gain of the closed feedback loop just does not exceed the threshold.

In one step of the method according to the invention, the first division frequency is reduced to a second division frequency if, in the vicinity of the first division frequency, exceeding the predetermined limit value by the real transfer function is to be expected. In other words, the second division frequency is reduced to a value below a cut-off frequency at which the gain of the feedback loop is expected to be less than the limit.

Subsequently, only above an insertion frequency in response to the second division frequency, a phase or frequency shift is applied to suppress feedback. The insertion frequency may be, for example, a fixed amount of, for example, 50 Hz, 100 Hz or 200 Hz below the second division frequency, or may assume a value of the second division frequency reduced by linear or other predetermined factor.

The method according to the invention adapts the pitch frequency between a first frequency range, in which a phase or frequency shift is necessary to prevent feedback, and a second frequency range, in which this is not required, depending on the feedback path. Thus, advantageously, the frequency range is minimized in which occur due to the phase shift interfering artifacts. In this case, the method also makes it possible to derive an evaluation or prediction of the real transfer function for a frequency range below the division frequency from an estimate of the first transfer function in the first frequency range. This is particularly advantageous, since an estimation is usually carried out only in a frequency range which is endangered by feedback above a cutoff frequency Among other things, to conserve resources of the hearing aid.

The invention also relates to a device for suppressing acoustic feedback in a hearing aid. The hearing aid has an acousto-electric input transducer, signal processing and an electro-acoustic output transducer. The device is in signal communication with the hearing aid, in particular, the device receives information from the hearing aid to a signal received via the microphone and a signal output to the listener.

The device is designed to divide an acoustic frequency range to be transmitted by the hearing aid into a first frequency range above a first pitch frequency and a second frequency range below the first pitch frequency.

The apparatus is further configured to estimate a first transfer function of a feedback loop via the electroacoustic output transducer, an acoustic feedback path, the acousto-electric input transducer, and the signal processing in the first frequency range as an illustration of a real transfer function across the feedback loop.

The device is also designed to evaluate the first transfer function as to whether the behavior of the first transfer function in the vicinity of the first division frequency is to be expected to exceed a predetermined limit value by the real transfer function.

Furthermore, the device is designed, when in the environment of the first division frequency exceeding a predetermined limit value by the real transfer function is not expected to increase the first division frequency far enough to a second division frequency, that all values of a gain of the first transfer function for frequencies smaller when the second division frequency is smaller than the predetermined limit value.

Finally, the device is designed, if it is to be expected in the vicinity of the first division frequency exceeding a predetermined limit value by the real transfer function, to reduce the first division frequency to a second division frequency.

In addition, the device is designed to set in the hearing aid a phase or frequency change for feedback suppression in the signal processing only above an insertion frequency in response to the second division frequency.

Furthermore, the invention relates to an inventive system of a hearing aid and a device according to the invention. It is conceivable that the device is part of the hearing aid, for example, implemented as a separate unit or as part of the signal processing of the hearing aid. But it is also conceivable that the device is an external device and is implemented in a separate unit such as a remote control, a converter or even by an application on a smartphone.

The device according to the invention and the system according to the invention share the advantages of the method according to the invention.

Further advantageous developments of the invention are specified in the dependent claims.

In a conceivable embodiment of the method according to the invention, in the step of evaluating the first transfer function, exceeding the predetermined limit value by the first transfer function is to be expected when the first transfer function increases towards the first division frequency.

It is possible in a simple manner to determine functional values in the environment above the first division frequency for the estimated first transfer function and in this way to evaluate the behavior of the first transfer function, in particular also to detect whether this increases in the first division frequency. According to the invention that the behavior of a real transfer function of the environment and the hearing aid in an environment of the pitch frequency is similar to the behavior of the estimated first transfer function above the first division frequency, the behavior of the real transfer function and thus the feedback behavior of the hearing aid for Frequencies below the first division frequency are predicted. Thus, from the fact that the first transfer function increases above the first division frequency, it can be expected and concluded that the real transfer function also exceeds the limit value below the first division frequency in a frequency range. Conversely, if the first transfer function does not increase, it can also be concluded that the limit value is not exceeded by the real transfer function even below the first division function. Accordingly, it is then possible to shift the first division frequency by this frequency range down to a second division frequency.

In one conceivable embodiment of the method according to the invention, a second transfer function of a feedback loop in a third frequency range below the first division frequency is determined as a function of the first transfer function of the closed feedback loop. The determining may comprise deriving the second transfer function from the first transfer function, for example by assuming a value of the lowest frequency of the first transfer function as a constant value of the second transfer function for the third frequency range or a part thereof or the second transfer function linearly or in another way the first transfer function is interpolated. Preferably, the third frequency range is adjacent to the first frequency range Pitch frequency. Preferably, the third frequency range comprises only a part of the second frequency range, for example a half, a third, a quarter or a tenth of the bandwidth of the second frequency range.

Determining a second transfer function by means of interpolation advantageously makes it possible to more accurately predict a real transfer function of the acoustic environment and of the hearing aid even with more complex behavior and to determine the second division frequency even more reliably.

In a conceivable embodiment of the method according to the invention, the predetermined limit value of a gain of the first or second transfer function is 0 dB minus a stability distance.

With a gain of 0 dB in the feedback loop, the limit for feedback is reached. By determining the pitch frequency with a safe margin down from the critical value, it is advantageously ensured that no unwanted feedback occurs.

In one possible embodiment of the method according to the invention, after the step (S40) of increasing the division frequency or step (S50) of decreasing the division frequency, the method proceeds by estimating a first transfer function of a closed feedback loop (S20).

In each case, when an altered first transfer function in a changed first frequency range is estimated again with a changed division frequency, the method according to the invention is advantageously able to adapt to changing conditions such as acoustic environment or changed seat of the hearing aid.

In one embodiment of the method according to the invention, the division frequency is greater than 1 kHz.

Usually, feedback occurs as whistles in higher frequency ranges. The method according to the invention is advantageously limited to a frequency range above 1 kHz in order to avoid artifacts in the particularly sensitive range of the fundamental frequencies of the speech and to save resources in the signal processing of the hearing aid.

In one possible embodiment of the method according to the invention, the pitch frequency is less than 2 kHz.

The method according to the invention is based, in particular, on the knowledge that below 2 kHz there is a correlation between the behavior of a feedback path at different frequencies. It is therefore possible, in particular in frequency ranges below 2 kHz, to conclude from estimated characteristics of a feedback path at one frequency to the characteristics of the feedback path at another frequency. The method according to the invention uses this knowledge to advantageously determine from the estimated first transfer function above the division frequency a second transfer function in a third frequency range below the division frequency, without having to estimate it costly.

The above-described characteristics, features, and advantages of this invention, as well as the manner in which they will be achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which will be described in detail in conjunction with the drawings.

Fig. 1

eine beispielhafte schematische Darstellung eines erfindungsgemäßen Hörhilfegeräts;

Fig. 2

eine schematische Darstellung eines erfindungsgemäßen Systems;

Fig. 3

ein schematisches Ablaufdiagramm eines erfindungsgemäßen Verfahrens;

Fig. 4

eine beispielhafte geschätzte Transferfunktion eines Rückkopplungspfades und

Fig. 5

eine schematische Darstellung in Funktionsblöcken einer möglichen Implementierung eines erfindungsgemäßen Hörhilfegeräts bzw. Systems.

Show it:

Fig. 1

an exemplary schematic representation of a hearing aid according to the invention;

Fig. 2

a schematic representation of a system according to the invention;

Fig. 3

a schematic flow diagram of a method according to the invention;

Fig. 4

an exemplary estimated transfer function of a feedback path and

Fig. 5

a schematic representation in functional blocks of a possible implementation of a hearing aid device or system according to the invention.

Fig. 1 shows a basic structure of a hearing aid according to the invention 100. In a hearing aid housing 1 for carrying behind the ear are one or more microphones, also referred to as acousto-electrical converter 2, incorporated for receiving the sound or acoustic signals from the environment. However, the invention is not limited to BTE hearing aids, but may equally find application in IdO or CiC hearing aids. The microphones 2 are acousto-electrical converters 2 for converting the sound into first electrical audio signals. A signal processing device 3, which is likewise arranged in the hearing aid housing 1, processes the first audio signals. The output signal of the signal processing device 3 is transmitted to a loudspeaker or receiver 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. But it is also another electro-mechanical transducer conceivable, such as a bone conduction. The power supply of the hearing aid and in particular the signal processing device 3 is effected by a likewise integrated into the hearing aid housing 1 battery. 5

The hearing aid device 100 also has an inventive device 6 for suppressing an acoustic Rücckopplung on. This is in signal communication with the signal processing device 3 in order to acquire information about an acoustic signal received by the microphone 2 and a signal output to the receiver 4. In addition, the device 6 is able to influence the signal processing device 3 via the signal connection, for example to activate a phase shift in a frequency range or to change this frequency range. It is equally conceivable that the function of the device 6 is implemented in the signal processing device 3, for example as circuits in an ASIC or as a function block in a signal processor.

Fig. 2 shows the basic structure of a system 200 according to the invention, consisting of a hearing aid 100 and a separate device 6. The signal connection between the device 6 is preferably realized wirelessly, for example via an inductive coupling, as it is also used in binaural hearing aids for coupling. Conceivable, however, are other electromagnetic transmissions with low energy consumption such as Bluetooth. Also conceivable are optical transmission or conducted transmission.

In this case, the device 6 can be a dedicated device or even a multifunctional device such as a remote control, a media converter (for example, a Bluetooth induction loop) or a smartphone.

Fig. 3 shows a schematic flow diagram of a method according to the invention.

In a step S10, an acoustic frequency range transmitted by the hearing aid device 100 is split into a first frequency range FB1 above a first pitch frequency TF and a second frequency range FB2 below the first pitch frequency TF. This division can be done in the signal processing device 3 or in the device 6 itself. The first division frequency TF may be a predetermined value or may have resulted from previous steps.

In a step S20, a first transfer function of a closed loop transfer function (CLTF) is estimated via the electro-acoustic output transducer, an acoustic feedback path, the acousto-electric input transducer and the signal processing in the first frequency range FB1. For example, algorithms can be used for estimation which minimize an error between the real transmission or transfer function of the feedback loop via receiver 4, microphone 2 and signal processing 3 and a parameterized function and thus determine the parameters (for example LMS). This estimation function is usually part of a back-up suppression and is therefore only for a back-endangered frequency range. According to the invention, this is the first frequency range FB1 above the first pitch frequency TF. The estimated transfer function is an approximate mapping of the real transfer function in the first frequency range FB1.

In order to enable a reliable estimation of the first transfer function also for correlated signals, it is conceivable in one embodiment of the method according to the invention that a phase modulation and / or frequency shift is applied in the first frequency range FB1 whose insertion frequency is below the first division frequency TF. In this way it is ensured that with a steady increase in the shift function a sufficient Effect on the pitch frequency TF is achieved in order to estimate the second transfer function reliable.

In a step S30, the first transfer function is evaluated as to whether an exceeding of the predetermined limit value AG by the real transfer function is to be expected in an environment of the first division frequency TF. From the fact that the first transfer function is a parameterized approximation function for the real transfer function in the feedback loop in the first frequency range FB1, it is first possible to deduce from the behavior of the first transfer function the behavior of the real transfer function in the first frequency range FB1. Furthermore, the real transfer function obeys certain mathematical and acoustic laws, so that values of the real transfer function for the first frequency range FB1 can also be used to deduce functional values in an adjacent frequency range FB2. According to the invention, therefore, the behavior of the real transfer function in an environment of the first division frequency TF is inferred from the values of the first estimated transfer function in the first frequency range FB1 in the step S30.

Within the meaning of the invention, an environment is to be understood as meaning a frequency range which can also extend to frequencies outside the first frequency range FB1, for example to frequencies below the first division frequency TF. These may be frequencies immediately below the pitch frequency TF, for example 20, 50 or 100 Hertz below. As the example explained below for a transfer function in Fig. 4 shows, but can also be assumed a decreasing behavior of the gain of the transfer function at a distance of up to one kilohertz.

If, therefore, the first transfer function drops to the first division frequency TF, so can also for frequencies in a third frequency range FB3 below the first division frequency TF, a fall in the real transfer function can be assumed. The evaluation then shows that the real transfer function does not exceed the predetermined limit value below the first division frequency TF up to a frequency spacing of 100, 200, 500 or even 1000 Hz.

In the simplest case, it can also be assumed for the evaluation that the real transfer function constantly maintains or at least does not exceed the value of the first transfer function directly at or above the first division frequency TF.

However, it is also conceivable that a second transfer function of the closed feedback loop is determined in a third frequency range FB3 below the first division frequency TF as a function of the first transfer function of the closed feedback loop. The third frequency range FB3 is below the first pitch frequency TF. Below the first division frequency TF there is no estimate of the CLTF. However, there is a correlation between the behavior of the CLTF above the first division frequency TF and below the first division frequency TF, so that according to the invention a second transfer function below the division frequency TF for the third frequency range FB3 can be determined from the first transfer function. This determination can be carried out most simply by assuming for the second transfer function in a predetermined frequency range, for example the third frequency range FB3, a value of the first transfer function, eg the value at the lowest frequency for which it was estimated, as a constant function value. The determination may also be performed, for example, by linear or polynomial functions. Other functions are conceivable. Advantageously, the determination of a transfer function by means of these functions requires a significantly lower expenditure of computing power than the estimation by means of acoustic signals. In this case, depending on the selected function for determining, the result of the determination is particularly close to a real transfer function, if the third frequency range FB3 is located directly below the first division frequency TF. However, it is also conceivable that the third frequency range FB3 does not directly adjoin the first pitch frequency TF. As the correlation decreases with increasing frequency spacing, the third frequency range FB3 preferably comprises only a part of the second frequency range FB2.

In a conceivable step S40, the first division frequency TF is increased to a second division frequency TF2 if, in an environment of the first division frequency TF, exceeding of the predetermined limit value AG by the real transfer function is not to be expected. This may be the case, for example, if the first transfer function drops to the first division frequency TF, ie the function values decrease with decreasing frequency. According to the exemplary transfer function of Fig. 4 however, it may already be sufficient if the function value of the first transfer function at the division frequency TF or in the immediate vicinity is smaller than the limit value AG of the amplification.

The first division frequency TF may then be increased to a second division frequency TF2 such that all values of a gain of the first transfer function of a closed feedback loop for frequencies less than the increased second division frequency TF2 are less than the predetermined limit AG.

The predetermined limit AG results from the fact that the total gain of the closed feedback loop, taking into account the phase angle, must be less than or equal to one. In order to generate no feedback in case of errors in determining and short-term fluctuations in the acoustic conditions, a safety margin is preferably provided in the selection of the predetermined limit value. This can be for example a distance of -2 dB, -3 dB or -6 dB.

If a second transfer function was determined in step S30 for evaluation, then if all values of the particular second transfer function are smaller than a predetermined limit value AG, it is ensured that no feedback occurs below the previous first division frequency TF. For the estimated first transfer function, which was estimated as a function of the frequency for the first frequency range FB1 above the original first division frequency TF, the frequency value is increased until the value of the estimated first transfer function is greater than or equal to the predetermined limit value AG. The increased second division frequency TF2 is then the last preceding frequency value. In this way it is ensured that for all values below the increased second division frequency TF2 the conditions for a feedback are not given and therefore a feedback suppression with possible artifacts can be dispensed with.

In a step S50, if from the evaluation of step S30 exceeding the limit value AG by the real transfer function is to be expected, the first division frequency TF is lowered to a second division frequency TF2. The distance from pitch frequency TF2 to TF can advantageously follow the course of the exemplary transfer function of FIG Fig. 4 be removed. For example, the cut-off frequency can be lowered by 100, 200, 500 or even 1000 Hz.

It is exploited in an advantageous manner that in general the gain of the hearing aid for low frequencies with a greater distance from the pitch frequency TF of 100 Hz, 200 Hz or 500 Hz in the second frequency range FB2 is below the feedback threshold.

If a second transfer function for the third frequency range FB3 below the first division frequency TF has been determined in step S30, then the first division frequency TF can advantageously be reduced to a second division frequency TF2 such that all values of a gain of the second transfer function TF2 of a closed feedback loop for frequencies less than the reduced second division frequency TF2 are less than the predetermined threshold AG.

In a further step S60, a phase change for feedback suppression in the signal processing is applied only above an insertion frequency as a function of the second division frequency TF2. As already stated, it is advantageous for estimating the first transfer function if the phase or frequency shift already begins below the division frequency TF, so that a reliable estimation is already possible for correlated signals at the division frequency TF or TF2. The insertion frequency may be, for example, a fixed amount of, for example, 50 Hz, 100 Hz, or 200 Hz below the second division frequency TF2, or may assume a value of the second division frequency TF2 reduced by linear or other predetermined factor. It is conceivable that the dependency reflects the sensitivity of the ear to artifacts and decreases in comparison with a distance linear to the pitch frequency TF or TF2.

As ensured in steps S40 and S50, the feedback conditions for frequencies below this second division frequency TF2 are not met, so that no suppression measures are required and artefacts of the suppression function in this frequency range can be avoided.

In a conceivable embodiment of the method according to the invention, the method with the second division frequency TF2 is continued as new output value with step S20, that is to say the first division frequency TF is set equal to the second division frequency TF2 and a new second division frequency TF2 'is determined by steps S20 to S50 , In this way, the inventive method is able to adapt to changing acoustic conditions, be it one other room, other ambient noise or a changed seat of the hearing aid.

Fig. 4 shows an exemplary estimated transfer function of a feedback path. The frequency f in Hz is plotted on the x-axis, and the amplification of an exemplary CLTF in dB on the y-axis. In the first frequency range FB1 above the pitch frequency TF, an estimate of the CLTF is made as part of a feedback suppression activated in this first frequency range FB1. In the second frequency range FB2 below the pitch frequency TF, there is no feedback suppression and therefore no estimation of the transfer function CLTF. However, as indicated by the arrow K (for correlation), there is a correlation between the values of the transfer function above the division frequency TF and values below. Therefore, from the estimated values for the frequency range FB1, it is also possible to determine a transfer function for a frequency range FB3 which lies below the pitch frequency TF. For example, it could be assumed in a simple approximation that the drop of the transfer function continues above FT in the region below FT and thus the transfer function remains below a predetermined limit AG, at which no feedback occurs.

Fig. 5 shows a schematic representation in function blocks of a possible implementation of a hearing aid device or system according to the invention.

First, components of a conventional hearing aid are shown. A microphone 2 receives an audio signal, converts it into an electrical signal that is processed by a signal processing HP of the hearing aid according to the impairment of the hearing aid wearer and is output via a handset 4 to the ear of the wearer. Other components such as battery, housing or controls are in Fig. 5 not shown, but part of the hearing aid according to the invention.

In the illustrated embodiment of the hearing aid according to the invention the audio signal of the microphone 2 is further divided into a first frequency range FB1 and a second frequency range FB2. This can be done by separate high and low pass filters or a simple filter bank. This is followed by an estimate of the transfer function in the first frequency range FB1 by means of a feedback control FBC (English: feed back controller). Subsequent to the signal processing HP, a phase or frequency distortion FD takes place in the first frequency range FB1 in order to take countermeasures against the feedback risk detected by the feedback control, by changing the phase or by frequency shifting. However, in order to detect a possible risk of feedback even in the frequency range FB2 which is not monitored by the feedback controller, the feedback suppressor device 6 according to the invention receives information from the feedback controller FBC via the estimated transfer function as well as from the signal processing HP via further signal changes in the hearing aid , The device 6 is therefore able to determine directly from the estimated external transfer function a transfer function for a closed feedback loop CLTF for the first frequency range FB1, as well as according to the inventive idea based on the correlation between the first frequency range FB1 and second frequency range FB2 at least to determine a transfer function from the estimated transfer function for the first frequency range FB1 in a subarea FB3 of the second frequency range FB2. In this way, the device 6 is able to increase the pitch frequency TF in different subunits of the hearing aid when there is no risk of feedback and in particular to decrease when there is a risk of feedback in the second frequency range FB2.

The device 6 may be part of the internal signal processing 3, as a separate device in the hearing aid be provided or as an external device that is wirelessly or via a wire connection with the hearing aid in signal communication.

Although the invention has been further illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims (10)

1. Method for suppressing acoustic feedback in a hearing aid device (100), wherein the hearing aid device has an acoustoelectric input transducer (2), signal processing (3) and an electroacoustic output transducer (4) and wherein the method exhibits the steps:

   (S10) dividing an acoustic frequency range transmitted by the hearing aid device (100) into a first frequency range (FB1) above a first split-band frequency (TF) and a second frequency range (FB2) below the first split-band frequency (TF);

   (S20) estimating a first transfer function as mapping of a real transfer function of a feedback loop via the electroacoustic output transducer (4), an acoustic feedback path, the acoustoelectric input transducer (2) and the signal processing (3) in the first frequency range (FB1);

   (S30) assessing the first transfer function, with regard to a predetermined limit value (AG), as to whether a transgression of the predetermined limit value (AG) by the real transfer function is to be expected from the behavior of the first transfer function in an environment of the first split-band frequency (TF) ;

   (S40) increasing the first split-band frequency (TF) to a second split-band frequency (TF2) if a transgression of the predetermined limit value (AG) by the real transfer function is not to be expected in the environment of the first split-band frequency (TF), so that all the values of a gain of the first transfer function for frequencies less than the increased second split-band frequency (TF2) are less than the predetermined limit value (AG) or

   (S50) reducing the first split-band frequency (TF) to a second split-band frequency (TF2) if a transgression of the predetermined limit value (AG) by the real transfer function is to be expected in the environment of the first split-band frequency (TF), and

   (S60) applying a phase or frequency change for feedback suppression in the signal processing only above an inception frequency in dependence on the second split-band frequency (TF2),

   characterized
   in that in step (S30) a transgression of the predetermined limit value (AG) by the real transfer function is to be expected in the environment of the fist split-band frequency (TF) if the first transfer function rises toward the first split-band frequency (TF), or
   wherein in step (S30) a second transfer function of the closed feedback loop is determined in a third frequency range (FB3) below the first split-band frequency (TF) in dependence on the first transfer function of the closed feedback loop and a transgression of the predetermined limit value (AG) by the real transfer function is to be expected in the environment of the first split-band frequency (TF) if the second transfer function exceeds the predetermined limit value (AG) in the third frequency range (FB3).
2. Method according to Claim 1, wherein in step (S50) the second split-band frequency (TF2) is equal to the first split-band frequency (TF) minus a predetermined frequency spacing.
3. Method according to either of the preceding claims, wherein the predetermined limit value (AG) of a gain of the first or second transfer function is 0 dB minus a stability margin.
4. Method according to one of the preceding claims, wherein, after step (S40) of increasing the first split-band frequency (TF) or step (S50) of reducing the split-band frequency (TF), it is continued with step (S20) of estimating a first transfer function of a feedback loop (S20).
5. Method according to one of the preceding claims, wherein the first split-band frequency (TF) is greater than 1 kHz and the second split-band frequency (TF2) is greater than 700 Hz.
6. System of a hearing aid device (100) and a device (6) for suppressing acoustic feedback for the hearing aid device (100), wherein the hearing aid device (100) has an acoustoelectric input transducer (2), signal processing (3) and an electroacoustic output transducer (4) and wherein the device (6) has a signal connection to the hearing aid device (100);
   wherein the device is designed to divide an acoustic frequency range to be transmitted by the hearing aid device (100) into a first frequency range (FB1) above a first split-band frequency (TF) and a second frequency range (FB2) below the first split-band frequency (TF); wherein the device is designed to estimate a first transfer function as mapping of a real transfer function of a feedback loop via the electroacoustic output transducer (4), an acoustic feedback path, the acoustoelectric input transducer (2) and the signal processing (3) in the first frequency range (FB1); wherein the device is designed to assess the first transfer function, with regard to a predetermined limit value (AG), as to whether a transgression of the predetermined limit value (AG) by the real transfer function is to be expected from the behavior of the first transfer function in an environment of the first split-band frequency (TF);
   wherein the device (6) is designed, if a transgression of a predetermined limit value (AG) by the real transfer function is not to be expected in the environment of the first split-band frequency (TF), to increase the first split-band frequency (TF) to a second split-band frequency (TF2) by such an amount that all the values of a gain of the first transfer function for frequencies less than the second split-band frequency (TF2) are less than the predetermined limit value (AG),
   the device is also designed, if a transgression of a predetermined limit value (AG) by the real transfer function is to be expected in the environment of the first split-band frequency (TF), to reduce the first split-band frequency (TF) to a second split-band frequency (TF2); and
   the device is designed to adjust in the hearing aid device a phase or frequency change for feedback suppression in the signal processing (3) only above an inception frequency in dependence on the second split-band frequency (TF2),
   characterized
   in that the device is designed, for assessment, to check the first transfer function as to whether the first transfer function rises toward the split-band frequency (TF) and in this case a transgression of the predetermined limit value (AG) by the real transfer function is to be expected in the environment of the first split-band frequency (TF), or
   in that the device is designed, for assessing the first transfer function, to determine a second transfer function of the closed feedback loop in a third frequency range (FB3) below the first split-band frequency (TF) in dependence on the first transfer function of the feedback loop and to assess whether the second transfer function exceeds the predetermined limit value (AG) in the third frequency range (FB3) and in this case a transgression of the predetermined limit value (AG) by the real transfer function is to be expected in the environment of the first split-band frequency (TF).
7. System according to Claim 6, wherein the device is designed to determine the second split-band frequency (TF2) from the first split-band frequency (TF) minus a predetermined frequency spacing.
8. System according to either of Claims 6 and 7, wherein the predetermined limit value (AG) of a gain of the first or second transfer function is 0 dB minus a stability margin.
9. System according to one of Claims 6 to 8, wherein the device (6) is designed to estimate a changed first transfer function to a changed split-band frequency (TF) and determine a changed second transfer function to the changed split-band frequency (TF).
10. System according to one of Claims 6 to 9, wherein the first split-band frequency (TF) is greater than 1 kHz and the second split-band frequency (TF2) is greater than 700 Hz.

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