CA1240431A - Speech additive distribution equipment for conferencing system - Google Patents
Speech additive distribution equipment for conferencing systemInfo
- Publication number
- CA1240431A CA1240431A CA000503048A CA503048A CA1240431A CA 1240431 A CA1240431 A CA 1240431A CA 000503048 A CA000503048 A CA 000503048A CA 503048 A CA503048 A CA 503048A CA 1240431 A CA1240431 A CA 1240431A
- Authority
- CA
- Canada
- Prior art keywords
- gain
- loss
- predominant
- output
- level
- 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.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B3/00—Line transmission systems
- H04B3/02—Details
- H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/42—Systems providing special services or facilities to subscribers
- H04M3/56—Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/002—Applications of echo suppressors or cancellers in telephonic connections
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M3/00—Automatic or semi-automatic exchanges
- H04M3/42—Systems providing special services or facilities to subscribers
- H04M3/56—Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities
- H04M3/568—Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities audio processing specific to telephonic conferencing, e.g. spatial distribution, mixing of participants
Abstract
Abstract of the Disclosure A speech additive distribution equipment for a telephone conference is disclosed. The speech additive distribution equipment comprises a channel signal processing unit assigned to at least three channels. Each channel signal processing circuit comprises an echo canceller to cancel an echo signal from the transmitting side fed back to the receiving side, an amplifier and attenuator circuits to adjust levels of an output of the echo canceller and a transmitting signal transmitted through the channel signal processing circuit, an ERL
determining circuit to determine an echo cancellation on the basis of the output from the echo canceller and a signal level on the transmitting side, and a gain/loss computing circuit to compute a loss in a predominant voice condition and a gain and a loss in an inferior voice condition. The speech additive distribution equipment further comprises additive distribution circuits each operative to add the outputs of the amplifier circuits provided in the channel signal processing circuits except for the one assigned to itself, and a predominant channel detection unit for detecting a predominant channel and inferior channels on the basis of output levels of the amplifier circuits to suitably control the gain and loss of each channel according to the predominant and inferior voice conditions. Thus, this equipment makes it possible to prevent "singing" due to the variation of the cancellation with time.
determining circuit to determine an echo cancellation on the basis of the output from the echo canceller and a signal level on the transmitting side, and a gain/loss computing circuit to compute a loss in a predominant voice condition and a gain and a loss in an inferior voice condition. The speech additive distribution equipment further comprises additive distribution circuits each operative to add the outputs of the amplifier circuits provided in the channel signal processing circuits except for the one assigned to itself, and a predominant channel detection unit for detecting a predominant channel and inferior channels on the basis of output levels of the amplifier circuits to suitably control the gain and loss of each channel according to the predominant and inferior voice conditions. Thus, this equipment makes it possible to prevent "singing" due to the variation of the cancellation with time.
Description
Specification Title of the Invention Speech Additi~e Distribution ]Equipment For Conferencing Syste~m Back roun~ of the Invention The present invention relates to a speech additive distributlon equipment using an echo canceller used in speech conferences etc~
In speech conerences, there has been used additive distributiQn e~uipment to add and synthesize speech signals transmitted from a plurality of con~erence attendants to transmi~ the synthesis speech signals to the respective conference attendants.
In such speech conferences/ for the purpose of preventing a voice of the conference attendant himselE
from being fed back to a telephone receiver during con~ersa~ion, a technique is employed to add only speech signals transmitted from o~her conference attendants except for the speech signal from the concerne~ conference attendan~ itself. Hitherto, circuit arrangement using an echo canceller has been known as such an additlve : di~tribution equipment.
: For instance, conference telephone system as shown in the Japanese Patent Laid-open No, 57-133754 comprises echo cancellers to cancel hn echo signal fed back via ~ hybrid adapted ~or converting from 2-wire to ,~
:31 2~3~.
4-wire operation, additive distribution circuits, each being operative to add speech signals of channels except for ~he one assigned to itself to deliver the speech signals thus added to ~he receiver side of the conference attendant, and overload protecting circuits operative to controL outputs of said additive di~tribution circuits so that overload condition does not occur in each receivin~
path of said echo cancellers and 4-wire transmission paths.
This conference telephone system can provide following advantages: (1) There is no possibility that the transmission path is in overload cnndition. (2) Received sound volume is not lowered. (3) Echo loss is not d~graded, thus making it possible to prevent ~'singingn.
14) Excellent speech quality can be obtained.
EIowever, the drawback with such an additive distribution equipment using the above-mentioned echo canceller is that echo cancellation or echo rejection level ~referred to E~L hereinater) o~ the echo canceller varies with time, with the result that "singing" due ~o ~0 the variation; o~ the cancellation with time cannot be avoided.
Summary of the Invention An object of the present invention is to provid~
a speech additive distribution equipment fo~ a ;~ 2S conferencil!g system which~makes i~ poss1ble to pr-event singing~ caused by changes of echo cancellation wi~h time.
Another object of the present invention is to
In speech conerences, there has been used additive distributiQn e~uipment to add and synthesize speech signals transmitted from a plurality of con~erence attendants to transmi~ the synthesis speech signals to the respective conference attendants.
In such speech conferences/ for the purpose of preventing a voice of the conference attendant himselE
from being fed back to a telephone receiver during con~ersa~ion, a technique is employed to add only speech signals transmitted from o~her conference attendants except for the speech signal from the concerne~ conference attendan~ itself. Hitherto, circuit arrangement using an echo canceller has been known as such an additlve : di~tribution equipment.
: For instance, conference telephone system as shown in the Japanese Patent Laid-open No, 57-133754 comprises echo cancellers to cancel hn echo signal fed back via ~ hybrid adapted ~or converting from 2-wire to ,~
:31 2~3~.
4-wire operation, additive distribution circuits, each being operative to add speech signals of channels except for ~he one assigned to itself to deliver the speech signals thus added to ~he receiver side of the conference attendant, and overload protecting circuits operative to controL outputs of said additive di~tribution circuits so that overload condition does not occur in each receivin~
path of said echo cancellers and 4-wire transmission paths.
This conference telephone system can provide following advantages: (1) There is no possibility that the transmission path is in overload cnndition. (2) Received sound volume is not lowered. (3) Echo loss is not d~graded, thus making it possible to prevent ~'singingn.
14) Excellent speech quality can be obtained.
EIowever, the drawback with such an additive distribution equipment using the above-mentioned echo canceller is that echo cancellation or echo rejection level ~referred to E~L hereinater) o~ the echo canceller varies with time, with the result that "singing" due ~o ~0 the variation; o~ the cancellation with time cannot be avoided.
Summary of the Invention An object of the present invention is to provid~
a speech additive distribution equipment fo~ a ;~ 2S conferencil!g system which~makes i~ poss1ble to pr-event singing~ caused by changes of echo cancellation wi~h time.
Another object of the present invention is to
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provide a speech additi.ve distribution equipment for a conferericing system which has a function to discriminate between a predominant. or voiced channel and o~her inerior or unvoiced channels in terms of levels of received speech signals to suitably control ~he gain and loss of each channel according to the predominant and inferior voice conditj.ons~
A further object of the present invention is to provide a speech additive distribution equipment Eor a conferencing sys~em wherein when the equipment is applied to a speech conferencing system having different channel losses, the equipment can promptly perform balance between respective channels.
According to the present invention, there is provided a speech adclitive distribution equipment for conferencing system comprising: a channel signal processing means comprising at least three channel signal processing circuits, each channel ~ignal processi~g : circuit including a receiving side for receiving a channel . 20 ~signal, a transmitting side Eor transmitting the channel :~ signal, an echo cance1ler for canceling an echo signal fed ; b~ek ~o said receiving side from said transmitting side, means for adjusting levels oE an output of the echo cancelIer and a ~ransmittin~ signal transmittecl ~hrough the~transmitting fiide of the channel signal processing eircuitr ERL determining means for determining an echo rejection level on the ba~is of the output from the echo :
cancell~r and a signal level on the transmitting siae, gain/loss computing means responsi~e to the echo rejection level from the ERL determi.ning means and a gain of the outpu~ of the echo canceller adjus~ed to be constant hy the level adjusting means to compute a :Loss in a predominant voice condition and a gain and a loss in an inEerior voice condition; an additive distribution circuit means having at least three adders each corresponding to each of the channel signal processing circuit, each o~ the adders being adapted for adding the outputs of the echo cancellers level-adjusted by said level adjusting means provided in the channel signal processing circuits except ~or the one assigned to itself and supplying the resulting sum signaL to the transmi~ting side via the level adjusting rneans, a predominant channel detectlon unit for comparing respective output levels of the echo cancellers provided in the three channel signal processing circuits to judge that the channel condition of the channel signal processing circuit including the echo canceller havîng the maximum output level is predominan~ and to judge that the channel oondition of the remainlng channel signal processing circuits are in~erior, thereby to control the level adjusting means provided in the channel signal processing circuit judged to be predominant on the basis ; 25 of the gain and loss in the predominant voice condition from ~he gain/loss computing means of the channel signal processing means and to control the level adjusting means ~2~
provided in the channel signal processing circui.t6 judged to be inferior on the basi~ of the gain and loss in ~he inferior voice condition from the gain/loss computing means of the channel signal proce~sing means.
The level adjusting means comprises amplifier means to control the level of the echo canceller and attenuating means ~o attenuate the level. of the transmitting signal. The preclominant channel detection unit is operative to giv~ the gain and loss in the predominant voice condition to the amplifier means and the attenuating means provided in the channel signal processing circuit judged to be predominant, respectively, and to give the ~ain and loss in the inferior voice condition to the amplifier means and the attenuating means provided in the channel signal processin~ circuit judged to be infexior, respectively.
The level adjusting means ~ay further comprises a ;~ gain detection circuit to detect a control gain necessary : for allowing the ouput level of the amplifier means to be :
; ~0 kep~ constant on the basis of the output level of the echo ;~ canceller.
When the echo rejection level is represented by . ERL, the gain and loss in the predominant voice condition are represented by G~ and L~, respsctiveIy, the gain ~25~:and loss in the inferior volce condltion are represented : by GN~ and LN~, respectivley, and a quasi-singing margin is represented by m, the gain/loss computing means , ,, , : :
L3~.
is operative to compute the los~ LN~I in the predomin~nt voice condl.tion and the gain GNV and LNV in the inferior voice conditi~n so that the following inequalities ho:Ld, G~ - ERL ~ LV ~ m <0, and G - ERL - ~ + m <0.
Brief Description of the Drawing_ The features and advantayes of a speech additive distribution equipment for a conferencing system according to the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which:
Fiy. 1 is a block diagram illustrating an embodiment of a speech additive clistribut.ion equipment for a conferencing system according to ~he present invention, Fig. 2 is a block diagram illustrating a channel signal proce~sing unit provided in the speech additive distribution equipment shown in Fi~. 1, Fig. 3 is a circult diayram illustratin~ a gain and loss computing unit providecl in the channel signal processing unit shown in Fig. 2, and Fig. 4 is a circuit diagram illustrating a predominant channel detection unit provided in the speech additive dis~ribution equipmen~. shown in Fig~ 1.
Detailed Description of Preferred Embodimetlt I'he present invention will be described in detail : in connection with a preferre~ em~odiment with reference ~ 6 --' ' to Figs. 1 to 4~
As shown in Fig. 1, an additive c}istribution equipment of the preferred embodiment according to the present inventiorl roughly comprises a channel signal processin~3 ~nit of the entirety is repr,esented by reference numeral 10, an additi~e distribution unit 20 of which construction is si~llar to the conventional one, and a predominant channel detection unit 30. These units will be described later in more detail.
For the hrevity of the explanation in this embodime~t, reference is made to the case where three conference attendants talk each other by making use of the above-mentioned addi~ive dis~ribu~ion equipment.
~ccordingly, the channel signal processing unit 10 is provided with three channel signal processing circuits lOA, lOB and lOC of the same construction. FigO
2 shows the detail of the channel signal processing circuit 10A taken a~ an example. 5ince a digital echo . canceller which will be reerred to 112 is employed in 20 this embodiment, ~the channel si~nal processing circuit lOA
~: :
is provided with an analog-to-digi-tal (A/D) converter 110 on the signal receiving side and a digital-to-analog (D/A) converter 170 on the signal transmitting side. The echo canceller 112 is comprised of a digital VLSI having an 5 input terminal SIN ~or a speech signal as a receiving signal incoming throu~h the A~/D conver~er 110, an input terminaL RIN .~or a speech signal as a trarismitting ~'~
::
, ~2~
signal outgoin~ through ~he D/A converter 170, and an output terminal SOU~r~ The echo canceller 112 respond~
~o ~he incoming and outgoing speech signals to cancel an echo signal from the transmittinc3 side Eed back to the receivillg side.
The channel signal processing circuit lOA further comprises an ERL de~ermination circ~it 120 for determining an ERL~ The ERL determina~ion circuit L20 is operative ~o computer an ERL ~dB~ including t.he echo canceller 112 on the basis of l~vels P~ and P~ of input and output signals to and from the echo canceller 112 by using the equation expressed as ERL = PS ~ P~(dB). It is to be noted that the ERI. can be measured solely when a signal having a sufficiently large level is input to the echo canceller 112 and an output signal from the output terminal SOuT includes only an echo component internally fed back ~hereto. Such a condition is called "single talk". However~ it is difEicult to actually discriminate the complete single talk. Accordingly, the ERL
2Q determination circui~ 120 judges that the system is in the single talk when a condition, P5 >PR, lasts for a more than pr~determined time interval to hold this cancellation E~L at this time. As shQwn in Fi~. 2, the ERL
: determination circuit 120 comprises a power detector 121 to detect the power level PoUT of the echo canceller 112, a power detector 112 to detect the power level PIN
of the transmitting signal, a divider 123 ~o divide the : - 8 -O .
., .
,, :
power PoUT detected by the detector 121 by the power PIN detected by the detector 122, and a linear to-dB
converter to convert the output PoU~l/PI~ of the divider 123 into an ERL hy using the equation expressed as ERL = 20 log ~Po~T/pIN) The channel signal processing circuit lOA has a further function to adJust an output level o~ the echo canceller 112 and a level of the transmittin~ signal. l'o realize this,'the channel signal processing circuit lOA is provided with a variable gain amplifier circuit 130, a gain detection circuit 140 for effecting an au~omatic: gain control (AGC~ of the amplifier circuit 130~ and an attenuator circuit L50. The amplifier circuit 130 compr1ses a ~elector 131 for selecting a ~ain GV in a predominant voice condition or a gain GNV in an inferior voice condition under control of the predominant channel detection unit 30, a register 132 for holding the output ~G~ or GNVj selected by the selector 131, and an amplifier 133 configured as a multiplier for ~ultiplyin~
the output of the echo canceller 112 by the selected gain f~om the re~ister 132. The qain detection circuit 140 functions to detect a control gain necessary for allowing the output 1evel of the amplifier circuit 130 to be kept constant on :the basis of the output level of the echo canceller 112. The ~ain detection circuit 140 has a ~:
characteristic of high speed response to detect an average level of an output of the echo canceller 112 over a .. , , ..
... . .
, , relatively long time to output a leve] PV to the predo~inant channel detection unit 30. For instance, the gain detection circuit 140 comprises an amplifier 141 configured as a multipLier 1~1 for multiplying the output of the echo canceller 112 by the gain GV in the predominant voice condition, a power detector 142 for detecting the power level of the amplifier 141, a comparator 143 for comp~riny an output P~ of the power detector with a target power level THagC, and an up/down or reversible counter 14~ operative in response to the output of the comparator 1~3 directly or through an inverter 144 to produce the above-mentivned gain GV in the predominant voice condition~ Further, the attenuator circuit 150 co~prises a selector 151 for selecting a loss LV in the predominant VQiCe condition or a loss ~ V in the inferior voice condition under control of the ~; peedominant channel detection unit 30, a regis~er 152 to hold the loss ~: or LNV~ selected by the selector 151, and an attenuator 153 configured as a multiplier for ~0 attenuaeing the level of the transmitting signal on th~
basis of the selected loss from the register 152.
The channel signal processing circuit lOA further comprises a gain/loss compu~ing circuit 160 which responds to the ERL fro~ the ERL determination circuit 1?0 and the :
gain~V in the predominant voice condition for computing the loss LV in the predominant vo.ice condition and the gain ~N~ and the loss L,NV in the inferior voice ':
, .
~L2~
condition~ A~ shown in FigO 3, the gain/loss computingcircuit 160 comprises suhtractors 161, 162 and 163, an adder 16~, and selec~ors 165, 166 and lZ~J. The gain/loss computing circuit 160 is operative to compute the gain GV or GNV of the amplifier circuit 130 and the loss or attenuation L~ or LNV of the attenuation circuit 150 on the hasis of the following equations:
~Vi max ~0 dB, LTR ~ Gvi) ....
G~Vi - min (~ ERLi ~ ~ Vi )' LVi ~ max (Gvi ~ ~RL ~ m~ LNV~
where m i5 a quasi-singing margin and LTR i3 a terminal receiving loss e.g. 10 dB.
The above-mentioned additive distribution unit 20 comprises three adders 20A, 20B and 20C provided correspondingly to the three channel signal processing circuits lOA, lOB and lOC. E~ch adder is operative to add the power outputs C~iS from the variable gain amplifier : circuits 130 provided in the signal processing GirCUitS
lOA, lOB and lOC except For the one corresponding to i~s~lf, and supplying the resuLting sum signal a~ the : transmitting signal CHlR to the attenuator 150. Further, ~: the above-mentioned predomlnant channel detection unit 30 is operative to compare respective output levels ~PV) f :~ ~ the gain detection circuits 140 provided in the three channel signaL processing circuits to judge that the chdnnel con~ition of the channeL signal processing circuit including the gain detection circuit 140 having the ::~
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,, .
' ~
"
~2~ 3~.
f~laXimUm output :L~ve1 is predominant and to ~udge that the channel condition of the ~ema:ining channel signal processing circuits are inferlor, therehy tG contl.ol the ampliFier circuit 130 and the a~tenua~or circit 150 provided in the channel signal proc~ssing circuit jud~ed to be predominant on the basis oE the gain and loss ln the pre~ominan~ voice concliti.on and to controL the amplifier circuit 130 and the attenuator circuit 150 provided in the channel signal proces~ing circuits judged to be inferior on the basis of the gain and loss in ~he inferior voice condition.
The operation of the additive distribution unit 20 thus configure~ will no~ ~e described.
It is assumed that the predominant channel detection unit ~0 judges that the c~annel condition of the channel signal processing circuit lOA is predominant and the channel condition of the channel signal processing ; circuits 10B and 1.0~ are inferior. The selector 131 provided in the cirouit lOA responds to a control signal C~l indicating the predominant conditio-n to select the gain ~Vl in the predominant voice condition obtained ~rom the gain detection circui~ 140 to feed it to the ampliier 133 on t~le basis of the equation ~1~. Further, the selector 151 pro~ided in th~ circuit lUA also responds to this control signal CHl to select the loss l.~l in the predominant voice condition computecl by the computing circuit 160 on the basis of t~le equation (3) to feed it to - 12 ~
. . .
, ` : ' ' , ~l2~3~.
provide a speech additi.ve distribution equipment for a conferericing system which has a function to discriminate between a predominant. or voiced channel and o~her inerior or unvoiced channels in terms of levels of received speech signals to suitably control ~he gain and loss of each channel according to the predominant and inferior voice conditj.ons~
A further object of the present invention is to provide a speech additive distribution equipment Eor a conferencing sys~em wherein when the equipment is applied to a speech conferencing system having different channel losses, the equipment can promptly perform balance between respective channels.
According to the present invention, there is provided a speech adclitive distribution equipment for conferencing system comprising: a channel signal processing means comprising at least three channel signal processing circuits, each channel ~ignal processi~g : circuit including a receiving side for receiving a channel . 20 ~signal, a transmitting side Eor transmitting the channel :~ signal, an echo cance1ler for canceling an echo signal fed ; b~ek ~o said receiving side from said transmitting side, means for adjusting levels oE an output of the echo cancelIer and a ~ransmittin~ signal transmittecl ~hrough the~transmitting fiide of the channel signal processing eircuitr ERL determining means for determining an echo rejection level on the ba~is of the output from the echo :
cancell~r and a signal level on the transmitting siae, gain/loss computing means responsi~e to the echo rejection level from the ERL determi.ning means and a gain of the outpu~ of the echo canceller adjus~ed to be constant hy the level adjusting means to compute a :Loss in a predominant voice condition and a gain and a loss in an inEerior voice condition; an additive distribution circuit means having at least three adders each corresponding to each of the channel signal processing circuit, each o~ the adders being adapted for adding the outputs of the echo cancellers level-adjusted by said level adjusting means provided in the channel signal processing circuits except ~or the one assigned to itself and supplying the resulting sum signaL to the transmi~ting side via the level adjusting rneans, a predominant channel detectlon unit for comparing respective output levels of the echo cancellers provided in the three channel signal processing circuits to judge that the channel condition of the channel signal processing circuit including the echo canceller havîng the maximum output level is predominan~ and to judge that the channel oondition of the remainlng channel signal processing circuits are in~erior, thereby to control the level adjusting means provided in the channel signal processing circuit judged to be predominant on the basis ; 25 of the gain and loss in the predominant voice condition from ~he gain/loss computing means of the channel signal processing means and to control the level adjusting means ~2~
provided in the channel signal processing circui.t6 judged to be inferior on the basi~ of the gain and loss in ~he inferior voice condition from the gain/loss computing means of the channel signal proce~sing means.
The level adjusting means comprises amplifier means to control the level of the echo canceller and attenuating means ~o attenuate the level. of the transmitting signal. The preclominant channel detection unit is operative to giv~ the gain and loss in the predominant voice condition to the amplifier means and the attenuating means provided in the channel signal processing circuit judged to be predominant, respectively, and to give the ~ain and loss in the inferior voice condition to the amplifier means and the attenuating means provided in the channel signal processin~ circuit judged to be infexior, respectively.
The level adjusting means ~ay further comprises a ;~ gain detection circuit to detect a control gain necessary : for allowing the ouput level of the amplifier means to be :
; ~0 kep~ constant on the basis of the output level of the echo ;~ canceller.
When the echo rejection level is represented by . ERL, the gain and loss in the predominant voice condition are represented by G~ and L~, respsctiveIy, the gain ~25~:and loss in the inferior volce condltion are represented : by GN~ and LN~, respectivley, and a quasi-singing margin is represented by m, the gain/loss computing means , ,, , : :
L3~.
is operative to compute the los~ LN~I in the predomin~nt voice condl.tion and the gain GNV and LNV in the inferior voice conditi~n so that the following inequalities ho:Ld, G~ - ERL ~ LV ~ m <0, and G - ERL - ~ + m <0.
Brief Description of the Drawing_ The features and advantayes of a speech additive distribution equipment for a conferencing system according to the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings in which:
Fiy. 1 is a block diagram illustrating an embodiment of a speech additive clistribut.ion equipment for a conferencing system according to ~he present invention, Fig. 2 is a block diagram illustrating a channel signal proce~sing unit provided in the speech additive distribution equipment shown in Fi~. 1, Fig. 3 is a circult diayram illustratin~ a gain and loss computing unit providecl in the channel signal processing unit shown in Fig. 2, and Fig. 4 is a circuit diagram illustrating a predominant channel detection unit provided in the speech additive dis~ribution equipmen~. shown in Fig~ 1.
Detailed Description of Preferred Embodimetlt I'he present invention will be described in detail : in connection with a preferre~ em~odiment with reference ~ 6 --' ' to Figs. 1 to 4~
As shown in Fig. 1, an additive c}istribution equipment of the preferred embodiment according to the present inventiorl roughly comprises a channel signal processin~3 ~nit of the entirety is repr,esented by reference numeral 10, an additi~e distribution unit 20 of which construction is si~llar to the conventional one, and a predominant channel detection unit 30. These units will be described later in more detail.
For the hrevity of the explanation in this embodime~t, reference is made to the case where three conference attendants talk each other by making use of the above-mentioned addi~ive dis~ribu~ion equipment.
~ccordingly, the channel signal processing unit 10 is provided with three channel signal processing circuits lOA, lOB and lOC of the same construction. FigO
2 shows the detail of the channel signal processing circuit 10A taken a~ an example. 5ince a digital echo . canceller which will be reerred to 112 is employed in 20 this embodiment, ~the channel si~nal processing circuit lOA
~: :
is provided with an analog-to-digi-tal (A/D) converter 110 on the signal receiving side and a digital-to-analog (D/A) converter 170 on the signal transmitting side. The echo canceller 112 is comprised of a digital VLSI having an 5 input terminal SIN ~or a speech signal as a receiving signal incoming throu~h the A~/D conver~er 110, an input terminaL RIN .~or a speech signal as a trarismitting ~'~
::
, ~2~
signal outgoin~ through ~he D/A converter 170, and an output terminal SOU~r~ The echo canceller 112 respond~
~o ~he incoming and outgoing speech signals to cancel an echo signal from the transmittinc3 side Eed back to the receivillg side.
The channel signal processing circuit lOA further comprises an ERL de~ermination circ~it 120 for determining an ERL~ The ERL determina~ion circuit L20 is operative ~o computer an ERL ~dB~ including t.he echo canceller 112 on the basis of l~vels P~ and P~ of input and output signals to and from the echo canceller 112 by using the equation expressed as ERL = PS ~ P~(dB). It is to be noted that the ERI. can be measured solely when a signal having a sufficiently large level is input to the echo canceller 112 and an output signal from the output terminal SOuT includes only an echo component internally fed back ~hereto. Such a condition is called "single talk". However~ it is difEicult to actually discriminate the complete single talk. Accordingly, the ERL
2Q determination circui~ 120 judges that the system is in the single talk when a condition, P5 >PR, lasts for a more than pr~determined time interval to hold this cancellation E~L at this time. As shQwn in Fi~. 2, the ERL
: determination circuit 120 comprises a power detector 121 to detect the power level PoUT of the echo canceller 112, a power detector 112 to detect the power level PIN
of the transmitting signal, a divider 123 ~o divide the : - 8 -O .
., .
,, :
power PoUT detected by the detector 121 by the power PIN detected by the detector 122, and a linear to-dB
converter to convert the output PoU~l/PI~ of the divider 123 into an ERL hy using the equation expressed as ERL = 20 log ~Po~T/pIN) The channel signal processing circuit lOA has a further function to adJust an output level o~ the echo canceller 112 and a level of the transmittin~ signal. l'o realize this,'the channel signal processing circuit lOA is provided with a variable gain amplifier circuit 130, a gain detection circuit 140 for effecting an au~omatic: gain control (AGC~ of the amplifier circuit 130~ and an attenuator circuit L50. The amplifier circuit 130 compr1ses a ~elector 131 for selecting a ~ain GV in a predominant voice condition or a gain GNV in an inferior voice condition under control of the predominant channel detection unit 30, a register 132 for holding the output ~G~ or GNVj selected by the selector 131, and an amplifier 133 configured as a multiplier for ~ultiplyin~
the output of the echo canceller 112 by the selected gain f~om the re~ister 132. The qain detection circuit 140 functions to detect a control gain necessary for allowing the output 1evel of the amplifier circuit 130 to be kept constant on :the basis of the output level of the echo canceller 112. The ~ain detection circuit 140 has a ~:
characteristic of high speed response to detect an average level of an output of the echo canceller 112 over a .. , , ..
... . .
, , relatively long time to output a leve] PV to the predo~inant channel detection unit 30. For instance, the gain detection circuit 140 comprises an amplifier 141 configured as a multipLier 1~1 for multiplying the output of the echo canceller 112 by the gain GV in the predominant voice condition, a power detector 142 for detecting the power level of the amplifier 141, a comparator 143 for comp~riny an output P~ of the power detector with a target power level THagC, and an up/down or reversible counter 14~ operative in response to the output of the comparator 1~3 directly or through an inverter 144 to produce the above-mentivned gain GV in the predominant voice condition~ Further, the attenuator circuit 150 co~prises a selector 151 for selecting a loss LV in the predominant VQiCe condition or a loss ~ V in the inferior voice condition under control of the ~; peedominant channel detection unit 30, a regis~er 152 to hold the loss ~: or LNV~ selected by the selector 151, and an attenuator 153 configured as a multiplier for ~0 attenuaeing the level of the transmitting signal on th~
basis of the selected loss from the register 152.
The channel signal processing circuit lOA further comprises a gain/loss compu~ing circuit 160 which responds to the ERL fro~ the ERL determination circuit 1?0 and the :
gain~V in the predominant voice condition for computing the loss LV in the predominant vo.ice condition and the gain ~N~ and the loss L,NV in the inferior voice ':
, .
~L2~
condition~ A~ shown in FigO 3, the gain/loss computingcircuit 160 comprises suhtractors 161, 162 and 163, an adder 16~, and selec~ors 165, 166 and lZ~J. The gain/loss computing circuit 160 is operative to compute the gain GV or GNV of the amplifier circuit 130 and the loss or attenuation L~ or LNV of the attenuation circuit 150 on the hasis of the following equations:
~Vi max ~0 dB, LTR ~ Gvi) ....
G~Vi - min (~ ERLi ~ ~ Vi )' LVi ~ max (Gvi ~ ~RL ~ m~ LNV~
where m i5 a quasi-singing margin and LTR i3 a terminal receiving loss e.g. 10 dB.
The above-mentioned additive distribution unit 20 comprises three adders 20A, 20B and 20C provided correspondingly to the three channel signal processing circuits lOA, lOB and lOC. E~ch adder is operative to add the power outputs C~iS from the variable gain amplifier : circuits 130 provided in the signal processing GirCUitS
lOA, lOB and lOC except For the one corresponding to i~s~lf, and supplying the resuLting sum signal a~ the : transmitting signal CHlR to the attenuator 150. Further, ~: the above-mentioned predomlnant channel detection unit 30 is operative to compare respective output levels ~PV) f :~ ~ the gain detection circuits 140 provided in the three channel signaL processing circuits to judge that the chdnnel con~ition of the channeL signal processing circuit including the gain detection circuit 140 having the ::~
..
,, .
' ~
"
~2~ 3~.
f~laXimUm output :L~ve1 is predominant and to ~udge that the channel condition of the ~ema:ining channel signal processing circuits are inferlor, therehy tG contl.ol the ampliFier circuit 130 and the a~tenua~or circit 150 provided in the channel signal proc~ssing circuit jud~ed to be predominant on the basis oE the gain and loss ln the pre~ominan~ voice concliti.on and to controL the amplifier circuit 130 and the attenuator circuit 150 provided in the channel signal proces~ing circuits judged to be inferior on the basis of the gain and loss in ~he inferior voice condition.
The operation of the additive distribution unit 20 thus configure~ will no~ ~e described.
It is assumed that the predominant channel detection unit ~0 judges that the c~annel condition of the channel signal processing circuit lOA is predominant and the channel condition of the channel signal processing ; circuits 10B and 1.0~ are inferior. The selector 131 provided in the cirouit lOA responds to a control signal C~l indicating the predominant conditio-n to select the gain ~Vl in the predominant voice condition obtained ~rom the gain detection circui~ 140 to feed it to the ampliier 133 on t~le basis of the equation ~1~. Further, the selector 151 pro~ided in th~ circuit lUA also responds to this control signal CHl to select the loss l.~l in the predominant voice condition computecl by the computing circuit 160 on the basis of t~le equation (3) to feed it to - 12 ~
. . .
3~.
the at~e.nllator 153 fo~ preverltion of singing.
On the other hand, selectols ~corresponding to the selector l31~ provi~led in tne channel ~ignal processing circuits 10B and l0C respond to control signals CH~ and CH3 indicatillg ~he inferior condition to select the gains G~lV2 and GNV3 which are set to the maximum value within a range where the system is not placed in the quasi singing to feed them to amplifiers (corresponding ~o ~he amplifier 133). Further, selectors (corresponding -to the selector 151) provided in the channel signal processing circuits l0B and 70C respond to control signals C~2 and CH3 indicating the inferior condition to select losses LN~2 and ~ V3 in the inferivr voice condition computed by the computiny circuit 160 on the bas.is of the equation (l~ to feed them to attenuators ~cvrresponding to the attenuator l53), thus providing a necessary 2cho canceIlation ~o prevent the system f L om s ing ing O
~: When the additive distri'oution equipment according to the present invention is applied to a speech conferencing system having different channel losses, it can reduce the difference between receiving levels of d1fferent channels.
~ Wamely, since the respective amplifier circuits : 25 have AGC unctions~ it is possible to evaluate respective channel lo~ses on the basis of the gains given by the :-~ AGC. Accordingly, ~n average receiving level can be :~:
......
' ~;
:
:~2~ 3~.
ev~lu3ted on the basis of the above-rnentioned channel losses. This makes it possible to allow the receivin~
levelc, ~o be equal ~.o each other by insertirlg suitable iosses in the transmission chan~e]s up to the terminal equipment. Thus, the equip~ent according to the present invention makes it possible to mînimize the difference between receiving leve:Ls, thus providing grea~ly improved speech quality.
In the above-mentionecl embodiment, i~ has been described that the digital echo canceller is used.
Without limiting tc this imp~ementa~ion, the present invention can be similarly applied to the equipment using an analog echo canceller.
.
. ~
:
:, ..
the at~e.nllator 153 fo~ preverltion of singing.
On the other hand, selectols ~corresponding to the selector l31~ provi~led in tne channel ~ignal processing circuits 10B and l0C respond to control signals CH~ and CH3 indicatillg ~he inferior condition to select the gains G~lV2 and GNV3 which are set to the maximum value within a range where the system is not placed in the quasi singing to feed them to amplifiers (corresponding ~o ~he amplifier 133). Further, selectors (corresponding -to the selector 151) provided in the channel signal processing circuits l0B and 70C respond to control signals C~2 and CH3 indicating the inferior condition to select losses LN~2 and ~ V3 in the inferivr voice condition computed by the computiny circuit 160 on the bas.is of the equation (l~ to feed them to attenuators ~cvrresponding to the attenuator l53), thus providing a necessary 2cho canceIlation ~o prevent the system f L om s ing ing O
~: When the additive distri'oution equipment according to the present invention is applied to a speech conferencing system having different channel losses, it can reduce the difference between receiving levels of d1fferent channels.
~ Wamely, since the respective amplifier circuits : 25 have AGC unctions~ it is possible to evaluate respective channel lo~ses on the basis of the gains given by the :-~ AGC. Accordingly, ~n average receiving level can be :~:
......
' ~;
:
:~2~ 3~.
ev~lu3ted on the basis of the above-rnentioned channel losses. This makes it possible to allow the receivin~
levelc, ~o be equal ~.o each other by insertirlg suitable iosses in the transmission chan~e]s up to the terminal equipment. Thus, the equip~ent according to the present invention makes it possible to mînimize the difference between receiving leve:Ls, thus providing grea~ly improved speech quality.
In the above-mentionecl embodiment, i~ has been described that the digital echo canceller is used.
Without limiting tc this imp~ementa~ion, the present invention can be similarly applied to the equipment using an analog echo canceller.
.
. ~
:
:, ..
Claims (13)
1. A speech additive distribution equipment for conferencing system comprising:
a channel signal processing means comprising at least three channel signal processing circuits, each of said channel signal processing circuits including a receiving side for receiving a channel signal, a transmitting side for transmitting the channel signal, an echo canceller for cancelling an echo signal fed back to said receiving side from said transmitting side, means for adjusting levels of an output of said echo canceller and a transmitting signal transmitted through the transmitting side of said channel signal processing circuit, ERL
determining means for determining an echo rejection level on the basis of said output from said echo canceller and a signal level on said transmitting side, and gain/loss computing means responsive to said echo rejection level from said ERL determining means and a gain of the output of the echo canceller adjusted to be constant by said level adjusting means to compute a loss in a predominant voice condition and a gain and a loss in an inferior voice condition;
an additive distribution circuit means having at least three adder means each corresponding to each of said channel signal processing circuits, each of said adder means being adapted for adding the outputs of the echo cancellers level-adjusted by said level adjusting means except for the one corresponding to itself, and supplying the resulting sum signal as said transmitting signal to said transmitting side via said level adjusting means corresponding to itself; and a predominant channel detection means for comparing respective output levels of said echo cancellers to judge that the channel condition of said channel signal processing circuit including the echo canceller having the maximum output level is predominant and to judge that the channel condition of the remaining channel signal processing circuits are inferior, thereby to control the level adjusting means provided in the channel signal processing circuit judged to be predominant on the basis of said gain and loss in said predominant voice condition from said gain/loss computing means of said channel signal processing means and to control the level adjustment means provided in the channel signal processing circuits judged to be inferior on the basis of said gain and loss in said inferior voice condition from said gain/loss computing means of said channel signal processing means.
a channel signal processing means comprising at least three channel signal processing circuits, each of said channel signal processing circuits including a receiving side for receiving a channel signal, a transmitting side for transmitting the channel signal, an echo canceller for cancelling an echo signal fed back to said receiving side from said transmitting side, means for adjusting levels of an output of said echo canceller and a transmitting signal transmitted through the transmitting side of said channel signal processing circuit, ERL
determining means for determining an echo rejection level on the basis of said output from said echo canceller and a signal level on said transmitting side, and gain/loss computing means responsive to said echo rejection level from said ERL determining means and a gain of the output of the echo canceller adjusted to be constant by said level adjusting means to compute a loss in a predominant voice condition and a gain and a loss in an inferior voice condition;
an additive distribution circuit means having at least three adder means each corresponding to each of said channel signal processing circuits, each of said adder means being adapted for adding the outputs of the echo cancellers level-adjusted by said level adjusting means except for the one corresponding to itself, and supplying the resulting sum signal as said transmitting signal to said transmitting side via said level adjusting means corresponding to itself; and a predominant channel detection means for comparing respective output levels of said echo cancellers to judge that the channel condition of said channel signal processing circuit including the echo canceller having the maximum output level is predominant and to judge that the channel condition of the remaining channel signal processing circuits are inferior, thereby to control the level adjusting means provided in the channel signal processing circuit judged to be predominant on the basis of said gain and loss in said predominant voice condition from said gain/loss computing means of said channel signal processing means and to control the level adjustment means provided in the channel signal processing circuits judged to be inferior on the basis of said gain and loss in said inferior voice condition from said gain/loss computing means of said channel signal processing means.
2. A speech additive distribution equipment as set forth in claim 1, wherein said level adjustment means comprises amplifier means to control said level of said echo canceller and attenuating means to attenuate said level of said transmitting signal.
3. A speech additive distribution equipment as set forth in claim 2, wherein said predominant channel detection means is operative to give said gain and loss in said predominant voice condition to the amplifier means and the attenuating means provided in said channel signal processing circuit judged to be predominant, respectively, and to give said gain and loss in said inferior voice condition to the amplifier means and the attenuating means provided in said channel signal processing circuit judged to be inferior respectively.
4. A speech additive distribution equipment as set forth in claim 2, wherein said level adjustment means further comprises a gain detection circuit to detect a control gain necessary for allowing the output level of said amplifier means to be kept constant on the basis of the output level of said echo canceller.
5. A speech additive distribution equipment as set forth in claim 1, wherein said ERL determining means comprises a first power detector for detecting the output level of said echo canceller, a second power detector for detecting the level of said transmitting signal, a divider for dividing an output of said first power detector by an output of said second power detector, and a converter to convert an output of said divider into the echo rejection level.
6. A speech additive distribution equipment as set forth in claim 2, wherein said amplifier means comprises a selector to select said gain in the predominant voice condition or the gain in the inferior voice condition under control of said predominant channel detection means, a register to hold an output selected by said selector, and a multiplier to multiply the output of said echo canceller by the selected gain from the register.
7. A speech additive distribution equipment as set forth in claim 2, wherein said attenuating means comprises a selector to select said loss in the predominant voice condition or the loss in the inferior voice condition from said gain/loss computing means under control of said predominant channel detection means, a register to hold an output selected by said selector, and an attenuator to attenuate the level of said transmitting signal on the basis of the loss held by said register.
8. A speech additive distribution equipment as set forth in claim 4, wherein said gain detection circuit comprises a multiplier to multiplier the output of said echo canceller by said gain in the predominant voice condition, a level detector to detect the output of said multiplier, a comparator to compare the output of said level detector with a target level, and a reversible counter responsive to the compared result of said comparator to produce said gain in the predominant voice condition.
9. A speech additive distribution equipment as set forth in claim 1, wherein when said echo rejection level is represented by ERL, said gain and loss in said predominant voice condition are represented by GV and LV, respectively, said gain and loss in said inferior voice condition are represented by GNV and LNV, respectively, ad a quasi-singing margin is represented by m, said computing means computes said loss LNV in said predominant voice condition and said gain GNV and LNV in said inferior voice condition so that the following inequalities hold, GV - ERL - LV + m < 0, and GNV - ERL - LNV + m < 0.
10. A speech additive distribution equipment as set forth in claim 9, wherein said gain/loss computing means comprises a first subtractor for subtracting said quasi-singing margin m from said echo rejection level ERL, an adder for adding an output (ERL-m) to said loss LNV
in said inferior voice condition, a first selector for selecting said gain GV in said predominant voice condition or an output (ERL-M+LNV) of said adder to obtain said gain GNV in said inferior voice condition by using the equation expressed as min (GV, ERL+LNV-m).
in said inferior voice condition, a first selector for selecting said gain GV in said predominant voice condition or an output (ERL-M+LNV) of said adder to obtain said gain GNV in said inferior voice condition by using the equation expressed as min (GV, ERL+LNV-m).
11. A speech additive distribution equipment as set forth in claim 10, wherein said gain/loss computing means further comprises a second subtractor for subtracting said gain GV in said predominant voice condition from a predetermined terminal processing loss represented by LTR, and a second selector for selecting an output (LTR-GV) of said second subtractor or a loss of zero dB to obtain said loss LNV in said inferior voice condition by using the equation expressed as max (0 dB, LTR-GV).
12. A speech additive distribution equipment as set forth in claim 11, wherein said gain/loss computing means further comprises a third subtractor for subtracting said output (ERL-m) of said first subtractor from said gain GV in the predominant voice condition, and a third selector for selecting an output (GV-ERL+m) of said third subtractor or said loss LNV in said inferior voice condition to obtain said loss LNV in said predominant voice condition by using the equation expressed as max (GV-ERL+m, LNV).
13. A speech additive distribution equipment as set forth in claim 4, wherein said predominant channel detection means comprises comparator circuitry for comparing respective outputs of said gain detection means in said three channel signal processing circuits, and gate circuitry to responsive to an comparison output from said comparator circuitry to produce a control signal having one logical state to said channel signal processing circuit judged to be predominant and to produce control signals having the other logical state to said channel signal processing circuits judged to be inferior.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP40499/'85 | 1985-03-01 | ||
| JP4049985 | 1985-03-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1240431A true CA1240431A (en) | 1988-08-09 |
Family
ID=12582253
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000503048A Expired CA1240431A (en) | 1985-03-01 | 1986-02-28 | Speech additive distribution equipment for conferencing system |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4741025A (en) |
| JP (1) | JPH0638621B2 (en) |
| CA (1) | CA1240431A (en) |
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-
1986
- 1986-02-28 CA CA000503048A patent/CA1240431A/en not_active Expired
- 1986-02-28 JP JP61043789A patent/JPH0638621B2/en not_active Expired - Lifetime
- 1986-03-03 US US06/835,685 patent/US4741025A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62154A (en) | 1987-01-06 |
| US4741025A (en) | 1988-04-26 |
| JPH0638621B2 (en) | 1994-05-18 |
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