EP0903960B1 - Antenne gebildet durch eine Vielzahl von akustischen Detektoren - Google Patents

Antenne gebildet durch eine Vielzahl von akustischen Detektoren Download PDF

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Publication number
EP0903960B1
EP0903960B1 EP98460031A EP98460031A EP0903960B1 EP 0903960 B1 EP0903960 B1 EP 0903960B1 EP 98460031 A EP98460031 A EP 98460031A EP 98460031 A EP98460031 A EP 98460031A EP 0903960 B1 EP0903960 B1 EP 0903960B1
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EP
European Patent Office
Prior art keywords
sensors
antenna
antenna according
processing
acoustic
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Expired - Lifetime
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EP98460031A
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English (en)
French (fr)
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EP0903960A1 (de
Inventor
Wolfgang Tager
Grégoire Le Tourneur
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Orange SA
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France Telecom SA
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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
    • H04R3/005—Circuits for transducers, loudspeakers or microphones for combining the signals of two or more microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/40—Details of arrangements for obtaining desired directional characteristic by combining a number of identical transducers covered by H04R1/40 but not provided for in any of its subgroups
    • H04R2201/401—2D or 3D arrays of transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/40—Details of arrangements for obtaining desired directional characteristic by combining a number of identical transducers covered by H04R1/40 but not provided for in any of its subgroups
    • H04R2201/403—Linear arrays of transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/40—Details of arrangements for obtaining desired directional characteristic by combining a number of identical transducers covered by H04R1/40 but not provided for in any of its subgroups
    • H04R2201/405—Non-uniform arrays of transducers or a plurality of uniform arrays with different transducer spacing

Definitions

  • the present invention relates to an acoustic antenna formed from a plurality of discrete acoustic transducers, in particular an acoustic receiving antenna, that is to say formed by a plurality of acoustic sensors or microphones. Being given the principle of reciprocity, the invention also applies to an antenna emission acoustics.
  • the main purpose of an acoustic receiving antenna is to reduce all defects in reception while retaining useful information, i.e. information issued by the speaker or by the useful source.
  • Acoustic signals received on the antenna sensors are deteriorated by: (1) other issuers; (2) multi-path propagation; (3) in some cases, a echo; (4) electronic noise from sensors and amplifiers; and (5) possibly, the quantization noise for digital processing.
  • disturbances (1) to (3) will be say “spatially coherent” or simply “coherent” while the disturbances (4) and (5) are said to be “inconsistent”.
  • Antenna processing can be seen as a dot product in the frequency domain.
  • the signal at the end of the processing is expressed in the form:
  • a conventional antenna processing consists of putting the signal back in phase, possibly weighting the sensors to establish a compromise between opening of the main lobe and the level of the secondary lobes, and calculating this sum.
  • We can express it by a set of coefficients: w m ( f ) g m ( f ) e j 2 ⁇ f vs d 1 m with g m ( f ) real and positive
  • these equations are based on a propagation model which is very well adapted in free field without obstacles.
  • the propagation model can be replaced by measurements.
  • the vectors d 2 ( f ) represent measured propagation vectors.
  • the network Since we only use fractions of sensibilities of the sensors, the network produces a response which has a signal / noise ratio lower than it would be if we used the full sensitivity of each sensor. Else hand, if the distance between the sensors is too large or too small compared to the wavelength, antenna performance drops.
  • document FR-A-2 472 326 describes a method of optimization of a linear geometry of acoustic antenna, with conventional summation of the signals sensors. We can consider that it is a linear delay-sum antenna at variable spacing. This antenna only works well around a frequency in narrow band and the antenna is relatively large compared to the wavelength.
  • the document FR-A-2 722 637 describes a geometry antenna in which the sensors are distributed in a horizontal plane on a line concave towards a speaker. We add the signals from the sensors in phase.
  • the antenna is decomposed into sub-antennas each characterized by a specific spacing between sensors and each assigned to a part of the frequency band. In bass frequencies, we always encounter difficulties.
  • the treatments mentioned so far do not solve certain difficulties because, on the one hand, the sound signals to be processed belong to a frequency spectrum to broadband, occupying several octaves, for example from 100 to 8000 Hz and, on the other hand, there are near-field sound sources for which is not verified the propagation of sound waves by plane waves.
  • a small conventional antenna cannot be selective at low frequencies.
  • An object of the present invention is to provide an antenna processing which improves the existing conventional treatment, starting from a treatment of superdirective genre in which the module is processed so as not to distort useful signal from a near-field acoustic source which respects a number of constraints.
  • Another object of the invention consists in providing an antenna composed of a plurality of acoustic sensors whose output signals are processed, the signal processing output being higher in quality than the output signal from a state antenna of the technique when the useful acoustic source is in the near field.
  • Another object of the invention consists in providing, an antenna whose processing provides better selectivity at low frequencies.
  • said processing is carried out by an operator mathematical in a flowchart called superdirective-module-phase or SDMP whose the input data is the antenna geometry and model data propagation, weighting data and stress data mentioned above, and whose output data are, in the frequency domain, the coefficients of a plurality of digital filters as numerous as the sensors acoustic.
  • an antenna formed of a plurality acoustic sensors, a first part placed in front of a useful source near consists of sensors aligned in a first row and a second part placed behind the first row in relation to the near useful source consists of sensors aligned in at least a second row.
  • the common direction of the rows of sensors in the first and second parts are transverse to the mean direction of useful acoustic waves.
  • the common direction of the rows of sensors in the first and second parts are slightly oblique to the direction mean useful acoustic waves.
  • the sensors of the first part are distributed symmetrically in a logarithmic fashion around the median sensor.
  • the sensors of the first part are selectively assigned to several sub-antennas, each sub-antenna being associated with a determined frequency band and the sensors selectively assigned to this sub-antenna delivering output signals which are processed by conventional processing, the frequency bands being contiguous and the whole of them not falling below practically 1 kHz, each processing consisting of a specific filtering and the the output signals of each specific filter being summed.
  • each output signal from a sensor is filtered by a filter that performs, at the same time, the SDMP algorithm for bass frequencies, cutting into frequency bands according to the antenna method logarithmic, and classical channel formation for frequencies not processed by the SDMP algorithm.
  • a propagation model is used.
  • Fig. 1 symbolically shows the SDMP 10 organization chart which receives input data of a set 11 containing the digital data relating to the topographic location of the antenna sensors as well as the useful source, a set 12 containing the data relating to the linear constraints, of a set 13 containing the spatial weighting data, of a set 14 containing the data relating to the constraints on the chosen reduction of the inconsistent noise, and a set 15 containing the data relating to the definitions of the sub-antennas.
  • the flowchart 10 delivers output data to a set 16, the data of output being relative to a set of coefficients of M digital filters in the domain frequency, M being equal to the number of sensors of the antenna.
  • the antenna is formed by two acoustic sensors or microphones 21 and 22 placed one behind the other in relation to a useful speaker or acoustic source 23.
  • the sensors 21 and 22 and the useful source 23 are aligned.
  • the distance d between sensors is, for example, 30 cm and is equal to the distance from sensor 21 to the source 23.
  • This very simple antenna thus symbolizes sound pickup in the near field.
  • the two sensors have a omnidirectional directivity diagram.
  • the outputs of sensors 21 and 22 are respectively connected to the inputs of low-pass filters 24 and 25 whose outputs are connected to the inputs of a summator 26 which outputs the antenna output signal at 27.
  • the directivity factor tends to infinity if the frequency tends to zero.
  • the processing is less robust, because the useful signal is weak at the output.
  • FIG. 5 shows an embodiment of a processing - filtering, summation - at the output of sensors 21 and 22 in the field temporal.
  • the outputs of sensors 21 and 22 are respectively connected to the inputs microphone amplifiers 28 and 29 whose outputs are respectively connected at the inputs of analog-digital converters 30 and 31 whose outputs are respectively connected to the memory inputs 32 and 33 made up of registers with shift comprising, for example, thirty-two cells each.
  • the lateral exit of a memory cell 30, associated with sensor 24, is connected to a door input 34.1.n the second input of which receives a signal of coefficient h.l.n.
  • the lateral exit of a memory cell 31, associated with sensor 25, is connected to a door entry 34.2.n whose second input receives a signal of coefficient h.2.n.
  • the parameters n mentioned above vary discreetly from one to thirty-two depending on the rank of the cell in the shift register.
  • the outputs of doors 34.1.n and 34.2.n are connected to the corresponding inputs of a digital summing device 26 whose output delivers at 27 the antenna signal.
  • Fig. 6 the variation of the directivity factor as a function of the frequency, in hypothesis (a), is indicated by the curve al, which decreases from 25 dB to 5 dB below of 100 Hz, shows that we improve performance at low frequencies compared to those of a conventional antenna indicated by the curve Id.
  • the curve 2a indicates the variation of the reduction.
  • curve 1b shows that the low frequency performance up to 5 dB, i.e. where solutions classics don't work well.
  • Curve 2b corresponds to the variation of the minimum reduction imposed.
  • curve 1c shows that we can gain between 2 dB for low frequencies and 0.6 dB for high.
  • Line 2c identical to line 2d corresponds to the variation of the minimum reduction imposed.
  • a useful source 100 U-shaped antenna comprising thirteen sensors 101 to 113 which in the example described are forward-facing cardioid directivity pattern sensors, i.e. the region containing source 100 relative to the antenna.
  • the first nine sensors 101 at 109 are aligned symmetrically around the sensor 105 on a first straight line D1
  • the two following sensors 110 and 111 are arranged on a second straight line D2
  • the two last sensors 112 and 113 on a third straight line D3.
  • Lines D1, D2 and D3 are parallel and perpendicular to a straight line D4 passing through the sensor 105 and on which the useful source 100 is installed.
  • the distance from the source 100 to the right D1 is 60 cm and the lines D2 and D3 are respectively placed behind the right D1 at 15 and 30 cm.
  • the sensors 110 and 112 are aligned behind the sensor 101 and sensors 111 and 113 are aligned behind sensor 109 so that train the legs of the U.
  • the intervals between the sensors 105, 104, 103, 102 and 101 vary increasing logarithmically and symmetrically to intervals between sensors 105, 106, 107, 108 and 109.
  • the interval is 2.5 cm; between 104 and 103, it is 2.5 cm; between 103 and 102, 5 cm; and between 102 and 101, 10 cm
  • the sensor 110 is placed 15 cm behind sensor 101, like 111 behind 109, and sensor 112 is placed 15 cm behind sensor 110, like 113 behind 112.
  • FIG. 8 illustrates the frequency implementation of the filtering output signals from sensors 101 to 113 in Fig. 7.
  • the sensor 101 supplies a amplifier A01 followed by an analog-digital converter B01 followed by a circuit C01 operating according to the Fast Fourier transformation algorithm (TFR with zero padding) connected to the serial input of a D01 filter whose output is connected to an input corresponding of an SOM adder.
  • TFR Fast Fourier transformation algorithm
  • the parallel input of filter D01 receives the clearance coefficients calculated by the SDMP flowchart for this filter.
  • Fig. 8 we have included the sensor 113 which supplies an amplifier A13 followed by an analog-digital converter B13 followed by a circuit c13, operating like circuit C01, connected to the serial input of a filter D13, the output of which is connected to a corresponding input of the SOM adder.
  • the parallel input of filter D13 receives also a set of coefficients calculated by the SDMP organization chart.
  • the output of the SOM adder is connected to a circuit E operating according to a Reverse Fast Fourier Transformation algorithm (TFRI with Overlap Add) followed by a digital analog converter F which delivers the output signal from the antenna.
  • TFRI with Overlap Add Reverse Fast Fourier Transformation algorithm
  • the algorithm can be performed in real time using a DSP (Texas Instruments C50).
  • the antenna of FIG. 7 in four sub-antennas including the first three, in which the sensors 101 to 109 operate from the right D1, are used to cover three octaves at high frequencies and the fourth in which all the sensors 101 to 113 intervene is used for cover low frequencies from 0 to 1 kHz.
  • the sensors 101 to 109 are symmetrically distributed in a logarithmic manner, which allows in a way known per se to reduce the number of sensors, here to nine A number of five sensors per octave band is sufficient.
  • the sensors 103 to 107 are used, constituting the first sub-antenna, for the band 4 to 7 kHz; sensors 102, 103, 105, 107 and 108, constituting the second sub-antenna, for the band 2 to 4 kHz; and the sensors 101, 102, 105, 108 and 109, constituting the third sub-antenna, for the band 1 to 2 kHz.
  • the processing involves all the sensors 101 to 113 using the algorithm of the invention, that is to say taking into account the module differences and phase differences on sensors 110 to 113, of a similar to the processing mentioned above for the antenna of FIG. 2.
  • the treatment according to the invention is useful for a wide band of frequencies, for example for speech a band going from 20 Hz to 7 kHz.
  • a variant of the antenna of FIG. 6 comprises, opposite a source useful 200, thirteen sensors 201 to 213 with directivity diagram in cardioid.
  • the nine first sensors 201 to 209 are aligned symmetrically around the sensor 205 on a first straight line D1, the two sensors along 210 and 211 are arranged on a second line D2 and the last two sensors 212 and 213 on a third line D3.
  • Lines D1 to D3 are parallel and perpendicular to a line D4 passing through the sensor 205 and the useful source 200.
  • the mutual distances between the lines D1 to D3 and the source 200 are identical to those mentioned in About the antenna of Fig. 6.
  • the mutual distances between the sensors 201 to 209 are identical to those that exist between sensors 101 to 109.
  • Sensors 210 and 212 are aligned behind the middle of segment 201-202 and the sensors 211 and 213 aligned behind the middle of the segment 208-209. In depth, their mutual distances are the same as in FIG. 7. The offsets of the sensors 210 at 213 towards the center of the antenna earns it the antenna designation in Pi.
  • Pi antenna output signals are processed according to the flowchart superdirective-module-phase of the invention.
  • FIG. 10 another variant of the antenna of FIG. 6 has in front of a useful source 300, thirteen sensors 301 to 313 with a cardioid directivity diagram.
  • the first nine sensors 301 to 309 have, on the right D1, the same arrangement as the first nine sensors of FIG. 6.
  • the last four sensors 310 to 313 are successively aligned according to the same line D4 in FIG. 6, behind 305 so as to form, with the sensors 301 to 309, a T-shaped antenna.
  • the distance between the sensors 310 and 305 is 10 cm, as between sensors 311 and 310, between 312 and 311, and between 313 and 312.
  • T-antenna output signals are processed according to the flowchart superdirective-module-phase of the invention.
  • a set 11 which contains the digital data relating to the topographic location of the antenna sensors as well as the useful source. This set 11 also contains data relating to the propagation and / or, as mentioned above, measures of responses pulse.

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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)
  • Variable-Direction Aerials And Aerial Arrays (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
  • Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Claims (11)

  1. Antenne gebildet durch eine Vielzahl von akustischen Detektoren, dadurch gekennzeichnet, dass die Ausgangssignale der Detektoren einer Verarbeitung des Optimalgewinntyps unterworfen werden, mit einer Auflage, was das Modul betrifft, und einer nicht linearen Auflage, die die Dämpfung des inkohärenten Rauschens festlegt,
    wobei die theoretische Formulierung dieser Auflagen die folgende ist: g(f)α H 1(f) = e - j 2 πfτ und g(f)gH (f) < 1 R min wobei die erste Auflage bedeutet, dass die gesamte Übertragungsfunktion eine reine τ-Verzögerung ist und die zweite Auflage bedeutet, dass für die Dämpfung inkohärenten Rauschens eine Grenze festgelegt ist.
  2. Antenne nach Anspruch 1, dadurch gekennzeichnet, dass die Verarbeitung noch einer weiteren Auflage unterworfen wird, die die Präsenz einer oder mehrerer Nullen des Optimalgewinndiagramms in eine oder bestimmte Richtungen bedeutet, das heißt: C(f)gH (f) = p(f) wobei C(f) eine Matrix von Ausbreitungsvektoren ist und
    p(f) ein komplexer Verstärkungsvektor für jeden Ausbreitungsvektor ist.
  3. Antenne nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Verarbeitung durch einen mathematischen Operator in einem so genannten Optimalgewinn-Modul-Phase-Organigramm oder SDMP konkretisiert wird, dessen Eingangsdaten die Geometriedaten der Antenne und des Ausbreitungsmodells, die Gewichtungsdaten und die Daten in Zusammenhang mit den oben genannten Auflagen sind, und dessen Ausgangsdaten im Frequenzbereich die Koeffizienten einer Vielzahl digitaler Filter sind, die so zahlreich wie die akustischen Detektoren sind.
  4. Antenne nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass sie aus einer Mehrzahl von akustischen Detektoren gebildet ist, von welchen ein erster Teil, gegenüber einer nahen Nutzquelle angeordnet aus Detektoren besteht, die in einer ersten Reihe ausgerichtet sind, und ein zweiter Teil hinter der ersten Reihe in Bezug auf die nahe Nutzquelle angeordnet aus Detektoren besteht, die in mindestens einer zweiten Reihe ausgerichtet sind.
  5. Antenne nach Anspruch 4, dadurch gekennzeichnet, dass die gemeinsame Richtung der Reihen Detektoren im ersten und zweiten Teil quer zur mittleren Richtung der akustischen Nutzwellen ist.
  6. Antenne nach Anspruch 4, dadurch gekennzeichnet, dass die gemeinsame Richtung der Reihen Detektoren im ersten und zweiten Teil in Bezug auf die mittlere Richtung der akustischen Nutzwellen leicht schräg ist.
  7. Antenne nach einem der Ansprüche 4 bis 6, dadurch gekennzeichnet, dass die Detektoren des ersten Teils symmetrisch auf logarithmische Art um den mittleren Detektor verteilt sind.
  8. Antenne nach Anspruch 7, dadurch gekennzeichnet, dass die Detektoren des ersten Teils selektiv mehreren Unterantennen zugewiesen sind, wobei jede Unterantenne mit einem bestimmten Band Frequenzen assoziiert ist und die selektiv dieser Unterantenne zugewiesenen Detektoren Ausgangssignale abgeben, die durch eine herkömmliche Verarbeitung behandelt werden, wobei die Frequenzbänder aneinander stoßend sind und ihre Einheit nicht unter praktisch 1 kHz sinkt, wobei jede Verarbeitung aus einer spezifischen Filterung besteht und die Ausgangssignale jedes spezifischen Filters summiert werden.
  9. Antenne nach Anspruch 8, dadurch gekennzeichnet, dass jedes Ausgangssignal eines Detektors von einem Filter gefiltert wird, das gleichzeitig den SDMP-Algorithmus für die niedrigen Frequenzen, das Teilen in Frequenzbänder nach der Methode der logarithmischen Antenne und die klassische Bildung des Kanals für Frequenzen durchführt, die nicht nach dem SDMP-Algorithmus verarbeitet werden.
  10. Antenne nach einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, dass man ein Ausbreitungsmodell verwendet.
  11. Antenne nach einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, dass man eine Messung der Ausbreitungsvektoren verwendet.
EP98460031A 1997-09-10 1998-08-13 Antenne gebildet durch eine Vielzahl von akustischen Detektoren Expired - Lifetime EP0903960B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9711458 1997-09-10
FR9711458A FR2768290B1 (fr) 1997-09-10 1997-09-10 Antenne formee d'une pluralite de capteurs acoustiques

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EP0903960A1 EP0903960A1 (de) 1999-03-24
EP0903960B1 true EP0903960B1 (de) 2003-10-29

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US (1) US6160757A (de)
EP (1) EP0903960B1 (de)
JP (1) JP4491081B2 (de)
DE (1) DE69819273T2 (de)
FR (1) FR2768290B1 (de)

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US6978159B2 (en) * 1996-06-19 2005-12-20 Board Of Trustees Of The University Of Illinois Binaural signal processing using multiple acoustic sensors and digital filtering
US6987856B1 (en) 1996-06-19 2006-01-17 Board Of Trustees Of The University Of Illinois Binaural signal processing techniques
US7157649B2 (en) * 1999-12-23 2007-01-02 New Transducers Limited Contact sensitive device
FR2808391B1 (fr) * 2000-04-28 2002-06-07 France Telecom Systeme de reception pour antenne multicapteur
CN1440628A (zh) 2000-05-10 2003-09-03 伊利诺伊大学评议会 干扰抑制技术
GB0116310D0 (en) * 2001-07-04 2001-08-29 New Transducers Ltd Contact sensitive device
US7274794B1 (en) 2001-08-10 2007-09-25 Sonic Innovations, Inc. Sound processing system including forward filter that exhibits arbitrary directivity and gradient response in single wave sound environment
WO2003015459A2 (en) * 2001-08-10 2003-02-20 Rasmussen Digital Aps Sound processing system that exhibits arbitrary gradient response
US6937938B2 (en) 2002-09-04 2005-08-30 Stanley A. Sansone Method and apparatus for interferometry, spectral analysis, and three-dimensional holographic imaging of hydrocarbon accumulations and buried objects
US6871149B2 (en) * 2002-12-06 2005-03-22 New Transducers Limited Contact sensitive device
US7512448B2 (en) 2003-01-10 2009-03-31 Phonak Ag Electrode placement for wireless intrabody communication between components of a hearing system
US7945064B2 (en) * 2003-04-09 2011-05-17 Board Of Trustees Of The University Of Illinois Intrabody communication with ultrasound
US7076072B2 (en) 2003-04-09 2006-07-11 Board Of Trustees For The University Of Illinois Systems and methods for interference-suppression with directional sensing patterns
US7317764B2 (en) * 2003-06-11 2008-01-08 Lucent Technologies Inc. Method of signal transmission to multiple users from a multi-element array
WO2005115050A1 (en) * 2004-05-19 2005-12-01 Harman International Industries, Incorporated Vehicle loudspeaker array
WO2008156700A2 (en) * 2007-06-15 2008-12-24 Worcester Polytechnic Institute Precision location methods and systems
BRPI0910799A2 (pt) * 2008-07-08 2015-09-29 Koninkl Philips Electronics Nv método, método de operar uma pluralidade de unidades de iluminação, e, aparelho

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US4536887A (en) * 1982-10-18 1985-08-20 Nippon Telegraph & Telephone Public Corporation Microphone-array apparatus and method for extracting desired signal
US5473701A (en) * 1993-11-05 1995-12-05 At&T Corp. Adaptive microphone array
US5715319A (en) * 1996-05-30 1998-02-03 Picturetel Corporation Method and apparatus for steerable and endfire superdirective microphone arrays with reduced analog-to-digital converter and computational requirements

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FR2768290B1 (fr) 1999-10-15
FR2768290A1 (fr) 1999-03-12
EP0903960A1 (de) 1999-03-24
US6160757A (en) 2000-12-12
DE69819273T2 (de) 2004-07-22
DE69819273D1 (de) 2003-12-04
JP4491081B2 (ja) 2010-06-30
JPH11146494A (ja) 1999-05-28

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