United States Patent [19]
`United States Patent [19]
`Marash et ai.
`Marash et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006049607 A
`US006049607A
`[11] Patent Number:
`[11] Patent Number:
`[45] Date of Patent:
`[45] Date of Patent:
`
`6,049,607
`6,049,607
`Apr. 11, 2000
`Apr. 11, 2000
`
`[54] INTERFERENCE CANCELING METHOD
`[54]
`INTERFERENCE CANCELING METHOD
`AND APPARATUS
`AND APPARATUS
`
`[75] Inventors: Joseph Marash, Haifa; Baruch
`[75]
`Inventors: Joseph Marash, Haifa; Baruch
`Berdugo, Kiriat-Ata, both of Israel
`Berdugo, Kiriat-Ata, both of Israel
`
`[73] Assignee: Lamar Signal Processing, Yokneam,
`[73] Assignee: Lamar Signal Processing, Yokneam,
`Israel
`Israel
`
`[21] Appl. No.: 09/157,035
`[21] Appl. No.: 09/157,035
`[22]
`Filed:
`Sep. 18, 1998
`[22] Filed:
`Sep. 18, 1998
`
`[51]
`Int. CI? ............................... H04M 9/08; H03R 3/00
`[51] Int. Cl.7 ............................. .. H04M 9/08; H03R 3/00
`[52] U.S. CI. ............................ 379/410; 379/407; 381192;
`[52] US. Cl. .......................... .. 379/410; 379/407; 381/92;
`381194.1; 367/121
`381/941; 367/121
`[58] Field of Search ..................................... 379/407, 406,
`[58] Field of Search ................................... .. 379/407, 406,
`379/408,409,410,411,416; 381192, 94.1,
`379/408, 409, 410, 411, 416; 381/92, 94.1,
`91.2,94.7,155; 367/116, 117, 118, 119-127;
`91.2, 94.7, 155; 367/116, 117, 118, 119—127;
`708/322
`708/322
`
`[56]
`[56]
`
`References Cited
`References Cited
`
`U.S. PATENT DOCUMENTS
`U.S. PATENT DOCUMENTS
`
`4,965,834 10/1990 Miller ..................................... 381194.1
`4,965,834 10/1990 Miller ................................... .. 381/941
`5,226,016
`7/1993 Christman
`367/135
`5,226,016
`7/1993 Christman ............................... 367/135
`5,627,799
`5/1997 Hoshuyama ............................ 367/121
`5,627,799
`5/1997 Hoshuyama ..
`367/121
`5,825,898 10/1998 Marash ...................................... 381192
`5,825,898 10/1998 Marash .................................... .. 381/92
`
`Primary Examiner—Forester W. Isen
`Primary Examiner~orester W. Isen
`Assistant Examiner—Jacques Saint-Surin
`Assistant Examiner-Jacques Saint-Surin
`Attorney, Agent, or Firm—Frommer Lawrence & Haug
`Attorney, Agent, or Firm~rommer Lawrence & Haug
`LLP; Thomas J. Kowalski
`LLP; Thomas J. KoWalski
`
`[57]
`[57]
`
`ABSTRACT
`ABSTRACT
`
`Interference canceling is provided for canceling, from a
`Interference canceling is provided for canceling, from a
`target signal generated from a target source, an interference
`target signal generated from a target source, an interference
`signal generated by an interference source. The beam splitter
`signal generated by an interference source. The beam splitter
`beam-splits the target signal into a plurality of band-limited
`beam-splits the target signal into a plurality of band-limited
`target signals band-limited frequency bands and beam-splits
`target signals band-limited frequency bands and beam-splits
`the interference signal into corresponding band-limited fre
`the interference signal into corresponding band-limited fre(cid:173)
`quency bands. The adaptive ?lter adaptively ?lters each
`quency bands. The adaptive filter adaptively filters each
`band-limited interference signal from each corresponding
`band-limited interference signal from each corresponding
`band-limited target signal. The inhibitor can permit the
`band-limited target signal. The inhibitor can permit the
`adaptive ?lter to adapt or change coef?cients When a signal
`adaptive filter to adapt or change coefficients when a signal(cid:173)
`to-noise ratio of the reference signal exceeds a predeter
`to-noise ratio of the reference signal exceeds a predeter(cid:173)
`mined threshold, to be determined periodically, over a
`mined threshold, to be determined periodically, over a
`signal-to-noise ratio of the main signal. The beam selector
`signal-to-noise ratio of the main signal. The beam selector
`selects at least one of a plurality of beams for adaptive
`selects at least one of a plurality of beams for adaptive
`?ltering by the adaptive ?lter representing a direction from
`filtering by the adaptive filter representing a direction from
`Which the main signal is received. The beam selector selects
`which the main signal is received. The beam selector selects
`beams simultaneously to improve accuracy and, in
`beams simultaneously to improve accuracy and, in
`particular, selects a beam having a fixed direction and a
`particular, selects a beam having a ?xed direction and a
`beam which rotates in direction. The noise gate gates the
`beam Which rotates in direction. The noise gate gates the
`main signal adaptively ?ltered by the adaptive ?lter by
`main signal adaptively filtered by the adaptive filter by
`opening the noise gate when a signal-to-noise ratio at the
`opening the noise gate When a signal-to-noise ratio at the
`near end is above a predetermined threshold and closing the
`near end is above a predetermined threshold and closing the
`noise gate when the signal-to-noise ratio at the near end is
`noise gate When the signal-to-noise ratio at the near end is
`beloW the predetermined threshold. When the target signal
`below the predetermined threshold. When the target signal
`represents speech generated at a near end of a
`represents speech generated at a near end of a
`teleconference, the adaptive filter cancels an echo present in
`teleconference, the adaptive ?lter cancels an echo present in
`the reference signal broadcast to a far end of the telecon(cid:173)
`the reference signal broadcast to a far end of the telecon
`ference.
`ference.
`
`37 Claims, 7 Drawing Sheets
`37 Claims, 7 Drawing Sheets
`
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`
`RTL607_1001-0001
`
`Realtek 607 EX. 1001
`
`

`
`u.s. Patent
`U.S. Patent
`
`Apr. 11,2000
`Apr. 11, 2000
`
`Sheet 1 0f 7
`Sheet 1 of 7
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`6,049,607
`6,049,607
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`RTL607_1001-0002
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`

`
`u.s. Patent
`U.S. Patent
`
`Apr. 11,2000
`Apr. 11, 2000
`
`Sheet 2 0f 7
`Sheet 2 of 7
`
`6,049,607
`6,049,607
`
`I
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`Tap Delay Line
`
`FIG. 2
`FIG. 2
`
`RTL607_1001-0003
`
`

`
`u.s. Patent
`U.S. Patent
`
`Apr. 11,2000
`Apr. 11, 2000
`
`Sheet 3 0f 7
`Sheet 3 of 7
`
`6,049,607
`6,049,607
`
`306ip
`306~~--------------~
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`Low Pass
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`Filter Coefficient
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`Tap Delay Line
`
`Decimation by n
`Decimation by n
`
`FIG. 3
`FIG. 3
`
`RTL607_1001-0004
`
`

`
`Apr. 11, 2000
`Apr. 11, 2000
`
`Sheet 4 of 7
`Sheet 4 0f 7
`
`6,049,607
`6,049,607
`
`u.s. Patent
`U.S. Patent
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`128 Points Delay Line
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`128 Points Buffer
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`FIG. 4
`
`RTL607_1001-0005
`
`

`
`u.s. Patent
`U.S. Patent
`
`Apr. 11,2000
`Apr. 11, 2000
`
`Sheet 5 0f 7
`Sheet 5 of 7
`
`6,049,607
`6 049 607
`a
`a
`
`500
`
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`Near End
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`516
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`SNR
`SNR
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`SNR Near
`SNR Near
`
`FIG. 5
`FIG. 5
`
`RTL607_1001-0006
`
`

`
`u.s. Patent
`U.S. Patent
`Demodulation coefficients
`Demodulation coefficients
`(cyclic buffer)
`(cyclic buffer)
`
`Apr. 11,2000
`Apr. 11, 2000
`
`Sheet 6 0f 7
`Sheet 6 of 7
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`FIG. 6
`FIG. 6
`
`RTL607_1001-0007
`
`

`
`Apr. 11, 2000
`
`Sheet 7 of 7
`
`6,049,607
`
`u.s. Patent
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`
`6,049,607
`6,049,607
`
`1
`1
`INTERFERENCE CANCELING METHOD
`INTERFERENCE CANCELING METHOD
`AND APPARATUS
`AND APPARATUS
`
`RELATED APPLICATIONS
`RELATED APPLICATIONS
`
`Reference is made to co-pending US. application Ser.
`Reference is made to co-pending U.S. application Ser.
`Nos. 08/672,899 (allowed), 09/130,923, 08/840,159,
`Nos. 08/672,899 (allowed), 09/130,923, 08/840,159,
`09/059,503 and 09/055,709, each of Which is hereby incor
`09/059,503 and 09/055,709, each of which is hereby incor(cid:173)
`porated herein by reference; and each and every document
`porated herein by reference; and each and every document
`cited in those applications, as well as each and every
`cited in those applications, as Well as each and every
`document cited herein, is hereby incorporated herein by
`document cited herein, is hereby incorporated herein by
`reference.
`reference.
`
`FIELD OF THE INVENTION
`FIELD OF THE INVENTION
`
`The present invention relates to an interference canceling
`The present invention relates to an interference canceling
`method and apparatus and, for instance, to an echo canceling
`method and apparatus and, for instance, to an echo canceling
`method and apparatus Which provides echo-canceling in full
`method and apparatus which provides echo-canceling in full
`duplex communication, especially teleconferencing commu
`duplex communication, especially teleconferencing commu(cid:173)
`nications.
`nications.
`
`BACKGROUND OF THE INVENTION
`BACKGROUND OF THE INVENTION
`
`Tele-conferencing plays an extremely important role in
`Tele-conferencing plays an extremely important role in
`communications today. The teleconference, particularly the
`communications today. The teleconference, particularly the
`telephone conference call, has become routine in business,
`telephone conference call, has become routine in business,
`in part because teleconferencing provides a convenient and
`in part because teleconferencing provides a convenient and
`inexpensive forum by Which distant business interests com
`inexpensive forum by which distant business interests com(cid:173)
`municate. Internet conferencing, Which provides a personal
`municate. Internet conferencing, which provides a personal
`forum by which the speakers can see one another, is enor(cid:173)
`forum by Which the speakers can see one another, is enor
`mously popular on the home front, in part because it brings
`mously popular on the home front, in part because it brings
`together distant family and friends Without the need for
`together distant family and friends without the need for
`expensive travel.
`expensive travel.
`In a teleconferencing system, the sounds present in a
`In a teleconferencing system, the sounds present in a
`room, hereinafter referred to as the "near-end room" such as
`room, hereinafter referred to as the “near-end room” such as
`those of a near-end speaker are received by a microphone, 35
`those of a near-end speaker are received by a microphone,
`35
`transmitted to a "far end system" and broadcast by a far-end
`transmitted to a “far end system” and broadcast by a far-end
`loudspeaker. Similarly, the far-end speaker is received by the
`loudspeaker. Similarly, the far-end speaker is received by the
`far-end microphones and transmitted to the near-end system,
`far-end microphones and transmitted to the near-end system,
`and broadcast by the near-end loudspeaker. The near-end
`and broadcast by the near-end loudspeaker. The near-end
`microphone receives the broadcasted sounds along With
`microphone receives the broadcasted sounds along with 40
`40
`their reverberations and transmits them back to the far-end,
`their reverberations and transmits them back to the far-end,
`together With the desired signals generated by, for example,
`together with the desired signals generated by, for example,
`speakers at the near-end, thereby resulting in a disturbing
`speakers at the near-end, thereby resulting in a disturbing
`echo heard by the speaker at the far-end. The far-end speaker
`echo heard by the speaker at the far-end. The far-end speaker
`will hear himself after the sound has traveled to the near-end 45
`Will hear himself after the sound has traveled to the near-end
`45
`system and back, thereby resulting in a delayed echo Which
`system and back, thereby resulting in a delayed echo which
`Will annoy and confuse the far-end speaker. The problem is
`will annoy and confuse the far-end speaker. The problem is
`compounded in video and internet conferencing systems
`compounded in video and internet conferencing systems
`Where the delay is more extremely pronounced.
`where the delay is more extremely pronounced.
`The simplest way to overcome the problem of echo is by
`The simplest Way to overcome the problem of echo is by
`blocking the near-end microphone While the far-end signal is
`blocking the near-end microphone while the far-end signal is
`broadcast by the near-end loudspeaker. Sometimes referred
`broadcast by the near-end loudspeaker. Sometimes referred
`to as “ducking”, the technique of blocking the microphone
`to as "ducking", the technique of blocking the microphone
`is effectively a half-duplex communication. Problematically,
`is effectively a half-duplex communication. Problematically,
`if the microphone is blocked for a prolonged period to avoid
`if the microphone is blocked for a prolonged period to avoid 55
`55
`transmission of the reverberations, the half-duplex commu(cid:173)
`transmission of the reverberations, the half-duplex commu
`nication becomes a significant drawback because the far-end
`nication becomes a signi?cant draWback because the far-end
`speaker Will lose too much of the near-end speaker. In the
`speaker will lose too much of the near-end speaker. In the
`video or Internet conferencing system, Where the delay
`video or Internet conferencing system, where the delay
`created by the communication lines is extreme, ducking
`created by the communication lines is extreme, ducking 60
`60
`becomes quite annoying.
`becomes quite annoying.
`A more complex method to avoid echo is to employ an
`A more complex method to avoid echo is to employ an
`echo canceling system Which measures the signals send
`echo canceling system which measures the signals send
`from the far-end and broadcast it the near-end loudspeaker,
`from the far-end and broadcast it the near-end loudspeaker,
`estimates the resulting signal present at the near-end micro
`estimates the resulting signal present at the near-end micro- 65
`65
`phone (including the reverberations) and subtracts those
`phone (including the reverberations) and subtracts those
`signals representing the echo from the near-end microphone
`signals representing the echo from the near-end microphone
`
`2
`2
`signals. The echo-free signals are then transmitted back to
`signals. The echo-free signals are then transmitted back to
`the far-end system.
`the far-end system.
`In order to reduce the echo from the near-end microphone
`In order to reduce the echo from the near-end microphone
`signal, it is required to obtain the transfer function that
`signal, it is required to obtain the transfer function that
`expresses the relationship betWeen the near-end loudspeaker
`5 expresses the relationship between the near-end loudspeaker
`signal and the reverberations as they actually appear at the
`signal and the reverberations as they actually appear at the
`near-end microphone. This transfer function depends on the
`near-end microphone. This transfer function depends on the
`relative position of the near-end loudspeaker to the near-end
`relative position of the near-end loudspeaker to the near-end
`microphone, the room structure, position of the system and
`microphone, the room structure, position of the system and
`10 even the presence of people in the room. Since it is impos(cid:173)
`even the presence of people in the room. Since it is impos
`10
`sible to predict these parameters a priori, it is preferred that
`sible to predict these parameters a priori, it is preferred that
`the echo-canceling system updates the transfer function
`the echo-canceling system updates the transfer function
`continuously in real time.
`continuously in real time.
`The adaptation process by Which the echo-canceling
`The adaptation process by which the echo-canceling
`15
`15 system is updated in real time may be an LMS (least means
`system is updated in real time may be an LMS (least means
`square) adaptive ?lter (WidroW, et al., Proc. IEEE, vol. 63,
`square) adaptive filter (Widrow, et aI., Proc. IEEE, vol. 63,
`pp. 1692-1716, Proc. IEEE, vol. 55, No. 12, December
`pp. 1692—1716, Proc. IEEE, vol. 55, No. 12, December
`1967) With the far-end signal used as the reference signal.
`1967) with the far-end signal used as the reference signal.
`The LMS ?lter estimates the interference elements (echoes)
`The LMS filter estimates the interference elements (echoes)
`20
`present in the interfered channel by multiplying the refer
`20 present in the interfered channel by multiplying the refer(cid:173)
`ence channel by a filter and subtracting the estimated
`ence channel by a ?lter and subtracting the estimated
`elements from the interfered signal. The resulting output is
`elements from the interfered signal. The resulting output is
`used for updating the ?lter coef?cients. The adaptation
`used for updating the filter coefficients. The adaptation
`process will converge when the resulting output energy is at
`process Will converge When the resulting output energy is at
`25
`25 a minimum, leaving an echo-free signal.
`a minimum, leaving an echo-free signal.
`Important to the adaptation process is the selection of the
`Important to the adaptation process is the selection of the
`siZe of the adaptation step of the ?lter coefficients. In the
`size of the adaptation step of the filter coefficients. In the
`standard LMS algorithm the step siZe is controlled by a
`standard LMS algorithm the step size is controlled by a
`predetermined adaptation coef?cient, the level of the refer
`predetermined adaptation coefficient, the level of the refer-
`30
`30 ence channel and the output level. In other words, the
`ence channel and the output level. In other Words, the
`adaptation process Will have bigger steps for strong signals
`adaptation process will have bigger steps for strong signals
`and smaller steps for Weaker signals.
`and smaller steps for weaker signals.
`A better behaved system is one in which its adaptation
`A better behaved system is one in Which its adaptation
`steps are independent of the reference channel levels. This is
`steps are independent of the reference channel levels. This is
`accomplished by normaliZing the adaptation coef?cient by
`accomplished by normalizing the adaptation coefficient by
`the reference channel energy, this method is called the
`the reference channel energy, this method is called the
`NormaliZed Least Mean Square (NLMS) as, for example,
`Normalized Least Mean Square (NLMS) as, for example,
`described in see for example "A Family of Normalized LMS
`described in see for example “A Family of Normalized LMS
`Algorithms”, Scott C. Douglas, IEEE Signal Processing
`Algorithms", Scott C. Douglas, IEEE Signal Processing
`Letters, Vol. 1, No.3, March 1994. It should be noted that
`Letters, Vol. 1, No. 3, March 1994. It should be noted that
`the energy estimator, if not designed properly, may fail to
`the energy estimator, if not designed properly, may fail to
`track When large and fast changes in the level of the
`track when large and fast changes in the level of the
`reference channel occur. Thus, the normalized coefficient
`reference channel occur. Thus, the normaliZed coef?cient
`may be too big during the transition period, and the ?lter
`may be too big during the transition period, and the filter
`coef?cient may diverge.
`coefficient may diverge.
`Another problem is that the adaptive process feeds the
`Another problem is that the adaptive process feeds the
`output back to determine the new filter coefficients. When
`output back to determine the neW ?lter coef?cients. When
`the interfering elements in the signal are less pronounced
`the interfering elements in the signal are less pronounced
`50 than the non-interfering signal, there is not much to reduce
`than the non-interfering signal, there is not much to reduce
`and the filter may diverge or converge to a wrong value
`and the ?lter may diverge or converge to a Wrong value
`Which results in signal distortions.
`which results in signal distortions.
`When properly converged, the adaptive ?lter actually
`When properly converged, the adaptive filter actually
`estimates the transfer function between the far-end loud(cid:173)
`estimates the transfer function betWeen the far-end loud
`speaker signal and the echo elements in the main channel.
`speaker signal and the echo elements in the main channel.
`However, changes in the room will effect a change in the
`HoWever, changes in the room Will effect a change in the
`transfer function and the adaptive process Will adapt itself to
`transfer function and the adaptive process will adapt itself to
`the new conditions. Sudden or quick changes, in particular,
`the neW conditions. Sudden or quick changes, in particular,
`will take the adaptive filter time to adjust for and an echo
`Will take the adaptive ?lter time to adjust for and an echo
`will be present until the filter adapts itself to the new
`Will be present until the ?lter adapts itself to the neW
`conditions.
`conditions.
`In order to improve the audio quality, sometimes a num(cid:173)
`In order to improve the audio quality, sometimes a num
`ber of microphones are used instead of a single one. This
`ber of microphones are used instead of a single one. This
`system either selects a different microphone each time
`system either selects a different microphone each time
`someone is speaking in the room or creates a directional
`someone is speaking in the room or creates a directional
`beam using a linear combination of microphones. By mul
`beam using a linear combination of microphones. By mul(cid:173)
`tiplexing the microphones or steering the directional audio
`tiplexing the microphones or steering the directional audio
`
`RTL607_1001-0009
`
`

`
`6,049,607
`6,049,607
`
`3
`3
`beam, the relationship between the loudspeaker signal and
`beam, the relationship between the loudspeaker signal and
`the audio signal obtained by the microphones can be
`the audio signal obtained by the microphones can be
`changed. Problematically, each time such a transition takes
`changed. Problematically, each time such a transition takes
`place, an echo will "leak" into the system until the new
`place, an echo Will “leak” into the system until the neW
`condition has been studied by the adaptive ?lter. To alloW
`condition has been studied by the adaptive filter. To allow
`the use of a steerable directional beam and prevent the
`the use of a steerable directional beam and prevent the
`transient echo, one can either perform continuous echo
`transient echo, one can either perform continuous echo
`canceling on each of the microphones separately or on each
`canceling on each of the microphones separately or on each
`of the microphone combinations (the combinations of
`of the microphone combinations (the combinations of
`microphones could be in?nite). HoWever, the increase in the
`microphones could be infinite). However, the increase in the 10
`10
`computation load required to perform numerous echo
`computation load required to perform numerous echo(cid:173)
`canceling systems concurrently on each of the microphones
`canceling systems concurrently on each of the microphones
`or allowable beams is not realistic.
`or alloWable beams is not realistic.
`An ef?cient echo-canceling system is needed Which Will
`An efficient echo-canceling system is needed which will
`reduce the echo drastically. HoWever, because of the large
`reduce the echo drastically. However, because of the large 15
`15
`dynamic ranges required by the microphone to be able to
`dynamic ranges required by the microphone to be able to
`pick up very loW voices, the microphone Will most likely
`pick up very low voices, the microphone will most likely
`pick up some of the residual echo as well. The residual echo
`pick up some of the residual echo as Well. The residual echo
`is most disturbing When no other signal is present but less
`is most disturbing when no other signal is present but less
`noticed When a full duplex discussion is taking place.
`noticed when a full duplex discussion is taking place.
`Another problem typical to multi-user conferencing sys
`Another problem typical to multi-user conferencing sys(cid:173)
`tems is that the background noise from several systems is
`tems is that the background noise from several systems is
`transmitted to all the participating systems and it is preferred
`transmitted to all the participating systems and it is preferred
`that this noise be reduced to a minimum. The beam forming
`that this noise be reduced to a minimum. The beam forming
`process reduces the background noise but not enough to
`process reduces the background noise but not enough to
`account for the plurality of systems.
`account for the plurality of systems.
`
`OBJECTS AND SUMMARY OF THE
`OBJECTS AND SUMMARY OF THE
`INVENTION
`INVENTION
`
`4
`4
`broadcast from a far end of the teleconference. It is preferred
`broadcast from a far end of the teleconference. It is preferred
`that the adaptive ?lter is an adaptive ?lter array With each
`that the adaptive filter is an adaptive filter array with each
`adaptive ?lter in the array ?ltering a different frequency
`adaptive filter in the array filtering a different frequency
`band. In the exemplary embodiment the adaptive ?lter
`band. In the exemplary embodiment the adaptive filter
`5 estimates a transfer function of the reference signal broad(cid:173)
`estimates a transfer function of the reference signal broad
`cast from the far end.
`cast from the far end.
`The adaptive ?lter of the present invention may further
`The adaptive filter of the present invention may further
`comprise an inhibitor. The inhibitor permits the adaptive
`comprise an inhibitor. The inhibitor permits the adaptive
`?lter to adapt (change coefficients) When a signal-to-noise
`filter to adapt (change coefficients) when a signal-to-noise
`ratio of the reference signal exceeds a predetermined thresh
`ratio of the reference signal exceeds a predetermined thresh(cid:173)
`old over a signal-to-noise ratio of the main signal.
`old over a signal-to-noise ratio of the main signal.
`Preferably, the inhibitor determines the predetermined
`Preferably, the inhibitor determines the predetermined
`threshold periodically.
`threshold periodically.
`The beam splitter of the exemplary embodiment of the
`The beam splitter of the exemplary embodiment of the
`present invention is a DFT ?lter bank using single side band
`present invention is a DFT filter bank using single side band
`modulation. Additionally, the present invention may com(cid:173)
`modulation. Additionally, the present invention may com
`prise a beam selector for selecting at least one of a plurality
`prise a beam selector for selecting at least one of a plurality
`of beams for adaptive ?ltering by the adaptive ?lter repre
`of beams for adaptive filtering by the adaptive filter repre(cid:173)
`senting a direction from Which the main signal is received.
`senting a direction from which the main signal is received.
`20 In this case, the adaptive filter updates coefficients repre(cid:173)
`In this case, the adaptive ?lter updates coef?cients repre
`senting the transform function and comprehensively stores
`senting the transform function and comprehensively stores
`the coef?cients for each beam selected by the beam selector.
`the coefficients for each beam selected by the beam selector.
`In the exemplary embodiment, the beam selector selects the
`In the exemplary embodiment, the beam selector selects the
`plurality of the beams for simultaneous adaptive ?ltering by
`plurality of the beams for simultaneous adaptive filtering by
`25
`25 the adaptive filter. Further, the beam selector may select a
`the adaptive ?lter. Further, the beam selector may select a
`beam having a fixed direction and a beam which rotates in
`beam having a ?xed direction and a beam Which rotates in
`direction.
`direction.
`The present invention may further comprise a noise gate
`The present invention may further comprise a noise gate
`for gating the main signal adaptively ?ltered by the adaptive
`30 for gating the main signal adaptively filtered by the adaptive
`?lter by opening the noise gate When a signal-to-noise ratio
`filter by opening the noise gate when a signal-to-noise ratio
`at the near end is above a predetermined threshold and
`at the near end is above a predetermined threshold and
`closing the noise gate When the signal-to-noise ratio at the
`closing the noise gate when the signal-to-noise ratio at the
`near end is belo