EP0467499A2 - Appareil audio avec fonction de suppression de réaction acoustique - Google Patents

Appareil audio avec fonction de suppression de réaction acoustique Download PDF

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Publication number
EP0467499A2
EP0467499A2 EP91301941A EP91301941A EP0467499A2 EP 0467499 A2 EP0467499 A2 EP 0467499A2 EP 91301941 A EP91301941 A EP 91301941A EP 91301941 A EP91301941 A EP 91301941A EP 0467499 A2 EP0467499 A2 EP 0467499A2
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EP
European Patent Office
Prior art keywords
data
band
audio
frequency
multiplier
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91301941A
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German (de)
English (en)
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EP0467499A3 (en
Inventor
Takahiko c/o Pioneer Ohmori Plant Terada
Yoshinobu c/o Pioneer Ohmori Plant Takamura
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Pioneer Corp
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Pioneer Electronic Corp
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Filing date
Publication date
Application filed by Pioneer Electronic Corp filed Critical Pioneer Electronic Corp
Publication of EP0467499A2 publication Critical patent/EP0467499A2/fr
Publication of EP0467499A3 publication Critical patent/EP0467499A3/en
Withdrawn legal-status Critical Current

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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

Definitions

  • the present invention relates to an audio apparatus provided with an anti-howl function.
  • Audio apparatuses provided with an anti-howl system have widely been introduced and among them is an apparatus which has both a pitch converter and a band-rejection filter interposed between a microphone and a loudspeaker, as disclosed in Japanese Patent Application Laid Open No. 60-28399 (1975).
  • That apparatus is arranged such that an audio signal from a microphone 1 is supplied via a microphone amplifier 2 to a pitch converter circuit 3.
  • the pitch converter circuit 3 is provided for varying the frequency of an input audio signal.
  • An output signal from the pitch converter circuit 3 is then fed to a band-rejection filter 4 which actually is a comb filter exhibiting a filter effect in which band-rejection center frequencies are allocated at approximately equal intervals as shown in Fig. 2.
  • an output signal from the band-rejection filter 4 is amplified by a power amplifier 5 for activating a is transmitted to the pitch converter 3 where it is varied in frequency response.
  • the audio signal varied in the frequency passes the band-rejection filter 4 and then, supplied through the power amplifier 5 to the loudspeaker 6 where it is turned to an acoustic output.
  • a portion of the acoustic output is picked up by the microphone 1, a loop causing a howl is established.
  • the frequency of a feedback audio signal derived from an acoustic input is also varied by the pitch converter 3. It is now assumed that the audio signal from the microphone 1, which has a frequency of f a as shown in Fig.
  • a feedback audio signal having a frequency of f b (Fig. 3B) after a duration 7 of traveling once throughout the loop. After another duration of 7 traveling once more throughout the loop, it is further converted to a re- feedback audio signal having a frequency of f c (Fig. 3C). If the frequency f c is identical to a band-rejection center frequency in the band-rejection filter 4, the audio signal of f c frequency is blocked by the band-rejection filter 4 and thus, howling will be prevented.
  • band-rejection center frequencies allocated at intervals of a smaller distance in the band-rejection filter 4 for rejecting unwanted howl generating signals.
  • a problem then arises that when a distance between the two adjacent band-rejection center frequencies is reduced, the gain of a frequency band between the same becomes attenuated and thus, the quality of a reproduced sound will be degraded.
  • An audio apparatus is provided with an antihowl system for input of audio signals from a microphone, in which at least one notch filter in which the band-rejection center frequency varies with time is provided in a transmission line of the audio signals.
  • FIG. 1 is a block diagram showing a prior art audio apparatus provided with an antihowl system
  • Fig. 4 illustrates an improved audio apparatus of the present invention in which an output signal from a micro phone 1 is at first fed to a microphone amplifier 2 of which output port is connected to an A/D converter 7.
  • the A/D converter 7 is coupled at output to a DSP (digital signal processor) 9 which is controlled by a microcomputer 10 as will be described later in more detail.
  • the DSP 9 is also coupled at output to a D/A converter 8 where a digital audio signal from the DSP 9 is converted into an analog audio signal.
  • the output of the D/A converter 8 is connected via a power amplifier 5 to a loudspeaker 6 in the same manner as of the prior art.
  • Fig. 5 schematically illustrates an arrangement of the DSP 9.
  • a digital signal from the A/D converter 7 is fed to an input interface 13 in the DSP 9.
  • the input interface 13 is coupled to a data bus 14 which in turn is connected to a data memory 12 provided for temporary storage of signal data and also, to one of the two outputs of a multiplier 15.
  • the other output of the multiplier 15 is coupled to a buffer memory 16 provided for storage of coefficient data.
  • the buffer memory 16 is coupled to a coefficient RAM 17 which holds a plurality of coefficient data.
  • a timing signal from a sequence controller 20, described later one of the coefficient data stored in the RAM 17 is retrieved and transferred to the buffer memory 16 for storage.
  • the coefficient data retained in the buffer memory 16 is then supplied to the multiplier 15.
  • an ALU (arithmetic logic unit) 18 for accumulating calculated outputs of the multiplier 15.
  • the ALU 18 has a couple of inputs; one for receiving a calculated output from the multiplier 15 and the other for communicating to the data bus 14.
  • the output of the ALU 18 is coupled to an accumulator 19 which is in turn connected at output to the data bus 14.
  • the data bus 14 is also connected to a memory controller circuit 22 provided for control on writing and reading of data into and from an external memory 21 for producing delay data.
  • the data bus 14 is further connected to an output interface 23 which delivers a digital audio signal, i.e. the output of the DSP 9, to the D/A converter 7.
  • the operational timing in the two interfaces 13 and 23, the multiplier 15, the coefficient RAM 17, the ALU 1, the accumulator 19, and the memory controller circuit 22 is controlled by the sequence controller 20 which is driven according to a processing program loaded in a program memory 24 and also, in response to a command from the microcomputer 10.
  • a keyboard 11 is also connected to the microcomputer 10 for providing various commands through manipulation to the same and keyboard entry will direct the microcomputer 10 for control over the writing of coefficient data into RAM 17.
  • a microphone signal fed to the A/D converter 7 is converted in each predetermined sampling period into a digital audio signal form and then, transmitted via the interface 13 to the data memory 12 for storage.
  • a coefficient data read out from the RAM 17 is fed to the buffer memory 16 for temporary storage.
  • the sequence controller 20 is then activated for determining the timing of: reading data from the interface 13, transferring data from the data memory 12 to the multiplier 15 selectively, issuing coefficient data from the RAM 17, triggering the multiplication on the multiplier 15 and the summing on the ALU 18, releasing an output from the accumulator 19, issuing data of calculated results from the interface 23, and so on.
  • the appropriate timing for operation allows both coefficient data 0:1 from the buffer memory 16 and data d 1 from the data memory 12 to be simultaneously fed into the multiplier 15 where they are multiplied to ⁇ 1 ⁇ d 1 . Subsequently, ⁇ 1 ⁇ d 1 is calculated by the ALU 18 to 0+ ⁇ 1 ⁇ d 1 which is in turn stored in the accumulator 19.
  • coefficient data a 2 from the buffer memory 16 and data d 2 from the data memory 12 are multiplied in the multiplier 15 to ⁇ 2 ⁇ d 2 .
  • the input of a 2 'd, is then combined by the ALU 18 with ⁇ 1 ⁇ d 1 fetched from the accumulator 19 to ⁇ 1 ⁇ d 1 + ⁇ 2 °d 2 which is also stored in the accumulator 19.
  • a sum total from E ⁇ i ⁇ d i is obtained.
  • a delay data associated with e.g. a reflected sound corresponding data is read out from the data memory 12 and transmitted via the data bus 14 to the memory controller circuit 22.
  • the memory controller circuit 22 is then activated to write a series of the supplied data into the external memory 21 in sequence so that after completion of the writing, the data can be retrieved in the form of a delay data at the end of a predetermined delay time data interval.
  • the delay data is then fed via the data bus 14 to the data memory 12 for storage and will be ready for use in the foregoing calculation.
  • the DSP 9 in the audio apparatus of the present invention is also embodied in the form of an equivalent circuit, as shown in Fig. 6, which serves as a secondary IIR filter.
  • a coefficient multiplier 31 and a delay device 32 are coupled in combination to the input terminal which receives an audio data signal.
  • the delay device 32 is then connected at output to another coefficient multiplier 33 and to another delay device 34 which is in turn coupled at output to a further coefficient multiplier 35.
  • the outputs of their respective coefficient multipliers 31, 33, and 35 are all communicated to an adder 36.
  • the adder 36 is then coupled at output to a delay device 37.
  • the delay device 37 is connected at output to a coefficient multiplier 38 and also, to another delay device 39.
  • the delay device 39 is coupled at output to another coefficient multiplier 40 and both the coefficient multipliers 38 and 40 are communicated at output to the adder 36.
  • the delay time of each delay device 32, 34, 37, or 39 is equal to one sampling period. Accordingly, data fed to the multiplier 33 comes one sampling period earlier than that fed to the multiplier 31 and data fed to the multiplier 35 comes two sampling periods earlier than the same.
  • the DSP 9 is actuated in the following manner.
  • input audio signal data d n is read out from an n-th location in the data memory 12 and simultaneously, the coefficient data a 2 is retrieved from the RAM 17. Both data are transferred to the buffer memory 16 and multiplied in the multiplier 15. The multiplication a 1 ⁇ d n is then added to 0 by the ALU 18 at the third step-two steps after the first step. And, the resultant sum is stored in the accumulator 19.
  • signal data d n - 1 is read out from an (n-1)-th location in the data memory 12 and multiplied by the coefficient data a 1 from the RAM 17 in the multiplier 15.
  • the multiplication a 1 ⁇ d n-1 is then added, at the fourth step, by the ALU 18 to a stored value (the sum calculated at the third step) from the accumulator 19 and the resultant sum is also stored in the accumulator 19.
  • an input signal data IN is transferred to an (n-2)-th location in the data memory 12 and also, to the multiplier 15 where it is multiplied by the coefficient data ao.
  • the multiplication a 0 ⁇ IN is added, at the fifth step, by the ALU 18 to a stored value (the sum at the fourth step) from the accumulator 19 and the resultant sum is stored in the accumulator 19.
  • signal data d n+2 is read out from an (n + 2)-th location in the data memory 12 and multiplied by the coefficient data b 2 from the RAM 17 in the multiplier 15.
  • the multiplication b 2 ⁇ d n+2 is then added, at the sixth step, by the ALU 18 to a stored value (the sum at the fifth step) from the accumulator 19 and the resultant sum is also stored in the accumulator 19.
  • signal data d n+1 is read out from an (n+1)-th location in the data memory 12 and multiplied by the coefficient data b 1 from the RAM 17 in the multiplier 15.
  • the multiplication b 1 ⁇ d n+1 is then added, at the seventh step, by the ALU 18 to a stored value (the sum calculated at the sixth step) from the accumulator 19 and the resultant sum is also stored as an output data in the accumulator 19.
  • the coefficient data ao, a 1 , a 2 , bi, and b 2 have been read from an internal memory (not shown) in the microcomputer 10 and transferred to a predetermined coefficient data area in the RAM 17.
  • the coefficient data area contains a plurality of coefficient data groups; each data group consisting of the coefficient data ao, a 1 , a 2 , bi, and b 2 and having different values of A and B, in which the data are stored in the order of a 2 , a 1 , ao, b 2 , and b 1 from the first storage location in the address space.
  • the coefficient data groups having a 2 , a 1 , ao, b 2 , and b 1 allocated in one group are retrieved and stored in a sequence of F 1 , F 2 ,..., Fs, F 1 + ⁇ F 1 , F 2 + ⁇ F 2 ,..., F 4 +5 ⁇ F 4 , and F 5 +5 ⁇ F 5 as shown in Fig. 7.
  • the data groups F 1 to F 5 are provided for determining the band-rejection center frequencies f 1 to f 5 of the first to fifth notch filters respectively.
  • the center frequencies f 1 to f 5 are also designated as reference frequencies, in which f 1 ⁇ f 2 ⁇ f 3 ⁇ f 4 ⁇ f 5 .
  • the data group F 1 + ⁇ F 1 is prepared for providing a band-rejection center frequency of f 1 + ⁇ f 1 where f 1 is the reference frequency and ⁇ f 1 is a unit frequency shift.
  • the data group F 1 +2 ⁇ F 1 is prepared for providing a band-rejection center frequency of f 1 plus 2xAfi.
  • the data groups F 1 +3 ⁇ F 1 , F 1 + 4 ⁇ F 1 , and F 1 + 5 ⁇ F 1 are adopted for providing band-rejection center frequencies obtained by adding 3 ⁇ f 1 , 4 ⁇ f 1 , and 5 ⁇ f 1 to f 1 respectively.
  • the other data groups F 2 , F 3 , F 4 , and F 5 are provided for similar purpose.
  • the frequency shifts Df 1 , ⁇ f 2 , ⁇ f 3 , ⁇ f 4 , and ⁇ f 5 in a unit time need not be the same and can be determined independently.
  • the coefficient data are retrieved from the first location in the address space by a timing signal given from the sequence controller 20; for example, a 2 , a 1 , ao, b 2 , and b 1 of the data group F 1 , a 2 , a 1 , ao, b 2 , and b 1 of the data group F 2 , and so on in sequence.
  • the coefficient data groups F 1 to F 5 retrieved are then multiplied by sampling signal data of the first timing respectively and F 1 + ⁇ F 1 to F 5 + ⁇ F 5 are multiplied by sampling signal data of the second timing respectively.
  • the coefficient data groups F 1 +2 ⁇ F 1 to F 5 +2 ⁇ F 5 , F 1 +3 ⁇ F 1 to F 5 + 3 ⁇ 5 , F 1 +4 ⁇ F 1 to F 5 + 4AFs, and F 1 +5 ⁇ F 1 to F 5 +5 ⁇ F 5 are multiplied and these steps will be repeated.
  • the band-rejection center frequencies of the first to fifth notch filters are determined, as shown in Fig. 8, f 1 to f 5 for the coefficient data groups F 1 to F 5 respectively, f 1 + ⁇ f 1 to f 5 + ⁇ f 5 for F 1 + ⁇ F 1 to F 5 + ⁇ F 5 , f 1 + 2 ⁇ f 1 to f 5 + 2 ⁇ f 5 for F 1 + 2 ⁇ F 1 to F 5 + 2 ⁇ F 5 , f 1 + 3 ⁇ f 1 to f 5 + 3 ⁇ f 5 for F 1 + 3 ⁇ F 1 to F 5 + 3 ⁇ F 5 , f 1 + 4 ⁇ f 1 to f 5 + 4 ⁇ f 5 for F 1 + 4 ⁇ F 1 to F 5 + 4AFs, and f 1 + 5 ⁇ f 1 to f 5 + 5 ⁇ f 5 for F 1 +5 ⁇ F 1 to F 5 +5 ⁇ F 5 .
  • the band-rejection center frequency of each notch filter will vary with time.
  • the first notch filter shifts the band-rejection center frequency from f 1 which is the reference frequency denoted by the numeral 1 to f 1 + ⁇ f 1 denoted by 2, to f 1 + 2Afi denoted by 3, to f 1 + 3Afi denoted by 4, to f 1 + 4 ⁇ f 1 denoted by 5, and to f 1 + 5Afi denoted by 6, as shown in Fig. 9.
  • the second to fifth notch filters change with time their respective band-rejection center frequencies f 2 , f 3 , f 4 , and fs, shown in Fig. 9, in the same manner.
  • the first to fifth notch filters are intended to be not always equal in the size of frequency shift. It is a common practice in a particular range (namely 1 kHz to 4 kHz) of frequencies which involves more howls to provide an increased number of notch filters as compared with the other band of frequencies, in which the frequency shift of a band-rejection center frequency may be minimized and also, the shifting speed per unit time may be increased. It is preferred that for example, the shift of the band-rejection center frequency ranging from 1 kHz and 4 kHz is 2 Hz and the shifting speed is 1 Hz per unit time.
  • the DSP 9 is chiefly provided in the arrangement of the embodiment according to the present invention, it may be replaced with another device(s).
  • a plurality of notch filters of secondary IIR type 41 1 , 41 2 ,..., 41 n may be interposed between the A/D converter 7 and the D/A converter 8 as shown in Fig. 10.
  • Each of the notch filters 41 1 , 41 2 ,..., 41 n which are different in the band-rejection center frequency is arranged so that its band-rejection center frequency is varied by changing a coefficient for multiplication with the controller circuit 42.
  • Those notch filters may also be arranged for constituting an analog circuit.
  • Fig. 11 illustrates another embodiment of the present invention in the form of an audio apparatus which is constructed by adding a frequency modulation circuit 43 to the arrangement portrayed in Fig. 10.
  • the frequency modulation circuit 43 is provided with a memory (not shown) for varying the frequency of a digital audio signal by writing the signal into the memory and reading it out from the same at a different speed from the writing speed.
  • the frequency modulation circuit 43 is well known, for example, as a tone controller disclosed in Japanese Patent Application Laid-Open No. 61-118797(1986) or 61-121096(1986). So, the details of the circuit will not be described.
  • Such a frequency modulation circuit may be formed with the DSP, in which the writing and reading of data into and from the external RAM 21 shown in Fig.
  • the audio apparatus provided with an antihowl system has notch filters arranged across the transmission line of an audio signal from a microphone for varying with time the band-rejection center frequency. Accordingly, the notch filters having different band-rejection center frequencies can closely be aligned throughout a particular band of frequencies which tends to cause daunting howls and thus, block unwanted audio signals which are bound to develop a loop causing a howl. Consequently, howls will be eliminated without deterioration in the quality of a reproduced sound.

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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Filters That Use Time-Delay Elements (AREA)
EP19910301941 1990-07-16 1991-03-08 Audio apparatus with anti-howl function Withdrawn EP0467499A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP187676/90 1990-07-16
JP18767690A JPH0477093A (ja) 1990-07-16 1990-07-16 ハウリング防止機能を備えた音響装置

Publications (2)

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EP0467499A2 true EP0467499A2 (fr) 1992-01-22
EP0467499A3 EP0467499A3 (en) 1992-05-27

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EP19910301941 Withdrawn EP0467499A3 (en) 1990-07-16 1991-03-08 Audio apparatus with anti-howl function

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JP (1) JPH0477093A (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0584649A1 (fr) * 1992-08-27 1994-03-02 Alcatel SEL Aktiengesellschaft Circuit pour dispositifs électro-acoustiques
EP0592787A1 (fr) * 1992-09-08 1994-04-20 Alcatel SEL Aktiengesellschaft Procédé pour améliorer l'affaiblissement du signal local sur des dispostifs électro-acoustiques
EP0600164A1 (fr) * 1992-09-08 1994-06-08 Alcatel SEL Aktiengesellschaft Procédé pour l'amélioration de la qualité de transmission d'un dispositif électro-acoustique
EP0976208A1 (fr) * 1996-07-26 2000-02-02 Shure Brothers Incorporated Elimination de la reaction acoustique a l'aide d'un algorithme de filtre coupe-bande adaptatif
EP1938309A2 (fr) * 2005-09-30 2008-07-02 Motorola, Inc. Procede et systeme permettant de supprimer la regeneration du signal audio
JP2014042103A (ja) * 2012-08-21 2014-03-06 Oki Electric Ind Co Ltd ハウリング抑圧装置及びプログラム、並びに、適応ノッチフィルタ及びプログラム
CN105228056A (zh) * 2015-10-21 2016-01-06 西安航空学院 一种消除麦克风啸叫的方法及系统

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0750897A (ja) * 1993-02-19 1995-02-21 Onkyo Corp 音声信号増幅装置

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4091236A (en) * 1976-09-07 1978-05-23 The University Of Akron Automatically tunable notch filter and method for suppression of acoustical feedback
US4232192A (en) * 1978-05-01 1980-11-04 Starkey Labs, Inc. Moving-average notch filter
EP0197758A2 (fr) * 1985-04-02 1986-10-15 Matsushita Electric Industrial Co., Ltd. Appareil pour restituer le son
JPS631295A (ja) * 1986-06-20 1988-01-06 Matsushita Electric Ind Co Ltd 拡声装置
JPS6315598A (ja) * 1986-07-08 1988-01-22 Matsushita Electric Ind Co Ltd ハウリング抑圧装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4091236A (en) * 1976-09-07 1978-05-23 The University Of Akron Automatically tunable notch filter and method for suppression of acoustical feedback
US4232192A (en) * 1978-05-01 1980-11-04 Starkey Labs, Inc. Moving-average notch filter
EP0197758A2 (fr) * 1985-04-02 1986-10-15 Matsushita Electric Industrial Co., Ltd. Appareil pour restituer le son
JPS631295A (ja) * 1986-06-20 1988-01-06 Matsushita Electric Ind Co Ltd 拡声装置
JPS6315598A (ja) * 1986-07-08 1988-01-22 Matsushita Electric Ind Co Ltd ハウリング抑圧装置

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
JOURNAL OF THE AUDIO ENGINEERING SOCIETY. vol. 32, no. 3, March 1984, NEW YORK US pages 144 - 150; J.RODDNEY COX: 'Squealer Killer with Real-Time Equalization' *
PATENT ABSTRACTS OF JAPAN vol. 12, no. 200 (E-619)9 June 1988 & JP-A-63 001 295 ( MATSUSHITA ELECTRIC IND CO LTD ) *
PATENT ABSTRACTS OF JAPAN vol. 12, no. 221 (E-625)23 June 1988 & JP-A-63 015 598 ( MATSUSHITA ELECTRIC IND CO LTD ) *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0584649A1 (fr) * 1992-08-27 1994-03-02 Alcatel SEL Aktiengesellschaft Circuit pour dispositifs électro-acoustiques
EP0592787A1 (fr) * 1992-09-08 1994-04-20 Alcatel SEL Aktiengesellschaft Procédé pour améliorer l'affaiblissement du signal local sur des dispostifs électro-acoustiques
EP0600164A1 (fr) * 1992-09-08 1994-06-08 Alcatel SEL Aktiengesellschaft Procédé pour l'amélioration de la qualité de transmission d'un dispositif électro-acoustique
EP0976208A1 (fr) * 1996-07-26 2000-02-02 Shure Brothers Incorporated Elimination de la reaction acoustique a l'aide d'un algorithme de filtre coupe-bande adaptatif
EP0976208A4 (fr) * 1996-07-26 2006-08-16 Shure Acquisition Holdings Inc Elimination de la reaction acoustique a l'aide d'un algorithme de filtre coupe-bande adaptatif
EP1938309A2 (fr) * 2005-09-30 2008-07-02 Motorola, Inc. Procede et systeme permettant de supprimer la regeneration du signal audio
EP1938309A4 (fr) * 2005-09-30 2011-02-23 Motorola Inc Procede et systeme permettant de supprimer la regeneration du signal audio
JP2014042103A (ja) * 2012-08-21 2014-03-06 Oki Electric Ind Co Ltd ハウリング抑圧装置及びプログラム、並びに、適応ノッチフィルタ及びプログラム
CN105228056A (zh) * 2015-10-21 2016-01-06 西安航空学院 一种消除麦克风啸叫的方法及系统
CN105228056B (zh) * 2015-10-21 2018-06-19 西安航空学院 一种消除麦克风啸叫的方法及系统

Also Published As

Publication number Publication date
EP0467499A3 (en) 1992-05-27
JPH0477093A (ja) 1992-03-11

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