EP0411360B1 - Method and apparatus for interference suppression in speech signals - Google Patents

Method and apparatus for interference suppression in speech signals Download PDF

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Publication number
EP0411360B1
EP0411360B1 EP19900113320 EP90113320A EP0411360B1 EP 0411360 B1 EP0411360 B1 EP 0411360B1 EP 19900113320 EP19900113320 EP 19900113320 EP 90113320 A EP90113320 A EP 90113320A EP 0411360 B1 EP0411360 B1 EP 0411360B1
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Prior art keywords
signal
adaptive filter
microphone
means
passenger compartment
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EP19900113320
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German (de)
French (fr)
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EP0411360A1 (en
Inventor
Jürgen Dr. Kässer
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Blaupunkt-Werke GmbH
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Blaupunkt-Werke GmbH
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Priority to DE19893925589 priority patent/DE3925589C2/en
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    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10LSPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
    • G10L21/00Processing of the speech or voice signal to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility
    • G10L21/02Speech enhancement, e.g. noise reduction or echo cancellation
    • G10L21/0208Noise filtering
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10LSPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
    • G10L21/00Processing of the speech or voice signal to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility
    • G10L21/02Speech enhancement, e.g. noise reduction or echo cancellation
    • G10L21/0208Noise filtering
    • G10L21/0216Noise filtering characterised by the method used for estimating noise
    • G10L2021/02161Number of inputs available containing the signal or the noise to be suppressed
    • G10L2021/02166Microphone arrays; Beamforming
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2410/00Microphones
    • H04R2410/05Noise reduction with a separate noise microphone
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2499/00Aspects covered by H04R or H04S not otherwise provided for in their subgroups
    • H04R2499/10General applications
    • H04R2499/13Acoustic transducers and sound field adaptation in vehicles

Description

  • Die Erfindung geht aus von einem Verfahren nach der Gattung des Hauptanspruchs und umfaßt ferner eine Anordnung zur Durchführung des erfindungsgemäßen Verfahrens. The invention proceeds from a method according to the preamble of the main claim and further comprising an arrangement for implementing the method according to the invention.
  • Zur Erkennung von Sprache sind verschiedene Verfahren bekannt, bei denen jedoch die Erkennungssicherheit durch Hintergrundgeräusche beeinträchtigt wird. For recognizing speech Various methods are known, but where the detection reliability is impaired by background noise. Derartige störende Schallereignisse treten beispielsweise in einem fahrenden Kraftfahrzeug auf, in welchem auch das Autoradio eingeschaltet ist. Such interfering sound events occur, for example in a moving motor vehicle, in which also the car radio is switched on.
  • Aus dem vorveröffentlichten Bericht über die "36 TH IEE Vehicular Technologie Conference" ist ein Verfahren zur Minderung der Störung einer Telefonverbindung durch Außengeräusche des Fahrzeuges bekannt. From the previously published report on the "36 TH IEE Vehicular Technology Conference", a method to reduce interference of a telephone connection by external noise of the vehicle is known. Nach diesem Verfahren werden die Außengeräusche mit einem außerhalb des Fahrgastraumes angebrachten Mikrofone aufgenommen und dessen Signale mit dem Mikrofonsignal des Telefonhandapparates zur Geräuschminderung verknüpft. According to this method, the external sounds are recorded with an attached outside the passenger compartment and microphones whose signals to the microphone signal of the telephone handset connected to the noise reduction. Zur Minderung der Störung eines Telefonates durch einen Autoradiolautsprecher im Fahrzeug ist es außerdem aus EP 56 587 bekannt, den Schallpegel des Lautsprechers bei der Herstellung einer Telefongesprächsverbindung abzusenken. To reduce the interference of a telephone call by a car stereo speakers in the vehicle, it is also known from EP 56 587 to lower the sound level of the loudspeaker in making a telephone call.
  • Die vorliegende Erfindung betrifft ein anderes Gebiet der Erkennung der Sprachsignale, nämlich von Sprachbefehlen in einem Kraftfahrzeug. The present invention relates to another area of ​​the recognition of the speech signals, namely, voice commands in a vehicle. Hier steht die eindeutige Zuordnung eines Befehlswortes des Fahrers oder Beifahrers im Vordergrund. Here is the unambiguous assignment of the driver and passenger instruction word in the foreground. Daher befriedigt eine Absenkung des Schallpegels von Fahrzeuglautsprechern nicht. Therefore, a reduction of the sound level of the vehicle speakers not satisfied. Auch bei abgesenktem Pegel können in der Sendung Worte auftreten, die - wenn auch unerwünscht - als Befehlsworte wirken könnten. Even with the lowered level words can occur in the broadcast - could act as command words - albeit undesirable.
  • Diese Gefahr läßt sich durch die erfindungsgemäße Lösung der Aufgabe wesentlich verringern, die durch die Merkmale des Hauptanspruchs gekennzeichnet ist. This risk can be significantly reduced by the inventive solution of the problem, which is characterized by the features of the main claim.
  • Durchführung des erfindungsgemäßen Verfahrens erforderlichen Anordnungen können mit Mitteln der modernen Halbleitertechnik in einfacher Weise realisiert werden. Carrying out the process necessary arrangements can be realized by means of modern semiconductor technology in a simple manner.
  • Durch die in den Unteransprüchen aufgeführten Maßnahmen sind vorteilhafte Weiterbildungen und Verbesserungen der im Hauptanspruch angegebenen Erfindung und vorteilhafte Anordnungen zur Durchführung des erfindungsgemäßen Verfahrens möglich. By the provisions recited in the dependent claims, advantageous refinements and improvements of the main claim invention and advantageous arrangements for implementing the method according to the invention are possible.
  • Ein Ausführungsbeispiel der Erfindung ist in der Zeichnung anhand mehrerer Figuren dargestellt und in der nachfolgenden Beschreibung näher erläutert. An embodiment of the invention is illustrated in the drawing way of several figures and explained in detail in the following description. Es zeigt: It shows:
  • Fig. 1 Fig. 1
    eine schematische Darstellung einer erfindungsgemäßen Anordnung in einem Kraftfahrzeug und a schematic representation of an inventive arrangement in a motor vehicle and
    Fig. 2 Fig. 2
    ein Blockschaltbild einer erfindungsgemäßen Anordnung. a block diagram of an arrangement according to the invention.
  • Gleiche Teile sind in den Figuren mit gleichen Bezugszeichen versehen. Identical parts are provided in the figures with the same reference numerals.
  • In Fig. 1 sind von einem Kraftfahrzeug lediglich je ein Teil des Fahrgastraums 1 und des Motorraums 2 dargestellt. In Fig. 1, a part of the passenger compartment 1 and the engine compartment 2 are illustrated by a motor vehicle only ever. Ein Mikrofon 3 ist im Fahrgastraum, beispielsweise oberhalb der Windschutzscheibe, angeordnet und nimmt Sprache, Fahrgeräusche und Schall von einem Autoradio 5 auf, der von einem Lautsprecher 4 abgestrahlt wird. A microphone 3 is in the passenger compartment, for example, above the windscreen, arranged and takes language, driving noise and sound of a car radio 5, which is emitted from a speaker. 4 Das vom Mikrofon 3 abgegebene Summensignal Σ(t) wird einer Anordnung 6 zur Durchführung des erfindungsgemäßen Verfahrens zugeführt, an deren Ausgang 7 das weitgehend von Störungen befreite Sprachsignal D₂(t) abnehmbar ist. The light emitted by the microphone 3 sum signal Σ (t) of an assembly 6 for carrying out the method according to the invention is supplied to the output 7, the substantially freed of disorders speech signal D₂ (t) is removable.
  • Ein weiteres Mikrofon 8 ist im Motorraum 2 angeordnet, nimmt Fahrgeräusche auf und leitet diese als Signal F(t) an die Anordnung 6 weiter. A further microphone 8 is disposed in the engine compartment 2, takes driving sounds and directs it as a signal F (t) to the assembly 6 on. Schließlich wird das dem Lautsprecher 4 zugeführte Audiosignal als Signal A(t) ebenfalls der Anordnung 6 zugeleitet. Finally, the loudspeaker 4 is the input audio signal as a signal A (t) is also the arrangement 6 supplied. Falls keine monaurale Wiedergabe beim Autoradio vorgesehen ist, können mehrere Audiosignale A(t) abgenommen und der Anordnung 6 zugeführt werden. If none of monaural reproduction is provided at the car radio, a plurality of audio signals A (t) can be removed and the array are fed. 6
  • Bei den folgenden Betrachtungen werden die jeweiligen akustischen und elektrischen Signale gleichgesetzt. For the following examples the respective acoustic and electric signals are equated. Das infolge der Schallabstrahlung des Lautsprechers 4 vom Mikrofon 3 aufgenommene Signal unterscheidet sich vom Signal A(t) durch eine zunächst unbekannte Übertragungsfunktion. The signal due to the sound emission of the speaker 4 picked up by the microphone 3 differs from the signal A (t) by an initially unknown transfer function. Das auf das Mikrofon 3 einwirkende vom Lautsprecher 4 stammende Signal wird daher als A₁(t) bezeichnet. The force acting on the microphone 3 originating from the speaker 4 signal is therefore as A₁ (t). In ähnlicher Weise unterscheidet sich das vom Mikrofon 3 aufgenommene Fahrgeräusch F₁(t) von dem durch das Mikrofon 8 aufgenommenen Fahrgeräusch F(t). Similarly, the picked up by the microphone 3-noise F₁ (t) differs from the captured by the microphone 8-noise F (t). Das Summensignal ergibt sich somit zu Σ(t) = S(t) + F₁(t) + A₁(t). The sum signal is therefore given as Σ (t) = S (t) + F₁ (t) + A₁ (t).
  • Die Anteile des Summensignals F₁(t) und A₁(t) sind A₁(t) = H A x A(t) und F₁(t) = H F x F(t), The proportions of the sum signal F₁ (t) and A₁ (t) A₁ (t) = A x H A (t) and F₁ (t) = F H x F (t),
    wobei H A und H F die entsprechenden Übertragungsfunktionen sind und x eine Faltung bedeutet. wherein H A and H are the corresponding transfer functions F and x represents a convolution.
  • Um die Anteile F₁(t) und A₁(t) aus dem Summensignal zu entfernen, ist eine Kenntnis der zunächst unbekannten Funktionen H F und H A erforderlich. To the proportions F₁ (t) and A₁ (t) to remove from the sum signal, a knowledge of the initially unknown functions F and H H A is required. Hierzu dienen adaptive Filter, die in der Anordnung nach Fig. 2 vorgesehen sind. For this purpose are used adaptive filters which are provided in the arrangement of FIG. 2. Die Signale Σ(t) und F(t) werden von den Mikrofonen 3, 8 über geeignete Verstärker 11, 12 und Tiefpaßfilter 13, 14 Analog/Digital-Wandlern 15, 16 zugeführt. The signals Σ (t) and F (t) are supplied from the microphones 3, 8 through suitable amplifiers 11, 12 and low pass filters 13, 14, analog / digital converters 15, 16th Das Audiosignal A(t) wird ebenfalls über ein Tiefpaßfilter 17 einem Analog/Digital-Wandler 18 zugeleitet. The audio signal A (t) is also supplied via a low pass filter 17 to an analog / digital converter 18th Die Tiefpaßfilter begrenzen die Bandbreite der Signale auf einen Wert, der für das nachgeschaltete Spracherkennungssystem notwendig ist. The low pass filters to limit the bandwidth of the signals to a value which is necessary for downstream speech recognition system.
  • Ein erstes adaptives Filter 19 dient zusammen mit einem Korrelator 20 zur Ableitung des Signals A₁(t) aus dem Signal A(t). A first adaptive filter 19 is used together with a correlator 20 to derive the signal A₁ (t) from the signal A (t). In einem Subtrahierer 21 wird dann das Signal A₁(t) von dem Summensignal Σ(t) subtrahiert, wodurch das Signal D₁(t) entsteht. In a subtractor 21, the signal A₁ (t) from the sum signal Σ (t) whereby the signal D₁ (t) is then subtracted, is formed.
  • Ein weiteres adaptives Filter 22 und ein Korrelator 23 sind zur Ableitung des Signals F₁(t) aus dem Signal F(t) vorgesehen. Another adaptive filter 22 and a correlator 23 are used to derive the signal F₁ (t) from the signal F (t) is provided. Mit Hilfe eines weiteren Subtrahierers 24 wird das Signal F₁(t) von dem Signal D₁(t) subtrahiert. With the help of a further subtractor 24, the signal F₁ (t) of the signal D₁ (t) is subtracted. Am Ausgang 7 steht somit das Signal D₂(t) zur Weiterleitung an ein Spracherkennungssystem zur Verfügung. At the output 7 thus represents the signal D₂ (t) for transmission to a speech recognition system.
  • Das adaptive Filter 19 ist ein nichtrekursives Filter der Ordnung ungefähr 100 mit der Zielfunktion The adaptive filter 19 is a non-recursive filter of the order about 100 having the objective function Z₁(t) = (Σ(t)-H Z₁ (t) = (Σ (t) -H AZ AZ x A) ■ A(t) = 0 für H x A) ■ A (t) = 0 for H AZ AZ = H H = A A , .
    Figure imgb0001

    wobei ■ die Korrelationsfunktion bedeutet. ■ which means the correlation function. Die Zielfunktion nutzt aus, daß für das richtige H AZ das Signal [S(t) + F₁(t)] unkorreliert zum Audiosignal A(t) ist. The objective function utilizes the fact that for the proper H AZ the signal [S (t) + F₁ (t)] are uncorrelated to the audio signal A (t).
  • Die Berechnung der Filterkoeffizienten im einzelnen kann nach Standardverfahren der digitalen Signalverarbeitung erfolgen, wie sie beispielsweise im Aufsatz "Adaptive Noise Cancelling: Principles and Applications", Proceedings of the IEEE, Vol. 63, No. The calculation of the filter coefficients in detail can be made by standard methods of digital signal processing, such as those described in the article "Adaptive Noise Canceling: Principles and Applications", Proceedings of the IEEE, Vol 63, No.. 12, December 1975, Seiten 1692 bis 1716 beschrieben sind. 12, December 1975, pages 1692-1716. Die adaptiven Filter und die Korrelatoren können mit geeignet programmierten Signalprozessoren realisiert werden. The adaptive filters and the correlators can be implemented using suitably programmed signal processors.
  • Das Ausgangssignal D₁(t) des Subtrahierers 21 wird sowohl im Korrelator 20 verwendet als auch dem weiteren Subtrahierer 24 zugeführt. The output signal D₁ (t) of the subtractor 21 is used both in the correlator 20 as supplied to the further subtractor 24th Es ergibt sich zu D₁(t) = Σ(t) - H AZ x A(t). It is given by D₁ (t) = Σ (t) - H AZ x A (t).
  • Zur Bestimmung von H F wird das bereits von den Audiosignalen befreite Signal D₁(t) verwendet, welches sich aus Fahrgeräusch und Sprache zusammensetzt. For the determination of H F already freed from the audio signal D₁ (t) is used, which is composed of driving noise and speech. Diese sind ebenfalls unkorreliert, so daß sich das für das Audiosignal verwendete Verfahren auch für das Geräuschsignal anwenden läßt. These are also uncorrelated, so that the method used for the audio signal can also be applied to the sound signal. Dabei ist die Zielfunktion It is the objective function Z₂(t) = [(D₁(t) - H Z₂ (t) = [(D₁ (t) - H FZ FZ x F(t)] ■ F(t) = 0 für H x F (t)] ■ F (t) = 0 for H FZ FZ = H H = F F (t) (T)
    Figure imgb0002
  • Das Ausgangssignal des Subtrahieres 24 wird dann The output signal of the subtractor 24 is then D₂(t) = S(t) + (H D₂ (t) = S (t) + (H F F -H -H FZ FZ )xF(t) + [(H ) XF (t) + [(H A A -H -H AZ AZ )xA(t)] x F(t) ) XA (t)] x F (t)
    Figure imgb0003
  • Aus Gleichung (3) ist ersichtlich, daß sich das Ausgangssignal D₂(t) umso mehr dem Signal S(t) nähert, je besser die Annäherung von H FZ an H F bzw. H AZ an H A erfolgt. From equation (3) it is seen that the output signal D₂ (t) the more the signal S (t) passes, the better the approximation of FZ H to H or F AZ H occurs at H A. Auch bei einer nicht vollständigen Annäherung erfolgt eine deutliche Reduzierung des Störanteils. Even with an incomplete approach a significant reduction of interference component occurs.

Claims (5)

  1. Speech-signal interference-elimination method for speech-recognition purposes in a motor vehicle, in which method the speech is converted, along with other simultaneously occurring sound events, into an electrical composite signal by means of a microphone (3) and a sound signal (f (t)) from a reference microphone (8) disposed outside the passenger compartment is fed via an adaptive filter (22) and then subtracted from the composite signal Σ (t), characterized in that control signals (A (t)) for a loudspeaker (4) disposed in the passenger compartment are fed in parallel with the composite signal Σ (t) via a further adaptive filter (19) and subtracted from the composite signal Σ (t), in that the resultant signal is compared with the control signal (A (t)) and in that the comparison signals obtained in this process control the further adaptive filter (19).
  2. Method according to Claim 1, characterized in that the control signals are subjected to low-pass filtering and analogue/digital conversion upstream of the adaptive filter.
  3. Arrangement for carrying out the method according to Claim 1, having a first microphone (3) inside the passenger compartment and a second microphone (8) outside the passenger compartment and a first adaptive filter (22) in the output of the second microphone, and having first means (24) for subtracting the output signal F₁ (t) of the adaptive filter (22) from the output signal D (t) of the first microphone (3), and having a correlator (23) for controlling the adaptive filter (22), characterized by a second adaptive filter (19) for control signals which control, in parallel therewith, a loudspeaker (4) disposed in the passenger compartment, by second means (21) for subtracting the output signal A₁ (t) of the second adaptive filter (19) from the output signal of the first microphone (3), which second means (21) are disposed upstream of the first means (24), and by a second correlator (20) which controls the second adaptive filter (19) and to which the control signals and the output signal of the second subtraction means (21) can be fed for the purpose of comparison.
  4. Arrangement according to Claim 3, characterized in that low-pass filters (13, 14, 17) and A/D converters (15, 16, 18) are connected downstream of the microphones (3, 8) and the control-signal output for the loudspeaker (4).
  5. Arrangement according to Claim 4, characterized in that the order of the adaptive filter is about 100.
EP19900113320 1989-08-02 1990-07-12 Method and apparatus for interference suppression in speech signals Expired - Lifetime EP0411360B1 (en)

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DE19893925589 DE3925589C2 (en) 1989-08-02 1989-08-02 Method and arrangement for eliminating glitches from speech signals

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EP0624046A1 (en) * 1993-05-06 1994-11-09 Adam Opel Ag Noise-compensated hands-free communication apparatus in motor vehicles
EP0729288A2 (en) * 1995-02-27 1996-08-28 Nec Corporation Noise canceler
US5825898A (en) * 1996-06-27 1998-10-20 Lamar Signal Processing Ltd. System and method for adaptive interference cancelling
US6178248B1 (en) 1997-04-14 2001-01-23 Andrea Electronics Corporation Dual-processing interference cancelling system and method
US6363345B1 (en) 1999-02-18 2002-03-26 Andrea Electronics Corporation System, method and apparatus for cancelling noise
US6594367B1 (en) 1999-10-25 2003-07-15 Andrea Electronics Corporation Super directional beamforming design and implementation
US6738482B1 (en) 1999-09-27 2004-05-18 Jaber Associates, Llc Noise suppression system with dual microphone echo cancellation
US7447320B2 (en) 2001-02-14 2008-11-04 Gentex Corporation Vehicle accessory microphone
US7616768B2 (en) 2001-02-14 2009-11-10 Gentex Corporation Vehicle accessory microphone having mechanism for reducing line-induced noise
US8350683B2 (en) 1999-08-25 2013-01-08 Donnelly Corporation Voice acquisition system for a vehicle

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DE4106405C2 (en) * 1990-03-23 1996-02-29 Ricoh Kk Noise suppressor for a speech recognition system
JP3176474B2 (en) * 1992-06-03 2001-06-18 沖電気工業株式会社 Adaptive noise canceller apparatus
IT1272653B (en) * 1993-09-20 1997-06-26 Alcatel Italia Method of noise reduction, in particular for automatic speech recognition, and act to implement the same filter
GB9515762D0 (en) 1995-08-01 1995-10-04 Eev Ltd Imaging apparatus
DE19813285B4 (en) * 1998-03-26 2005-12-01 Bayerische Motoren Werke Ag Method for the automatic measurement of speech intelligibility in motor vehicles
DE19818609C2 (en) * 1998-04-20 2000-06-15 Deutsche Telekom Ag Method and apparatus for noise filtering
JP2002514775A (en) * 1998-05-06 2002-05-21 フオルクスヴアーゲン アクチエンゲゼルシヤフト Working method and working apparatus of the speech support system in a vehicle
US7120261B1 (en) 1999-11-19 2006-10-10 Gentex Corporation Vehicle accessory microphone
US8682005B2 (en) 1999-11-19 2014-03-25 Gentex Corporation Vehicle accessory microphone
DE10046238B4 (en) * 2000-09-19 2007-04-19 Robert Bosch Gmbh Method for processing audio signals
US7467084B2 (en) 2003-02-07 2008-12-16 Volkswagen Ag Device and method for operating a voice-enhancement system
US6690310B1 (en) * 2003-02-13 2004-02-10 Northrop Grumman Corporation Method and apparatus for adaptively compensating for an inaccuracy in an analog-to-digital converter
US7912228B2 (en) 2003-07-18 2011-03-22 Volkswagen Ag Device and method for operating voice-supported systems in motor vehicles
DE502005001127D1 (en) 2004-08-10 2007-09-13 Volkswagen Ag Language support system for a motor vehicle
EP1879180B1 (en) * 2006-07-10 2009-05-06 Harman Becker Automotive Systems GmbH Reduction of background noise in hands-free systems
EP1914726A1 (en) * 2006-10-16 2008-04-23 SiTel Semiconductor B.V. base station of a telephone system and telephone system comprising such as a base station

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DE3741253A1 (en) * 1987-12-05 1989-06-15 Blaupunkt Werke Gmbh Method and circuit arrangement for selbsttaetigen stoergeraeuschabhaengigen lautstaerkeregelung

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0624046A1 (en) * 1993-05-06 1994-11-09 Adam Opel Ag Noise-compensated hands-free communication apparatus in motor vehicles
EP0729288A2 (en) * 1995-02-27 1996-08-28 Nec Corporation Noise canceler
US5825898A (en) * 1996-06-27 1998-10-20 Lamar Signal Processing Ltd. System and method for adaptive interference cancelling
US6178248B1 (en) 1997-04-14 2001-01-23 Andrea Electronics Corporation Dual-processing interference cancelling system and method
US6363345B1 (en) 1999-02-18 2002-03-26 Andrea Electronics Corporation System, method and apparatus for cancelling noise
US9283900B2 (en) 1999-08-25 2016-03-15 Magna Electronics Inc. Accessory mounting system for a vehicle
US8350683B2 (en) 1999-08-25 2013-01-08 Donnelly Corporation Voice acquisition system for a vehicle
US8531279B2 (en) 1999-08-25 2013-09-10 Magna Electronics Inc. Accessory mounting system for a vehicle
US6738482B1 (en) 1999-09-27 2004-05-18 Jaber Associates, Llc Noise suppression system with dual microphone echo cancellation
US6594367B1 (en) 1999-10-25 2003-07-15 Andrea Electronics Corporation Super directional beamforming design and implementation
US7447320B2 (en) 2001-02-14 2008-11-04 Gentex Corporation Vehicle accessory microphone
US7616768B2 (en) 2001-02-14 2009-11-10 Gentex Corporation Vehicle accessory microphone having mechanism for reducing line-induced noise

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DE3925589C2 (en) 1994-03-17
EP0411360A1 (en) 1991-02-06
DE3925589A1 (en) 1991-02-14
JPH0370324A (en) 1991-03-26

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