111111111111111111111111111111111111111111111111111111111111111111111111111
`USOO5263019A
`US005263019A
`[11] Patent Number:
`Patent Number:
`[11]
`[45] Date of Patent:
`Date of Patent:
`[45]
`
`5,263,019
`5,263,019
`Nov. 16, 1993
`Nov. 16, 1993
`
`United States Patent [191
`United States Patent [19]
`Chu
`Chu
`
`[54] METHOD AND APPARATUS FOR
`[54] METHOD AND APPARATUS FOR
`ESTIMATING THE LEVEL or ACOUSTIC
`ESTIMATING THE LEVEL OF ACOUSTIC
`FEEDBACK BETWEEN A LOUDSPEAKER
`FEEDBACK BETWEEN A LOUDSPEAKER
`AND MICROPHONE
`AND MICROPHONE
`[75]
`Inventor: Peter L. Chu, Needham, Mass.
`Inventor: Peter L. ebu, Needham, Mass.
`[75]
`[73]
`Assignee: PictureTel Corporation, Peabody,
`[73] Assignee: PictureTel Corporation, Peabody,
`Mass.
`Mass.
`[21]
`Appl. No.: 837,729
`[21] Appl. No.: 837,729
`[22]
`Filed:
`Feb. 19, 1992
`[22] Filed:
`Feb. 19, 1992
`
`OTHER PUBLICATIONS
`OTHER PUBLICATIONS
`P. L. ehu, "Quadrature Mirror Filter Design for an
`P. L. Chu, “Quadrature Mirror Filter Design for an
`Arbitrary Number of Equal Bandwidth Channels",
`Arbitrary Number of Equal Bandwidth Channels”,
`IEEE Trans. on ASSP, ASSP-33, No.1, Feb., 1985, pp.
`IEEE Trans. on ASSP, ASSP-33, No. 1, Feb., 1985, pp.
`203-218.
`203-218.
`P. L. Chu, "Fast Gaussian Random Noise Generator,"
`P. L. Chu, “Fast Gaussian Random Noise Generator,”
`IEEE Trans. ASSP, ASSP-37, No. 10, Oct., 1989, pp.
`IEEE Trans. ASSP, ASSP-37, No. 10, Oct., 1989, pp.
`1593-1597.
`l593~1597.
`D. L. Duttweiler, "A Twelve-Channel Digital Voice
`D. L. Duttweiler, “A Twelve-Channel Digital Voice
`-Echo Canceller," IEEE Transactions on Communica(cid:173)
`Echo Canceller,” IEEE Transactions on Communica
`tions, COM-26, No.5, May, 1978, pp. 647-653.
`tions, COM-26, No. 5, May, 1978, pp. 647-653.
`
`(List continued on next page.)
`(List continued on next page.)
`Primary Examiner-Douglas W. Olms
`Primary Examiner-Douglas W. Olms
`Assistant Examiner-Shick Hom
`Assistant Examiner-Shick Hom
`Attorney, Agent, or Firm-Fish & Richardson
`Attorney, Agent, or Firm—Fish & Richardson
`[57]
`ABSTRACT
`[57]
`ABSTRACT
`An improved echo cancelling device for reducing the
`An improved echo cancelling device for reducing the
`effects of acoustic feedback between a loudspeaker and
`effects of acoustic feedback between a loudspeaker and
`microphone in a communication system. The device
`microphone in a communication system. The device
`includes an adjustable filter for receiving a loudspeaker
`includes an adjustable ?lter for receiving a loudspeaker
`signal and generating in response thereto an echo esti(cid:173)
`signal and generating in response thereto an echo esti
`mation signal. The device subtracts the echo estimation
`mation signal. The device subtracts the echo estimation
`signal from the microphone signal to produce an echo
`signal from the‘ microphone signal to produce an echo
`corrected microphone signal. During periods of time
`corrected microphone signal. During periods of time
`when the microphone signal is substantially derived
`when the microphone signal is substantially derived
`from acoustic feedback between the loudspeaker and
`from acoustic feedback between the loudspeaker and
`the microphone, the device adjusts transfer characteris(cid:173)
`the microphone, the device adjusts transfer characteris
`tics of the filter to reduce the echo corrected micro(cid:173)
`tics of the ?lter to reduce the echo corrected micro
`phone signal. The improvement includes estimating
`phone signal. The improvement includes estimating
`from the adjusted transfer characteristics an energy
`from the adjusted transfer characteristics an energy
`transfer ratio representative of the ratio of the energy of
`transfer ratio representative of the ratio of the energy of
`the microphone signal to the energy of the loudspeaker
`the microphone signal to the energy of the loudspeaker
`signal. The device compares the microphone signal to
`signal. The device compares the microphone signal to
`the energy transfer ratio multiplied by the loudspeaker
`the energy transfer ratio multiplied by the loudspeaker
`signal to identify periods of time when the microphone
`signal to identify periods of time when the microphone
`signal is substantially derived from acoustic feedback
`signal is substantially derived from acoustic feedback
`between the loudspeaker and the microphone.
`. between the loudspeaker and the microphone.
`
`18 Claims, 7 Drawing Sheets
`18 Claims, 7 Drawing Sheets
`
`[63]
`[63]
`
`[511
`[51]
`[521
`[52]
`[58]
`[58]
`
`[56]
`[56]
`
`Related US. Application Data
`Related U.S. Application Data
`Continuation-impart of Ser. No. 659,579, Feb. 21, 1991,
`Continuation-in-part ofSer. No. 659,579, Feb. 21,1991,
`which is a continuation-in-part of Ser. No. 640,477,
`which is a continuation-in-part of Ser. No. 640,477,
`Jan. 11, 1991, abandoned, Continuation of Ser. No.
`Jan. 11, 1991, abandoned, Continuation of Ser. No.
`637,016, Jan. 4, 1991, abandoned.
`637,016, Jan. 4, 1991, abandoned.
`Int. CI.s ................................................ H04J I/DO
`Int. Cl.5 .............................................. .. H04J 1/00
`U.s. CI .................................... 370/32.1; 379/406;
`US. Cl. ................................. .. 370/324; 379/406;
`381/83
`381/83
`Field of Search ................. .. 370/32.l, 32; 381/46,
`Field of Search ................... 370/32.1, 32; 381/46,
`381/47, 66, 71, 83; 379/345, 392, 410, 406
`381/47,66,71,83; 379/345, 392,410,406
`References Cited
`References Cited
`U.S. PATENT DOCUMENTS
`U.S. PATENT DOCUMENTS
`4,064,378 12/1977 Kitayama et al. .............. .. 179/1702
`4,064,378 12/1977 Kitayama et aI. ................ 179/170.2
`4,126,770 11/1978 Tamura et aI. ................... 179/170.2
`4,126,770 1l/1978 Tamura et al. . . . . . .
`. . . .. 179/1702
`4,232,400 11/1980 Yamamoto et al.
`...... .. 455/305
`4,232,400 11/1980 Yamamoto et aI. ................ 455/305
`4,479,036 l0/l984 Yamamoto et al.
`179/1702
`4,479,036 10/1984 Yamamoto et al. ............. 179/170.2
`4,525,856 6/1985 Admiraal et al.
`.... .. 381/93
`4,525,856 6/1985 AdmiraaJ et aI. ..................... 381/93
`4,539,675 9/1985 Fisher .... ..
`370/32.l
`4,539,675 9/1985 Fisher ................................. 370/32.1
`4,589,137 5/1986 Miller .................................... 381/94
`4,589,137 5/1986 Miller ................ ..
`. 381/94
`4,633,046 12/1986 Kitayama etal.
`370/321
`4,633,046 12/1986 Kitayama et aJ .................. 370/32.1
`4,658,426 4/1987 Chabries et al. ...................... 381/94
`. . . .. 381/94
`4,658,426 4/1987 Chabries et a1. . . . .
`4,677,676 6/1987 Eriksson ................................ 381/71
`381/71
`4,677,676 6/1987 Eriksson ........ ..
`4,677,677 6/1987 Eriksson ................................ 381/71
`4,677,677 6/ 1987 Eriksson ........ ..
`381/71
`4,683,590 7/1987 Miyoshi et a1
`381/71
`4,683,590 7/1987 Miyoshi et al. ....................... 381/71
`4,769,847 9/1988 Taguchi ................................ 381/94
`4,837,834 6/1989 Allie ...................................... 381/71
`4,965,823 10/1990 Nakagawa et a]
`. 379/406
`4,965,823 10/1990 Nakagawa et aI. ................. 379/406
`5,117,418 5/1992 Chaffee et aI. ..................... 370/32.1
`5,117,418 5/1992 Chaffee et al. ............... .. 370/321
`FOREIGN PATENT DOCUMENTS
`FOREIGN PATENT DOCUMENTS
`2191363 10/1986 United Kingdom .
`2191363 10/1986 United Kingdom.
`
`4,769,847 9/ 1988 Taguchi . . . . . . .
`
`. . . .. 381/94
`
`4,837,834 6/1989 Allie . . . . . . . . . . . . . . . . .
`
`. . . .. 381/71
`
`RTL607_1022-0001
`
`Realtek 607 Ex. 1022
`
`

`
`5,263,019
`5,263,019
`Page 2
`Page 2
`
`OTHER PUBLICATIONS
`OTHER PUBLICATIONS
`
`S. Gay, “Fast Converging Subbancl Acoustic Echo
`S. Gay, "Fast Converging Subband Acoustic Echo
`Cancellation Using RAP on the WE® DSP/16A,”
`Cancellation Using RAP on the WE@ DSP/16A,"
`Proceedings of ICASSP, 1990, pp. 1141-1144.
`Proceedings of ICASSP, 1990, pp. 1141-1144.
`A. Gilloire, “Experiments with Sub-band Acoustic
`A. Gilloire, "Experiments with Sub-band Acoustic
`Echo Cancellers for Teleconferencing,” Proceedings of
`Echo Cancellers for Teleconferencing," Proceedings of
`ICASSP, 1987, pp. 2141-2144.
`ICASSP, 1987, pp. 2141-2144.
`M. J. Gingell, B. G. Hay, and L. D. Humphrey, “A
`M. J. Gingell, B. G. Hay, and L. D. Humphrey, "A
`Block Mode Update Echo Canceller Using Custon
`Block Mode Update Echo Canceller Using Custon
`LSI," GLOBECOM Conference Record, vol. 3, Nov.,
`LS1,” GLOBECOM Conference Record, vol. 3, Nov.,
`1983, pp. 1394-1397.
`1983, pp. 1394-1397.
`D. G. Messerschmitt, "Echo Cancellation in Speech
`D. G. Messerschmitt, “Echo Cancellation in Speech
`and Data Transmission," IEEE Journal on Selected
`and Data Transmission,” IEEE Journal on Selected
`Topics in Communications, IEEE Journal on Selected
`Topics in Communications, IEEE Journal on Selected
`Topics in Communications, SAC-2 No. 2, Mar., 1984,
`Topics in Communications, SAC-2 No.2, Mar., 1984,
`pp. 283-296.
`pp. 283-296.
`
`Ying G. Tao, Kevin D. Kolwicz, C. W. K. Gritton, and
`Ying G. Tao, Kevin D. Kolwicz, C. W. K. Gritton, and
`Donald D. Duttweiler, "A Cascadable VLSI Echo
`Donald D. Duttweiler, “A Cascadable VLSI Echo
`Canceller", IEEE Journal on Selected Topics in Com(cid:173)
`Canceller", IEEE Journal on Selected Topics in Com
`munications, SAC-2, No.2, Mar., 1984, pp. 297-303.
`munications, SAC-2, No. 2, Man, 1984, pp. 297-303.
`S. Yamamoto, S. Kitayama, J. Tamura, and H. Ishigami,
`S. Yamamoto, S. Kitayama, J. Tamura, and H. Ishigami,
`"An Adaptive Echo Canceller with Linear Predictor,"
`“An Adaptive Echo Canceller with Linear Predictor,”
`The Transactions of the IECE of Japan, vol. E62, No.
`The Transactions of the IECE of Japan, vol. E62, No.
`12, Dec., 1979, pp. 851-857.
`12, Dec., 1979, pp. 851-857.
`R. Frenzel and M. E. Hennecke, "A Robust Echo Com(cid:173)
`R. Frenzel and M. E. Hennecke, “A Robust Echo Com
`pensator: Implementation & Realtime Measurements",
`pensator: Implementation & Realtime Measurements”,
`IEEE ASSP Workshop on Applications on Signal Pro(cid:173)
`IEEE ASSP Workshop on Applications on Signal Pro
`cessing to Audio & Acoutics, Oct. 20-23, 1991, New
`cessing to Audio & Acoutics, Oct. 20-23, 1991, New
`Paltz, N.Y.
`Paltz, NY.
`Hua Ye and Bo-Xiu Wu, "A New Double-Talk Detec(cid:173)
`Hua Ye and Bo-Xiu Wu, “A New Double-Talk Detec
`tion Algorithm Based on the Orthogonality Theorm",
`tion Algorithm Based on the orthogonality Theorm”,
`IEEE Transaction on Communications, vol. 39, No. 11,
`.IEEE Transaction on Communications, vol. 39, No. 11,
`Nov. 1991, pp. 1542-1545.
`Nov. 1991, pp. 1542-1545.
`
`RTL607_1022-0002
`
`

`
`u.s. Patent
`
`Nov. 16, 1993
`
`Sheet 1 of 7
`
`5,263,019
`
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`
`RTL607_1022-0003
`
`

`
`u.s. Patent
`US. Patent
`
`Nov. 16, 1993
`Nov. 16, 1993
`
`Sheet 2 of 7
`Sheet 2 of 7
`
`5,263,019
`5,263,019
`
`• • •
`~
`'-
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`
`RTL607_1022-0004
`
`

`
`u.s. Patent
`
`Nov. 16, 1993
`
`Sheet 3 of 7
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`5,263,019
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`RTL607_1022-0005
`
`

`
`u.s. Patent
`US. Patent
`
`Nov. 16, 1993
`Nov. 16, 1993
`
`Sheet 4 of 7
`Sheet 4 of 7
`
`5,263,019
`5,263,019
`
`JII
`Nn· /Sn(iJ/
`AGE-g
`TENP-g
`En(iJ - NnoNn
`
`.-----&.--'0 JIG
`
`WIN/Mi
`
`FIG.4A
`FIG. 4A
`
`FIG.4B
`C? m FIG. 415’
`
`mm: /s,, (11/ _
`
`Nn • TENP
`AGE· L,
`TENP· 0
`En (0- Nn oNn
`
`w m m;
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`
`RTL607_1022-0006
`
`

`
`u.s. Patent
`
`Nov. 16, 1993
`
`Sheet 5 of 7
`
`5,263,019
`
`. - - - - - -........ S'n (j)" G·D· Sn(i}
`
`110
`
`EKABLE TAP I'EIGHT
`ADJUSTNEKT
`
`DISABLE TAP
`If EIGHT ADJUSTIIENT
`
`116
`
`120
`
`flECONPUTE G AS
`fOLLOII'S:
`I" L-I
`
`r (hfl) -hI /-2)) 2
`
`lIt!
`
`110
`
`FIG. 5
`
`RTL607_1022-0007
`
`

`
`u.s. Patent
`US. Patent
`
`Nov. 16, 1993
`Nov. 16, 1993
`
`Sheet 6 of 7
`Sheet 6 of 7
`
`5,263,019
`5,263,019
`
`CPNI'IITE KEJlEKBEIUTIPN ESTINATE
`
`III
`
`/ • L-I
`1: (!J(/}-1I(/-1))2
`/. P
`
`NP
`
`FIG. 6
`
`RTL607_1022-0008
`
`

`
`u.s. Patent
`US. Patent
`
`Nov. 16, 1993
`Nov. 16, 1993
`
`Sheet 7 of 7
`Sheet 7 of 7
`
`5,263,019
`5,263,019
`
`41tJ '-.....
`
`41/ '--......,.
`
`SELECT THE SAIIPiES {)f THE BAND
`LlIIITED ECHtJ CtJHHECTED IIICHtJPHtJNE
`SICNAL lin (i) fHtJlI THE LAST TlftJ
`SECtJNDS
`.. ,
`1
`
`SECIIENT THE SELECTED SAIIPLES
`INTtJ ItJtJ BLtJCtS, 'EACH BLtJCt
`CtJrEHINC A /tJ msec TillE PEHIOD
`
`.. ,
`1
`414 '-- CALCULATE THE ArEHACE ENEHcr
`tJf lin (i) tJrEH EACH BLtJCt
`.. ,
`1
`41G -- ENEHcr tJf THIS BLtJet AS THE ENEHcr
`
`SELECT THE BLOCt IfITH THE
`IIINIIIUII ENEHcr AND USE THE
`
`Of THE ESTIIIATE Of ENEHcr Of
`THE BACtCHOUND NOISE IN BAND n
`tJf THE IIICHtJPHtJNE SICNAL
`
`FIG. 7
`FIG. 7
`
`RTL607_1022-0009
`
`

`
`1
`1
`
`METHOD AND APPARATUS FOR ESTIMATING
`METHOD AND APPARATUS FOR ESTIMATING
`THE LEVEL OF ACOUSTIC FEEDBACK
`- THE LEVEL OF ACOUSTIC FEEDBACK
`BETWEEN A LOUDSPEAKER AND
`BETWEEN A LOUDSPEAKER AND
`MICROPHONE
`MICROPHONE
`
`5,263,019
`5,263,019
`2
`2
`Electrically simulating the acoustic feedback is diffi
`Electrically simulating the acoustic feedback is diffi(cid:173)
`cult since the acoustic feedback is determined by the
`cult since the acoustic feedback is determined by the
`acoustic characteristics of the room containing the mi(cid:173)
`acoustic characteristics of the room containing the mi
`crophone and speaker. This is complicated by variations
`crophone and speaker. This is complicated by variations
`S in the acoustic characteristics of different rooms and by
`in the acoustic characteristics of different rooms and by
`the dramatic changes in a given room's characteristics
`the dramatic changes in a given room’s characteristics
`which occur if the microphone or loudspeaker is
`This is a continuation-in-part of co-pending U.S. ap-
`which occur if the microphone or loudspeaker is
`This is a continuation-in-part of co-pending U.S. ap
`moved, or if objects are moved in the room.
`plication Ser. No. 07/659,579, filed Feb. 21,1991 which
`plication Ser. No. 07/659,579, ?led Feb. 21, 1991 which
`moved, or if objects are moved in the room.
`To compensate for the changing characteristics of the
`To compensate for the changing characteristics of the
`is a continuation-in-part of U.S. application Ser. No.
`is a continuation-in-part of U.S. application Ser. No.
`room, many echo cancellation devices model the
`640,477, filed Jan. 11, 1991 (now abandoned) which is a 10 room, many echo cancellation devices model the
`640,477, ?led J an. 11, 1991 (now abandoned) which is a
`room’s characteristics with an adaptive ?lter which
`continuation of U.S. application Ser. No. 637,016 filed
`room's characteristics with an adaptive filter which
`continuation of U.S. application Ser. No. 637,016 ?led
`adjusts with changes in the room. More speci?cally, the
`Jan. 4, 1991 (now abandoned).
`adjusts with changes in the room. More specifically, the
`Jan. 4, 1991 (now abandoned).
`electric signal used to drive the telephone’s loudspeaker
`electric signal used to drive the telephone's loudspeaker
`BACKGROUND OF THE INVENTION
`BACKGROUND OF THE INVENTION
`is applied to a stochastic gradient least-means-squares
`is applied to a stochastic gradient least-means-squares
`adaptive ?lter whose tap weights are set to estimate the
`The invention relates generally to reducing unwanted IS adaptive filter whose tap weights are set to estimate the
`The invention relates generally to reducing unwanted
`room’s acoustic response. The output of the ?lter, be
`audio or acoustic feedback in a communication system,
`room's acoustic response. The output of the filter, be-
`audio or acoustic feedback in a communication system,
`lieved to estimate the acoustic echo, is then subtracted
`and particularly to an adaptive acoustic echo cancella-
`lieved to estimate the acoustic echo, is then subtracted
`and particularly to an adaptive acoustic echo cancella
`from the microphone signal to eliminate the component
`tion device for suppressing acoustic feedback between
`from the ~icrophone. signal to. eliminate the co~ponent
`tion device for suppressing acoustic feedback between
`of the microphone signal derived from acoustic feed
`of the Dllcrophone ~Ignal denved f~0f!' a~ustlc feed-
`the loudspeaker and microphone of a telephone unit in
`the loudspeaker and microphone of a telephone unit in
`back. The resultant “echo corrected” signal is then sent
`a teleconferencing system. The telephone unit of a typi- 20 bac~. The resultant echo corrected sl~al ~s then sent
`a teleconferencing system. The telephone unit of a typi
`to listeners at the far end of the communication system.
`cal audio conferencing system includes a loudspeaker
`to hsteners at the far end o.f the commuOicatlOn s~stem.
`cal audio conferencing system includes a loudspeaker
`To assure that the adaptive ?lter accurately estimates
`To ass~re that the adaptlv~ filter a~curately estimates
`for broadcasting an incoming telephone signal into an
`for broadcasting an incoming telephone signal into an
`the room’s response, the device monitors the echo cor
`the roof!' s respon~e, the deVice moOitors th~ echo c?r-
`entire room. Similarly, the telephone's microphone is
`entire room. Similarly, the telephone’s microphone is
`rected signal. During moments when no one is speaking
`~ected Slgn~l. Dunng moments ~hen no one. IS sp:akmg
`typically designed to pick up the voice of any person
`typically designed to pick up the voice of any person
`into the microphone, the adaptive ?lter adjusts its tap
`25
`within the room and transmit the voice to a remote 25 mt~ the microphone, the adaptive filter adjusts Its tap
`within the room and transmit the voice to a remote
`weights such that the energy of the echo corrected
`weights such that the energy of the echo corrected
`d f th
`.
`t'
`ystem
`t th "
`telephone at the far end of the communication system.
`I h
`te ep one a
`e ,ar en 0
`e commuOica Ion s
`.
`.
`I .
`. .
`I h
`h
`f h
`h
`signal is at a minimum. In theory, the energy of the echo
`fi _
`.
`U \'k
`I h d h Id t I h
`t
`signa IS at a mimmum. n t eory, t e energy 0 t e ec 0
`Unlike conventional hand held telephone sets, confer
`e ep one ~e s, c~~ e~
`e
`n I e conventlo!'a an
`corrected signal is minimized when the adaptive filter
`corrected signal is minimized when the adaptive ?lter
`ence telephone units are prone to acoustic feedback
`ence telephone uOits are pro.ne to ac?ustlc fee ac
`removes from the microphone signal an accurate rep-
`removes from the microphone signal an accurate rep
`between the loudspeaker unit and microphone. For
`between the l?uds~eaker U~lt a.nd mlcropho!,~. For 30 lica of the acoustic feedback. However, the adaptive
`lica of the acoustic feedback. However, the adaptive
`example, a voice signal .which is broadcast into the
`example, a vOice Signal .w~lch IS bro~dcast m 0 the
`process must be disabled whenever a person speaks into
`process must be disabled whenever a person speaks into
`room by the loudspeaker unit may be picked up by the
`rO?m by the loudspeaker: uOit may be picked up by the
`the microphone. Otherwise, the unit will attempt to
`the microphone. Otherwise, the unit will attempt to
`microphone and transmitted back over the telephone
`microphone and transmitted back over the telephone
`adjust the tap weights in an effort to eliminate the
`adjust the tap weights in an effort to eliminate the
`lin~s. As a result, persons at the f~r en~ of the communi-
`speech.
`lines. As a result, persons at the far end of the communi
`speech.
`cation system hear an echo of their voice. The echo lags
`cation syst~m h~ar an echo of their .vOlce. Th.e echo lags 35 Accordingly, echo cancellation devices which em-
`Accordingly, echo cancellation devices which em
`35
`the person’s voice by the round trip delay time for the
`th~ per?on s VOlC~ by the round t~p delay tln:'e for the
`ploy adaptive filters for estimating a room's response
`ploy adaptive ?lters for estimating a room’s response
`voice signal. Typically, the echo is more noticeable as
`vOice signal. Typically, the :cho ~s more noticeable .as
`typically include a "double-talk" detection device
`typically include a “double-talk” detection device
`the lag between the person’s voice and the echo in
`the lag between. the p~rs~n s vo!ce and the ec~o I?-
`which monitors the microphone signal to determine
`which monitors the microphone signal to determine
`creases. Accordingly, it is particularly annoying in
`c~eases. Accor~mgly, It IS pa!tlcularly .annoym~ m
`when a person is speaking into the microphone. One
`when a person is speaking into the microphone. One
`video conferencing systems which transmit both video
`Video conferencmg systems which transmit both Video 40 such detector, described in D. L. Duttweiler, "A
`such detector, described in D. L. Duttweiler, “A
`40
`and audio information over the same telephone lines.
`and audio information over the same telephone lines.
`Twelve Channel Digital Echo Canceller", IEEE Trans.
`Twelve Channel Digital Echo Canceller”, IEEE Trans.
`The additional time required to transmit video data
`The additional time required to transmit video data
`On Comm., Volcom-26, No.5, May 1978, declares
`On Comm, Volcom-26, No. 5, May 1978, declares
`increases the round trip delay of the audio signal,
`increases the round trip delay of the audio signal,
`double talk when a sample of the microphone signal is
`double talk when a sample of the microphone signal is
`thereby extending the lag between a person’s voice and
`thereby extending the lag between a person's voice and
`greater than or equal to one-half the largest sample of
`greater than or equal to one-half the largest sample of
`the echo.
`the echo.
`45. the loudspeaker signal within the last N samples, where
`the loudspeaker signal within the last N samples, where
`45.
`Many conference telephones avoid echo by allowing
`N is a constant equal to the maximum delay between the
`Many conference telephones avoid echo by allowing
`N is a constant equal to the maximum delay between the
`only half duplex communication (that is, by allowing
`only half duplex communication (that is, by allowing
`loudspeaker and the microphone. If someone is speak-
`loudspeaker and the microphone. If someone is speak
`communication over the phone line to occur in only one
`communication over the phone line to occur in only one
`ing into the microphone, the energy of the microphone
`ing into the microphone, the energy of the microphone
`direction at a time) thereby preventing feedback. For
`direction at a time) thereby preventing feedback. For
`signal is typically at least half that of the loudspeaker
`signal is typically at least half that of the loudspeaker
`example, when the loudspeaker unit is broadcasting a
`example, when the loudspeaker unit is broadcasting a SO signal. Accordingly, the above described double talk
`signal. Accordingly, the above described double talk
`voice, the telephone disables the microphone to prevent
`detector properly concludes that someone is speaking
`voice, the telephone disables the microphone to prevent
`detector properly concludes that someone is speaking
`the loudspeaker signal from being fed back by the mi
`the loudspeaker signal from being fed back by the mi-
`into the microphone and disables the adaptive filter
`into the microphone and disables the adaptive ?lter
`crophone.
`crophone.
`from adjusting its taps.
`from adjusting its taps.
`While a half duplex system avoids echo, it often cuts
`If the loudspeaker and microphone are far apart from
`While a half duplex system avoids echo, it often cuts
`If the loudspeaker and microphone are far apart from
`off a person’s voice in mid-sentence. For example, when
`off a person's voice in mid-sentence. For example, when SS each other, the microphone includes little or no acous-
`each other, the microphone includes little or no acous
`55
`both parties'speak simultaneously, the telephone unit
`both parties' speak simultaneously, the telephone unit
`tic feedback from the loudspeaker. Further when some-
`tic feedback from the loudspeaker. Further when some
`allows communication in only one direction, thereby
`allows communication in only one direction, thereby
`one is speaking softly into the microphone, the energy
`one is speaking softly into the microphone, the energy
`clipping the voice of one party.
`clipping the voice of one party.
`of the soft voice component of the microphone signal is
`of the soft voice component of the microphone signal is
`Some loudspeaker telephones employ echo cancella
`Some loudspeaker telephones employ echo cancella-
`not alone greater than half the energy of loudspeaker
`not alone greater than half the energy of loudspeaker
`tion in an attempt to allow full-duplex communication 60 signal. Accordingly, the above described doubletalk
`tion in an attempt to allow full-duplex communication
`signal. Accordingly, the above described doubletalk
`60
`detector falsely concludes that no one is speaking into
`without echo. Conventional echo cancellation devices
`without echo. Conventional echo cancellation devices
`detector falsely concludes that no one is speaking into
`attempt to remove from the microphone signal the com-
`the microphone and therefore enables the adaptive filter
`attempt to remove from the microphone signal the com
`the microphone and therefore enables the adaptive ?lter
`ponent believed to represent the acoustic feedback.
`to adjust its taps. The filter accordingly begins adjusting
`to adjust its taps. The filter accordingly begins adjusting
`ponent believed to represent the acoustic feedback.
`More specifically, these devices prepare an electric
`the taps in an effort to reduce the echo-corrected micro-
`More speci?cally, these devices prepare an electric
`the taps in an effort to reduce the echo-corrected micro
`signal which simulates the acoustic feedback between 65 phone signal to zero. Thus, by falsely concluding that
`signal which simulates the acoustic feedback between
`phone signal to zero. Thus, by falsely concluding that
`65
`the loudspeaker and the microphone. This electric sig
`no one is speaking into the microphone, the device
`the loudspeaker and the microphone. This electric sig-
`no one is speaking into the microphone, the device
`nal is subtracted from the microphone signal in an at-
`begins to cut off the voice of the person speaking into
`nal is subtracted from the microphone signal in an at
`begins to cut off the voice of the person speaking into
`the microphone.
`tempt to remove the echo.
`the microphone.
`tempt to remove the echo.
`
`RTL607_1022-0010
`
`

`
`I=L-\
`l:
`«h.(l) -
`I=P
`
`hn<1 - 2»2
`
`5,263,019
`5,263,019
`4
`4
`3
`3
`signal to the room reverberation estimate. During peri
`If the loudspeaker is placed close to the microphone,
`If the loudspeaker is placed close to the microphone,
`signal to the room reverberation estimate. During peri(cid:173)
`the energy of the microphone signal may exceed half
`the energy of the microphone signal may exceed half
`ods of time when the echo corrected microphone signal
`ods of time when the echo corrected microphone signal
`the energy of the loudspeaker signal regardless of
`the energy of the loudspeaker signal regardless of
`is less than the room reverberation estimate, the device
`is less than the room reverberation estimate, the device
`whether someone is speaking into the microphone. For
`whether someone is speaking into the microphone. For
`enables the signal clipper to attenuate the echo cor(cid:173)
`enables the signal clipper to attenuate the echo cor
`example, if the room includes ambient background 5
`example, if the room includes ambient background
`rected microphone signal. More speci?cally, for em
`rected microphone signal. More specifically, for em(cid:173)
`noise such as generated by a fan, the microphone picks
`noise such as generated by a fan, the microphone picks
`bodiments in which the adjustable ?lter is a digital ?lter,
`bodiments in which the adjustable filter is a digital filter,
`up this sound and adds it to the substantial acoustic
`up this sound and adds it to the substantial acoustic
`the device calculates the room reverberation estimate
`the device calculates the room reverberation estimate
`feedback caused by the close proximity of the micro(cid:173)
`feedback caused by the close proximity of the micro
`according to the formula:
`according to the formula:
`phone and loudspeaker. Accordingly, the energy of the
`phone and loudspeaker. Accordingly, the energy of the
`microphone signal may exceed the half of the energy of 10
`microphone signal may exceed the half of the energy of
`the loudspeaker signal even when the loudspeaker is the
`the loudspeaker signal even when the loudspeaker is the
`only source of speech in the room. In this case, the
`only source of speech in the room. In this case, the
`above described doubletalk detector falsely concludes
`above described doubletalk detector falsely concludes
`that someone is always speaking into the microphone
`that someone is always speaking into the microphone
`and therefore permanently disables the adaptive ?lter
`and therefore permanently disables the adaptive filter 15 where REn(i) is the room reverberation estimate in
`where RE,,(i) is the room reverberation estimate in
`from adjusting its taps.
`band n at tap i, EI is the loudspeaker energy value, L is
`from adjusting its taps.
`band n at tap i, E! is the loudspeaker energy value, L is
`Therefore, one object of the present invention is to
`the number of taps for the filter, P is a constant which
`Therefore, one object of the present invention is to
`the number of taps for the ?lter, P is a constant which
`provide an acoustic echo cancellation device which
`is slightly greater than the propagation time (in samples)
`provide an acoustic echo cancellation device which
`is slightly greater than the propagation time (in samples)
`includes an improved double talk detector for determin
`~ncludes an improve.d doubl~ tal.k detector.for determin-
`for the acoustic signal to propagate from the loud-
`for the acoustic signal to propagate from the loud
`ing when someone is speaking into the microphone.
`mg when someone IS speakmg mto the microphone.
`20 speaker to the microphone, and hn(j) is the tap value of
`speaker to the microphone, and h,,(j) is the tap value of
`20
`?lter tap j in band it (see also Equation 10 supra).
`SUMMARY OF THE INVENTION
`filter tap j in band n (see also Equation 10 supra).
`SUMMARY OF THE INVENTION
`Other objects, features and advantages of the inven
`Other objects, features and advantages of the inven(cid:173)
`The invention relates to an improved echo cancelling
`The invention relates to an improved echo cancelling
`tion are apparent from the following description of
`tion are apparent from the following description of
`device for reducing the effects of acoustic feedback
`device for reducing the effects of acoustic feedback
`particular preferred embodiments taken together with
`particular preferred embodiments taken together with
`between a loudspeaker and microphone in a communi- 25
`between a loudspeaker and microphone in a communi
`the drawings.
`25
`the drawings.
`cation system. The device includes an adjustable filter
`cation system. The device includes an adjustable ?lter
`for receiving a loudspeaker signal and generating in
`for receiving a loudspeaker signal and generating in
`BRIEF DESCRIPTION OF THE DRAWINGS
`BRIEF DESCRIPTION OF THE DRAWINGS
`response thereto an echo estimation signal. The device
`response thereto an echo estimation signal. The device
`FIG. 1 is a block diagram of an echo cancellation
`FIG. 1 is a block diagram of an echo cancellation
`subtracts the echo estimation signal from the micro(cid:173)
`subtracts the echo estimation signal from the micro
`device.
`device.
`’
`phone signal to produce an echo corrected microphone
`phone signal to produce an echo corrected microphone 30
`FIG.