EP2182739A1 - Adaptive microphone system for a hearing aid and accompanying operating method - Google Patents

Adaptive microphone system for a hearing aid and accompanying operating method Download PDF

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Publication number
EP2182739A1
EP2182739A1 EP09168233A EP09168233A EP2182739A1 EP 2182739 A1 EP2182739 A1 EP 2182739A1 EP 09168233 A EP09168233 A EP 09168233A EP 09168233 A EP09168233 A EP 09168233A EP 2182739 A1 EP2182739 A1 EP 2182739A1
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Prior art keywords
microphone
noise
microphones
directivity
adaptation parameter
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EP09168233A
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German (de)
French (fr)
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EP2182739B1 (en
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Eghart Fischer
Henning Dr. Puder
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Sivantos Pte Ltd
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Siemens Medical Instruments Pte Ltd
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R25/00Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
    • H04R25/40Arrangements for obtaining a desired directivity characteristic
    • H04R25/407Circuits for combining signals of a plurality of transducers
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2430/00Signal processing covered by H04R, not provided for in its groups
    • H04R2430/03Synergistic effects of band splitting and sub-band processing
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00Circuits for transducers, loudspeakers or microphones
    • H04R3/005Circuits for transducers, loudspeakers or microphones for combining the signals of two or more microphones

Definitions

  • the invention relates to a specified in claim 1 method for suppressing microphone noise and specified in claim 7 associated microphone system.
  • Disturbances are defined on the one hand as signals that are incident from undesired directions, for example outside a predetermined angular range about the 0 ° direction and on the other hand as microphone noise, which is amplified when forming the directivity, especially in low-frequency areas.
  • microphone noise increases when the directivity of a directional microphone is increased.
  • the microphone signals of several microphones are adaptively filtered as a function of at least one parameter.
  • the directivity of the directional microphone obtained in this case is adjusted by changing the at least one parameter such that the sum of noise power including microphone noise is reduced or minimal.
  • the residual noise consists in half of residual ambient noise and residual microphone noise.
  • the overall disturbance is minimal, but not for the subjective sound impression of a user of the acoustic system. Due to rapidly changing signal components and wide subband signals, disturbing microphone noise is noticeable to the user over and over again. Particularly non-stationary interferers, such as speech, cause a brief transition to directional operation. If the interferer is then again not active, there is a delayed fading to the omnidirectional operation, so that noise flags are audible for a short time.
  • the stated object is achieved with the method for operating a microphone system of independent claim 1 and the microphone system of independent claim 7.
  • the method can be carried out separately for a plurality of frequency subbands. This provides improved directivity with simultaneous noise suppression.
  • the noise carpet may be determined using Wiener filters or non-linear power estimators.
  • Wiener filters or non-linear power estimators An advantage of this is a simple and robust noise power determination.
  • the value of the microphone noise number can be predetermined depending on the microphone, with a data sheet value of the microphone noise of the microphones and at least one distance of the microphones from one another being taken into account.
  • the interference power by directivity can include amplified microphone noise and power from unwanted signal sources.
  • the range of values can be chosen such that the microphone noise amplified by the directivity is masked by the stationary portion of the background noise.
  • the invention also provides a microphone system having at least two omnidirectional microphones emitting microphones, the microphones being electrically interconnected to form a directivity.
  • the microphone system comprises at least one filter unit with at least one adaptation parameter for adaptively filtering the at least two microphone signals to obtain the directivity and a control unit with which the at least one adaptation parameter is variable such that the sum of interference power is reduced.
  • the value range of the at least one adaptation parameter is limited, wherein the control unit the limits are determined from a comparison of the noise floor of the ambient noise with a microphone noise figure.
  • the at least one filter unit can have separate filters for a plurality of frequency subbands, so that the change in the at least one adaptation parameter can be carried out separately in a plurality of frequency subbands.
  • the noise carpet may be detected by means of Wiener filters or non-linear power estimators in the control unit.
  • the value of the microphone noise number in the control unit can be predetermined as a function of the microphone, whereby a data sheet value of the microphone noise of the microphones and at least one distance of the microphones from one another are taken into account.
  • the spurious power by directivity may include amplified microphone noise and power from unwanted signal sources.
  • the value range can be selected by the control unit such that the stationary portion of the background noise masks the microphone noise amplified by the directivity.
  • the invention also claims a hearing aid with a microphone system according to the invention for carrying out a method according to the invention. This offers the advantage that hearing aid users no longer perceive the resulting microphone noise perceptually.
  • FIG. 1 shows a differential microphone of the first order.
  • Two microphones 1, 2 receive a time-dependent sound signal s (t).
  • a microphone noise signal n 1 (t) or n 2 (t) mixes with the ideal microphone signals.
  • the respective sum signals are digitized with an analog-to-digital converter and thus provide the digital, noisy microphone signals x 1 (k) and x 2 (k).
  • the differential microphone of the first order can also be used as in FIG. 1 represented by two FIR filter units 3, 4 with the transfer functions 1 + az -1 and -az -1 realize.
  • the filter coefficients can not be chosen freely, but depend on the adaptation parameter a. This dependence, which results from conversion of the filtering from the differential microphone, ensures that the output signal after the directional microphone processing contains the signal from the 0 ° direction (useful signal direction) unchanged, independently of the choice of the parameter a. In order to optimize the adaptation parameter a, this is adapted to the respective one adapted acoustic situation.
  • the value of the adaptation parameter a is supplied from an output of a control unit 6 to the filter units 3, 4.
  • the power of the interference signal ST and the microphone noise MR are qualitatively plotted against the adaptation parameter a.
  • a sum signal SUM from the two signals ST and MR represents the total interference power for the directional microphone.
  • the adaptation of the directional microphone to a specific interference source or the optimization of the parameter a can be carried out, for example, by a gradient method comparable to the LMS method (least mean squares). But there are also other embodiments conceivable. With the gradient method, the adaptation condition is very simple. It can be determined by minimizing the average output signal power of the directional microphone. This will be like in FIG. 1 represented the output signal y (k) of the control unit 6 supplied.
  • the minimization of the average output signal power is only possible because it is ensured by the special choice of the filter coefficients in dependence of the parameter a, that the useful signal from the 0 ° direction is not changed.
  • the disturbance consists of two components: microphone noise and interference from signal sources that come from unwanted directions.
  • An attenuation of direction-dependent signal sources can be achieved by selecting the parameter a> 0.
  • a 2
  • the range in the 0 ° direction is determined - in this case +/- 60 ° - in which incident signal sources are not or only slightly attenuated.
  • the method achieves that the sum of the interference powers, i. of microphone noise and signal sources from undesired directions, in each frequency band is minimized.
  • a disadvantage of this adaptation is that due to a finite processing time with rapidly changing interference signals, such as voice from undesired direction, the adaptation parameter a can not be readjusted so quickly to suppress unwanted microphone noise. As a result, for a short time microphone noise as so-called noise flags is disturbing audible. This is where the invention starts. At the price of a reduced directivity, the microphone noise is suppressed by limiting the range which the adaptation parameter a can assume depending on the ambient noise. This makes it possible to mask the disturbing noise flags by ambient noise.
  • the limitation of the adaptation parameter a is in FIG. 2 clarified by a zul .
  • FIG. 3 is according to the invention
  • a stationary noise carpet NF of ambient noise in 48 signal sub-bands determined. This is plotted as a bar graph with the signal power P in dB.
  • the microphone signals x 1 (k) and x 2 (k) inputs of the control unit 6 supplied.
  • a theoretical value of the microphone noise MN is determined as a function of the frequency f.
  • the range of the adaptation of the parameter a as a function of the frequency f is now limited so that it is no longer possible for the adaptation to select the directional microphone setting so that the resulting microphone noise is above the measured noise carpet NF, ie perceptually perceived by the user.
  • the inventive step is to use the noise carpet NF for activating the directional microphone mode in each band and not the overall signal level or noise level. This ensures that short-term transient interferers do not lead to a fading into the directional microphone mode and thus to perceptible microphone noise, among other things by noise flags.
  • methods which are known from the Wiener filter-based, single-channel noise reduction can be used, or non-linear power estimators, which follow increasing level values more slowly than falling ones.
  • An analogue structure and an analogous method are used for directional microphones of higher orders.
  • Preferred application finds the microphone system and the associated method in hearing aids.

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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Neurosurgery (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Fittings On The Vehicle Exterior For Carrying Loads, And Devices For Holding Or Mounting Articles (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)

Abstract

The method involves filtering two microphone signals of respective microphones (1, 2) by finite impulse response filter units (3, 4), respectively. Directivities of the microphones are adjusted by changing an adaptation parameter to minimize the sum of interference power by a control unit (6). Noise floor of ambient noise is compared with a microphone noise number by the control unit, and a limit of value range of the adaptation parameter is determined based on the comparison result of the control unit. An independent claim is also included for a microphone system comprising an onmidirectional directional microphone.

Description

Die Erfindung betrifft ein im Patentanspruch 1 angegebenes Verfahren zur Unterdrückung von Mikrofonrauschen und ein im Patentanspruch 7 angegebenes zugehöriges Mikrofonsystem.The invention relates to a specified in claim 1 method for suppressing microphone noise and specified in claim 7 associated microphone system.

Bei Akustiksystemen und insbesondere bei Hörgeräten ist es vorteilhaft, mehrere Mikrofonsignale zu kombinieren und räumlich und spektral so zu filtern, dass das Ausgangssignal möglichst geringe Störanteile enthält. Störungen werden dabei einerseits als Signale definiert, die aus unerwünschten Richtungen, beispielsweise außerhalb eines vorgegebenen Winkelbereichs um die 0°-Richtung einfallen und andererseits als Mikrofonrauschen, das beim Ausbilden der Richtwirkung vor allem in tieffrequenten Bereichen verstärkt wird. Insbesondere besteht das Problem, dass das Mikrofonrauschen steigt, wenn die Richtwirkung eines Richtmikrofons erhöht wird.In acoustic systems and in particular in hearing aids, it is advantageous to combine several microphone signals and to spatially and spectrally filter them so that the output signal contains the lowest possible interference components. Disturbances are defined on the one hand as signals that are incident from undesired directions, for example outside a predetermined angular range about the 0 ° direction and on the other hand as microphone noise, which is amplified when forming the directivity, especially in low-frequency areas. In particular, there is the problem that the microphone noise increases when the directivity of a directional microphone is increased.

In der DE 10 2004 052 912 A1 werden ein Akustiksystem und ein Verfahren angegeben, die Störleistungen bei Richtmikrofonen so weit wie möglich unterdrücken. Dazu werden die Mikrofonsignale mehrerer Mikrofone in Abhängigkeit mindestens eines Parameters adaptiv gefiltert. Die Richtwirkung des hierbei erhaltenen Richtmikrofons wird durch Verändern des mindestens einen Parameters derart eingestellt, dass die Summe von Störleistungen einschließlich Mikrofonrauschen reduziert bzw. minimal ist. So wird je nach Rauschverteilung zwischen einem direktionalen Betrieb und einem omnidirektionalen Betrieb umgeblendet.In the DE 10 2004 052 912 A1 An acoustic system and a method are specified which suppress interference power in directional microphones as far as possible. For this purpose, the microphone signals of several microphones are adaptively filtered as a function of at least one parameter. The directivity of the directional microphone obtained in this case is adjusted by changing the at least one parameter such that the sum of noise power including microphone noise is reduced or minimal. Thus, depending on the noise distribution between a directional operation and an omnidirectional operation blended.

Das in der DE 10 2004 062 912 A1 beschriebene Verfahren führt zu einer Minimierung der Summenleistung aus Mikrofonrauschen und Umgebungsrauschen. Das Restrauschen besteht hälftig aus Rest-Umgebungsrauschen und Rest-Mikrofonrauschen. Im mathematischen Sinne ist die Gesamtstörung minimal, allerdings nicht für den subjektiven Klangeindruck eines Nutzers des Akustiksystems. Durch sich schnell ändernde Signalanteile und breite Teilbandsignale ist für den Nutzer immer wieder störendes Mikrofonrauschen wahrnehmbar. Besonders instationäre Störer, wie Sprache, verursachen ein kurzzeitiges Umblenden in den direktionalen Betrieb. Ist der Störer dann wieder nicht aktiv, erfolgt ein verzögertes Umblenden auf den omnidirektionalen Betrieb, so dass kurzzeitig Rauschfahnen hörbar sind.That in the DE 10 2004 062 912 A1 described method leads to a minimization of the total power of microphone noise and ambient noise. The residual noise consists in half of residual ambient noise and residual microphone noise. In the mathematical sense, the overall disturbance is minimal, but not for the subjective sound impression of a user of the acoustic system. Due to rapidly changing signal components and wide subband signals, disturbing microphone noise is noticeable to the user over and over again. Particularly non-stationary interferers, such as speech, cause a brief transition to directional operation. If the interferer is then again not active, there is a delayed fading to the omnidirectional operation, so that noise flags are audible for a short time.

Es ist Aufgabe der Erfindung diese Nachteile zu überwinden und eine Vorrichtung und ein dazugehöriges Verfahren anzugeben, welche wahrnehmbares Mikrofonrauschen verhindern.It is an object of the invention to overcome these disadvantages and to provide a device and an associated method which prevent perceptible microphone noise.

Gemäß der Erfindung wird die gestellte Aufgabe mit dem Verfahren zum Betrieb eines Mikrofonsystems des unabhängigen Patentanspruchs 1 und dem Mikrofonsystem des unabhängigen Patentanspruchs 7 gelöst.According to the invention, the stated object is achieved with the method for operating a microphone system of independent claim 1 and the microphone system of independent claim 7.

Die Erfindung gibt ein Verfahren zum Betrieb eines Mikrofonsystems mit mindestens zwei omnidirektionalen, Mikrofonsignale abgebenden Mikrofonen an, wobei die Mikrofone zur Bildung einer Richtwirkung elektrisch miteinander verschaltet sind. Das Verfahren umfasst folgende Schritte:

  • adaptives Filtern der mindestens zwei Mikrofonsignale mit mindestens einem Adaptionsparameter,
  • Einstellen der Richtwirkung durch Verändern des mindestens einen Adaptionsparameters derart, dass die Summe von Störleistungen minimiert wird, und
  • Begrenzen des Wertebereichs des mindestens einen Adaptionsparameters, wobei die Grenzen aus einem Vergleich des Rauschteppichs des Umgebungsrauschens mit einer Mikrofonrauschzahl ermittelt werden.
Dies bietet den Vorteil, dass der Adaptionsbereich eines adaptiven differentiellen Richtmikrofons abhängig vom stationären Anteil des Hintergrundrauschens ist, wodurch die Richtwirkung immer so gewählt wird, dass das durch die Richtwirkung entstehende, instationäre Mikrofonrauschen fast immer durch den stationären Anteil des Hintergrundrauschens maskiert wird. Damit wird situationsangepasst ein ruhiger Klangeindruck ohne Rauschartefakte bei gleichzeitig maximal möglicher Richtwirkung erzielt.The invention provides a method for operating a microphone system with at least two omnidirectional microphone-emitting microphones, wherein the microphones are electrically interconnected to form a directivity. The method comprises the following steps:
  • adaptively filtering the at least two microphone signals with at least one adaptation parameter,
  • Setting the directivity by changing the at least one adaptation parameter such that the sum of noise power is minimized, and
  • Limiting the range of values of the at least one adaptation parameter, the limits being determined from a comparison of the noise floor of the ambient noise with a microphone noise figure.
This offers the advantage that the adaptation range of an adaptive differential directional microphone is dependent on the stationary portion of the background noise, whereby the directivity is always chosen so that the transient microphone noise resulting from the directivity is almost always masked by the stationary portion of the background noise. This situation adapted to a quiet sound impression achieved without noise artifacts with maximum possible directivity.

In einer Weiterbildung kann das Verfahren für mehrere Frequenzteilbänder getrennt ausgeführt werden. Dies bietet eine verbesserte Richtwirkung bei gleichzeitiger Rauschfahnenunterdrückung.In a further development, the method can be carried out separately for a plurality of frequency subbands. This provides improved directivity with simultaneous noise suppression.

In einer weiteren Ausführungsform kann der Rauschteppich mit Hilfe von Wiener-Filtern oder nicht linearen Leistungsschätzern ermittelt werden. Vorteilhaft daran ist eine einfache und robuste Rauschleistungsbestimmung.In another embodiment, the noise carpet may be determined using Wiener filters or non-linear power estimators. An advantage of this is a simple and robust noise power determination.

Des Weiteren kann der Wert der Mikrofonrauschzahl mikrofonabhängig vorgegeben werden, wobei ein Datenblattwert des Mikrofonrauschens der Mikrofone und mindestens ein Abstand der Mikrofone zueinander berücksichtigt werden. Vorteilhaft daran ist die Verwendung von mikrofonspezifischen Parametern.Furthermore, the value of the microphone noise number can be predetermined depending on the microphone, with a data sheet value of the microphone noise of the microphones and at least one distance of the microphones from one another being taken into account. An advantage of this is the use of microphone-specific parameters.

In einer Weiterbildung können die Störleistungen durch Richtwirkung verstärktes Mikrofonrauschen und Leistungen von unerwünschten Signalquellen umfassen.In a further development, the interference power by directivity can include amplified microphone noise and power from unwanted signal sources.

In vorteilhafter Weise kann der Wertebereich so gewählt werden, dass das durch die Richtwirkung verstärkte Mikrofonrauschen durch den stationären Anteil des Hintergrundrauschens maskiert wird.Advantageously, the range of values can be chosen such that the microphone noise amplified by the directivity is masked by the stationary portion of the background noise.

Die Erfindung gibt auch ein Mikrofonsystem mit mindestens zwei omnidirektionalen, Mikrofonsignale abgebenden Mikrofonen an, wobei die Mikrofone zur Bildung einer Richtwirkung elektrisch miteinander verschaltet sind. Das Mikrofonsystem umfasst mindestens eine Filtereinheit mit mindestens einem Adaptionsparameter zum adaptiven Filtern der mindestens zwei Mikrofonsignale zur Erzielung der Richtwirkung und eine Steuereinheit, mit der der mindestens eine Adaptionsparameter derart veränderbar ist, dass die Summe von Störleistungen reduziert wird. Der Wertebereich des mindestens einen Adaptionsparameters wird begrenzt, wobei durch die Steuereinheit die Grenzen aus einem Vergleich des Rauschteppichs des Umgebungsrauschens mit einer Mikrofonrauschzahl ermittelt werden.The invention also provides a microphone system having at least two omnidirectional microphones emitting microphones, the microphones being electrically interconnected to form a directivity. The microphone system comprises at least one filter unit with at least one adaptation parameter for adaptively filtering the at least two microphone signals to obtain the directivity and a control unit with which the at least one adaptation parameter is variable such that the sum of interference power is reduced. The value range of the at least one adaptation parameter is limited, wherein the control unit the limits are determined from a comparison of the noise floor of the ambient noise with a microphone noise figure.

In einer Weiterbildung kann die mindestens eine Filtereinheit für mehrere Frequenzteilbänder getrennte Filter aufweisen, so dass die Veränderung des mindestens einen Adaptionsparameters in mehreren Frequenzteilbändern getrennt ausführbar ist.In a refinement, the at least one filter unit can have separate filters for a plurality of frequency subbands, so that the change in the at least one adaptation parameter can be carried out separately in a plurality of frequency subbands.

In einer weiteren Ausführungsform kann der Rauschteppich mit Hilfe von Wiener-Filtern oder nicht linearen Leistungsschätzern in der Steuereinheit ermittelt werden.In a further embodiment, the noise carpet may be detected by means of Wiener filters or non-linear power estimators in the control unit.

Vorteilhaft kann der Wert der Mikrofonrauschzahl in der Steuereinheit mikrofonabhängig vorgegeben werden, wobei ein Datenblattwert des Mikrofonrauschens der Mikrofone und mindestens ein Abstand der Mikrofone zueinander berücksichtigt werden.Advantageously, the value of the microphone noise number in the control unit can be predetermined as a function of the microphone, whereby a data sheet value of the microphone noise of the microphones and at least one distance of the microphones from one another are taken into account.

Des Weiteren können die Störleistungen durch Richtwirkung verstärktes Mikrofonrauschen und Leistungen von unerwünschten Signalquellen umfassen.Furthermore, the spurious power by directivity may include amplified microphone noise and power from unwanted signal sources.

In einer Weiterbildung kann durch die Steuereinheit der Wertebereich so gewählt werden, dass der stationäre Anteil des Hintergrundrauschens das durch die Richtwirkung verstärkte Mikrofonrauschen maskiert.In a development, the value range can be selected by the control unit such that the stationary portion of the background noise masks the microphone noise amplified by the directivity.

Die Erfindung beansprucht auch ein Hörgerät mit einem erfindungsgemäßen Mikrofonsystem zum Ausführen eines erfindungsgemäßen Verfahrens. Dies bietet den Vorteil, dass Hörgerätenutzer das resultierende Mikrofonrauschen perzeptiv nicht mehr wahrnehmen.The invention also claims a hearing aid with a microphone system according to the invention for carrying out a method according to the invention. This offers the advantage that hearing aid users no longer perceive the resulting microphone noise perceptually.

Weitere Besonderheiten und Vorteile der Erfindung werden aus den nachfolgenden Erläuterungen eines Ausführungsbeispiels anhand von schematischen Zeichnungen ersichtlich.Other features and advantages of the invention will become apparent from the following explanations of an embodiment with reference to schematic drawings.

Es zeigen:

Figur 1:
ein Prinzipschaltbild eines Mikrofonsystems erster Ordnung,
Figur 2:
ein Diagramm zur Optimierung des Adaptionsparameters,
Figur 3:
einen Verlauf des Rauschteppichs und des Mikrofonrauschens in Abhängigkeit der Frequenz und
Figur 4:
einen Verlauf des Grenzwerts des Adaptionsparameters in Abhängigkeit der Frequenz.
Show it:
FIG. 1:
a schematic diagram of a microphone system first order,
FIG. 2:
a diagram for optimizing the adaptation parameter,
FIG. 3:
a course of the noise carpet and the microphone noise as a function of frequency and
FIG. 4:
a profile of the limit value of the adaptation parameter as a function of the frequency.

Figur 1 zeigt ein Differentialmikrofon erster Ordnung. Zwei Mikrofone 1, 2 nehmen ein zeitabhängiges Schallsignal s(t) auf. Zu den idealen Mikrofonsignalen mischt sich jeweils ein Mikrofonrauschsignal n1(t) bzw. n2(t). Die jeweiligen Summensignale werden mit einem Analog-Digital-Wandler digitalisiert und liefern so die digitalen, rauschbehafteten Mikrofonsignale x1(k) und x2(k). FIG. 1 shows a differential microphone of the first order. Two microphones 1, 2 receive a time-dependent sound signal s (t). In each case, a microphone noise signal n 1 (t) or n 2 (t) mixes with the ideal microphone signals. The respective sum signals are digitized with an analog-to-digital converter and thus provide the digital, noisy microphone signals x 1 (k) and x 2 (k).

Bekannt zur Erzielung einer Richtwirkung, aber in Figur 1 nicht dargestellt, ist es, die beiden Mikrofonsignale x1(k) und x2(k) kreuzweise zu subtrahieren. Dabei werden die Signale in den entsprechenden Pfaden mit Zeitgliedern verzögert und ein Differenzsignal wird mit einem Adaptionsparameter a multipliziert. Die resultierenden Signale werden addiert und zur Entzerrung in Nutzsignalrichtung einem Equalizer 5 mit einer Übertragungsfunktion H z = 1 1 - z - 2

Figure imgb0001
zugeführt. Die Entzerrung liefert ein Monoausgangssignal y(k).Known for achieving a directivity, but in FIG. 1 not shown, is to cross-subtract the two microphone signals x 1 (k) and x 2 (k). The signals are delayed in the corresponding paths with timers and a difference signal is multiplied by an adaptation parameter a. The resulting signals are added and for equalization in Nutzsignalrichtung an equalizer 5 with a transfer function H z = 1 1 - z - 2
Figure imgb0001
fed. The equalization provides a mono output signal y (k).

Das Differentialmikrofon erster Ordnung lässt sich aber auch wie in Figur 1 dargestellt durch zwei FIR-Filtereinheiten 3, 4 mit den Übertragungsfunktionen 1+az-1 und -a-z-1 realisieren. Die Filterkoeffizienten können dabei nicht frei gewählt werden, sondern hängen von dem Adaptionsparameter a ab. Durch diese Abhängigkeit, die sich durch Umrechnung der Filterung aus dem differentiellen Mikrofon ergibt, ist sichergestellt, dass das Ausgangssignal nach der Richtmikrofonverarbeitung das Signal aus der 0°-Richtung (Nutzsignalrichtung) unverändert enthält, unabhängig von der Wahl des Parameters a. Zur Optimierung des Adaptionsparameters a wird dieser an die jeweilige akustische Situation angepasst. Bei a=-1 ist keine Richtwirkung vorhanden, das Mikrofonsystem besitzt omnidirektionalen Charakter, bei a=0 wird der Schall aus der Richtung 180° gedämpft und bei größer werdendem a wandern die Notches (= Richtungen stärkster Dämpfung) im Richtdiagramm nach vorne. Der Wert des Adaptionsparameter a wird von einem Ausgang einer Steuereinheit 6 den Filtereinheiten 3, 4 zugeführt.The differential microphone of the first order can also be used as in FIG. 1 represented by two FIR filter units 3, 4 with the transfer functions 1 + az -1 and -az -1 realize. The filter coefficients can not be chosen freely, but depend on the adaptation parameter a. This dependence, which results from conversion of the filtering from the differential microphone, ensures that the output signal after the directional microphone processing contains the signal from the 0 ° direction (useful signal direction) unchanged, independently of the choice of the parameter a. In order to optimize the adaptation parameter a, this is adapted to the respective one adapted acoustic situation. At a = -1 there is no directivity, the microphone system has an omnidirectional character, at a = 0 the sound is attenuated from the direction 180 ° and with increasing a the notches (= directions of greatest attenuation) move forward in the directional diagram. The value of the adaptation parameter a is supplied from an output of a control unit 6 to the filter units 3, 4.

Mit größerer Richtwirkung, das heißt mit zunehmendem a, steigt aber auch das Mikrofonrauschen an. Wünschenswert ist es aber, dass die gesamte Störleistung eines Richtmikrofons so gering wie möglich ist. Deshalb ist einerseits die Richtwirkung des Richtmikrofons so einzustellen, dass der Schall einer Störquelle so gut wie möglich unterdrückt wird und andererseits das Mikrofonrauschen möglichst gering zu halten. In Figur 2 ist zum besseren Verständnis die Leistung des Störsignals ST und das Mikrofonrauschen MR über dem Adaptionsparameter a qualitativ aufgetragen. Ein Summensignal SUM aus den beiden Signalen ST und MR stellt die Gesamtstörleistung für das Richtmikrofon dar. Durch bekannte Verfahren, wie beispielsweise in DE 10 2004 052 912 A1 offenbart, gelingt es, das Minimum der Summenkurve SUM zu finden und den entsprechenden Parameterwert amin für die adaptiven Filter 3, 4 einzusetzen.With larger directivity, that is with increasing a, but also increases the microphone noise. However, it is desirable that the total interference power of a directional microphone is as low as possible. Therefore, on the one hand to adjust the directivity of the directional microphone so that the sound of a source of interference is suppressed as well as possible and on the other hand to keep the microphone noise as low as possible. In FIG. 2 For better understanding, the power of the interference signal ST and the microphone noise MR are qualitatively plotted against the adaptation parameter a. A sum signal SUM from the two signals ST and MR represents the total interference power for the directional microphone. By known methods, such as in DE 10 2004 052 912 A1 discloses, it is possible to find the minimum of the sum curve SUM and to use the corresponding parameter value a min for the adaptive filter 3, 4.

Die Adaption des Richtmikrofons an eine konkrete Störquelle bzw. die Optimierung des Parameters a kann beispielsweise durch eine Gradientenmethode vergleichbar dem LMS-Verfahren (least mean squares) erfolgen. Es sind aber auch andere Ausführungsvarianten denkbar. Bei der Gradientenmethode ist die Adaptionsbedingung sehr einfach. Sie kann durch Minimierung der mittleren Ausgangssignalleistung des Richtmikrofons ermittelt werden. Dazu wird wie in Figur 1 dargestellt das Ausgangssignal y(k) der Steuereinheit 6 zugeführt.The adaptation of the directional microphone to a specific interference source or the optimization of the parameter a can be carried out, for example, by a gradient method comparable to the LMS method (least mean squares). But there are also other embodiments conceivable. With the gradient method, the adaptation condition is very simple. It can be determined by minimizing the average output signal power of the directional microphone. This will be like in FIG. 1 represented the output signal y (k) of the control unit 6 supplied.

Zur Adaption des Richtmikrofons ist die Minimierung der mittleren Ausgangssignalleistung nur deshalb möglich, weil durch die spezielle Wahl der Filterkoeffizienten in Abhängigkeit des Parameters a sichergestellt ist, dass das Nutzsignal aus der 0°-Richtung nicht verändert wird. Die Minimierung der Gesamtleistung (= Nutzsignal + Störung) ist somit äquivalent zur Minimierung der Leistung der Störung. Die Störung setzt sich dabei aus zwei Komponenten zusammen: Mikrofonrauschen und Störungen von Signalquellen, die aus unerwünschten Richtungen einfallen. Eine Dämpfung von richtungsabhängigen Signalquellen kann durch die Wahl des Parameters a>0 erreicht werden. Durch die Begrenzung auf einen Maximalwert, zum Beispiel a=2, legt man den Bereich in der 0°-Richtung fest - in diesem Fall +/- 60° -, in dem einfallende Signalquellen nicht oder nur gering gedämpft werden. Erlaubt man dem adaptiven Verfahren zusätzlich, den Parameter a auch kleiner als 0 zu wählen, wird zwar die Richtwirkung verringert, aber damit auch die Leistung des Mikrofonrauschens abgesenkt. Bei a=-1 tritt keine Richtwirkung mehr auf und das Mikrofonsystem der Mikrofone 1, 2 wirkt ausschließlich omnidirektional.For the adaptation of the directional microphone, the minimization of the average output signal power is only possible because it is ensured by the special choice of the filter coefficients in dependence of the parameter a, that the useful signal from the 0 ° direction is not changed. The minimization of the total power (= useful signal + interference) is therefore equivalent to minimizing the power of the disturbance. The disturbance consists of two components: microphone noise and interference from signal sources that come from unwanted directions. An attenuation of direction-dependent signal sources can be achieved by selecting the parameter a> 0. By limiting to a maximum value, for example a = 2, the range in the 0 ° direction is determined - in this case +/- 60 ° - in which incident signal sources are not or only slightly attenuated. If the adaptive method is also allowed to select the parameter a smaller than 0, the directivity is reduced, but the microphone noise is also reduced. At a = -1 no directivity occurs and the microphone system of the microphones 1, 2 acts exclusively omnidirectional.

Durch die Adaption des Parameters a in einzelnen Frequenzbändern erreicht das Verfahren, dass die Summe der Störleistungen, d.h. von Mikrofonrauschen und von Signalquellen aus unerwünschten Richtungen, in jedem Frequenzband minimiert wird.By adapting the parameter a in individual frequency bands, the method achieves that the sum of the interference powers, i. of microphone noise and signal sources from undesired directions, in each frequency band is minimized.

Nachteilig an dieser Adaption ist, dass infolge einer endlichen Verarbeitungszeit bei sich rasch verändernden Störsignalen, beispielsweise Sprache aus unerwünschter Richtung, der Adaptionsparameter a nicht so rasch nachgeregelt werden kann, um unerwünschtes Mikrofonrauschen zu unterdrücken. Dadurch wird für einen Nutzer kurzzeitig Mikrofonrauschen als sogenannte Rauschfahnen störend hörbar. Hier setzt die Erfindung an. Um den Preis einer verminderten Richtwirkung wird das Mikrofonrauschen unterdrückt, indem der Bereich, den der Adaptionsparameter a einnehmen kann, abhängig vom Umgebungsrauschen begrenzt wird. Dadurch gelingt es, die störenden Rauschfahnen durch Umgebungsrauschen zu maskieren. Die Begrenzung des Adaptionsparameters a ist in Figur 2 durch azul verdeutlicht.A disadvantage of this adaptation is that due to a finite processing time with rapidly changing interference signals, such as voice from undesired direction, the adaptation parameter a can not be readjusted so quickly to suppress unwanted microphone noise. As a result, for a short time microphone noise as so-called noise flags is disturbing audible. This is where the invention starts. At the price of a reduced directivity, the microphone noise is suppressed by limiting the range which the adaptation parameter a can assume depending on the ambient noise. This makes it possible to mask the disturbing noise flags by ambient noise. The limitation of the adaptation parameter a is in FIG. 2 clarified by a zul .

Mit Hilfe der Darstellungen der Figuren 3 und 4 wird die Erfindung näher erläutert. Gemäß Figur 3 wird erfindungsgemäß zunächst ein stationärer Rauschteppich NF des Umgebungsrauschens in 48 Signalteilbändern bestimmt. Dieses ist als Balkendiagramm mit der Signalleistung P in dB eingezeichnet. Zur Bestimmung des Umgebungsrauschens NF werden wie in Figur 1 dargestellt die Mikrofonsignale x1(k) und x2(k) Eingängen der Steuereinheit 6 zugeführt. Aus Datenblattwerten der Mikrofone 1,2 und dem Abstand der beiden Mikrofone 1, 2 zueinander wird ein theoretischer Wert des Mikrofonrauschens MN, auch als Mikrofonrauschzahl bezeichnet, in Abhängigkeit der Frequenz f ermittelt.With the help of the representations of the FIGS. 3 and 4 the invention will be explained in more detail. According to FIG. 3 is according to the invention First, a stationary noise carpet NF of ambient noise in 48 signal sub-bands determined. This is plotted as a bar graph with the signal power P in dB. To determine the ambient noise NF, as in FIG. 1 represented the microphone signals x 1 (k) and x 2 (k) inputs of the control unit 6 supplied. From data sheet values of the microphones 1, 2 and the distance of the two microphones 1, 2 from each other, a theoretical value of the microphone noise MN, also referred to as microphone noise number, is determined as a function of the frequency f.

In einem weiteren Schritt wird nun der Bereich der Adaption des Parameters a in Abhängigkeit der Frequenz f nach oben so beschränkt, dass es für die Adaption nicht mehr möglich ist, die Richtmikrofoneinstellung so zu wählen, dass das resultierende Mikrofonrauschen über dem gemessenen Rauschteppich NF liegt, d.h. perzeptiv vom Nutzer wahrgenommen werden kann. In Figur 4 ist der Grenzwert A des Adaptionsparameters a in Abhängigkeit von den 48 Signalteilbängern in Form von vertikalen Balken dargestellt. Für die untere Begrenzung gilt immer a=-1. Aus den Figuren 3 und 4 ist ersichtlich, dass für kleinere Differenzen aus Umgebungsrauschen NF und Mikrofonrauschen MN der obere Grenzwert A des Adaptionsparameters a kleiner wird.In a further step, the range of the adaptation of the parameter a as a function of the frequency f is now limited so that it is no longer possible for the adaptation to select the directional microphone setting so that the resulting microphone noise is above the measured noise carpet NF, ie perceptually perceived by the user. In FIG. 4 the limit value A of the adaptation parameter a is represented in the form of vertical bars as a function of the 48 signal subbands. For the lower bound always a = -1. From the FIGS. 3 and 4 It can be seen that for smaller differences from ambient noise NF and microphone noise MN, the upper limit A of the adaptation parameter a becomes smaller.

Der erfinderische Schritt liegt darin, den Rauschteppich NF für die Aktivierung des Richtmikrofonmodus in den einzelnen Bändern zu nutzen und nicht den Gesamtsignalpegel oder den Störsignalpegel. Damit ist sichergestellt, dass kurzzeitige instationäre Störer nicht zu einem Umblenden in den Richtmikrofonmodus und damit zu wahrnehmbarem Mikrofonrauschen, u.a. durch Rauschfahnen, führen. Zur Berechnung des Rauschteppichs NF in den einzelnen Bändern können Verfahren genutzt werden, die aus der Wiener-Filter basierten, einkanaligen Geräuschreduktion bekannt sind, oder nicht lineare Leistungsschätzer, die ansteigenden Pegelwerten langsamer folgen als abfallenden.The inventive step is to use the noise carpet NF for activating the directional microphone mode in each band and not the overall signal level or noise level. This ensures that short-term transient interferers do not lead to a fading into the directional microphone mode and thus to perceptible microphone noise, among other things by noise flags. For the calculation of the noise floor NF in the individual bands, methods which are known from the Wiener filter-based, single-channel noise reduction can be used, or non-linear power estimators, which follow increasing level values more slowly than falling ones.

Ein analoger Aufbau und ein analoges Verfahren werden für Richtmikrofone höherer Ordnungen angewandt. Bevorzugte Anwendung findet das Mikrofonsystem und das zugehörige Verfahren bei Hörgeräten.An analogue structure and an analogous method are used for directional microphones of higher orders. Preferred application finds the microphone system and the associated method in hearing aids.

BezugszeichenlisteLIST OF REFERENCE NUMBERS

1, 21, 2
Mikrofonmicrophone
3, 43, 4
Filtereinheitfilter unit
55
Equalizerequalizer
66
Steuereinheitcontrol unit
aa
Adaptionsparameteradaptation parameter
amin a min
minimaler Adaptionsparameter aminimal adaptation parameter a
azul a perm
zulässiger Adaptionsparameter apermissible adaptation parameter a
AA
Grenzwert des Adaptionsparameters aLimit value of the adaptation parameter a
ff
Frequenzfrequency
MRMR
Mikrofonrauschenmicrophone noise
MNMN
MikrofonrauschzahlMicrophone noise figure
n1(t), n2(t)n 1 (t), n 2 (t)
MikrofonrauschsignalMicrophone noise signal
NFNF
Geräuschteppichnoise floor
PP
Störleistunginterference power
SUMSUM
SummengeräuschCumulative noise
STST
Störgeräuschinterference
x1(k), x2(k)x 1 (k), x 2 (k)
Mikrofonsignalmicrophone signal
y(k)y (k)
Ausgangssignaloutput

Claims (13)

Verfahren zum Betrieb eines Mikrofonsystems mit mindestens zwei omnidirektionalen, Mikrofonsignale abgebenden Mikrofonen (1, 2), wobei die Mikrofone zur Bildung einer Richtwirkung elektrisch miteinander verschaltet sind, durch: - adaptives Filtern der mindestens zwei Mikrofonsignale mit mindestens einem Adaptionsparameter (a) und - Einstellen der Richtwirkung durch Verändern des mindestens einen Adaptionsparameters (a) derart, dass die Summe (SUM) von Störleistungen (ST, MR) minimiert wird, gekennzeichnet durch: - Begrenzen des Wertebereichs des mindestens einen Adaptionsparameters (a), wobei die Grenzen (A) aus einem Vergleich des Rauschteppichs (NF) des Umgebungsrauschens mit einer Mikrofonrauschzahl (MN) ermittelt werden. Method for operating a microphone system having at least two omnidirectional microphones emitting microphones (1, 2), wherein the microphones are electrically interconnected to form a directivity by: adaptively filtering the at least two microphone signals with at least one adaptation parameter (a) and Adjusting the directivity by changing the at least one adaptation parameter (a) such that the sum (SUM) of interference power (ST, MR) is minimized, characterized by : Limiting the range of values of the at least one adaptation parameter (a), the limits (A) being determined from a comparison of the noise floor (NF) of the ambient noise with a microphone noise figure (MN). Verfahren nach Anspruch 1,
dadurch gekennzeichnet,
dass es für mehrere Frequenzteilbänder getrennt ausgeführt wird.
Method according to claim 1,
characterized,
that it is carried out separately for several frequency subbands.
Verfahren nach Anspruch 1 oder 2,
dadurch gekennzeichnet,
dass der Rauschteppich (NF) mit Hilfe von Wiener-Filtern oder nicht linearen Leistungsschätzern ermittelt wird.
Method according to claim 1 or 2,
characterized,
that the noise floor (NF) is determined using Wiener filters or non-linear power estimators.
Verfahren nach einem der Ansprüche 1 bis 3,
dadurch gekennzeichnet,
dass der Wert der Mikrofonrauschzahl (MN) mikrofonabhängig vorgegeben wird, wobei ein Datenblattwert des Mikrofonrauschens der Mikrofone (1, 2) und mindestens ein Abstand der Mikrofone (1, 2) zueinander berücksichtigt werden.
Method according to one of claims 1 to 3,
characterized,
that the value of the microphone noise number (MN) is predetermined depending on the microphone, with a data sheet value of the microphone noise of the microphones (1, 2) and at least one distance between the microphones (1, 2) are considered each other.
Verfahren nach einem der vorigen Ansprüche,
dadurch gekennzeichnet,
dass die Störleistungen (SUM) durch Richtwirkung verstärktes Mikrofonrauschen (MR) und Leistungen von unerwünschten Signalquellen (ST) umfassen.
Method according to one of the preceding claims,
characterized,
that the stray powers (SUM) comprise directivity enhanced microphone noise (MR) and undesired signal source (ST) power.
Verfahren nach einem der vorigen Ansprüche,
dadurch gekennzeichnet,
dass der Wertebereich (A) so gewählt wird, dass das durch die Richtwirkung verstärkte Mikrofonrauschen (MR) durch den stationären Anteil des Hintergrundrauschens (NF) maskiert wird.
Method according to one of the preceding claims,
characterized,
in that the value range (A) is selected so that the microphone noise (MR) amplified by the directivity is masked by the stationary portion of the background noise (LF).
Mikrofonsystem umfassend - mindestens zwei omnidirektionale, Mikrofonsignale abgebende Mikrofone (1, 2), wobei die Mikrofone (1, 2) zur Bildung einer Richtwirkung elektrisch miteinander verschaltet sind, - mindestens eine Filtereinheit (3, 4) mit mindestens einem Adaptionsparameter (a) zum adaptiven Filtern der mindestens zwei Mikrofonsignale zur Erzielung der Richtwirkung und - eine Steuereinheit (6), mit der der mindestens eine Adaptionsparameter (a) derart veränderbar ist, dass die Summe (SUM) von Störleistungen reduziert wird, dadurch gekennzeichnet, - dass der Wertebereichs des mindestens einen Adaptionsparameters (a) begrenzbar ist, wobei durch die Steuereinheit (6) die Grenzen (A) aus einem Vergleich des Rauschteppichs (NF) des Umgebungsrauschens mit einer Mikrofonrauschzahl (MN) ermittelbar sind. Comprising microphone system at least two omnidirectional microphones emitting microphones (1, 2), the microphones (1, 2) being electrically interconnected to form a directivity, - At least one filter unit (3, 4) with at least one adaptation parameter (a) for adaptively filtering the at least two microphone signals to obtain the directivity and a control unit (6) with which the at least one adaptation parameter (a) can be changed in such a way that the sum (SUM) of interference power is reduced, characterized, - That the range of values of the at least one adaptation parameter (a) can be limited, wherein by the control unit (6) the limits (A) from a comparison of the noise carpet (NF) of the ambient noise with a microphone noise figure (MN) can be determined. Mikrofonsystem nach Anspruch 7,
dadurch gekennzeichnet,
dass die mindestens eine Filtereinheit (3, 4) für mehrere Frequenzteilbänder getrennte Filter aufweist, so dass die Veränderung des mindestens einen Adaptionsparameters (a) in mehreren Frequenzteilbändern getrennt ausführbar ist.
Microphone system according to claim 7,
characterized,
the at least one filter unit (3, 4) having separate filters for a plurality of frequency sub-bands, so that the change in the at least one adaptation parameter (a) can be executed separately in a plurality of frequency subbands.
Mikrofonsystem nach Anspruch 7 oder 8,
dadurch gekennzeichnet,
dass der Rauschteppich (NF) mit Hilfe von Wiener-Filtern oder nicht linearen Leistungsschätzern in der Steuereinheit ermittelbar ist.
Microphone system according to claim 7 or 8,
characterized,
that the noise floor is determined (NF) with the aid of Wiener filters or non-linear power estimators in the control unit.
Mikrofonsystem nach einem der Ansprüche 7 bis 9,
dadurch gekennzeichnet,
dass der Wert der Mikrofonrauschzahl (MN) mikrofonabhängig vorgebbar ist, wobei ein Datenblattwert des Mikrofonrauschens der Mikrofone (1, 2) und mindestens ein Abstand der Mikrofone (1, 2) zueinander berücksichtigt werden.
Microphone system according to one of claims 7 to 9,
characterized,
that the value of the microphone noise number is depending on the microphone can be predetermined (MN), wherein a data sheet value of the microphone noise of the microphones (1, 2) and at least one distance between the microphones (1, 2) are considered each other.
Mikrofonsystem nach einem der Ansprüche 7 bis 10,
dadurch gekennzeichnet,
dass die Störleistungen (SUM) durch Richtwirkung verstärktes Mikrofonrauschen (MR) und Leistungen von unerwünschten Signalquellen (ST) umfassen.
Microphone system according to one of claims 7 to 10,
characterized,
that the stray powers (SUM) comprise directivity enhanced microphone noise (MR) and undesired signal source (ST) power.
Mikrofonsystem nach einem der Ansprüche 7 bis 11,
dadurch gekennzeichnet,
dass durch die Steuereinheit (6) der Wertebereich (A) so wählbar ist, dass der stationäre Anteil des Hintergrundrauschens (NF) das durch die Richtwirkung verstärkte Mikrofonrauschen (MR) maskiert.
Microphone system according to one of claims 7 to 11,
characterized,
in that the value range (A) can be selected by the control unit (6) such that the stationary portion of the background noise (NF) masks the microphone noise (MR) amplified by the directivity.
Hörgerät mit einem Mikrofonsystem nach einem der Ansprüche 7 bis 12 zum Ausführen des Verfahrens nach einem der Ansprüche 1 bis 6.Hearing aid with a microphone system according to one of claims 7 to 12 for carrying out the method according to one of claims 1 to 6.
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