EP1853089B1 - Method for elimination of feedback and for spectral expansion in hearing aids. - Google Patents

Method for elimination of feedback and for spectral expansion in hearing aids. Download PDF

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Publication number
EP1853089B1
EP1853089B1 EP07106332A EP07106332A EP1853089B1 EP 1853089 B1 EP1853089 B1 EP 1853089B1 EP 07106332 A EP07106332 A EP 07106332A EP 07106332 A EP07106332 A EP 07106332A EP 1853089 B1 EP1853089 B1 EP 1853089B1
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signal
feedback
mixing
spectral
input signal
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French (fr)
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EP1853089A3 (en
EP1853089A2 (en
EP1853089B2 (en
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Ulrich Kornagel
Tom Weidner
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Sivantos GmbH
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Siemens Audioligische Technik GmbH
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
    • H04R25/45—Prevention of acoustic reaction, i.e. acoustic oscillatory feedback
    • H04R25/453—Prevention of acoustic reaction, i.e. acoustic oscillatory feedback electronically
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2430/00—Signal processing covered by H04R, not provided for in its groups
    • H04R2430/03—Synergistic effects of band splitting and sub-band processing

Definitions

  • the present invention relates to a method for suppressing feedback whistles in hearing devices by determining or predetermining a frequency range that is subject to feedback risk, and receiving an input signal having a spectral component in the feedback-prone frequency range.
  • the present invention relates to corresponding hearing devices.
  • the feedback whistles could be suppressed for example by so-called notch filter.
  • the loop gain is reduced at the frequency at which feedback or feedback whistles would occur. Due to this reduction, the amplitude condition for feedback whistles is no longer met.
  • Another way to suppress the feedback whistles is to perform a corresponding signal compensation.
  • This feedback compensation approach digitally replicates the feedback path and compensates for its effect.
  • these approaches to feedback reduction can significantly audibly distort the output signal, especially if the input stage of the acoustic system is designed for only a low spectral bandwidth.
  • EP 0 969 692 A1 an apparatus and method for processing speech.
  • LPC analysis Linear Predictive Coding
  • the object of the present invention is therefore to improve the signal quality of acoustic systems which are subject to feedback.
  • this object is achieved by a method for suppressing feedback whistling in a hearing device by determining or predetermining a frequency range which is subject to feedback, and receiving an input signal with a spectral component in the feedback-prone frequency range, and reducing the amplitude of said spectral component of the input signal and mixing the reduced spectral component with a synthetic signal, so that in the said spectral range, the power of the total signal after mixing substantially equal to the power before reducing.
  • a hearing device is provided with a feedback suppression device and a signal input device for receiving an input signal, wherein the feedback suppression device has a reduction unit for reducing the amplitude of a spectral component of the input signal and a mixing unit for mixing the reduced spectral component with a synthetic signal such that in said spectral range the power of the overall signal after mixing substantially equal to the power before reducing.
  • the invention is based on the idea to substitute a part of an internal signal of the hearing by a synthetic signal and to mix with this. By substituting, the amplitude condition for the feedback whistling is no longer satisfied.
  • the synthetic signal is generated with a nonlinearity from the input signal.
  • a synthetic signal in response to the input signal can be generated.
  • the synthetic signal may also be generated by frequency shifting a spectral band of the input signal. This also makes it possible to generate a synthetic signal as a function of the input signal in a simple manner in the desired frequency range.
  • the spectral envelope of a signal mixed from the synthetic signal and a part of the input signal is corrected by means of LPC analysis.
  • the signal character of the original input signal can be well maintained without feedback.
  • the correction can be done in combination with a common shape filtering.
  • further processing of the reduced signal and mixing is performed by adding the synthetic signal to the further processed, reduced signal just prior to signal output to an output transducer.
  • the suppression of the feedback whistle can be completely independent of the internal signal processing. This means that existing systems can also be easily retrofitted.
  • the input signal can be processed in a plurality of channels, wherein the substitution or mixing takes place only in that channel with the backward-endangered frequency range.
  • the effect of the feedback suppression can be selectively limited to one or more channels. It is advantageous if one or more features of the respective signal are obtained from at least two of the channels and considered for substitution or mixing. On the basis of the characteristics from the other channels, the quality of the synthetic signal can be improved.
  • signal components which cause the feedback whistling should be substituted.
  • This signal substitution should take place in the feedback-endangered frequency range. In this frequency range, therefore, not only the signal picked up by the microphone is processed and delivered via the receiver, but also the synthetically generated signal is processed or output.
  • the feedback loop can be interrupted and it can be prevented in case of linear system behavior unwanted oscillation.
  • the signal picked up by the microphone can be mixed with the synthetic signal in any ratio. This mixing can also be considered as a partial substitution. In this case, the effective amplification can be lowered to such an extent in the feedback loop that the amplitude condition for feedback is no longer satisfied. As a result, a certain proportion of the natural signal is retained.
  • Measures for the generation of synthetic signal components are, for example, the use of non-linearities, ie non-linear components with, for example, quadratic characteristic, magnitude characteristic curve, etc., or modulation approaches in which frequency components are spectrally shifted. Especially in low frequency position ( ⁇ 8 kHz) should also have a device for correcting the spectral envelope be provided to preserve a natural sound as much as possible.
  • a tool for this is, for example, the LPC analysis (linear predictive coding) in combination with shape filtering.
  • FIG. 1 is presented a concrete implementation example.
  • the original input signal of a microphone 2 is split into two complementary spectral ranges.
  • the switch 1 contains a band-stop filter 3 and a band-pass filter 4.
  • the signal is divided into a band-pass signal S_fb and a spectrally complementary signal S_kompl.
  • bandpass filtering low-pass or high-pass filtering can also be used.
  • the spectral range of the bandpass signal S_fb represents the band in which feedback whistles would arise without countermeasures.
  • the bandpass signal S_fb is multiplied by a factor a in a multiplier 5. Multiplied by this factor a (where 0 ⁇ a ⁇ 1), the bandpass signal S_fb is partially added back to the complementary signal S_kompl in the adder 6. The signal thus obtained passes through the regular signal processing 7, which would pass through the original signal even without compensation measure for feedback whistles.
  • the output signal of the microphone 2 is also used to generate the synthetic signal in the spectral range of the bandpass signal S_fb corresponding to the lower path of FIG. 1 used.
  • a suitable spectral band is cut out by means of a filter and copied into the spectral band of interest.
  • Corresponding means for generating a synthetic signal 8 are in the lower path of the circuit diagram of FIG. 1 shown.
  • the synthetic signal is weighted by a factor b. This weighting with the aid of a multiplier 9 can take place prior to entry into the means for generating the synthetic signal 8.
  • the synthetic signal is adjusted by means of a signal processing module 10 so that it can be added to the signal of the signal processing 7 of the upper path. This addition takes place in an adder 11 immediately before the signal output to an in FIG. 1 not shown output transducer.
  • the factors a and b are coordinated. They define the mixing ratio of synthetic and real signal component in the spectral range of the bandpass signal S_fb. The larger the factor a, the smaller must be the factor b and vice versa, so that the feedback whistling can be suppressed. In a first extreme case, a is close to 1 and b is close to 0, so that practically no signal substitution by a synthetic signal takes place in the spectral range of the bandpass signal S_fb. In a second extreme case, a is close to 0 and b is close to 1, which results in almost complete signal substitution by the synthetic signal in the spectral range of the bandpass signal S_fb.
  • FIG. 2 is a circuit diagram of a multi-channel device with subband synthesis and feature extraction reproduced.
  • the output signal of a microphone 20 is again decomposed into two channels.
  • the output signal of a microphone 20 serves as a first filter, for example, a high pass 21 and second Filter, for example, a low-pass filter 22.
  • the high-pass signal corresponds to a channel A and the low-pass signal to a channel B.
  • a hearing aid signal processing unit 23 and in the channel B a hearing aid signal processing unit 24 is arranged in the channel A.
  • the output signals of the two signal processing units 23 and 24 are added in an adder 25 and sent the sum signal to a handset 26.
  • a part of the acoustic output signal of the handset 26 is fed back to the microphone 20 via a feedback path 27. Since the feedback takes place primarily in the high-frequency channel A, a mixing stage 28 is connected between the high-pass filter 21 and the hearing aid signal processing unit 23, with which a synthetic signal can be mixed into the high-frequency channel.
  • a mixing stage 28 is connected between the high-pass filter 21 and the hearing aid signal processing unit 23, with which a synthetic signal can be mixed into the high-frequency channel.
  • To generate the synthetic signal one or more features of the high-frequency channel A are obtained by a feature extraction unit 29 and also one or more features of the low-frequency channel B by a feature extraction unit 30.
  • the features obtained by the units 29 and 30 are evaluated or compared in an evaluation unit 31.
  • the evaluation unit 31 is based on a model 32. This model includes a prior knowledge of ratios of high-pass to low-pass shares.
  • the evaluation unit 31 determines, for example, based on the spectral envelope, which is available as a feature from the high-frequency channel A, and the model 32, a mixing ratio for the mixing stage 28.
  • the evaluation unit 31 controls a signal generator 33, for. As a vocoder.
  • the signal generator 33 then supplies the synthetic signal to the mixer 28.
  • FIG. 2 shows a two-channel hearing aid.
  • the invention can also be applied to any other devices with two or more channels.

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  • Acoustics & Sound (AREA)
  • General Health & Medical Sciences (AREA)
  • Neurosurgery (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
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Abstract

The method involves determining a feedback-endangered frequency range. An input signal is received with a spectral portion in the frequency range. The known spectral portion of the input signal is reduced. The reduced spectral portion is mixed with a synthetic signal, in such a manner that in the spectral region, the efficiency of the entire signal corresponds to the efficiency before the reduction. The synthetic signal is produced by frequency shift from the input signal. A spectral envelope of the mixed signal is corrected with the help of linear predictive coding analysis. Independent claims are also included for the following: (1) a hearing device with feedback suppression device (2) a method for providing the spectral expansion in a hearing device.

Description

Die vorliegende Erfindung betrifft ein Verfahren zum Unterdrücken von Rückkopplungspfeifen bei Hörvorrichtungen durch Ermitteln oder Vorgeben eines Frequenzbereichs, der rückkopplungsgefährdet ist, und Empfangen eines Eingangssignals mit einem Spektralanteil in dem rückkopplungsgefährdeten Frequenzbereich. Außerdem bezieht sich die vorliegende Erfindung auf entsprechende Hörvorrichtungen.The present invention relates to a method for suppressing feedback whistles in hearing devices by determining or predetermining a frequency range that is subject to feedback risk, and receiving an input signal having a spectral component in the feedback-prone frequency range. In addition, the present invention relates to corresponding hearing devices.

In Akustiksystemen und insbesondere bei Hörgeräten mit mindestens einem Eingang (z. B. Mikrofon) und mindestens einem Ausgang (z. B. Hörer) besteht die Gefahr akustischer Rückkopplung. Bei ausreichend hoher Verstärkung beginnt das System zu oszillieren, was sich durch Pfeifen bemerkbar macht.In acoustic systems and in particular in hearing aids with at least one input (eg microphone) and at least one output (eg listener) there is a risk of acoustic feedback. If the gain is sufficiently high, the system starts to oscillate, which is noticeable by whistling.

Bislang konnte das Rückkopplungspfeifen beispielsweise durch sogenannte Notchfilter unterdrückt werden. Bei diesem Ansatz wird die Schleifenverstärkung bei derjenigen Frequenz reduziert, bei der Feedback- bzw. Rückkopplungspfeifen auftreten würde. Durch diese Absenkung ist die Amplitudenbedingung für Rückkopplungspfeifen nicht mehr erfüllt.So far, the feedback whistles could be suppressed for example by so-called notch filter. In this approach, the loop gain is reduced at the frequency at which feedback or feedback whistles would occur. Due to this reduction, the amplitude condition for feedback whistles is no longer met.

Eine weitere Möglichkeit, das Rückkopplungspfeifen zu unterdrücken besteht darin, eine entsprechende Signalkompensation durchzuführen. Bei diesem Feedbackkompensationsansatz wird der Rückkopplungspfad digital nachgebildet und seine Wirkung kompensiert. Diese Ansätze zur Feedbackreduktion können jedoch das Ausgangssignal deutlich hörbar verfälschen, insbesondere wenn die Eingangsstufe des Akustiksystems nur für eine geringe spektrale Bandbreite ausgelegt ist.Another way to suppress the feedback whistles is to perform a corresponding signal compensation. This feedback compensation approach digitally replicates the feedback path and compensates for its effect. However, these approaches to feedback reduction can significantly audibly distort the output signal, especially if the input stage of the acoustic system is designed for only a low spectral bandwidth.

Akustiksysteme mit schmalbandiger Eingangsstufe besitzen ferner den Nachteil, dass die akustische Qualität des Ausgangssignals in der Regel entsprechend gering ist.Acoustic systems with narrowband input stage also have the disadvantage that the acoustic quality of the output signal is usually correspondingly low.

Aus der Druckschrift EP 1 304 902 A1 ist ein Verfahren und eine Vorrichtung zur Störbefreiung eines redundanten akustischen Signals bekannt. Dabei wird ein Teilfrequenzbereich des Eingangssignals, in dem eine Störung konzentriert ist, entfernt. Anschließend wird die Intensität des verbleibenden Eingangssignals in einen beizubehaltenden Eingangssignalteil und einen weiterzuverarbeitenden Eingangssignalteil aufgeteilt. Aufgrund des weiterzuverarbeitenden Eingangsignalteils wird der entfernte Teilfrequenzbereich des Eingangssignals synthetisiert. Schließlich wird der beizubehaltende Eingangssignalteil und der synthetisierte Eingangssignalteil zum Hervorbringen eines gegenüber dem Eingangssignal störungsreduzierten Ausgangssignals zusammengeführt.From the publication EP 1 304 902 A1 For example, a method and apparatus for noise cancellation of a redundant acoustic signal is known. In this case, a sub-frequency range of the input signal in which a disturbance is concentrated is removed. Subsequently, the intensity of the remaining input signal is divided into an input signal part to be maintained and an input signal part to be further processed. Due to the further processed input signal part of the remote sub-frequency range of the input signal is synthesized. Finally, the input signal portion to be retained and the synthesized input signal portion are merged to produce an output reduced in interference with the input signal.

Aus der Druckschrift US 2004/0252853 A1 ist ein Verfahren zur Oszillationsunterdrückung bekannt, das auch bei Hörgeräten angewendet werden kann. Dabei wird die Phase eines Frequenzbands nach einem zufälligen Muster geändert, so dass die konstruktive Addition des Rückkopplungssignals mit dem Eingangssignal unterbrochen ist. Zur Phasenverschiebung wird der Verstärkungsfaktor mit einer komplexen Zahl multipliziert, die einen zufälligen Phasenwert und die Amplitude 1 besitzt.From the publication US 2004/0252853 A1 For example, a method for suppression of oscillation is known, which can also be applied to hearing aids. In this case, the phase of a frequency band is changed according to a random pattern, so that the constructive addition of the feedback signal is interrupted with the input signal. For phase shifting, the gain factor is multiplied by a complex number having a random phase value and the amplitude 1.

Weiterhin ist aus der Druckschrift DE 37 33 983 A1 ein Verfahren zum Dämpfen von Störschall in von Hörgeräten übertragenen Schallsignalen bekannt. Abhängig von den Steuersignalen in den einzelnen Frequenzfenstern werden die Amplituden der Störsignale in der jeweiligen Spektralverteilung abgesenkt und/oder die Grenzfrequenzen verschoben.Furthermore, from the document DE 37 33 983 A1 a method for attenuating noise in transmitted by hearing aids sound signals known. Depending on the control signals in the individual frequency windows, the amplitudes of the interference signals in the respective spectral distribution are lowered and / or the limit frequencies are shifted.

Ferner offenbart die Druckschrift EP 0 969 692 A1 eine Vorrichtung und eine Verfahren zum Verarbeiten von Sprache. Dabei wird insbesondere die LPC-Analyse (Linear Predictive Coding) zur Korrektur von Signalen erwähnt.Further, the document discloses EP 0 969 692 A1 an apparatus and method for processing speech. In particular, the LPC analysis (Linear Predictive Coding) for the correction of signals is mentioned.

Die Aufgabe der vorliegenden Erfindung besteht somit darin, die Signalqualität von Akustiksystemen, die rückkopplungsgefährdet sind, zu verbessern.The object of the present invention is therefore to improve the signal quality of acoustic systems which are subject to feedback.

Erfindungsgemäß wird diese Aufgabe gelöst durch ein Verfahren zum Unterdrücken von Rückkopplungspfeifen bei einer Hörvorrichtung durch Ermitteln oder Vorgeben eines Frequenzbereichs, der rückkopplungsgefährdet ist, und Empfangen eines Eingangssignals mit einem Spektralanteil in dem rückkopplungsgefährdeten Frequenzbereich, sowie Reduzieren der Amplitude des genannten Spektralanteils des Eingangssignals und Mischen des reduzierten Spektralanteils mit einem synthetischen Signal, so dass in dem genannten Spektralbereich die Leistung des Gesamtsignals nach dem Mischen im Wesentlichen der Leistung vor dem Reduzieren entspricht.According to the invention, this object is achieved by a method for suppressing feedback whistling in a hearing device by determining or predetermining a frequency range which is subject to feedback, and receiving an input signal with a spectral component in the feedback-prone frequency range, and reducing the amplitude of said spectral component of the input signal and mixing the reduced spectral component with a synthetic signal, so that in the said spectral range, the power of the total signal after mixing substantially equal to the power before reducing.

Entsprechend wird erfindungsgemäß bereitgestellt eine Hörvorrichtung mit einer Rückkopplungsunterdrückungseinrichtung und einer Signaleingangseinrichtung zum Empfangen eines Eingangssignals, wobei die Rückkopplungsunterdrückungseinrichtung eine Reduktionseinheit zum Reduzieren der Amplitude eines Spektralanteils des Eingangssignals und eine Mischeinheit zum Mischen des reduzierten Spektralanteils mit einem synthetischen Signal aufweist, so dass in dem genannten Spektralbereich die Leistung des Gesamtsignals nach dem Mischen im Wesentlichen der Leistung vor dem Reduzieren entspricht.According to the invention, a hearing device is provided with a feedback suppression device and a signal input device for receiving an input signal, wherein the feedback suppression device has a reduction unit for reducing the amplitude of a spectral component of the input signal and a mixing unit for mixing the reduced spectral component with a synthetic signal such that in said spectral range the power of the overall signal after mixing substantially equal to the power before reducing.

Der Erfindung liegt der Gedanke zugrunde, einen Teil eines internen Signals der Hörvorrichtung durch ein synthetisches Signal zu substituieren und mit diesem zu mischen. Durch das Substituieren wird die Amplitudenbedingung für das Rückkopplungspfeifen nicht mehr erfüllt.The invention is based on the idea to substitute a part of an internal signal of the hearing by a synthetic signal and to mix with this. By substituting, the amplitude condition for the feedback whistling is no longer satisfied.

Vorzugsweise wird das synthetische Signal mit einer Nichtlinearität aus dem Eingangssignal erzeugt. Auf diese Weise kann in dem gewünschten Frequenzbereich ein synthetisches Signal in Abhängigkeit von dem Eingangssignal erzeugt werden.Preferably, the synthetic signal is generated with a nonlinearity from the input signal. In this way, in the desired frequency range, a synthetic signal in response to the input signal can be generated.

Das synthetische Signal kann beispielsweise ebenso durch Frequenzverschiebung eines Spektralbands des Eingangssignals erzeugt werden. Auch hierdurch lässt sich in einfacher Weise in dem gewünschten Frequenzbereich ein synthetisches Signal in Abhängigkeit von dem Eingangssignal erzeugen.For example, the synthetic signal may also be generated by frequency shifting a spectral band of the input signal. This also makes it possible to generate a synthetic signal as a function of the input signal in a simple manner in the desired frequency range.

Vorteilhafterweise wird die spektrale Einhüllende eines aus dem synthetischen Signal und einem Teil des Eingangssignals gemischten Signals mit Hilfe einer LPC-Analyse korrigiert. Somit kann der Signalcharakter des ursprünglichen Eingangssignals ohne Rückkopplung gut beibehalten werden. Beispielsweise kann die Korrektur in Kombination mit einer gängigen Formfilterung erfolgen.Advantageously, the spectral envelope of a signal mixed from the synthetic signal and a part of the input signal is corrected by means of LPC analysis. Thus, the signal character of the original input signal can be well maintained without feedback. For example, the correction can be done in combination with a common shape filtering.

Entsprechend einer besonderen Ausführungsform der vorliegenden Erfindung erfolgt vor dem Mischen ein Weiterverarbeiten des reduzierten Signals und das Mischen durch Addieren des synthetischen Signals zu dem weiterverarbeiteten, reduzierten Signal unmittelbar vor einer Signalausgabe an einen Ausgangswandler. Damit kann die Unterdrückung des Rückkopplungspfeifens vollkommen unabhängig von der internen Signalverarbeitung erfolgen. Dies bedeutet, dass bestehende Systeme auch ohne weiteres nachgerüstet werden können.According to a particular embodiment of the present invention, prior to mixing, further processing of the reduced signal and mixing is performed by adding the synthetic signal to the further processed, reduced signal just prior to signal output to an output transducer. Thus, the suppression of the feedback whistle can be completely independent of the internal signal processing. This means that existing systems can also be easily retrofitted.

Weiterhin kann das Eingangssignal in mehreren Kanälen verarbeitet werden, wobei das Substituieren bzw. Mischen nur in demjenigen Kanal mit dem rückkopplungsgefährdeten Frequenzbereich erfolgt. Damit kann die Wirkung der Rückkopplungsunterdrückung gezielt auf einen oder mehrere Kanäle beschränkt werden. Dabei ist es günstig, wenn aus mindestens zwei der Kanäle je ein oder mehrere Merkmale des jeweiligen Signals gewonnen und für das Substituieren bzw. Mischen berücksichtigt werden. Anhand der Merkmale aus den anderen Kanälen kann so die Qualität des synthetischen Signals verbessert werden.Furthermore, the input signal can be processed in a plurality of channels, wherein the substitution or mixing takes place only in that channel with the backward-endangered frequency range. Thus, the effect of the feedback suppression can be selectively limited to one or more channels. It is advantageous if one or more features of the respective signal are obtained from at least two of the channels and considered for substitution or mixing. On the basis of the characteristics from the other channels, the quality of the synthetic signal can be improved.

Die vorliegende Erfindung wird nun anhand der beigefügten Zeichnungen näher erläutert, in denen zeigen:

FIG 1
ein Prinzipschaltbild einer Hörvorrichtung gemäß einer ersten Ausführungsform der vorliegenden Erfindung und
FIG 2
ein Prinzipschaltbild zur erfindungsgemäßen Teilbandsynthese eines Mehrkanalgeräts.
The present invention will now be explained in more detail with reference to the accompanying drawings, in which:
FIG. 1
a schematic diagram of a hearing aid according to a first embodiment of the present invention and
FIG. 2
a schematic diagram of the invention subband synthesis of a multi-channel device.

Die nachfolgend näher geschilderten Ausführungsbeispiele stellen bevorzugte Ausführungsformen der vorliegenden Erfindung dar.The embodiments described in more detail below represent preferred embodiments of the present invention.

Entsprechend der erfindungsgemäßen Grundidee sollen Signalanteile, die das Rückkopplungspfeifen verursachen, substituiert werden. Diese Signalsubstitution soll im feedbackgefährdeten Frequenzbereich erfolgen. In diesem Frequenzbereich wird also nicht ausschließlich das durch das Mikrofon aufgenommene Signal verarbeitet und über den Hörer abgegeben, sondern auch das synthetisch erzeugte Signal verarbeitet bzw. ausgegeben. Somit kann die Rückkopplungsschleife unterbrochen werden und es kann sich bei linearem Systemverhalten eine unerwünschte Oszillation unterbinden lassen.According to the basic idea according to the invention, signal components which cause the feedback whistling should be substituted. This signal substitution should take place in the feedback-endangered frequency range. In this frequency range, therefore, not only the signal picked up by the microphone is processed and delivered via the receiver, but also the synthetically generated signal is processed or output. Thus, the feedback loop can be interrupted and it can be prevented in case of linear system behavior unwanted oscillation.

Das durch das Mikrofon aufgenommene Signal kann mit dem synthetischen Signal in einem beliebigen Verhältnis gemischt werden. Dieses Mischen kann auch als Teilsubstitution betrachtet werden. Die effektive Verstärkung kann hierbei in der Rückkopplungsschleife soweit abgesenkt werden, dass die Amplitudenbedingung für Feedback nicht mehr erfüllt ist. Hierdurch bleibt ein gewisser Anteil des natürlichen Signals erhalten.The signal picked up by the microphone can be mixed with the synthetic signal in any ratio. This mixing can also be considered as a partial substitution. In this case, the effective amplification can be lowered to such an extent in the feedback loop that the amplitude condition for feedback is no longer satisfied. As a result, a certain proportion of the natural signal is retained.

Maßnahmen zur Erzeugung von synthetischen Signalkomponenten sind beispielsweise die Verwendung von Nichtlinearitäten, d. h. nichtlinearen Bauelementen mit beispielsweise quadratischer Kennlinie, Betragskennlinie usw. oder Modulationsansätze, bei denen Frequenzkomponenten spektral verschoben werden. Vor allem in niedriger Frequenzlage (< 8 kHz) sollte zusätzlich eine Vorrichtung zur Korrektur der spektralen Einhüllenden vorgesehen werden, um einen natürlichen Klang soweit wie möglich zu bewahren. Ein Werkzeug hierfür ist beispielsweise die LPC-Analyse (linear predictive coding) in Kombination mit Formfilterung.Measures for the generation of synthetic signal components are, for example, the use of non-linearities, ie non-linear components with, for example, quadratic characteristic, magnitude characteristic curve, etc., or modulation approaches in which frequency components are spectrally shifted. Especially in low frequency position (<8 kHz) should also have a device for correcting the spectral envelope be provided to preserve a natural sound as much as possible. A tool for this is, for example, the LPC analysis (linear predictive coding) in combination with shape filtering.

In vorteilhafter Weise genügt es bei der erfindungsgemäßen Unterdrückung von Rückkopplungspfeifen zu wissen, in welchem Frequenzband Rückkopplungspfeifen auftritt bzw. auftreten kann. Die Sollleistung im betreffenden Frequenzband wird nicht wie bei dem Notchfilteransatz reduziert. Vielmehr geht bei der erfindungsgemäßen Signalsubstitution in demjenigen Frequenzband, in dem Rückkopplungspfeifen auftritt, praktisch keine Leistung verloren. Außerdem muss der Rückkopplungspfad bei der erfindungsgemäßen Lösung nicht explizit bekannt sein, wie dies beim Feedback-Kompensationsansatz notwendig ist.In the case of the suppression of feedback whistles according to the invention, it is advantageously sufficient to know in which frequency band feedback whistling occurs or can occur. The nominal power in the relevant frequency band is not reduced as in the notch filter approach. Rather, virtually no power is lost in the signal substitution according to the invention in that frequency band in which feedback whistling occurs. In addition, the feedback path in the solution according to the invention need not be explicitly known, as is necessary in the feedback compensation approach.

In FIG 1 ist ein konkretes Realisierungsbeispiel vorgestellt. In einer Weiche 1 wird das Originaleingangssignal eines Mikrofons 2 in zwei komplementäre Spektralbereiche aufgeteilt. Im vorliegenden Fall enthält die Weiche 1 eine Bandsperre 3 und einen Bandpass 4. Demzufolge wird das Signal in ein Bandpass-Signal S_fb und in ein dazu spektral komplementäres Signal S_kompl geteilt. Statt der Bandpassfilterung kann auch eine Tiefpass- oder Hochpass-Filterung eingesetzt werden.In FIG. 1 is presented a concrete implementation example. In a switch 1, the original input signal of a microphone 2 is split into two complementary spectral ranges. In the present case, the switch 1 contains a band-stop filter 3 and a band-pass filter 4. As a result, the signal is divided into a band-pass signal S_fb and a spectrally complementary signal S_kompl. Instead of bandpass filtering, low-pass or high-pass filtering can also be used.

Der Spektralbereich des Bandpass-Signals S_fb stellt das Band dar, in dem ohne Gegenmaßnahmen Rückkopplungspfeifen entstehen würde. Das Bandpass-Signal S_fb wird in einem Multiplizierer 5 mit einem Faktor a multipliziert. Multipliziert mit diesem Faktor a (mit 0 < a < 1) wird das Bandpass-Signal S_fb zum Teil wieder zu dem komplementären Signal S_kompl in dem Addierer 6 hinzuaddiert. Das so gewonnene Signal durchläuft die reguläre Signalverarbeitung 7, die das ursprüngliche Signal auch ohne Kompensationsmaßnahme für Rückkopplungspfeifen durchlaufen wäre.The spectral range of the bandpass signal S_fb represents the band in which feedback whistles would arise without countermeasures. The bandpass signal S_fb is multiplied by a factor a in a multiplier 5. Multiplied by this factor a (where 0 <a <1), the bandpass signal S_fb is partially added back to the complementary signal S_kompl in the adder 6. The signal thus obtained passes through the regular signal processing 7, which would pass through the original signal even without compensation measure for feedback whistles.

Das Ausgangssignal des Mikrofons 2 wird auch zur Erzeugung des synthetischen Signals im Spektralbereich des Bandpass-Signals S_fb entsprechend dem unteren Pfad von FIG 1 verwendet. Beispielsweise wird mittels eines Filters ein geeignetes Spektralband ausgeschnitten und in das interessierende Spektralband kopiert. Entsprechende Mittel zum Erzeugen eines synthetischen Signals 8 sind in dem unteren Pfad des Schaltbilds von FIG 1 dargestellt. Das synthetische Signal wird mit einem Faktor b gewichtet. Diese Gewichtung mit Hilfe eines Multiplizierers 9 kann vor dem Eingang in die Mittel zur Erzeugung des synthetischen Signals 8 erfolgen. Anschließend wird das synthetische Signal mit Hilfe eines Signalverarbeitungsmoduls 10 so angepasst, dass es zu dem Signal der Signalverarbeitung 7 des oberen Pfads addiert werden kann. Diese Addition erfolgt in einem Addierer 11 unmittelbar vor der Signalausgabe an einen in FIG 1 nicht dargestellten Ausgangswandler.The output signal of the microphone 2 is also used to generate the synthetic signal in the spectral range of the bandpass signal S_fb corresponding to the lower path of FIG. 1 used. For example, a suitable spectral band is cut out by means of a filter and copied into the spectral band of interest. Corresponding means for generating a synthetic signal 8 are in the lower path of the circuit diagram of FIG. 1 shown. The synthetic signal is weighted by a factor b. This weighting with the aid of a multiplier 9 can take place prior to entry into the means for generating the synthetic signal 8. Subsequently, the synthetic signal is adjusted by means of a signal processing module 10 so that it can be added to the signal of the signal processing 7 of the upper path. This addition takes place in an adder 11 immediately before the signal output to an in FIG. 1 not shown output transducer.

Die Faktoren a und b sind aufeinander abgestimmt. Sie definieren das Mischungsverhältnis von synthetischem und realem Signalanteil im Spektralbereich des Bandpass-Signals S_fb. Je größer der Faktor a ist, desto kleiner muss der Faktor b sein und umgekehrt, so dass das Rückkopplungspfeifen unterdrückt werden kann. In einem ersten Extremfall ist a nahe 1 und b nahe 0, so dass praktisch keine Signalsubstitution durch ein synthetisches Signal im Spektralbereich des Bandpass-Signals S_fb erfolgt. In einem zweiten Extremfall ist a nahe 0 und b nahe 1, wodurch eine fast vollständige Signalsubstitution durch das synthetische Signal im Spektralbereich des Bandpass-Signals S_fb erfolgt.The factors a and b are coordinated. They define the mixing ratio of synthetic and real signal component in the spectral range of the bandpass signal S_fb. The larger the factor a, the smaller must be the factor b and vice versa, so that the feedback whistling can be suppressed. In a first extreme case, a is close to 1 and b is close to 0, so that practically no signal substitution by a synthetic signal takes place in the spectral range of the bandpass signal S_fb. In a second extreme case, a is close to 0 and b is close to 1, which results in almost complete signal substitution by the synthetic signal in the spectral range of the bandpass signal S_fb.

Gemäß einer Weiterbildung des Ausführungsbeispiels von FIG 1 können aus den Signalen des oberen Pfads Merkmale des Originalsignals extrahiert werden. Mit diesen Merkmalen lässt sich eine Korrektur der spektralen Einhüllenden in dem synthetisierten Band erreichen. In FIG 2 ist ein Schaltbild eines Mehrkanalgeräts mit Teilbandsynthese und Merkmalsextraktion wiedergegeben. Das Ausgangssignal eines Mikrofons 20 wird wiederum in zwei Kanäle zerlegt. Zu diesem Zweck dient als erstes Filter beispielsweise ein Hochpass 21 und als zweites Filter beispielsweise ein Tiefpass 22. Das Hochpasssignal entspricht einem Kanal A und das Tiefpasssignal einem Kanal B. In dem Kanal A ist eine Hörgerätesignalverarbeitungseinheit 23 und in dem Kanal B eine Hörgerätesignalverarbeitungseinheit 24 angeordnet. Die Ausgangssignale der beiden Signalverarbeitungseinheiten 23 und 24 werden in einem Addierer 25 addiert und das Summensignal an einen Hörer 26 geschickt.According to a development of the embodiment of FIG. 1 From the signals of the upper path, features of the original signal can be extracted. With these features, a correction of the spectral envelope in the synthesized band can be achieved. In FIG. 2 is a circuit diagram of a multi-channel device with subband synthesis and feature extraction reproduced. The output signal of a microphone 20 is again decomposed into two channels. For this purpose serves as a first filter, for example, a high pass 21 and second Filter, for example, a low-pass filter 22. The high-pass signal corresponds to a channel A and the low-pass signal to a channel B. In the channel A, a hearing aid signal processing unit 23 and in the channel B, a hearing aid signal processing unit 24 is arranged. The output signals of the two signal processing units 23 and 24 are added in an adder 25 and sent the sum signal to a handset 26.

Ein Teil des akustischen Ausgangssignals des Hörers 26 wird über einen Rückkopplungspfad 27 an das Mikrofon 20 rückgekoppelt. Da die Rückkopplung in erster Linie im hochfrequenten Kanal A erfolgt, ist zwischen dem Hochpass 21 und die Hörgerätesignalverarbeitungseinheit 23 eine Mischstufe 28 geschaltet, mit der ein synthetisches Signal in den Hochfrequenzkanal eingemischt werden kann. Zur Erzeugung des synthetischen Signals wird eines oder mehrere Merkmale des Hochfrequenzkanals A durch eine Merkmalsextraktionseinheit 29 und ebenfalls eines oder mehrere Merkmale des Tieffrequenzkanals B durch eine Merkmalsextraktionseinheit 30 gewonnen. Die durch die Einheiten 29 und 30 gewonnenen Merkmale werden in einer Auswerteeinheit 31 ausgewertet bzw. verglichen. Der Auswerteeinheit 31 liegt dabei ein Modell 32 zugrunde. Dieses Modell beinhaltet ein Vorwissen über Verhältnisse von Anteilen im Hochpassbereich zu Anteilen im Tiefpassbereich. Die Auswerteeinheit 31 ermittelt so beispielsweise anhand der spektralen Einhüllenden, die als Merkmal aus dem Hochfrequenzkanal A zur Verfügung steht, und dem Modell 32 ein Mischungsverhältnis für die Mischstufe 28. Außerdem steuert die Auswerteeinheit 31 einen Signalgenerator 33, z. B. einen Vocoder, an. Der Signalgenerator 33 liefert dann das synthetische Signal an die Mischstufe 28.A part of the acoustic output signal of the handset 26 is fed back to the microphone 20 via a feedback path 27. Since the feedback takes place primarily in the high-frequency channel A, a mixing stage 28 is connected between the high-pass filter 21 and the hearing aid signal processing unit 23, with which a synthetic signal can be mixed into the high-frequency channel. To generate the synthetic signal, one or more features of the high-frequency channel A are obtained by a feature extraction unit 29 and also one or more features of the low-frequency channel B by a feature extraction unit 30. The features obtained by the units 29 and 30 are evaluated or compared in an evaluation unit 31. The evaluation unit 31 is based on a model 32. This model includes a prior knowledge of ratios of high-pass to low-pass shares. The evaluation unit 31 thus determines, for example, based on the spectral envelope, which is available as a feature from the high-frequency channel A, and the model 32, a mixing ratio for the mixing stage 28. In addition, the evaluation unit 31 controls a signal generator 33, for. As a vocoder. The signal generator 33 then supplies the synthetic signal to the mixer 28.

Das Beispiel von FIG 2 zeigt ein Zweikanalhörgerät. Die Erfindung lässt sich aber auch auf beliebige andere Geräte mit zwei und mehr Kanälen anwenden.The example of FIG. 2 shows a two-channel hearing aid. However, the invention can also be applied to any other devices with two or more channels.

Claims (9)

  1. Method for suppressing feedback whistle in a hearing device by
    - establishing or predetermining a frequency range which is susceptible to feedback, and
    - receiving an input signal with a spectral component in the frequency range susceptible to feedback,
    characterised by
    - reducing the amplitude (5) of the said spectral component of the input signal so that a reduced spectral component remains, and
    - mixing (11) the reduced spectral component with a synthetic signal (8) to form a complete signal in the frequency range susceptible to feedback so that in said spectral range susceptible to feedback the output of the complete signal after mixing substantially corresponds to the output of the said spectral component before reduction.
  2. Method according to claim 1, the synthetic signal being generated with a non-linearity from the input signal.
  3. Method according to claim 1 or 2, the synthetic signal being generated by frequency shift of a spectral band of the input signal.
  4. Method according to one of the preceding claims, the spectral envelope of the mixed signal being corrected by means of an LPC analysis.
  5. Method according to claim 4, the correction taking place in combination with form filtering.
  6. Method according to one of the preceding claims, a further processing (7) of the reduced signal being carried out before mixing and the mixing being carried out by adding (11) the synthetic signal to the further processed, reduced signal immediately before a signal output to an output transducer.
  7. Method according to one of the preceding claims, the input signal being processed in a plurality of channels (A, B) and the mixing only being carried out in the channel with the frequency range susceptible to feedback.
  8. Method according to claim 7, one or more respective features of the respective signal (29, 30) being obtained from at least two of the channels (A, B) and considered for the mixing.
  9. Hearing device with
    - a feedback suppression device and
    - a signal input device for receiving an input signal,
    characterised in that
    - the feedback suppression device comprises a reduction unit (5) for reducing the amplitude of a spectral component of the input signal so that a reduced spectral component remains and
    - a mixing unit (11) for mixing the reduced spectral component with a synthetic signal to form a complete signal in the frequency range susceptible to feedback, so that in the feedback range susceptible to feedback the output of the complete signal after mixing substantially corresponds to the output of the said spectral component before the reduction.
EP07106332.5A 2006-05-04 2007-04-17 Method for elimination of feedback and for spectral expansion in hearing aids. Active EP1853089B2 (en)

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EP1853089A3 (en) 2007-12-26
EP1853089A2 (en) 2007-11-07
EP1853089B2 (en) 2013-09-25
DE502007001153D1 (en) 2009-09-10
DK1853089T3 (en) 2009-11-16
US8571243B2 (en) 2013-10-29
ATE438267T1 (en) 2009-08-15
DE102006020832A1 (en) 2007-11-15
DK1853089T4 (en) 2014-01-06
DE102006020832B4 (en) 2016-10-27

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