EP2357852A1 - Method for compensating for a feedback signal and hearing aid - Google Patents

Abstract

The method involves compensating a feedback signal (14), which is fed back from an loudspeaker (12) or a signal processor (17) to an input transducer device i.e. microphone (10). A probability (W) is determined, where a spectrum of an input signal possesses multiple spaced sections or notches using the probability. The input signal is collected directly from the microphone and provided as a difference signal between the signal from the microphone and a compensation signal. The compensation is changed or the processor is amplified in dependent upon the determined probability. An independent claim is also included for a hearing device that comprises a compensation device.

Description

The present invention relates to a method of compensating a feedback signal in a hearing apparatus having input transducer means, signal processing means and output transducer means by compensating for a feedback signal fed back from the output transducer means or the signal processing means to the input transducer means. Moreover, the present invention relates to a corresponding hearing device. A hearing device is understood here to mean any sound-transmitting device which can be worn in or on the head, in particular a hearing device, a headset, 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 usually integrated in 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

One of the biggest problems with hearing aids is the occurrence of feedback, which is often expressed by feedback whistles. In doing so, the sound leaving the loudspeaker of the hearing aid finds an acoustic feedback path to the microphones and is amplified again, which leads to the typical whistling or reverb effects. Modern hearing systems are able to adapt the feedback path to the facial expression of the user and to compensate the feedback signal accordingly, the corresponding unit of the hearing system is called the feedback compensator.

As will be shown below, an adaptive filter (the feedback compensator) simulates the acoustic feedback path by minimizing the energy after the subtraction point. The problem is that the desired or useful signal from the point of view of the coupling compensator forms the interference signal. Moreover, because of the gain caused by the hearing aid, the wanted signal is usually strongly correlated with the feedback signal, so that it is difficult to discriminate between the feedback signal and the wanted signal.

Therefore, the correct adjustment of the adaptation speed for the feedback path is extremely important. If the adaptation is too slow, a feedback whistle will be audible for a period of time. If the adaptation is too fast, so-called musical artifacts result, ie. H. the feedback compensator tries to suppress the useful signal. Frequently, feedback detectors are necessary for the correct adaptation speed. In addition, the performance of the feedback detector is very important to the performance of the complete feedback compensator.

A typical construction of a feedback compensator in a hearing aid with a feedback detector is shown in FIG FIG. 2 shown. A microphone 10 picks up a sound signal and passes it on to a signal processing device 11. The output signal resulting from the signal processing device 11 is forwarded to an output transducer or loudspeaker 12. The sound leaving the speaker 13 penetrates part of the eardrum or ear and the other part, it is fed back as a feedback signal 14 via the respective current feedback path 15 to the microphone 10. The feedback sound is summed with the useful signal 16 and the sum gives the acoustic input signal for the microphone 10.

The signal processing device 11 has a conventional signal processor 17 and a feedback compensator 18. Further, a feedback detector 19 is provided. The output signal of the signal processor 17 is supplied to both the speaker 12 and the feedback compensator 18. The latter simulates the feedback path and supplies a corresponding compensation signal, which is subtracted by a subtractor 20 from the signal of the microphone 10. The resulting signal is provided to the signal processor 17 as an input. In addition, it becomes the Generation of the feedback signal used in the feedback compensator 18.

The signal 30 from the microphone 10 and the difference signal 40 to the subtractor 20 are fed to the feedback detector 19, which determines whether or not there is a feedback situation. In response to this decision, the feedback compensator 18 and possibly also the signal processor 17 are controlled. The feedback compensator 18 is often an adaptive filter which attempts to model the acoustic feedback path. Ideally, the feedback compensator 18 filters the output signal of the signal processor 17 in the same way as the acoustic feedback path 15. This results in a complete suppression of the feedback signal 14 at the subtracter 20. Often, however, the feedback compensator 18 is mismatched or simply too slow for the rapid changes of the feedback path. Therefore, often one or more feedback detectors 19 are necessary to adjust the rate of adaptation of the feedback compensator 18. These feedback detectors 19 typically analyze either the microphone signal 30 before the subtractor 20 or the compensated signal 40 after the subtractor 20, which should be feedback-free. It is also possible, as already indicated above, to influence the signal processor 17, for example, by reducing the gain in such a way that feedback whistling is avoided.

1. 1. Kanalpegelbasierte Detektion:
   • Durch den Vergleich der Signalpegel in unterschiedlichen Frequenzkanälen ist es möglich, Rückkopplungspfeifen zu detektieren, indem entweder nach Pegelspitzen gesucht wird oder gewisse Pegel in bestimmten Frequenzbändern als Feedback klassifiziert werden.
2. 2. Auf sinusförmigen Signalanteilen basierende Detektion:
   • Es gibt mehrere Methoden, sinusförmige Signalanteile zu Detektieren. Wenn ein sinusförmiger Signalanteil in einem rückkopplungskritschen Frequenzbereich detektiert wird,
   • deutet dies auf eine Rückkopplung hin.
3. 3. Detektion einer Phasenmodulation:
   • Die beste Methode für die Rückkopplungsdetektion ist die Detektion einer Phasen- oder Frequenzmodulation, der das Ausgangssignal des Lautsprechers des Hörgeräts unterzogen wurde. Hierbei wird die Phase des Ausgangssignals mit einer niedrigen, nicht hörbaren Frequenz moduliert. Wenn genau diese Frequenz als Phasenmodulation am Eingang (Mikrofon) detektiert wird, handelt es sich aller Wahrscheinlichkeit nach um ein Rückkopplungssignal. Dieses Verfahren ist das robusteste Rückkopplungsdetektionsverfahren. Insbesondere auch was Fehldetektionen des Nutzsignals anbelangt.

Feedback detectors based on the following detection methods are heretofore known:

1. 1. Channel level based detection:
   • By comparing the signal levels in different frequency channels, it is possible to detect feedback whistles by either searching for level peaks or certain levels in certain frequency bands are classified as feedback.
2. 2. Detection based on sinusoidal signal components:
   • There are several methods for detecting sinusoidal signal components. If a sinusoidal signal component is detected in a feedback critical frequency range,
   • this indicates a feedback.
3. 3. Detection of a phase modulation:
   • The best method for feedback detection is the detection of a phase or frequency modulation that has been subjected to the output of the loudspeaker of the hearing aid. Here, the phase of the output signal is modulated with a low, inaudible frequency. If exactly this frequency is detected as a phase modulation at the input (microphone), it is most likely a feedback signal. This method is the most robust feedback detection method. In particular, as far as misdetections of the useful signal is concerned.

The problem with all these approaches is that a high level of feedback whistling is necessary to detect the feedback at all. Also, the detection of the phase modulation requires a stable phase input signal - a sine wave signal - to detect a modulation of this phase. This means that feedback whistles are necessary to suppress it. It is not possible to completely avoid whistling with all the methods described above.

• Kompensieren eines Rückkopplungssignals, das von der Ausgangswandlereinrichtung oder der Signalverarbeitungseinrichtung an die Eingangswandlereinrichtung rückgekoppelt wird, durch
• Ermitteln einer Wahrscheinlichkeit, mit der das Spektrum eines Eingangssignals, welches direkt von der Eingangswandlereinrichtung stammt oder welches ein Differenzsignal zwischen dem Signal direkt von der Eingangswandlereinrichtung und einem zu dem Kompensieren dienenden Kompensationssignal ist, mehrere untereinander gleich beabstandete Einschnitte besitzt,

• Verändern des Kompensierens oder einer Verstärkung der Signalverarbeitungseinrichtung in Abhängigkeit von der ermittelten Wahrscheinlichkeit.

The object of the present invention is thus to recognize a feedback situation as quickly as possible and, if appropriate, to take appropriate compensation measures. For this purpose, a corresponding method and a corresponding hearing device are to be provided. According to the invention, this object is achieved by a method for compensating a feedback signal in a hearing device having an input transducer device, a signal processing device and an output transducer device

• Compensating a feedback signal that is fed back from the output transducer means or the signal processing means to the input transducer means
• Determining a probability with which the spectrum of an input signal originating directly from the input transducer means, or which is a difference signal between the signal directly from the input transducer means and a compensation signal to be compensated, has a plurality of equidistant notches,

• Modifying the compensation or amplification of the signal processing device as a function of the determined probability.

• einer Eingangswandlereinrichtung,
• einem Signalverarbeitungseinrichtung zum Verarbeiten des von der Eingangswandlereinrichtung ausgegebenen Eingangssignals zu einem Ausgabesignal,
• einer Ausgangswandlereinrichtung zum Wandeln des Ausgabesignals zu einem akustischen Ausgangssignal und
• einer Kompensationseinrichtung zum Kompensieren eines Rückkopplungssignals, das von der Ausgangswandlereinrichtung oder der Signalverarbeitungseinrichtung an die Eingangswandlereinrichtung rückgekoppelt wird, sowie
• einer Detektionseinrichtung zum Ermitteln einer Wahrscheinlichkeit, mit der das Spektrum des Eingangssignals mehrere untereinander gleich beabstandete Einschnitte besitzt, wobei
• die Kompensationseinrichtung in Abhängigkeit von der ermittelten Wahrscheinlichkeit steuerbar ist.

In addition, the invention provides a hearing device

• an input transducer device,
• signal processing means for processing the input signal output from the input conversion means into an output signal;
• output transducer means for converting the output signal to an acoustic output signal and
• compensation means for compensating a feedback signal fed back from the output transducer means or the signal processing means to the input transducer means, as well as
• a detection device for determining a probability with which the spectrum of the input signal has several mutually equally spaced incisions, wherein
• the compensation device is controllable in dependence on the determined probability.

By "determining a likelihood" is also meant here the "detection" (i.e., 100% probability) of incisions (peak minima). In an advantageous manner, a feedback situation can therefore be recognized solely by the fact that equidistant notches are detected in the transfer function and their distance to a transfer function with compensated feedback is ascertained. Depending on this, then a corresponding compensation can be initiated without it has already come to a feedback whistle.

Preferably, the determination of the probability takes place during a speech break during the intended operation of the hearing device. As a rule, there is no useful signal in a speech break that could impair the adaptation and the detection.

The transfer function from the input signal to the output signal may correspond to a comb filter. Taking into account the feedback signal then results for the useful signal, a constant transfer function.

Furthermore, the determination of the probability can take place in a noisy frequency range of the input signal. Thus, a broadband input signal is usually given, in which numerous incisions can be clearly pronounced.

The feedback signal can be verified by frequency or phase modulating the output signal and the cuts in frequency or phase modulation to be analyzed. Thus, the security of the decision of the existence of a feedback situation can be increased.

Advantageously, the compensation is carried out by an adaptive filter and the adaptation speed is changed as a function of the determined probability.

In particular, the changing of the compensation may be such that the transfer function of a compensated signal resulting from a mixing of the input signal with a compensation signal for compensating the feedback signal to the output signal in the largest part of a predetermined spectral range to be influenced by the compensating essentially runs without gradients. If so, ideal compensation of the feedback signal is achieved.

FIG 1

eine Prinzipskizze eines Hörgeräts gemäß dem Stand der Technik;

FIG 2

ein Blockschaltbild eines Hörgeräts gemäß dem Stand der Technik;

FIG 3

eine Übertragungsfunktion eines Mikrofonsignals bei 100% Kompensation;

FIG 4

eine Übertragungsfunktion eines kompensierten Signals bei 100% Kompensation;

FIG 5

eine Übertragungsfunktion des Mikrofonsignals bei 80% Kompensation;

FIG 6

eine Übertragungsfunktion eines kompensierten Signals bei 80% Kompensation;

FIG 7

eine Übertragungsfunktion eines Mikrofonsignals bei 50% Kompensation;

FIG 8

eine Übertragungsfunktion eines kompensierten Signals bei 50% Kompensation;

FIG 9

eine Übertragungsfunktion eines Mikrofonsignals bei 30% Kompensation;

FIG 10

eine Übertragungsfunktion des kompensierten Signals mit 30% Kompensation und

FIG 11

ein Blockschaltbild eines Hörgeräts gemäß einer Ausführungsform der vorliegenden Erfindung.

The present invention will be further explained with reference to the accompanying drawings, in which:

FIG. 1

a schematic diagram of a hearing aid according to the prior art;

FIG. 2

a block diagram of a hearing aid according to the prior art;

FIG. 3

a transfer function of a microphone signal at 100% compensation;

FIG. 4

a transfer function of a compensated signal at 100% compensation;

FIG. 5

a transfer function of the microphone signal at 80% compensation;

FIG. 6

a transfer function of a compensated signal at 80% compensation;

FIG. 7

a transfer function of a microphone signal at 50% compensation;

FIG. 8

a transfer function of a compensated signal at 50% compensation;

FIG. 9

a transfer function of a microphone signal at 30% compensation;

FIG. 10

a transfer function of the compensated signal with 30% compensation and

FIG. 11

a block diagram of a hearing aid according to an embodiment of the present invention.

The embodiments described in more detail below represent preferred embodiments of the invention.

The basic approach of the present invention is to detect mis-adaptation to the feedback path without audible feedback whistling. The invention makes use of the comb filter effect, which is based on the superimposition of a useful signal with a feedback signal. Adding two correlated signals with a small delay results in a destructive or constructive overlay, and cuts or peaks can be detected in the frequency response (cf. FIG. 3 ). When the feedback compensator (FBC) is ideally adapted (100% compensation), the transfer function TM of the microphone signal 30 received from the microphone 10 (see FIG FIG. 2 ), a finite impulse response of a comb filter having a typical distribution of the approximately equally spaced notches 21. The transfer function TC of the compensated signal 40 to the compensated output signal is ideally perfectly flat, as shown in FIG FIG. 4 is shown. It has no slope and is constant over the whole considered frequency range (here from 2000 to 4000 Hz).

On the other hand, if the feedback compensator 18 is misadapted, the transfer function TM of the microphone input 16 to the output 13 is an infinite impulse response of a comb filter having a typical distribution with significant frequency spikes. In the FIGS. 5 and 6 the feedback compensation is 80%. So there is a mismatch of 20%. Opposite the picture of FIG. 3 are in FIG. 5 Already frequency peaks 22 in the transfer function TM of the microphone signal 30 to the output signal 13 somewhat pronounced. This mismatch results in that the transfer function TC of the compensated signal to the output signal 13 is no longer completely flat, which is shown in FIG FIG. 6 is indicated.

If the mismatch continues to increase, the 50% compensation results in the transfer functions according to the FIGS. 7 and 8 , In FIG. 7 Now clearly the equally spaced frequency peaks 23 can be seen, ie there is significant constructive overlays of the feedback signal 14 with the useful signal 16 in the frequency ranges of the frequency peaks 23rd

If the misadaptation continues to increase and the feedback compensation is, for example, only 30%, the transfer functions of FIGS. 9 and 10 , In the transfer function TM of the microphone signal now distinct frequency peaks 25 can be seen. The transfer function TC of the compensated signal 40 then also has distinct peaks 26 equally spaced apart from one another.

With complete feedback compensation (100%), therefore, the transfer function TM of the microphone signal 30 results in notches and the transfer function TC of the compensated signal 40 is completely flat, ie the feedback is perfectly compensated. The lower the degree of compensation, the more noticeable are the transfer functions, which are above the function average protrude. The tips are an indication that feedback whistling will or has already occurred. The advantage of the comb filter effect is therefore that the reduction of the degree of compensation from 100% to 0% is easily recognizable by the transfer functions.

From the FIGS. 3 to 10 It can be seen that the transfer function TM from the microphone signal 30 is primarily characterized by cuts 21 (minima compared to the functional average value) at 100% compensation, while at low compensation (30%) the transfer function is characterized primarily by frequency peaks 26 (maxima compared to the functional mean value) is. The transition from the incision-embossed transfer function to the peak embossed transfer function is fluid. The transition can be observed without audible artifacts. This is the basis of the present invention.

In the use of the effect, the problem arises that only the response level of the microphone signal 16 and the response level of the compensated output signal 13 can be observed and not the transfer function TM of the microphone signal 30. This means that one fold of the desired signal with the above shown transfer function TM receives. Consequently, robust detection methods are necessary, which are explained in more detail below.

1. 1. Notch/Peak-Abstand:
   • Aus den oben Dargestellten lässt sich erkennen, dass zwischen den Notches (Einschnitte) bzw. den Peaks (Frequenzspitzen) ein typischer Abstand gegeben ist. Der Abstand resultiert aus der Gesamtverzögerung der geschlossenen Schleife, die üblicherweise eine Summe der Hörgeräteverzögerung und der Rückkopplungspfadverzögerung ist. Diese Verzögerung ist für eine bestimmte Situation charakteristisch und ändert sich kaum. Davon ausgehend wird vorgeschlagen, aufeinanderfolgende Notches/Peaks zu detektieren. Wenn sich der Abstand zwischen ihnen in einem gewissen Bereich befindet, wird angenommen, dass die Notches/Peaks von dem Kammfiltereffekt herrühren und nicht von dem Nutzsignal. Wenn das Singal eher Notches aufweist, ist der Rückkopplungskompensator 18 gut adaptiert. Wenn eher Peaks auftreten, ist der Kompensator schlecht adaptiert. Für diese Wahrscheinlichkeit lässt sich ein Schwellwert definieren, anhand der über eine Erhöhung der Adaptionsgeschwindigkeit des Rückkopplungskompensators oder eine Verringerung der Verstärkung entschieden wird.
2. 2. Detektion in Sprechpausen:
   • Es ist vorteilhaft, die Notch-Peak-Detektion nur in Sprechpausen einzusetzen. Dabei kann man annehmen, dass das aktuelle Nutzsignal einem Rauschen entspricht, und man kann direkt von einer Notch-Detektion auf eine gut funktionierende Rückkopplungskompensation schließen.
3. 3. Detektion in verrauschten Frequenzbereichen:
   • Es ist ferner günstig, die Notch-Detektion in verrauschten Frequenzbereichen einzusetzen. Diese Frequenzbereiche werden nicht durch ein Nutzsignal beeinflusst, sondern nur durch Hintergrundrauschen. Folglich kann man von Notches in diesen Frequenzbereichen auf eine gut funktionierende Rückkopplungskompensation schließen.
4. 4. Vergleich einer Detektion im Mikrofoneingangssignal und im kompensierten Ausgangssignal:
   • Wie aus den obigen Übertragungsfunktionen hervorgeht, besteht meistens ein klarer Unterschied zwischen der Mikrofonübertragungsfunktion TM und der kompensierten Übertragungsfunktion TC. Es wird vorgeschlagen, die Notch/Peak-Detektion für beide Signale 30, 40 (vergleiche FIG 2) anzusetzen. Wenn während des bestimmungsgemäßen Betriebs des Hörgeräts eine Differenz festgestellt wird, ist es sehr wahrscheinlich, dass die Rückkopplungs-kompensation entsprechende Leistung erbringt. Der Unterschied kann vor allem bei 100% Kompensation deutlich erkannt werden (vergleiche FIG 3 und 4). Wenn die Einschnitte (Notches) im Spektrum des Mikrofonsignals 30 entdeckt werden, und keine entsprechenden Notches im Spektrum des kompensierten Signals 40 vorhanden sind, dann arbeitet die Rückkopplungs-kompensation in gewünschter Weise.
5. 5. Modulierte Notches:
   • Um zu verifizieren, dass ein Notch von dem Kammfiltereffekt herrührt, kann das Ausgangssignal auch einer nicht hörbaren Phasenmodulation (oder Frequenzmodulation) unterzogen werden. Diese Phasenmodulation wird zu einer Modulation der Notch-Peak-Frequenzen führen. Es kann dann ein geeigneter Notch/Peak-Detektor eingesetzt werden, mit dem die Notch/Peak-Frequenz über der Zeit beobachtet werden kann. Wenn diese Frequenz die gleiche Modulationsfrequenz wie die Phasenmodulation besitzt, ist der Kammfiltereffekt verifiziert. Dieses Verfahren ist das robusteste im Hinblick auf das Nutzsignal.

In general, the methods described below are independent and can be used both alone and in combination. Most of them are based on the detection of notches / peaks in the frequency spectrum. For this detection, there are some standard methods in which one can either view the spectrum itself with high resolution FFT or use several adaptive notch / peak detectors and the like. No specific method is used here. Rather, it is assumed that notch / peak detectors present, which calculate a kind of notch / peak probability.

1. 1. Notch / peak distance:
   • From the above, it can be seen that there is a typical distance between the notches (incisions) and the peaks (frequency peaks). The distance results from the total closed loop delay, which is usually a sum of the hearing aid delay and the feedback path delay. This delay is characteristic of a particular situation and hardly changes. Based on this, it is proposed to detect successive notches / peaks. If the distance between them is within a certain range, it is assumed that the notches / peaks are due to the comb filter effect and not the useful signal. If the signal is more notch, the feedback compensator 18 is well adapted. If more peaks occur, the compensator is poorly adapted. For this probability, a threshold can be defined, based on an increase in the adaptation speed of the feedback compensator or a reduction in the gain is decided.
2. 2. Detection in speaking pauses:
   • It is advantageous to use notch peak detection only during pauses in speech. It can be assumed that the current useful signal corresponds to a noise, and one can conclude directly from a Notch detection to a well-functioning feedback compensation.
3. 3. Detection in noisy frequency ranges:
   • It is also advantageous to use notch detection in noisy frequency ranges. These frequency ranges are not affected by a useful signal, but only by background noise. Consequently, one can conclude from notches in these frequency ranges to a well-functioning feedback compensation.
4. 4. Comparison of detection in the microphone input signal and in the compensated output signal:
   • As is apparent from the above transfer functions, there is usually a clear difference between the microphone transfer function TM and the compensated transfer function TC. It is proposed that notch / peak detection for both signals 30, 40 (cf. FIG. 2 ). If a difference is detected during normal operation of the hearing aid, it is very likely that the feedback compensation will provide adequate performance. The difference can be clearly recognized, especially with 100% compensation (cf. 3 and 4 ). If the notches are detected in the spectrum of the microphone signal 30 and there are no corresponding notches in the spectrum of the compensated signal 40, then the feedback compensation works as desired.
5. 5. Modulated notches:
   • In order to verify that a notch results from the comb filter effect, the output signal may also undergo inaudible phase modulation (or frequency modulation). This phase modulation will result in a modulation of the notch peak frequencies. A suitable notch / peak detector can then be used to monitor the notch / peak frequency over time can. If this frequency has the same modulation frequency as the phase modulation, the comb filter effect is verified. This method is the most robust in terms of the useful signal.

With the above methods, the quality of the feedback adaptation can be judged. When the actual feedback path changes and the adapted mimic feedback path no longer fits, the notches change to small peaks in the signal. From this, a suitable threshold can be defined, whereby the feedback path can be optimized before the hearing aid begins to whistle or with which the gain can be reduced before the device begins to whistle. The advantage of using the comb filter effect is therefore to be able to predict the occurrence of feedback whistles before it starts. Thus, the feedback path can be adapted early enough to prevent whistling. The invention is thus to examine the input signal with respect to contained comb filter portions in order to detect feedback-critical states at an early stage. In order to clearly recognize the comb filter as an effect of the incoming loudspeaker or receiver signal, several possibilities have been proposed above. Probably the most reliable is a combination of the conventional, so-called "phase shaker", in which the modulation of the output signal is used. As before, a modulation is impressed on the output signal, which then leads to a vibrating movement of the notches in the frequency response of the input signal. This provides an additional feature to identify feedback.

FIG. 11 shows an implementation of the method described above for determining a change of a feedback situation or for adaptation to a changed feedback situation in a hearing aid. The structure of the hearing device including the feedback path 15 substantially corresponds to that of FIG. 2 , It is therefore with respect to in FIG the same components and reference numbers to the description of FIG. 2 directed. Instead of the feedback detector 19, the hearing aid of FIG. 11 a notch detector 24, a threshold decision unit 27, a modulation detector 28, and an AND gate 29. The notch detector 24 picks up the microphone signal 30 and determines therefrom a probability w for a notch (incision, ie acute minimum) and the corresponding frequency f of the notch. In the threshold value decision unit 27, it is decided whether there is a deviation from the ideal case by comparing the probability w with a threshold value. A corresponding output signal is supplied to the AND gate 29.

The notch frequency f is supplied to the notch detector 24 to the modulation detector 28. This examines whether the Notchfrequenz f performs a vibrating motion. A corresponding output signal is passed to the AND gate 29. If the respective conditions are met in the two decision units 27 and 28, then the feedback compensator 18 is correspondingly driven with the output signal of the AND gate 29, z. B. the adaptation speed is changed.

For verification of the feedback situation, the hearing aid has, after the signal processor 17, a phase modulator 31 which phase-modulates the output signal to the loudspeaker 12. In the presence of a feedback situation, the feedback signal 14 is also phase modulated and the modulation is recordable via the signal path through the microphone 10 and the notch detector 24 in the modulation detector 28. If there is modulation and the probability for a notch falls below a certain threshold (cf. FIG. 5 . 7 and 9 ), the adaptation speed of the feedback compensator is increased.

LIST OF REFERENCE NUMBERS

1

hearing aid housing

2

microphone

3

Signal processing unit

4

Speaker or listener

5

battery

10

microphone

11

Signal processing device

12

Output transducers / speakers

13

sound

14

Feedback signal

15

Feedback path

16

payload

17

signal processor

18

feedback compensator

19

Feedback detector

20

subtractor

21

cuts

22

frequency peaks

23

frequency peaks

24

Notch detector

25

frequency peaks

26

frequency peaks

27

Schwellwertentscheidungseinheit

28

modulation detector

29

AND gate

30

microphone signal

31

phase modulator

40

compensated signal

f

Notch frequency

TM

Transfer function of the microphone signal

TC

Transfer function of the compensated signal

w

probability

Claims (9)

A method for compensating a feedback signal in a hearing device with an input transducer means (10), a signal processing means (17) and an output transducer means (12) Compensating a feedback signal (14) which is fed back from the output transducer means (12) or the signal processing means (17) to the input transducer means (10),
marked by Determining a probability (w) at which the spectrum of an input signal which originates directly from the input transducer means (10) or which is a difference signal between the signal directly from the input transducer means (10) and a compensation signal to be compensated, are equal to one another has spaced cuts (21), - Modifying the compensation or a gain of the signal processing device (17) in dependence on the determined probability (w). The method of claim 1, wherein the determination of the probability (w) takes place in a speaking phase during the intended operation of the hearing device. A method according to claim 1 or 2, wherein a transfer function (TM) from the input signal to the output signal corresponds to a comb filter. Method according to one of the preceding claims, wherein the determination of the probability takes place in a noisy frequency range of the input signal. Method according to one of the preceding claims, wherein the feedback signal (14) is verified by phase modulating the output signal and analyzing the notches (21) with respect to the phase modulation. Method according to one of the preceding claims, wherein the compensation is performed by an adaptive filter (18) and the adaptation speed is changed as a function of the probability (w). The method of claim 6, wherein modifying the compression is such that the transfer function of a compensated signal (40) resulting from a mixing of the input signal (30) with a compensation signal for compensating the feedback signal to the output signal in most of a predetermined one Spectral range, which is to be influenced by the compensation, runs substantially without slope. A method according to any one of the preceding claims, wherein the equidistant notches (21) of the signal downstream of the input transducer means (10) are directly compared with self-spaced cuts of a compensated signal (40) for validating detection of a feedback situation. Hearing device with an input transducer device (10), a signal processing device (17) for processing the input signal (30) output by the input transducer device (10) into an output signal, - Output transducer means (12) for converting the output signal to an acoustic output signal (13) and - Compensation means (18) for compensating a feedback signal (14), which is fed back from the output transducer means (12) or the signal processing means (17) to the input transducer means (10), characterized by - Detection means (24) for determining a probability (w), with which the spectrum of the input signal (30) has a plurality of mutually equally spaced notches (21), wherein - The compensation device (18) in dependence on the determined probability (w) is controllable.

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