EP1684543A1 - Method to suppress electro-acoustic feedback - Google Patents
Method to suppress electro-acoustic feedback Download PDFInfo
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- EP1684543A1 EP1684543A1 EP05001063A EP05001063A EP1684543A1 EP 1684543 A1 EP1684543 A1 EP 1684543A1 EP 05001063 A EP05001063 A EP 05001063A EP 05001063 A EP05001063 A EP 05001063A EP 1684543 A1 EP1684543 A1 EP 1684543A1
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- frequency
- level
- feedback
- microphone signal
- microphone
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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
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/02—Circuits for transducers, loudspeakers or microphones for preventing acoustic reaction, i.e. acoustic oscillatory feedback
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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
- H04R27/00—Public address systems
Definitions
- the invention relates to a method for suppressing electro-acoustic feedback in an audio system comprising a microphone which drives a loudspeaker system via an amplifier, in particular in the context of a public address system in accordance with the preamble of claim 1.
- the invention is in the field of electroacoustic performances, such as live music events.
- PA systems with microphones are used, with which voices and instruments are detected electroacoustically, amplified and played back via loudspeakers.
- This can lead to feedback of the amplified microphone signal over the range microphone amplifier that produce unpleasant loud sound events on the speakers.
- these feedbacks also referred to as feedback, when the detected by the microphone speaker sound signal passes in phase to the microphone payload the distance microphone amplifier.
- these signals can increasingly rock and generate loud and high sound amplitudes through the loudspeakers at a typical feedback frequency that changes over time.
- a previous countermeasure in terms of feedback effects provides to turn off the PA system or at least drastically reduce their gain.
- the generic method mentioned at the outset which proceeds in the time domain in the prior art, runs in the frequency range in which the microphone signal is converted by a fast Fourier transformation.
- that frequency is rated as a feedback frequency at which the maximum level of the microphone signal exceeds the threshold value in the form of a predetermined ratio of the maximum level of the microphone signal to the overall level of the microphone signal.
- the microphone signal is provided before the steps of the generic method by all-pass filtering in combination with the fast Fourier transform (FFT) of the time domain in a "bark" scaled frequency range transform.
- FFT fast Fourier transform
- the filtering out of the feedback frequency is narrow band, especially by means of a notch filter, which can be realized with a bandwidth of 1/60 octave and does not affect the Audionutzsignal by its use according to the invention.
- correction procedures for frequency and level are proposed according to the invention, which can be implemented in real time without loss of time.
- FIG. 1 shows a PA system typically used in live events, comprising a microphone 1 whose microphone signal is fed via a mixer 2 into a power amplifier 3 which drives a loudspeaker 4 with the amplified microphone signal.
- a microphone 1 whose microphone signal is fed via a mixer 2 into a power amplifier 3 which drives a loudspeaker 4 with the amplified microphone signal.
- the z. B. is used by an instrumentalist or singer, in-phase fed into the amplifier and then emitted by the speaker. This loop is indicated in Fig. 1 with a circular arrow.
- the formation of a feedback in the feedback loop is inhibited by detecting the level of the microphone signal on the microphone amplifier path, the readiness for the occurrence of a feedback being detected by the fact that the level of the microphone signal exceeds a threshold value.
- the frequency of the microphone signal at this critical level is evaluated as a feedback frequency and filtered out of the microphone signal to suppress feedback by means of a narrow band filter such as the notch filter whose frequency characteristic is shown in FIG.
- the microphone signal is transformed from the time domain to the frequency domain by a combination of a network of all-pass filters and a fast Fourier transform (FFT).
- FFT fast Fourier transform
- the level maximum is determined and subjected to error correction by means of two adjacent frequency values (FIG. 3). Once this level reaches a predetermined ratio of the overall level of the microphone signal (a threshold set thereby), the frequency at which that level occurs is rated as the feedback frequency and filtered out of the frequency spectrum by a narrow band filter. If necessary, a filter already existing in the vicinity of this frequency can be shifted to the position of this frequency and brought into effect.
- Fig. 3 shows the measured energy of some frequency pots.
- the correction of the maximum level is carried out in accordance with Fig. 4 via a tabular correction value k, which is anti-proportional to the value of the difference "peakdiff" of the maximum level at the frequency f (x) to the adjacent level at the frequency f (x + 1) ,
- the smaller the difference ("peakdiff", the larger the factor k and thus also the level correction value ⁇ p k (peakdiff).
- the filter frequency of the notch filter (FIG. 2) is preferably continuously updated accordingly.
Abstract
Description
Die Erfindung betrifft ein Verfahren zum Unterdrücken von elektroakustischer Rückkopplung (Feedback) in einem Audiosystem, das ein Mikrophon umfasst, das über einen Verstärker ein Lautsprechersystem treibt, insbesondere im Rahmen einer Beschallungsanlage in Übereinstimmung mit dem Oberbegriff des Anspruch 1.The invention relates to a method for suppressing electro-acoustic feedback in an audio system comprising a microphone which drives a loudspeaker system via an amplifier, in particular in the context of a public address system in accordance with the preamble of
Die Erfindung liegt auf dem Gebiet elektroakustischer Darbietungen, wie Live-Musik-Veranstaltungen. Bei derartigen Veranstaltungen kommen sogenannte PA-Anlagen mit Mikrophonen zum Einsatz, mit denen Stimmen und Instrumente elektroakustisch erfasst, verstärkt und über Lautsprecher wiedergegeben werden. Dabei kann es zu Rückkopplungen des verstärkten Mikrophonsignals über die Strecke Mikrophon-Verstärker kommen, die über die Lautsprecher unangenehm laute Schallereignisse produzieren. Insbesondere entstehen diese Rückkopplungen, auch als Feedback bezeichnet, wenn das vom Mikrophon erfasste Lautsprechertonsignal gleichphasig zum Mikrophon-Nutzsignal die Strecke Mikrophon-Verstärker durchläuft. Über die Rückkopplungsschleife können sich diese Signale zunehmend hochschaukeln und über die Lautsprecher hohe und höchste Schallamplituden mit einer typischen Rückkopplungsfrequenz erzeugen, die sich im Verlauf der Zeit ändert. Eine bisherige Gegenmaßnahme in Bezug auf Rückkopplungseffekte sieht vor, die PA-Anlage auszuschalten oder ihre Verstärkung zumindest drastisch zu vermindern. Alternativ ist es bekannt, den Bereich der Rückkopplungsfrequenz, soweit dieser durch Erfahrung ermittelt worden ist, mehr oder weniger breitbandig aus dem Audiofrequenzband herauszufiltern, wobei dieser Frequenzbereich jedoch bei der Wiedergabe fehlt. Eine noch wirksamere Maßnahme bietet das eingangs genannte gattungsgemäße Verfahren, welches die Rückkopplungsfrequenz selbsttätig ermittelt und ausfiltert. Dieses Verfahren läuft jedoch nicht unter allen praxisgerechten Umständen schnell und präzise genug sowie frei von einer Beeinträchtigung der Wiedergabequalität ab, weshalb ein Bedarf an einem Verfahren zum Unterdrücken von elektroakustischer Rückkopplung (Feedback) in einem Audiosystem der eingangs genannten Art besteht, das das Auftreten von Rückkopplungseffekten schnell und zuverlässig verhindert, ohne die Wiedergabequalität zu beeinträchtigen.The invention is in the field of electroacoustic performances, such as live music events. In such events, so-called PA systems with microphones are used, with which voices and instruments are detected electroacoustically, amplified and played back via loudspeakers. This can lead to feedback of the amplified microphone signal over the range microphone amplifier that produce unpleasant loud sound events on the speakers. In particular, these feedbacks, also referred to as feedback, when the detected by the microphone speaker sound signal passes in phase to the microphone payload the distance microphone amplifier. Through the feedback loop, these signals can increasingly rock and generate loud and high sound amplitudes through the loudspeakers at a typical feedback frequency that changes over time. A previous countermeasure in terms of feedback effects provides to turn off the PA system or at least drastically reduce their gain. Alternatively, it is known to filter out the range of the feedback frequency, as far as it has been determined by experience, more or less broadband from the audio frequency band, but this frequency range is missing in the playback. An even more effective measure is provided by the aforementioned generic method, which automatically determines and filters out the feedback frequency. This However, the method does not proceed quickly and accurately enough in all practical circumstances and is free from deterioration of the reproduction quality, and therefore, there is a need for a method for suppressing electro-acoustic feedback in an audio system of the type mentioned in the introduction, which rapidly speeds up the occurrence of feedback effects and reliably prevented without affecting the quality of reproduction.
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zum Unterdrücken von elektroakustischer Rückkopplung (Feedback) in einem Audiosystem zu schaffen, das Rückkopplungseffekte wirksam unterdrückt, ohne die Wiedergabequalität des Audiosystems zu beeinträchtigen.It is an object of the present invention to provide a method for suppressing electro-acoustic feedback in an audio system which effectively suppresses feedback effects without affecting the reproduction quality of the audio system.
Gelöst wird die Aufgabe durch die Merkmale des Anspruchs 1. Weitere Vorteile des erfindungsgemäßen Verfahrens sind in den Unteransprüchen angegeben.The object is achieved by the features of
Nach dem Grundgedanken der Erfindung läuft das eingangs genannte gattungsgemäße Verfahren, das im Stand der Technik im Zeitbereich abläuft, im Frequenzbereich ab, in welchen das Mikrophonsignal durch schnelle Fourier-Transformation überführt wird. Dabei wird erfindungsgemäß diejenige Frequenz als Rückkopplungsfrequenz gewertet, bei welcher der maximale Pegel des Mikrophonsignals den Schwellenwert in Gestalt eines vorbestimmten Verhältnisses des maximalen Pegels des Mikrophonsignals zum Gesamtpegel des Mikrophonsignals überschreitet.According to the basic concept of the invention, the generic method mentioned at the outset, which proceeds in the time domain in the prior art, runs in the frequency range in which the microphone signal is converted by a fast Fourier transformation. According to the invention, that frequency is rated as a feedback frequency at which the maximum level of the microphone signal exceeds the threshold value in the form of a predetermined ratio of the maximum level of the microphone signal to the overall level of the microphone signal.
Um beim erfindungsgemäßen Verfahren die Genauigkeit bei der Erkennung der Rückkopplungsfrequenz zu optimieren, ist vorgesehen, das Mikrophonsignal vor Ausführung der Schritte des gattungsgemäßen Verfahrens durch Allpassfilterung in Kombination mit der schnellen Fourier-Transformation (FFT) vom Zeitbereich in einen "bark"-skalierten Frequenzbereich zu transformieren.In order to optimize the accuracy in the detection of the feedback frequency in the method according to the invention, the microphone signal is provided before the steps of the generic method by all-pass filtering in combination with the fast Fourier transform (FFT) of the time domain in a "bark" scaled frequency range transform.
Bevorzugt erfolgt das Herausfiltern der Rückkopplungsfrequenz schmalbandig, vor allem mittels einem Notchfilter, das mit einer Bandbreite von 1/60 Oktave realisierbar ist und durch seinen erfindungsgemäßen Einsatz das Audionutzsignal nicht beeinträchtigt.Preferably, the filtering out of the feedback frequency is narrow band, especially by means of a notch filter, which can be realized with a bandwidth of 1/60 octave and does not affect the Audionutzsignal by its use according to the invention.
Um bei der hohen Erfassungsgeschwindigkeit von Anzeichen einer Rückkopplung die Rückkopplungsfrequenz und den dort auftretenden Pegel hinreichend genau ermitteln zu können, werden erfindungsgemäß Korrekturprozeduren an Frequenz und Pegel vorgeschlagen, die ohne Zeitverlust in Echtzeit realisierbar sind.In order to be able to determine the feedback frequency and the level occurring there with sufficient accuracy at the high detection speed of signs of feedback, correction procedures for frequency and level are proposed according to the invention, which can be implemented in real time without loss of time.
Folgende Korrekturprozeduren sind erfindungsgemäß vorgesehen:
- Der maximale Mikrophonpegel wird unter Bezug auf zwei benachbarte kleinere Pegel niedrigerer bzw. höherer Frequenz einer Fehlerkorrektur unterzogen. Bevorzugt wird die Rückkopplungsfrequenz unter Bezug auf zwei benachbarte Frequenzen mit kleinerem Mikrophonpegel als dem maximalen einer Fehlerkorrektur unterzogen. Dabei wird der Wert der Rückkopplungsfrequenz bevorzugt einer Korrektur unterworfen, indem er durch einen Wert ersetzt wird, der sich durch lineare Interpolation aus zwei benachbarten Frequenzwerten ergibt.
- Der Signalpegel bei der Rückkopplungsfrequenz wird relativ zu einem benachbarten Signalpegel einer Korrektur unterworfen. Bevorzugt erfolgt die Korrektur relativ zu demjenigen benachbarten Signalpegel von zwei benachbarten Signalpegeln, dessen Wert am nächsten zum Signalpegel bei der Rückkopplungsfrequenz liegt.
- The maximum microphone level is error corrected with respect to two adjacent smaller, lower and higher frequency levels, respectively. Preferably, the feedback frequency is error corrected with respect to two adjacent frequencies having a lower microphone level than the maximum. In this case, the value of the feedback frequency is preferably subjected to a correction by being replaced by a value resulting from linear interpolation from two adjacent frequency values.
- The signal level at the feedback frequency is subjected to correction relative to an adjacent signal level. Preferably, the correction is relative to the adjacent signal level of two adjacent signal levels whose value is closest to the signal level at the feedback frequency.
Zusammengefasst lassen sich mit dem erfindungsgemäßen Verfahren folgende Vorteile erzielen:
- Rückkopplungen lassen sich sehr schnell erkennen und gegensteuern, vor allen durch den Einsatz einer schnellen Fourier-Transformation (FFT).
- Rückkopplungen lassen sich genau erkennen und gegensteuern, vor allem durch Verwendung eines Netzwerks von Allpassfiltern zur Konvertierung der FFT in einen "bark"-skalierten Frequenzbereich.
- Das Audiosignal bzw. Mikrophonsignal wird durch den Einsatz sehr schmalbandiger Filter zur Unterdrückung von Rückkopplung so gut wie nicht beeinträchtigt.
- Durch Nachführen der Filterfrequenz des schmalbandigen Filters kann ein Auswandern der Rückkopplungsfrequenz zeitnah verfolgt werden.
- Feedback can be detected and counteracted very quickly, especially by using a fast Fourier transform (FFT).
- Feedback can be accurately detected and counteracted, especially by using a network of allpass filters to convert the FFT to a "bark" scaled frequency range.
- The audio signal or microphone signal is virtually unaffected by the use of very narrow band filters to suppress feedback.
- By tracking the filter frequency of the narrow-band filter, emigration of the feedback frequency can be tracked in a timely manner.
Schließlich ist erfindungsgemäß vorgesehen, das schmalbandige Filter zum Herausfiltern der Rückkopplungsfrequenz nachzuführen, wenn diese sich im Verlauf der Zeit ändert. Hierdurch kann der schmalbandige Ansatz der Ausfilterung auch bei Änderung der Rückkopplungsfrequenz beibehalten werden, ohne die Nachteile einer breitbandigeren Filterung für diesen Fall anwenden zu müssen.Finally, it is provided according to the invention to track the narrow-band filter for filtering out the feedback frequency, if this changes over time. In this way, the narrow-band approach of the filtering can be maintained even if the feedback frequency changes, without having to use the disadvantages of a broadband filtering for this case.
Nachfolgend wird die Erfindung anhand der Zeichnung beispielhaft näher erläutert; in dieser zeigen:
- Fig. 1
- schematisch eine PA-Audiosystem zur Verdeutlichung der Ausbildung einer Rückkopplungsschleife,
- Fig. 2
- die Filterkurve eines Notchfilters einer Bandbreite von 1/60 Oktave,
- Fig. 3
- schematisch anhand eines Frequenz/Pegel-Diagramms die Arbeitsweise einer Frequenzkorrekturprozedur,
- Fig. 4
- schematisch anhand eines Frequenz/Pegel-Diagramms die Arbeitsweise einer Pegelkorrekturprozedur.
- Fig. 1
- schematically a PA audio system to illustrate the formation of a feedback loop,
- Fig. 2
- the filter curve of a notch filter of a bandwidth of 1/60 octave,
- Fig. 3
- schematically the operation of a frequency correction procedure based on a frequency / level diagram,
- Fig. 4
- schematically using a frequency / level diagram, the operation of a level correction procedure.
In Fig. 1 ist eine typischerweise bei Live-Ereignissen zu Einsatz kommende PA-Anlage gezeigt, die ein Mikrophon 1 umfasst, dessen Mikrophonsignal über ein Mischpult 2 in einen Leistungsverstärker 3 eingespeist wird, der einen Lautsprecher 4 mit dem verstärkten Mikrophonsignal treibt. In dieser Anlage entsteht eine Feedback-Schleife bzw. Rückkopplungsschleife, wenn der vom Lautsprecher abgestrahlte Schall vom Mikrophon 1 eingefangen und zusammen mit dem Nutzsignal des Mikrophons, das z. B. von einem Instrumentalisten oder Sänger genutzt wird, gleichphasig in den Verstärker eingespeist und daraufhin vom Lautsprecher abgestrahlt wird. Diese Schleife ist in Fig. 1 mit einem kreisförmigen Pfeil bezeichnet.FIG. 1 shows a PA system typically used in live events, comprising a
Erfindungsgemäß wird die Ausbildung einer Rückkopplung in der Rückkopplungsschleife unterbunden, indem der Pegel des Mikrophonsignals auf der Mikrophon-Verstärkerstrecke erfasst wird, wobei die Bereitschaft für das Auftreten einer Rückkopplung dadurch erkannt wird, dass der Pegel des Mikrophonsignals einen Schwellenwert übersteigt. Die Frequenz des Mikrophonsignals bei diesem kritischen Pegel wird als Rückkopplungsfrequenz gewertet und aus dem Mikrophonsignal zur Unterdrückung der Rückkopplung mittels eines schmalbandigen Filters, wie etwa dem Notchfilter ausgefiltert, dessen Frequenzkennlinie in Fig. 2 gezeigt ist.According to the invention, the formation of a feedback in the feedback loop is inhibited by detecting the level of the microphone signal on the microphone amplifier path, the readiness for the occurrence of a feedback being detected by the fact that the level of the microphone signal exceeds a threshold value. The frequency of the microphone signal at this critical level is evaluated as a feedback frequency and filtered out of the microphone signal to suppress feedback by means of a narrow band filter such as the notch filter whose frequency characteristic is shown in FIG.
Um die Rückkopplungsfrequenz schnell und genau zu ermitteln, wird das Mikrophonsignal durch eine Kombination von einem Netzwerk aus Allpassfiltern und einer schnellen Fourier-Transformation (FFT) vom Zeitbereich in den Frequenzbereich transformiert. Durch diese Kombination, die einem "warped" FFT entspricht, entsteht ein "bark"-skaliertes Frequenzspektrum, das einer logarithmischen Skalierung sehr nahe kommt. In diesem Frequenzspektrum wird das Pegel-Maximum ermittelt und mit Hilfe von zwei benachbarten Frequenzwerten einer Fehlerkorrektur unterworfen (Fig. 3). Sobald dieser Pegel ein vorbestimmtes Verhältnis des Gesamtpegels des Mikrophonsignals (einen hierdurch festgelegten Schwellenwert) erreicht, wird die Frequenz, bei welcher dieser Pegel auftritt als Rückkopplungsfrequenz gewertet bzw. definiert und mittels eines schmalbandigen Filters aus dem Frequenzspektrum herausgefiltert. Gegebenenfalls kann ein in der Nähe dieser Frequenz bereits existierendes Filter an die Position dieser Frequenz verschoben und zur Wirkung gebracht werden.To quickly and accurately determine the feedback frequency, the microphone signal is transformed from the time domain to the frequency domain by a combination of a network of all-pass filters and a fast Fourier transform (FFT). By this combination, which corresponds to a "warped" FFT, This results in a "bark" scaled frequency spectrum, which comes very close to logarithmic scaling. In this frequency spectrum, the level maximum is determined and subjected to error correction by means of two adjacent frequency values (FIG. 3). Once this level reaches a predetermined ratio of the overall level of the microphone signal (a threshold set thereby), the frequency at which that level occurs is rated as the feedback frequency and filtered out of the frequency spectrum by a narrow band filter. If necessary, a filter already existing in the vicinity of this frequency can be shifted to the position of this frequency and brought into effect.
Fig. 3 zeigt die gemessene Energie einiger Frequenztöpfe. Die genaue Bestimmung der Rückkopplungsfrequenz erfolgt mit Hilfe einer linearen Interpolation, die in Fig. 3 durch zwei Geraden gezeigt ist. Zwei zur Rückkopplungsfrequenz benachbarte Frequenzwerte werden jeweils mit einer Steigung (+/-) versehen. Dadurch entsteht im Schnittpunkt der beiden Geraden die interpolierte Position der Frequenz mit maximaler Energie: 
Die Korrektur des maximalen Pegels erfolgt in Übereinstimmung mit Fig. 4 über einen tabellarischen Korrekturwert k, der antiproportional zum Wert der Differenz "peakdiff" des maximalen Pegels bei der Frequenz f(x) zum benachbarten Pegel bei der Frequenz f(x+1) verläuft. Je geringer die Differenz ("peakdiff" ist, desto größer wird der Faktor k und damit auch der pegelkorrekturwert Δp = k(peakdiff).The correction of the maximum level is carried out in accordance with Fig. 4 via a tabular correction value k, which is anti-proportional to the value of the difference "peakdiff" of the maximum level at the frequency f (x) to the adjacent level at the frequency f (x + 1) , The smaller the difference ("peakdiff", the larger the factor k and thus also the level correction value Δp = k (peakdiff).
Wenn die zu einem Zeitpunkt ermittelte Rückkopplungsfrequenz sich als Funktion der Zeit relativ geringfügig ändert, wird die Filterfrequenz des Notchfilters (Fig. 2) bevorzugt entsprechend ständig nachgeführt.If the feedback frequency determined at a time changes relatively slightly as a function of time, the filter frequency of the notch filter (FIG. 2) is preferably continuously updated accordingly.
Claims (13)
das Mikrophonsignal vor dem Schritt a) durch eine schnelle Fourier-Transformation (FFT) vom Zeitbereich in einen Frequenzbereich transformiert wird und dass diejenige Frequenz als Rückkopplungsfrequenz gewertet wird, bei welcher der maximale Pegel des Mikrophonsignals den Schwellenwert in Gestalt eines vorbestimmten Verhältnisses des maximalen Pegels des Mikrophonsignals zum Gesamtpegel des Mikrophonsignals überschreitet.Method for suppressing electro-acoustic feedback in an audio system comprising a microphone which drives a loudspeaker system via an amplifier, in particular in the context of a public address system, with the steps:
the microphone signal is transformed from the time domain into a frequency domain by a fast Fourier transform (FFT) prior to step a) and the frequency is considered to be the feedback frequency at which the maximum level of the microphone signal is the threshold in the form of a predetermined maximum level ratio of the Microphone signal to the overall level of the microphone signal exceeds.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP05001063A EP1684543A1 (en) | 2005-01-19 | 2005-01-19 | Method to suppress electro-acoustic feedback |
| US11/052,398 US20060159282A1 (en) | 2005-01-19 | 2005-02-07 | Method for suppressing electroacoustic feedback |
| CN200510008816.XA CN1809220A (en) | 2005-01-19 | 2005-02-23 | Method for constraining electroacoustic feedback |
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| Application Number | Priority Date | Filing Date | Title |
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| EP05001063A EP1684543A1 (en) | 2005-01-19 | 2005-01-19 | Method to suppress electro-acoustic feedback |
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| KR20180044324A (en) | 2015-08-20 | 2018-05-02 | 시러스 로직 인터내셔널 세미컨덕터 리미티드 | A feedback adaptive noise cancellation (ANC) controller and a method having a feedback response partially provided by a fixed response filter |
| US10540983B2 (en) | 2017-06-01 | 2020-01-21 | Sorenson Ip Holdings, Llc | Detecting and reducing feedback |
| CN109905811B (en) * | 2019-01-24 | 2021-02-26 | 珠海慧联科技有限公司 | Economical acoustic feedback control method and device |
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| US3183304A (en) * | 1962-03-07 | 1965-05-11 | Bell Telephone Labor Inc | Sound amplification system |
| US4232192A (en) * | 1978-05-01 | 1980-11-04 | Starkey Labs, Inc. | Moving-average notch filter |
| EP0599450A2 (en) * | 1992-11-25 | 1994-06-01 | Matsushita Electric Industrial Co., Ltd. | Sound amplifying apparatus with automatic howl-suppressing function |
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| WO2003036621A1 (en) * | 2001-10-22 | 2003-05-01 | Motorola, Inc., A Corporation Of The State Of Delaware | Method and apparatus for enhancing loudness of an audio signal |
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| US3257510A (en) * | 1962-10-15 | 1966-06-21 | Industrial Res Prod Inc | Feedback control apparatus |
| US4088835A (en) * | 1977-02-07 | 1978-05-09 | Rauland-Borg Corporation | Comprehensive feedback elimination system employing notch filter |
| JP3152160B2 (en) * | 1996-11-13 | 2001-04-03 | ヤマハ株式会社 | Howling detection prevention circuit and loudspeaker using the same |
| JP3984842B2 (en) * | 2002-03-12 | 2007-10-03 | 松下電器産業株式会社 | Howling control device |
| US7536022B2 (en) * | 2002-10-02 | 2009-05-19 | Phonak Ag | Method to determine a feedback threshold in a hearing device |
| US7664275B2 (en) * | 2005-07-22 | 2010-02-16 | Gables Engineering, Inc. | Acoustic feedback cancellation system |
| US20070104335A1 (en) * | 2005-11-09 | 2007-05-10 | Gpe International Limited | Acoustic feedback suppression for audio amplification systems |
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- 2005-01-19 EP EP05001063A patent/EP1684543A1/en not_active Withdrawn
- 2005-02-07 US US11/052,398 patent/US20060159282A1/en not_active Abandoned
- 2005-02-23 CN CN200510008816.XA patent/CN1809220A/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3183304A (en) * | 1962-03-07 | 1965-05-11 | Bell Telephone Labor Inc | Sound amplification system |
| US4232192A (en) * | 1978-05-01 | 1980-11-04 | Starkey Labs, Inc. | Moving-average notch filter |
| EP0599450A2 (en) * | 1992-11-25 | 1994-06-01 | Matsushita Electric Industrial Co., Ltd. | Sound amplifying apparatus with automatic howl-suppressing function |
| US5677987A (en) * | 1993-11-19 | 1997-10-14 | Matsushita Electric Industrial Co., Ltd. | Feedback detector and suppressor |
| WO2003036621A1 (en) * | 2001-10-22 | 2003-05-01 | Motorola, Inc., A Corporation Of The State Of Delaware | Method and apparatus for enhancing loudness of an audio signal |
Also Published As
| Publication number | Publication date |
|---|---|
| CN1809220A (en) | 2006-07-26 |
| US20060159282A1 (en) | 2006-07-20 |
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