SE506152C2 - Eliminating acoustic echoes in telephone call using digital audio terminal - Google Patents

Abstract

The method of eliminating acoustic echoes involves connecting a digital audio terminal (10) to an acoustic echo controller (14) implemented on an exchange (12). The echo characteristics of a room in which the terminal is placed are determined. A speech signal is detected on the echo controller. A calculated echo signal is eliminated from a second speech signal in the echo controller. A built in voice switching circuit (32) in the audio terminal is disconnected, if available. The echo controller simultaneously operates on several telephone calls.

Description

l5 20 25 30 506 152 2 with hands-free telephones. However, the voice switching function of hands-free phones is sensitive to background noise and sometimes blocks the weaker speaker in favor of a more efficient speaker.

Another known method for eliminating acoustic echoes is hands-free telephones, scmx has been specially designed for conference purposes, which telephones have a separate built-in echo cancellation function. An example is the conference telephone from KonfTel AB with the product name CU 100.

The sector for standardization of telecommunications at the International Telecommunication Union ITU, (ITU-T) has prepared a recommendation G.l67 03/93 for acoustic eco-controllers, which recommendation is hereby incorporated in the form of examples.

It is known that electric echoes can be reduced by the use of electric echo cancellers in telecommunication systems. The following publication relates to electric echo cancellers. However, none of these writings offer any solution to the problems that arise when acoustic echoes occur.

U.S. Patent No. 5,333,195, entitled "Telephone Network Speech Signal Enhancement", discloses a telephone exchange in which an electric echo canceller is realized (Figure 3). The patent specification GB 2 164 828 describes a digital hybrid apparatus for reduction as electrical echoes and which is to be used in a line circuit, used in a digital selection network Patent patent GB 2 232 BNsDoc | D; 10 15 20 25 30 860 describes an audio signal circuit for echo cancellation. It is mentioned that the circuit can be built into a cross-sectional circuit for a telephone line The patent specification HUS 3,769,466 describes a transmission system for telephony with echo cancellers The patent specification WO 94/18759 describes a method and a device for detecting disconnection means for the echo canceller in a telephone switch. 38 12 640 describes a transverse filter for reducing electrical echoes. el; One Swedish patent specification SE 446 291 describes a conference connection with realized electrical echo reduction. Summary The invention solves the problems described above in connection with hands-free telephones and acoustic echoes. The invention has several advantages over the state of the art, which solve similar problems. The šâs of the invention is an acoustic eco-control function realized in a digital exchange in a communication system. The acoustic acoustic control function (ABC) can be accessed from a hands-free telephone and does not need to be realized in said hands-free telephone.

The invention relates to a method and an arrangement in which the acoustic echoes are eliminated by the use of a device for controlling acoustic echoes in the gear unit. The echo control device directly controls the transceiver transmitting and receiving digital channels and performs adjustments and necessary eliminations for an effective duplex call.

BNSDOCID: 10 15 20 25 30 506 152 4 A first advantage obtained in the realization of the device for controlling acoustic echo in the exchange is that a standard hands-free telephone can be used and that the AEC function can be reached from the telephone, e.g. by entering a code on the phone. Consequently, the phone must be equipped with a speaker.

A second advantage obtained is that several telephones can share this function. The advantage of doing this is significant as the function is very expensive due to the need for power supply and the complexity of the AEC device.

E. 1 1. .

A better understanding of the procedure and the system in accordance with. The invention is obtained from the following detailed description together with the accompanying drawings, in which: Figure 1 shows a block diagram of an A-party telephone, which is connected to a PBX (subscriber exchange) comprising an acoustic echo controller (AEC device), and a B -parts telephone.

Figure 2 shows a block diagram of an acoustic eco-controller (AEC device).

Figure 3a shows a simplified block diagram of the telephones and the AEC device realized in the PBX, which diagram also shows the digital channels used for a call and how the acoustic echo is generated.

BNSDOCID: 10 15 20 25 30 5 506 352 Figure 3b shows a signal diagram of a test signal and its echo signal.

Figure 3c shows a signal diagram of signals that occur when the B-party speaks.

Figure 3d shows a signal diagram of signals that stop when the A-party and the B-party speak at the same time.

Figure 4 shows a flow chart of the acoustic echo minimization method in accordance with the invention. -è = _ m1- Ä. iv; _ i E:. Figure 1 shows a block diagram of a first telephone "fa" used by an A-party and connected to an nb fl ñ network (PBX) 12 comprising an acoustic echo controller (ARC device) 14 in accordance with the invention. A B-party's telephone 15 is also connected to the said PBX, since a telephone call is in progress between the A-party and the B-party. The B-party's telephone 15 may be permanently connected to the PBS, but may also be a telephone outside the PBX, as in this example. The first telephone 10 is a telephone which can be used as a digital audio telephone, which in this example is a hands-free telephone. The hands-free telephone 10 comprises a microphone 16 for receiving speech from the A-party, a first amplifier 18 for amplifying the speech and an A / D converter 20 for converting the analog speech signal into a digital signal which is transmitted on a digital line 22, which is connected to the exchange 12. BNSDOCID: The hands-free telephone 10 also includes a D / A converter 24 for converting digital speech signals from the B-party to analog speech signals. The digital speech signals are received on a digital line 26 from the PBX. A second amplifier 28 for amplifying the received analog speech signals and a speaker 30 for transmitting the analog speech signals to the A-party are also built into the telephone.

A voice switching circuit 32 in this example is connected between the first amplifier 18 and the A / D converter 20.

The voice switching circuit 32 is also connected between the second amplifier 28 and the D / A converter 24. The voice switching circuit 32 is realized in certain telephones and is used to simultaneously enable calls from one party and the purpose is to avoid problems with acoustic echo signals. The voice switching circuit 32 is switched off by switch 34, when the AEC 14 in the exchange is instead connected to the hands-free telephone 10.

The PBX 12 comprises an extension line unit (ELU) 40, to which the hands-free telephone 10 is connected, an interurban line unit (TLU) 42, to which the B-party telephone 15 is connected, a switching unit 44 (SU) for switching the telephone. or data signals in the PBX, a control memory (CS) 46 for controlling the switching, a central processor (CP) 48 the activities in the PBX, and the AEC- for controlling the PBX, the device 14 for eliminating acoustic echoes.

The ELU 40 is a common unit in a PBX and it is connected to the SU 44 by digital lines 50, 52. The TLU 42 is a common unit in a PBX and it is connected to the SU 44 by digital lines S2, BNSDOCID: , sne 152 S4. Said components ELU, SU, TLU are not described in detail because they are ordinary components in a gear. The device 14 for controlling acoustic echo is connected to the switching unit 44 through lines 58, 60, -62, A64. Said hands-free telephone can be permanently connected to said AEC, for example if the hands-free telephone is located in a meeting room, or the hands-free telephone 10 can be connected to said AEC on request. For example, the telephone 10 can be connected to the AEC by entering a code. Then, if the phone is equipped with a voice switching unit 32, it is disconnected when the AEC is connected. The AEC device 14 is connected to a power supply device 66 and in this example the AEC is part of a digital signal processor (DSP) in the PBX. The digital processor DSP is no longer described in this patent specification as it is a common device in a gear unit. The central processor 48 is connected to the AEC terminal 48 to control its activation and whose telephone calls it is to handle. In the same way as with a standard PBX, the central processor 48 is connected to the control memory.

L:,. 46, which in turn is connected to the switching unit ÃÉE 25 The switching unit 44 is connected to the central pggg cessor 48 via a line 68, on which control signals from the hands-free telephone are transmitted.

The second telephone 15 may be of any type, for example an ordinary telephone. It transmits speech on a transmitter: line 70 and receives speech on a receiver line 72, ¿where BNSDOCID; 10 15 20 25 30 BNSDOCID: 506 152 8 both lines are connected to an interurban line unit 42.

The system described in Figure 1 can also be an intercom system and in this case the interurban line (ELU) unit is replaced by an extension line unit for a number of extensions.

Figure 2 shows a block diagram of the device 14 for controlling acoustic echo. It comprises a detection unit 74 for detecting speech signals from the B-party, a test signal unit 76 for transmitting a test signal for requesting the hands-free echo characteristics of the room, the voice telephone is located, a processor 78 for estimating acoustic echo for to control the elimination of the echo signals and a summing network 80, where a calculated echo signal is reduced from an incoming speech signal.

The AEC 14 has two main tasks. The first is to determine the eco-characteristics of the room where the hands-free telephone is located. When the A-party wants to make a call and enter a code on his telephone, a request is sent from the hands-free telephone, via the PBX, to the central processor 48 on the line 68. Upon receipt of the request, CP 48 sends a start signal to the input 82 at the test signal unit 76 and to an input 84 of the acoustic echo estimator 78. The start signal resets the acoustic processor 78 and initiates a test signal TEST, which is sent to the hands-free telephone. on line 62 from the test signal unit 76. Handsfree telephone. year- placed in a room. The test signal TEST generates an acoustic echo signal in the room and the acoustic echo signal is transmitted on line 506152023) 9 sne # 52 64 to an input 86 of a test echo detector 88 in the acoustic echo estimator 78, which determines echo characteristics EC. This determination method is known and is not described in detail in this patent specification. The test signal and the echo test signal can be transmitted on each free speech channel through the PBX. In another embodiment, the test signal can be transmitted on channels assigned to speech, such as: aa ams: A-party and transmitted from the A-party. The second main task is to eliminate acoustic echoes from the A-party, which are caused by speech signals from the ïwïfB-party. A first speech signal is sent from the B-party on. a 60 to the input 90 of the detection unit 74. That speech channel is controlled in the usual manner by the first speech signal transmitted to the A-party on the line interface and the detection unit 74 sends the first speech signal to an input 92 of the estimation processor 78. The estimation processor 78 uses the space determined The EC and the detected first speech signal for calculating the echo signalïlë-Ãlril * 20 will appear on line 64 from the hands-free telephone and be received at an input 94 of the calculation network. The calculated echo signal is sent by the echo signal estimator 78 to an input 96 of the summing network 80. The summing network reduces the calculated echo signal from the echo signal received at the input 947 transmits the difference of an output 98 to the line S8 and - to the B party. This elimination of acoustic echo signals can be performed in a known manner and is not described in detail in this patent specification. Recommendations for a control unit? Acoustic echo can be found in the above-mentioned publication in fl- 'ü fl T G.l67 03/93. -.

BNSDOCID; Figure 3a shows a simplified block diagram of the system according to the invention comprising a device for controlling acoustic echo AEC, which has been realized in said PBX, and where the AEC device 14 is connected to hands-free the telephone 10. The telephones and the PBX are connected to each other by wires, as shown in the figure, and as described in Figures 1 and 2. When a connection is established between the A-party and the B-party, the PBX selects a first digital channel X1 for the number received by the A-party from the PBX. For speech transmitted from the A-party to the PBX, a second digital channel Y2 is selected or assigned. In SU 44, the speech from the B-party is switched from a third digital channel X3 to the first digital channel X1. For speech from the PBX to the B-party, a fourth digital channel Y4 is used. The switching is performed in a known manner and does not form part of the invention and consequently is not described in detail in this document. A digital channel is equivalent to a time slot in a frame, which is known in digital telecommunication networks and this is consequently not described further in this publication.

Figure 3a shows the device for controlling acoustic echo AEC connected on the A-side side of the switching unit SU in the PBX. Consequently, a speech signal from the B-party, on the digital channel X3, is switched to the first digital channel X1, before it is connected to the AEC device.

Figure 3a 'also shows how the echo signals behave.

Speech signals from the B-party are received at the hands-free telephone 10 and are sent by the loudspeaker LS into the room. Parts of the received speech go directly into the microphone and parts are returned, such as echo, from the walls and go into the output microphone (100, 102). Accordingly, all speech signals originating from BNSDOCID are called: 10 15 20 25 30 11 506 1152 from the B-party and are returned to the PBX from the hands-free telephone for acoustic echo signals. ie Figure 3b shows a signal diagram of the test signal TEST and its echo signal. The test signal TEST is transmitted at the request of the AEC on the first digital channel X1, on the line 62, to the hands-free telephone 10. The occurring echo signal TEST EKO is received by the AEC on the second digital channel Y2, on the incoming line 64. The echo signal analysis is carried out in accordance with the description in connection with Figure 2 and the eco - characteristics of the room are determined.

Figure 3c shows the speech signals which occur around the AEC. A speech signal BTAL from the B-letter is received by the AEC on the digital channel X1, on the path when the B-party speaks. 60, and is detected. The received speech signal BTÄL is transmitted to the A-party on the same digital channel X1, on line? An echo signal 62 BTAL EKO is received at the AEC on the digital channel Y2, on line 64. The AEC eliminates the echo signal BTAL EKO in accordance with the description in conjunction with Figure 2 and consequently no echo signal is transmitted from the AEC on the digital channel Y2 on line 58. sooo Figure 3d shows speech signals appearing around DEC A speech, "" M when the 'B-party and. The A-party speak at the same time. _ BTALs from the B-party are received by ABC on the digital channel X1, on the line The received signal BTAL is transmitted to the A-party on the same digital channel XI; i§â line 62. An echo signal BTAL EKO is received at ABC on your ~ digital channel Y2, on line 64. A speech signal Amkh from A the party is simultaneously received in the said AEC on the digital channel Y2, on the line 64- AEC eliminates echo signal- BNSDOCID: 10 15 20 25 30 5Û6 152 12 len BTAL EKO in accordance with the description in connection with figure 2 and this consequently results in no echo signal being transmitted from the said AEC on the digital channel Y2 on line 58, only the speech signal from the A-party ATAL.

The obvious advantages of realizing the device for controlling acoustic echo AEC in said PBX is that it can be shared by several hands-free telephones, which are connected to said PBX. Different hands-free telephones can use the AEC at different times. It is also possible that the AEC 14 can operate on a plurality of digital channels simultaneously. The number depends on the capacity of the AEC. It is also possible to connect several ABC devices in the said PBX.

Figure 4 shows various method steps performed in a preferred embodiment of the invention in order to eliminate acoustic echoes in connection with a telephone call between an A-party using a digital hands-free telephone and a B-party using an arbitrary telephone type. The process is also described with reference to Figures 1, 2 and 3.

The hands-free phone is connected to the said PBX.

At step 110, an acoustic echo control device is realized in the PBX and connected as described above. The device for controlling acoustic echo is realized in the digital signal processor DSP in the said PBX. The A-party wants to make a call and use the hands-free telephone. At step 112, he requests a service from the AEC in the PBX by entering a specific code or if a PC is used at as an interface, he requests the service via the PC. step 114, the hands-free telephone 10 is connected to the AEC device- BNSDOCID: 13 506; ° L52, which means that said AEC device 114 operates on digital channels X2, Y3, which are assigned A-partenaß fi š 'At step 116 it is shown that said AEC can operate in accordance with different methods. The preferred method is a method in which a test signal is used in order to determine the eco-characteristics of the room in which the hands-free telephone is located. In an alternative procedure, the eco-characteristics of the room can be calculated without a test signal. The speech signals are used directly to determine the echo characteristics of the room. Ekokáfš teristics is then determined iteratively.

At step 118, the eco-characteristic of the AEC room determines the use of a test signal TEST, which is transmitted from the device 14. A detailed description was made in conjunction with Figures 2 and 3.

At step 120, the telephone connection is established between the party and the B party. Establish a telephone connection in the year 20 allocation of digital channels (nialnakar) for the A-parc and the B-party. A first digital channel X1 is assigned for speech signals received by the A-party, a second digital channel Y2 is assigned for speech signals transmitted from the Party, a third digital channel X3 is assigned for speech signals transmitted from the Party. The B-party and a fourth digital channel Y4 are assigned for speech signals received by the B-party. The switching of digital channels is performed by the switching unit in the said PBX. A first speech signal BTAL is transmitted from the B party to the R party on the first and third channels X1, X3. At step 122, the speech signal BTAL is detected in the ABC device in BNSDOCID: 506 152 14 in accordance with the description of Figure 2. At step 124, an echo signal, which is returned from the A-party, is calculated in a manner described above. At step 126, the echo signal is reduced by the calculated echo signal in accordance with known methods for reducing echo signals in AEC devices. At step 128, it is checked whether the telephone connection is still connected, or if it is disconnected. If the telephone connection is still connected, steps 122, 124 and 126 are repeated until the telephone connection is disconnected. At step 130, the telephone connection is disconnected and, consequently, the hands-free telephone is disconnected from the AEC device.

If the hands-free telephone 10 is permanently connected to the AEC, time slots used by the hands-free telephone are always processed by the AEC. This may, for example, be a telephone in a conference room, which is always used as a hands-free telephone. It is also possible to connect the AEC device during a telephone call. The speech is then switched off for a very short time, at the same time as the test signal is transmitted and analyzed.

BNSDOCID:

Claims (12)

15 506) 1152 Ratentkrax A method for eliminating acoustic echoes in conjunction with a telephone call between an A-party using a digital audio terminal (10) in a room and a B-party 4 turns an arbitrary telephone type (15), where the digital audio terminal are connected to a digital exchange (12) in a telecommunication system, and for the telephone call a first digital channel (X1) is used for speech taken by the emo fi nav 10 A party and a second digital channel (Y2) is used for speech transmitted from The A-party, wherein said method comprises the steps of: - connecting the digital audio terminal (10) to a means (14) for acoustic echo control (AEC), so far realized in the exchange (12); of gas - determine the eco-characteristic (EC) of the room where the sound terminal is located; ¿Na - detect in said AEC a first speech signal (BTAL) xp§ the first digital channel (X1); - calculating an echo signal from the detected speech signal (BTAL) and the determined echo characteristic (EC) of the room; ~ and (gu - eliminate in the ABC device (14) the calculated echo signal from a second speech signal (BTAL EKO + ATAL), which is received in said AEC on the second digital channel (Y2), so that the speech signals from the Party to the B-party is sent without any disturbing echo signals. A method according to claim 1 comprising the steps of aut = Ješi. - disconnect a built-in voice switching circuit (32) in audio: terminal, if available. BNSDOCID: 10 15 20 25 30 506 152 16 A method according to claim 1 comprising the step of: - said AEC (14) simultaneously operating on several telephone connections. 4. System for eliminating acoustic echoes in connection with a telephone call between an A-party using a digital audio terminal in a room and a B-party using an arbitrary telephone type, wherein the digital audio terminal is connected to a digital exchange in a telecommunication system, and for the telephone call a first digital channel (X1) is used for speech received by the A-party and a second digital channel (Y2) is used for speech transmitted from the A-party, the system comprising: - an acoustic echo control device (14) (AEC) and operating on at least two realized in the exchange (12) digital channels (X1, Y2) assigned for a telephone call. A system according to claim 4 further comprising: - means for connecting the digital audio terminal (10) to the AEC device (14). A system according to claim 5 further comprising: - means for disconnecting the built-in switching circuit in the audio terminal, if available. 7. System for eliminating acoustic echoes in connection with a telephone call between an A-party using a digital audio terminal in a room and a B-party using an arbitrary telephone type, where the digital audio terminal is BNSDOCID: 10 15 20 25 172 45 45 connected to a digital exchange in a telecommunication system, the system comprising: web - a device (14) for controlling acoustic echo (ABC) in the exchange (12), said AEC being connected to the digital the audio terminal (10); a detection unit (74) in said AEC for detecting a speech signal transmitted from the B party (15): "w - means for calculating an echo signal caused by the speech signal; and f fl * - means for calculating in said ABC eliminate the calculated echo signal received from the A-party for the purpose of soooo speech signals from the A-party to the B-party without disturbing stör ëäï signals. "- a» A system according to claim 7 comprising; raaä - means for disconnecting the built-in voice switching circuit in the audio terminal, if available. 9. A method for eliminating the acoustic echoes associated with a telephone call between an A-party, which uses a digital audio terminal in a room, and a B-party, which uses an arbitrary telephone type, where the digital audio terminal is connected to a digital exchange in a telecommunication system, the method comprising the step of: - realizing a device (14) for controlling acoustic echo (ABC) in the digital exchange (12): ~ »? - connect the digital audio terminal (10) to the device (14) for acoustic echo control (AEC) in gear - 'send a test signal (TEST) from the AEC device (§Äï in gear to the digital audio terminal (l0)); BNSDOCID: _505152C2__ | _> 10 15 20 25 30 5Û6 152 ia - detect in. The ABC device (14) the acoustic echo emanating from the test signal in the room where the digital audio terminal is located; - determine in the AEC device the room - establish a telephone connection between the A-party and the B-party, whereby the A-party is connected to the AEC device (14) in the exchange and whereby a first digital channel (X1) is assigned for speech signals received by The A-party, (Y2) a second digital channel is assigned to speech signals transmitted by the A-party, a third digital channel (X3) is assigned to speech signals transmitted from the B-party and a fourth digital channel (Y4) is assigned to voice signals received by the B-party; - send a first voice signal (BTAL) from the B-party to The A-part on the first and third channels (X1, X3); - detecting in the AEC device (14) the first speech signal (BTAL) transmitted from the B-party on the first digital channel (X1); (BEKO) which is generated partly on - calculate an echo signal due to the detected signal, partly due to the echo characteristics of the room, and where the echo signal (BEKO) appears on the other channel (Y2); - receive the echo signal (BEKO) in the ABC device in the digital exchange; and - eliminate in the AEC device the calculated echo signal (BEKO); whereby - the A-party at the same time he sends a second speech signal (ATAL) to the B-party without disturbing echo signals being generated due to the first speech signal. BNSDOCID: 19 506 F52 A method according to claim 9, comprising the step of: - disconnecting the built-in voice switching circuit in the audible terminal, if available. A system for eliminating acoustic echoes in connection with a telephone call between an A-party and a B-party, the system comprising; T - a digital audio terminal (10) used by the A-party; A telephone (15) used by the B-party; - a digital switch (12) connected to the digital audio terminal (10); Ef '- an acoustic echo (AEQ) control device (14) in the digital exchange (12); "1" - means for connecting the digital audio terminal (10) to the device (14) for controlling acoustic echo (AE-c) in the switch; '- means for transmitting a test signal (TEST) from the AEC device in the switch to the digital audio terminal; Means for detecting in the AEC device (14) the acoustic echo originating from the test signal in the room where the digital audio terminal is located; means for determining the eco-characteristics of the room in the AEC device; Means for establishing a telephone connection between the A-party and the B-party, whereby digital channels are allocated for the telephone connection (X1, Y2, X3, Y4); - means for transmitting a first speech signal (BTAL) from the B-party to the A-party on assigned digital channels; I - means for detecting in the AEC device the first speech signal (BTAL) transmitted from the B party on the assigned digital channel (X3); BNSDOCID: 506 152 20 - means for calculating an echo signal (BTAL EKO), which is generated partly due to the detected signal, partly due to the echo characteristics of the room, and where the echo signal (BTAL EKO) appears on the second channel (Y2); 5 - means for receiving the echo signal (BTAL EKO) in the AEC device in the digital exchange; and - means for eliminating the calculated echo signal (BTAL EKO) in the AEC device; whereby the A-party can simultaneously send a second speech signal (ATAL) to the B-party without disturbing echo signals, which are generated from the first speech signal. A system according to claim 11, further comprising: means for disconnecting the built-in voice switching circuit in the audio terminal, if available. BNSDOCID: 11 sne A sz röxxmnmc rILL VISA rönxonmmcan sou USED IN THE DRAWING FIGURES: 5 AMP amplifier MIC microphone LS speaker BNSDOCID: