Source: https://patents.justia.com/patent/5734724
Timestamp: 2019-06-17 07:09:27
Document Index: 155711482

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US Patent for Audio communication control unit Patent (Patent # 5,734,724 issued March 31, 1998) - Justia Patents Search
Justia Patents Pseudo StereophonicUS Patent for Audio communication control unit Patent (Patent # 5,734,724)
Feb 28, 1996 - Nippon Telegraph and Telephone Corporation
FIG. 4 shows another prior art system, in which terminals 4 are each equipped with sound localization signal processing means 4A and interconnected to one another over network communication channels. In this case, the number C.sub.M of communication channels needed is at least M(M-1)/2, where M is the number of terminals 4 to be interconnected. This connection scheme is impractical because with the increase in the number M, the required number of channels to be interconnected for all possible combinations increases rapidly by the factor of about M.sup.2.
FIG. 5 schematically illustrates the general configuration of a multi-point teleconference system using the audio communication control unit according to the present invention. The audio communication control unit of the present invention, identified generally by 100, has a switching part 11, which is connected to a communication network 40 such as ISDN or LAN and is accessible by each terminal connected thereto. Owing to limitations on the capacity and the throughput of the audio communication control unit 100, the maximum number N of conference participants (or the number of terminals) who are allowed to simultaneously participate in a conference is prescribed, N being an integer equal to or greater than 3. For example, four conference participating terminals TM-1 to TM-4 are connected via communication network 40 and the switching part 11 to four of N input channels C.sub.1 to C.sub.4. The input channels C.sub.1 to C.sub.N are connected therethrough to an audio signal mixing control part 10, constituting a multi-point teleconference system which enables the conference participants to talk to one another. As described later in detail, the audio signal mixing control part 10 processes the audio signal originated from each terminal by using one kind of sound image control parameters relating to a sound image such as levels (or level, attenuation, amplification, etc.), delays, phases and transfer functions or a desired combination thereof so that at least one set of the sound image control parameters operates on audio signals from one terminal and other sets of the sound image control parameters operate on audio signals from other terminals.
FIG. 6 illustrates in block form the basic configuration of the audio communication control unit 100 of the present invention for use in the system of FIG. 5. The switching part 11 selectively connects the communication channels from terminals requesting to participate in a conference to the audio signal mixing control part 10 via the N input channels C.sub.1 to C.sub.N. The audio signal mixing control part 10 comprises: a channel branching part 13 by which audio signals fed to the N input channels C.sub.1 to C.sub.N from a maximum of N connected terminals are each branched into audio signals on predetermined K branch channels (where K is an integer equal to or greater than 2, and in FIG. 6, K is set to 2, each corresponding to one of left and right channels) B.sub.JL and B.sub.JR (J=1, . . . , N); a sound image control part 14 which controls N sets of K-channel branched audio signals by predetermined sound image control parameters; a mixing part 15 which mixes N channel-associated corresponding ones of N sets of sound-image controlled K-channel audio signals to generate K-channel mixed audio signals; and a terminal-associated branching part 16 which branches the K-channel mixed audio signals into N sets of K-channel signals, respectively, for input into the switching part 11. The channel branching part 13, the sound image control part 14 and the mixing part 15 constitute an audio signal processing part 25. The switching part 11 mediates therethrough the N sets of K-channel signals to the N conference participating terminals TM-1 to TM-N. In FIG. 6 two-channel (K=2) audio signals are each sent from the switching part 11 to one of the participating terminals over two down-link channels.
A description will be given of embodiments of the present invention in connection with the case where K=2, and when the reproducing parts of each terminal are loudspeakers, K.gtoreq.3 is also possible.
FIG. 8 illustrates a first embodiment of the audio communication control unit based on the basic configuration of FIG. 6 according to the present invention, wherein a plurality of terminals TM-1 to TM-M are connected via communication lines 40 to the audio communication control unit 100 of the present invention. In this embodiment, a principal speaker as an origin of audio signals is judged by monitoring the audio signals on the input channels C.sub.1 to C.sub.N from the switching part 11 connected to a plurality of participating terminals. In the audio communication control unit 100, the audio signals from all the participating terminals are processed so that listeners can distinguish the judged sound position originated from the principal speaker from the judged sound position originated from the speaker at any other terminal.
The utterance detection processing part 23B detects speech by, for instance, monitoring the power of the audio signal. When detecting speech, the speech detecting control part 23B supplies the signal processing control part 20 with a control signal representing the utterance. In FIG. 9 there is shown an example of the utterance detecting scheme in the utterance detection processing part 23B. On the basis of the input audio signal (FIG. 9A), an integrated power IT over a unit time (for 100 ms, for instance) (FIG. 9B) is estimated. Then the integrated power value IT is compared with an ON-detection threshold E.sub.ON and an OFF-detection threshold E.sub.OFF to judge the utterance at the terminal.
With a first utterance identification scheme, when the unit-time integrated power IT exceeds the ON-detection threshold E.sub.ON, utterance at the terminal concerned is immediately judged, and when the integrated power IT decreases lower than the OFF-detection threshold E.sub.OFF, it is immediately decided that the terminal is in the non-speaking or silent state. Therefore, utterance is judged during the diagonally shaded periods (a-b, c-d, f-g) in FIG. 9C. According to the first identification scheme, the utterance-silence judgement is frequently switched.
A second utterance identification scheme differs from the first scheme in that the former judged the utterance on the assumption that the utterance is assured to be continued for a certain period (T in FIG. 9D) after the unit-time integrated power IT falls below the OFF-detection threshold E.sub.OFF. According to this scheme, utterance is judged during the diagonally shaded periods (a-e, f-h) in FIG. 9D.
The audio signal originated from the terminal where utterance is detected in the utterance detection processing part 23B is selected in the speaker selecting part 24 in FIG. 8. The selected audio signal is provided to the audio signal processing part 25 via any one of selected audio signal channels A.sub.1 to A.sub.N. The audio signal processing part 25 includes the channel branching part 13, the sound image control part 14 and the mixing part 15 that are principal components of the present invention.
The signal processing control part 20 operates on control signals received from the multiplexing/demultiplexing part 22 and the utterance detection processing part 23B or a conference control signal from the video display control part 30. Taking into account the number of persons currently speaking, the number of persons requesting to speak and other conditions, for example, a chairperson who must preferentially be given the allowance to speak at all times, the signal processing control part 20 determines those of the selected audio signal channels corresponding to the terminals, whose audio signal is to be mixed, and their priorities. The speaker selecting part 24 connects the selected audio signal channels A.sub.1 to A.sub.N to the input channels positions following the determined priorities. In this embodiment, it is assumed that the audio signal originated from the principal speaker is mediated to the selected audio signal channel A.sub.1 and second to N-th speakers to the selected audio signal channels A.sub.2 to A.sub.N.
FIG. 10 illustrates a concrete example of the audio signal processing part 25, in which the branched audio signals are controlled using the interchannel phase relation as the sound image control parameter. A level control part 14A and a phase control part 14B constitute the sound image control part 14. The audio signals of the selected audio signal channels A.sub.1 to A.sub.N are attenuated by attenuators 4-1, 4-2, . . . , 4-N of the level control part. 14A to 1/2.sup.1/2 -, 1/N.sup.1/2 -, . . . , 1/N.sup.1/2 -fold levels, respectively. The audio signals outputted from the attenuators 4-1 to 4-N are branched at branch points 3-1, 3-2, . . . , 3-N in the channel branching part 13 to left- and right-channel signals on left and right branched channels B.sub.1L, B.sub.1R, . . . , B.sub.NL, B.sub.NR, respectively, which are fed to the phase control part 14B, wherein they are controlled by phase controllers 4-1L, 4-1R, 4-2L, 4-2R, . . . , 4-NL, 4-NR to be in-phase or 180 degrees out-of-phase with each other. The sound image control parameters such as attenuation and phase are set in the parameter setting part 14C under the control of the signal processing control part 20.
The audio signal originated from the principal speaker, that is, the signal of the selected audio signal channel A.sub.1 is attenuated by using the attenuator 4-1 to 1/2.sup.1/2 and branched at the branch point 3-1 to left- and right-channel signals, which are controlled by the phase controllers 4-1L and 4-1R to be in-phase with each other and provided to the mixers 5L and 5R, respectively. The left- and right-channel audio signals at the outputs of the mixers 5L and 5R correspond to the left- and right-channel audio signals at the receiving terminal. Hence, when listening over a stereo reproduction system, the listener at the receiving terminal is able to hear the audio sound on the selected audio signal channel A.sub.1 (originated from the principal speaker) in perspective with its sound image localized at the center of the reproduction system.
The audio signals of the selected audio signal channels A.sub.2 to A.sub.N are branched at the branch points 3-2 to 3-N into left and right channels after being attenuated by the attenuators 4-2 to 4-N, for example, 1/N.sup.1/2 -fold (N being the number of selected audio signal channels A.sub.1 to A.sub.N) So that the sum of the speech power levels of the audio signals on the selected audio signal channels A.sub.2 to A.sub.N, reproduced at each terminal, may be equal to or smaller than the level of the reprooduced speech of the principal speaker. The left-channel audio signals are held in-phase by the phase controllers 4-2L to 4-NL and applied to the mixer 5L, whereas the right-channel audio signals are phase inverted (multiplied by -1) by the phase controllers 4-2R to 4-NR and then applied to the mixer 5R.
When presented with sounds in opposite phase from the left and right channels in stereo reproduction, the listener could not perceive the sound images close to his head in perspective. Through utilization of this human hearing or auditory characteristic, the subordinate audio signals fed to the selected audio signal channels A.sub.2 to A.sub.N are perceived by the listener at each terminal without perspective (i.e. without a sense of distance about him) when he listens over the stereo reproduction system. On the other hand, the sound originated from the principal speaker is localized in a fixed position. The attenuators 4-1 to 4-N in the level control part 14A of the audio signal processing part 25 shown in FIG. 10 are to make the level of the sound originated from the principal speaker reproduced at each terminal larger than the sum of the levels of the sound originated from the other speakers. The difference of localization between the sound originated from the principal speaker and the sound originated from the other speakers is provided solely depending on whether the left- and right-channel audio signals are controlled to be in-phase or opposite phase-of-phase in the phase control part 14B.
FIG. 11 illustrates another embodiment of the audio signal processing part 25, which is designed so that at each terminal only the sound originated from the principal speaker is reproduced by using the left-hand loudspeaker, for instance, and mixed sound originated from all speakers are reproduced by the right-hand loudspeaker with its power level held equal to or lower than the power level of sound originated from the principal speaker. In the right channels B.sub.1R to B.sub.NR branched by the channel branching part 13, there are introduced the attenuators 4-1R, 4-2R, . . . , 4-NR of an attenuation factor N.sup.1/2 ; the attenuation of the attenuator 4-1L in the branched left channel B.sub.1L for the principal speaker is set to zero and an attenuation sufficiently larger than the attenuation factor N.sup.1/2 in the right channel, for example, an infinite attenuation, is set in each of the attenuators 4-2L, . . . , 4-NL of the left channels B.sub.2L to B.sub.NL (that is, the channels are held OFF). Accordingly, only the audio signal of the selected audio signal channel A.sub.1 for the principal speaker is applied to the left-channel mixer 5L without being attenuated and the signals of all the selected audio signal channels A.sub.1 to A.sub.N are applied to the right-channel mixer 5R after being attenuated by the attenuators 4-1R to 4-NR to an appropriate volume of, say, 1/N.sup.1/2.
The speaker selecting part 24 is provided when the sound image control parameters are set in the audio signal processing part 25 described later in respect of FIG. 10. In the case where in the audio signal processing part 25 of FIG. 10 the audio signals of any pair of left and right branched channels B.sub.JL and B.sub.JR can be set to be either in-phase or 180 degrees out-of-phase with each other and the attenuation factor can be set at 1 to 1/N.sup.1/2 for any speech selected channel A.sub.J, the speaker selecting part 24 is dispensable with setting the sound image control parameters for the input channel of the audio signal originated from the principal speaker and for the other channels in the parameter setting part 14C in the same relation as that between the parameter for the principal speaker's channel (selected audio signal channel A.sub.1) and the parameters for the other selected audio signal channels A.sub.2 to A.sub.N in FIG. 10. Similarly, when the attenuation factor for each branched channel can selectively set to any of 0, 1/N.sup.1/2 and 1/.infin. in the parameter setting part 14C, the speaker selecting part 24 is unnecessary.
FIG. 15 schematically illustrates, by way of example, the configuration of that one 21-J of the terminal-associated mixing control parts 21-1 to 21-N which corresponds to the terminal TM-J in the FIG. 14 embodiment. The terminal-associated mixing control part 21-J is composed of: conference selecting switches 7S-1 to 7S-Q which are supplied with left- and right-channel audio signals from the Q signal processing control parts 25-1 to 25-Q; a left-channel mixer 2-L connected to left-channel outputs of all the conference selecting switches 7S-1 to 7S-Q; and a right-channel mixer 2-R connected to right-channel outputs of the conference selecting switches 7S-1 to 7S-Q. In response to a participating conference designating control signal received from the terminal TM-J, the signal processing control part 20 turns ON one or more conference selecting switches (1.ltoreq.P.ltoreq.Q) corresponding to the designated conferences, thus selecting the designated conferences.
Instead of using the conference selecting arrangement that performs the aforementioned terminal-associated conference selection by the conference selecting switches 7S-1 to 7S-Q in FIG. 15, it is also possible to adopt an arrangement in which the terminal-associated branching part 16 is formed by a switch matrix logically having 2Q by (2Q.times.N) inputs/outputs and ON-OFF control of its contacts is made by the signal processing control part 20 on the basis of a conference selecting command from the terminal to supply the terminal-associated mixing control parts 21-1 to 21-N with only the audio signal of the conference designated by the terminal.
In this embodiment, the sets of channel branch points 3-1, . . . , 3-N of the channel branching part 16 and left and right signal processing parts 4-1L, 4-1R, 4-2L, 4-2R, . . . , 4-NL, 4-NR of the sound image control part 14, which correspond to the respective terminals, are shown as sound image processing parts 8-1, 8-2, . . . , 8-N, respectively. In FIG. 17 there is illustrated, by way of example, the sound image processing part 8-1. Based on the principle described previously with respect to FIG. 2, the sound image processing part 8-1 convolves, by convolvers 4-1L and 4-1R, acoustic transfer functions H.sub.1L and H.sub.1R into left and right audio signals branched at the channel branch point 3-1, respectively. The audio Signals resulting from the convolution are applied as left- and right-channel audio signals to the mixers 5L and 5R of the mixing part 15 in FIG. 16. The transfer functions H.sub.1L and H.sub.1R, which are convolved with the branched audio signals of the respective channels, can be determined corresponding to the spatial positions desired to localize reproduced sounds of the audio signals.
The switching part 11 selects J (where 1.ltoreq.J.ltoreq.M) communication lines from an unspecified number of communication lines 40 forming a communication circuit network, where M represents the number of terminals simultaneously connected to the network and usually M.ltoreq.N. Every selected communication line is connected as two channels for each one of terminals that simultaneously conduct audio communication. One of the two channels carries the input audio signal in this example and is connected to a decoding part 23-J (where J=1, 2, . . . , N). The other channel carries the output audio signal and is connected to a multiplexing part 22-J via the input channel C.sub.J. Each decoding part 23-J decodes the audio signal inputted thereto from the terminal connected thereto. The audio signal decoded in the decoding part 23-J is applied to an amplification factor setting part 35 and an amplifier 36-J.
The signal processing control part 20 receives a connection confirm signal and similar control signals that are transmitted from the respective terminals via the switching part 11. The signal processing control part 20 detects the number M of connected terminals from such control signals and sends the detected number M of connected terminals to the amplification factor setting part 35 and the parameter setting part 14C. The amplifier 36-J amplifies the input audio signal with an amplification factor G.sub.J, which is determined in the amplification factor setting part 35. For example, the amplification factor G.sub.J is determined such that the integrated power IT of the audio signal from the amplifier 36-J is equal for any channels.
The parameter setting part 14C sets acoustic transfer function H.sub.JL (.theta..sub.J) and H.sub.JR (.theta..sub.J) necessary for the sound image processing part 8-J to synthesize an audio signal for localization of the reproduced sound originated from the terminal TM-J of each point J at a different target position .theta..sub.J. The target positions .theta..sub.J and the acoustic transfer functions H.sub.JL (.theta..sub.J) and H.sub.JR (.theta..sub.J) have a one-to-one correspondence; hence, once the target position .theta..sub.J is determined for each input signal, the acoustic transfer functions H.sub.JL (.theta..sub.J) and H.sub.JR (.theta..sub.J) can be determined which are convolved with each audio signal. In this example, the target positions .theta..sub.J for the audio signals from respective terminals are determined on the basis of the number M of connected terminals. As exemplified in FIG. 18 wherein M=5, the target positions .theta..sub.J are determined at equiangular intervals of .DELTA..theta.=180/(M-1) degrees about the listener over at angular positions (+90.degree.)-(0.degree.)-(-90.degree.) from his left to right side in a horizontal plane. The target positions .theta..sub.J for the terminals TM-J at the respective points J are determined by 90-180(J-1)/(M-1) degrees according to the number M of connected terminals. Therefore, the target position spacing .DELTA..theta. is minimum in the case of using the maximum number N of connectable points (M=N).
In the sound image processing part 8-J, as described previously with respect to FIG. 17, the transfer functions H.sub.JL (.theta..sub.J) and H.sub.JR (.theta..sub.J) set by the parameter setting part 14C are convolved with the audio signal from the amplifier 36-J, and the convolved outputs are applied as left- and right-channel audio signals to the mixers 5L and 5R, respectively. In the case of binaural listening to these left- and right-channel audio signals by use of a headset, the listener can localize the sound image at the target position .theta..sub.J. The left- and right-channel audio signals from the sound image processing part 8-J are also provided to delay parts D-JL and D-JR, respectively.
On the other hand, the left-channel audio signal applied to each delay part D-JL is delayed for a time .tau..sub.JL and provided to the canceler 26-JL. The delay .tau..sub.JL is set to the sum of the delay by the audio signal processing in the mixer 5L and the delay by the audio signal processing at the branch point 6L. Consequently, the left-channel audio signal outputted from the delay part D-JL and that component of the left-channel mixed audio signal outputted from the branch point 6L which was applied to the mixer 5L from the sound image processing part 8-J become in-phase and they cancel each other in the canceler 26-JL. Accordingly, the audio signal component received from the terminal TM-J at each point J is eliminated from the left-channel mixed audio signal to be branched to the terminal TM-J and hence an echo can be prevented. Accordingly, the audio signal that is sent back to the terminal TM-J via the canceler 26-JL is only a mixed version of audio signals from the terminals other than TM-J. For the same reason as given above, the delay part D-JR delays the right-channel audio signal from the sound processing part 8-J for a time .tau..sub.JR and then applies it to the canceler 26-JR. The delay .tau..sub.JR is set to the sum of the delay by the audio signal processing in the mixer 5R and the delay by the audio signal processing at the branch 6R.
The echo-suppressed left- and right-channel audio signals outputted from the cancelers 26-JL and 26-JR are provided to the multiplexing part 22-J, wherein they are multiplexed and encoded, thereafter being sent via the switching part 11 to the terminals TM-J at the points J. In this way, each multiplexing part 22-J multiplexes audio signals of the left and right channels into a one-channel audio signal and encodes it. As a result, the multiplexed one-channel audio signal is encoded and then transmitted via the switching part 11 to the points J (1.ltoreq.J.ltoreq.M) over one communication line. Thus the delay difference between the communication lines by the use of two lines for the transmission of two-channel stereo signals can be avoided, and the number of communication lines used can be saved. By decoding the multiplexed audio signal and reproducing the sounds at each terminal, the listener at that terminal can localize the sounds from other terminals at desired target positions .theta..sub.J. This enables each listener to easily identify the other speakers and ensures high speech intelligibility. Additionally, no sound image position processing means is needed for the sound localization at each point and an economical system can be implemented.
Incidentally, the FIG. 16 embodiment is based on the assumption that two communication lines are used for the transmission of the two-channel stereo audio signals to each of the points J (1.ltoreq.J.ltoreq.M) from the audio communication control unit 100. In such an instance, one communication line is used for each of the left- and right-channel audio signals and the switching part 11 needs to perform three-switching for each point J. Further, the multiplexing and demultiplexing in the multiplexing part 22-J and at each point in FIG. 16 become unnecessary, but two coding parts 22-JL and 22-JR are needed for each terminal as a substitute for one multiplexing part 22-J. It is also necessary to connect the cancelers 26-JL and 26-JR to the inputs of the coding parts 22-JL and 22-JR for inputting thereinto audio signals.
In FIG. 20 there is illustrated the basic configuration of a fourth embodiment of the audio communication control unit of the present invention intended to overcome the disadvantage mentioned above. The main arrangement of the audio communication control unit of this embodiment can be formed by: the switching part 11; the sound image processing parts 8-J (J=1, 2, . . . , N, where N=6 in this example), each of which performs speech processing for localizing the position of the speaker's sound source by convolving transfer functions from the sound source to listener's both ears with the audio signal sent from one of the terminals TM-1 to TM-6; a combination assignment part 19 for assigning combinations of terminals in correspondence with multiple teleconferences; an mixing/branching parts 17-P (P=1, 2, . . . , Q, where Q=2 in this example); and a mixing part 12. Each mixing/branching part 17-P is composed of the left- and right-channel mixers 5L and 5R and the branch points 6L and 6R. The mixing part 12 comprises N left- and N right-channel mixers 2-JL and 2-JR (J=1, 2, . . . , where N=6 in this example). The components of the same kind are specified by suffixes J (1.ltoreq.J.ltoreq.N) and P (1.ltoreq.P.ltoreq.Q). The components for processing the audio signals of the left and right channels are similarly identified by suffixes L and R, respectively.
The operation of the audio communication control unit according to this embodiment will be described. The switching part 11 selects a communication line J (1.ltoreq.J.ltoreq.M) from among an unspecified number of lines forming the circuit network, M representing the number of terminals connected to the network at the same time. Usually, M.ltoreq.N, where N represents the maximum number of connectable terminals. In response to a communication start/end, terminal designate, connection confirmation or similar control signal received from one terminal, for instance, the switching part 11 selects the communication line J and couples it to the sound image processing part 8-J via the input channel C.sub.J in this example. The sound image processing part 8-J is identical in construction to that depicted in FIG. 17 and corresponds to a set of one branch point 3-J and left- and right-channel signal processing parts 4-JL and 4-JR in FIG. 6.
The parameter setting part 14C sets acoustic transfer functions H.sub.L (.theta..sub.J) and H.sub.R (.theta..sub.J) necessary for the sound image processing part 8-J to perform processing for generating an audio signal whose reproduced sound originated from each terminal TM-J is localized at a different target position .theta..sub.J. Since the target positions .theta..sub.J and the acoustic transfer functions H.sub.L (.theta..sub.J) and H.sub.R (.theta..sub.J) have a one-to-one correspondence, the acoustic transfer functions can be set once the target positions are determined. In this embodiment, based on the number M of connected terminals, the target positions .theta..sub.J for the sounds originated from the respective terminals are determined. As shown in FIG. 21C, the target positions .theta..sub.J are determined at equiangular intervals of 180/(M-1) degrees about the listener over at angular positions (+90.degree.)-(0.degree.)-(-90.degree.) from his left- to right side in a horizontal plane. That is, the target positions .theta..sub.J for the points J are determined by 90-180(J-1)/(M-1) degrees.
Since M=6 in the example of FIG. 21C, the target positions .theta..sub.J for the terminals TM-1 to TM-6 are as follows:
.theta..sub.J=1 =90.degree.-180.degree..times.(1-1)/(6-1)=+90.degree.
.theta..sub.J=2 =90.degree.-180.degree..times.(2-1)/(6-1)=+54.degree.
.theta..sub.J=3 =90.degree.-180.degree..times.(3-1)/(6-1)=+18.degree.
.theta..sub.J=4 =90.degree.-180.degree..times.(4-1)/(6-1)=-18.degree.
.theta..sub.J=5 =90.degree.-180.degree..times.(5-1)/(6-1)=-54.degree.
.theta..sub.J=6 =90.degree.-180.degree..times.(6-1)/(6-1)=-90.degree.
The sound image processing part 8-J convolves the acoustic transfer functions H.sub.L (.theta..sub.J) and H.sub.R (.theta..sub.J), set in the parameter setting part 14C for the terminal TM-J, with the audio signal fed from the amplifier 36-J, generating left- and right-channel stereo audio signals. Listening to sounds reproduced from the stereo audio signals binaurally, the listener localizes the sound image at the target position .theta..sub.J.
The left- and right-channel audio signals from the sound image processing part 80J are distributed to the Q terminal selecting switches 9.sub.1 -J, 9.sub.2 -J, . . . , 9.sub.Q -J. Based on the control information about communication start/end and the communication conference membership of each connected terminal instructed by the signal processing control part 20, the conference participating terminal selecting part 9C determines and sends terminal selecting information to the terminal selecting switch 9.sub.P -J. For instance, upon opening or closure of the teleconference P to which the terminal TM-J belongs, the conference participating terminal selecting part 9C transfers a control signal to the terminal selecting switch 9.sub.P -J to permit or inhibit the passage therethrough of audio signals. The terminal selecting switch 9.sub.P -J responds to the control signal to permit or inhibit the passage therethrough of audio signals. As the result of this, for example, in the combination of terminals shown in FIG. 21C, the audio signals originating from the terminals TM-1 to TM-3 are assigned to the mixing/branching part 17-1 and the audio signals from the terminals TM-3 to TM-6 are assigned to the mixing/branching part 17-2.
Turning now to FIG. 23, the internal construction of the mixing/branching part 17-P will be described. The left- and right-channel audio signals fed from each terminal selecting switch 9.sub.P -J are applied to the mixers 5L and 5R, respectively, and at the same time, they are provided to delay parts D-JL and D-JR as well. The mixer 5L mixes together N inputted left-channel audio signals and outputs the mixed left-channel audio signal to the branch point 6L. The mixer 5R similarly mixes together N inputted right-channel audio signals and outputs the mixed right-channel audio signal to the branch point 6R. The branch point 6L branches the mixed left-channel audio signal inputted thereto to N cancelers 26-JL (J=1, . . . , N). Likewise, the branch point 6R branches the mixed right-channel audio signal inputted thereto to N cancelers 26-JR (J=1, . . . , N).
The delay part D-JL delays for a time .tau..sub.JL the left-channel audio signal fed from the terminal selecting switch 9.sub.P -J and applies the delayed left-channel audio signal to the canceler 26-JL. The delay .tau..sub.JL is selected to be the sum of the delay by the audio signal processing in the mixer 4L and the delay by the audio signal processing in the branch point 6L. In consequence, the left-channel audio signal outputted from the delay part D-JL and that left-channel audio signal component in the left-channel mixed audio signal from the branch point 6L that was outputted from the terminal selecting switch 9.sub.P -J are synchronized with each other. The delay .tau..sub.JR of the delay part D-JR is also similarly determined, and the right-channel audio signal outputted from the delay part D-JR and that right-channel audio signal component in the right-channel mixed audio signal from the branch point 6R which was outputted from the terminal selecting switch 9P-L are synchronized with each other.
The cancelers 26-JL and 26-JR cancel the delayed audio signals fed from the delay parts D-JL and D-JR from the audio signals fed from the branch points 6L and 6R, respectively. As the result of this, the above-mentioned components cancel each other, and in the channel corresponding to each terminal TM-J, a mixed audio signal originating from other channels K (J.noteq.K) is obtained. This mixed audio signal is applied to the conference selecting switch 7-P. That is, the audio signal originating from each terminal TM-J is excluded from the audio signal that is transmitted to that terminal TM-J. Thus an echo can be cancelled which is attributed to the audio communication control unit 100 of this embodiment.
Turning back to FIG. 22, the conference selecting part 7C determines conference selecting information in response to teleconference P opening/closure information instructed by the signal processing control part 20. This conference selecting information is transferred to the conference selecting switch 7-P. For example, when the teleconference P is opened or closed, a control signal is transferred to the terminal selecting switch 9.sub.P -J to permit or inhibit the passage therethrough of audio signals. The conference selecting switch 7-P responds to the control signal from the conference selecting part 7C to permit or inhibit the passage therethrough of the audio signal outputs from the mixing/branching part 17-P, i.e. from the cancelers 26-JL and 26-JR.
The inter-combination mixers 2-JL and 2-JR respectively add the left- and right channels of Q combinations of terminals Ps selected by the conference selecting switches 7-P (P=1, . . . , Q) from J-th channels of the Q mixing/branching parts 17-P (P=1, . . . , Q) corresponding to the Q combinations of terminals. The reference character P.sub.S is the number of the combination of terminals (or the conference number) for which audio signals are mixed together and a maximum of Q combinations can be selected in the range of 0.ltoreq.P.sub.S .ltoreq.Q. The corresponding left- and right-channel audio signals of the selected combinations of terminals mixed together and the mixed audio signals are sent to each terminal TM-J, at which the user can listen to sounds from all the other terminals belonging to the selected multiple terminal combinations (multiple teleconferences). The audio signal originated from the terminal TM-J is sent to all the other terminals selecting those terminal combinations including the terminal TM-J. Each multiplexing/coding part 22-J multiples and encodes the left- and right-channel audio signals fed from the inter-combination mixing parts 2-JL and 2-JR. That is, the multiplexing/coding part 22J multiplexes the stereo audio signals corresponding to left and right channels into one-channel audio signals and encodes them. As a result, the encoded one-channel multiplexed signals are independently applied to the switching part 11 for each terminal TM-J and the one-channel multiplexed audio signals are transmitted to each terminal TM-J (1.ltoreq.J.ltoreq.M) over one communication line.
As described above, the embodiment of FIG. 22 has Q mixing/branching parts 17-1 to 17-Q corresponding to Q teleconferences, and upon receiving from each terminal TM-J the control signal designating one or more teleconferences in which the user of that terminal intends to participate (speak), the signal processing control part 20 applied the control signal to the conference participating terminal selecting part 9C. The conference participating terminal selecting part 9C turns ON so that one or more of the Q terminal selecting switches 9.sub.P -J (P=1, . . . , Q) for the audio signal originated from the terminal TM-J are mediated to the mixing/branching part 17-P corresponding to the teleconferences specified by the control signal. Therefore, the audio signal originated from the terminal TM-J can be connected to the one or more teleconferences designated by the terminal TM-J and its user can join the teleconferences. Additionally, the FIG. 22 embodiment has Q conference selecting switches 7-1 to 7-Q connected to the outputs of the Q mixing/branching part 17-1 to 17-Q. Upon receiving from each terminal TM-J the control signal designating one or more teleconferences the user of that terminal intends to monitor, the signal processing control part 20 passes the control signal to the conference selecting part 7C. The conference selecting part 7C responds to the control signal to turn OFF the conference selecting switches connected to the one or more mixing/branching parts corresponding to the teleconferences specified by the control signal, thereby mediating audio signals of the designated one or more teleconferences to the terminal TM-J.
The signal processing control part 20 receives, from respective terminals via the switching part 11, such control signals as those on communication start/end, connection confirmation and the membership of the teleconferences P assigned by combinations of connected terminals TM-J. The signal processing control part 20 detects according to these control signals the information on the connected terminal TM-J, the number M of connected terminals, communication start/end, the membership of the teleconferences P and the number of terminals belonging to each teleconference P. Additionally, the signal processing control part 20 sends information of the detected terminals and the number M of connected terminals to the amplification factor setting part 35, sends the communication start/end information to the conference participating terminal selecting part 9C and the conference selecting part 7C, sends the membership of each connected terminal TM-J in the teleconferences P to the conference participating terminal selecting part 9C, and sends the number M.sub.P of terminals belonging to each teleconference P to the parameter setting part 14C.
For each combination of terminals P, the parameter setting part 14C sets in the sound image processing parts 8-J acoustic transfer functions H.sub.L (.theta..sub.PJ) and H.sub.R (.theta..sub.PJ) that are convolved with the audio signals originated from all terminals TM.sub.P -J of the combination P relating to target positions TM.sub.PJ. In this embodiment, the target position .theta..sub.PJ for sound originated from each terminal TM-J is determined on the basis of the number M.sub.P of terminals belonging to the teleconference P detected in the signal processing control part 20. As exemplified in FIG. 21C, the respective target positions .theta..sub.PJ are determined at equiangular intervals of 180/(M.sub.P -1) degrees about the listener at angular positions (+90.degree.)-(0.degree.)-(-90.degree.) from his left to right side in a horizontal plane. Letting the numbers of terminals TM-J belonging to the teleconference P be J.sub.P (1.ltoreq.J.sub.P.ltoreq. .ltoreq.M.sub.P) in a sequential order, the target positions .theta..sub.PJ are determined by 90-180(J.sub.P -1)/(M.sub.P -1) degrees as described previously.
The one-channel audio signal originated from each terminal TM-J is distributed to Q terminal selecting switches 9.sub.P -J (P=1, . . . , Q). Each terminal selecting switch 9.sub.P -J controls passage therethrough of each one-channel audio signal in response to a control signal sent from the conference participating terminal selecting part 9C, and the audio signal having passed through the terminal selecting switch 9.sub.P -J is applied to the corresponding sound image processing part 8.sub.P -J. In each sound image processing part 8.sub.P -J the acoustic transfer functions H.sub.L (.theta..sub.PJ) and H.sub.R (.theta..sub.PJ), set in the parameter setting part 14C, are convolved with the audio signal outputted from the terminal selecting switch 9.sub.P -J to obtain a two-channel audio signal, which is fed to the mixing/branching part 17-P. There are provided N (J=1, . . . , N) sound image processing parts 8.sub.P -J for each set P of terminals, whereas in FIG. 22 the number of sound image processing part 8-J is only N. The terminal selecting switch 9.sub.P -J in FIG. 22 differs from the counterpart in this embodiment of FIG. 25 in that the former interrupts the two-channel audio signal. The mixing/branching part 17-P are exactly identical in construction and operation to that in FIG. 23.
The FIG. 25 embodiment differs from the embodiment of FIG. 22 in the order of processing audio signals. In the embodiment of FIG. 25, one-channel audio signals originated from respective terminals TM-J are grouped for each combination P (P=1, . . . , Q) of terminals, after which two-channel audio signal for sound localization at respective target positions is generated for each teleconference P. Accordingly, the respective terminals TM-J belonging to each teleconference P are allowed to set different target positions 8.sub.PJ independently for each teleconference P. That is, it is possible to set in the parameter setting part 14C the acoustic transfer functions H.sub.L (.theta..sub.PJ) and H.sub.R (.theta..sub.PJ) as sound image control parameters for enabling the listener to localize sounds originated from the terminals TM-J belonging to each teleconference P at respective target positions .theta..sub.PJ.
Now, a description will be given of a method how the spacing of target positions for sounds originated from respective terminals TM-N in each teleconference P is increased on the basis of the number M.sub.P of terminals belonging to the teleconference P. Consider the application of this method to the combinations of terminals shown in FIGS. 26A and 26B. Since the teleconference X is held among three terminals as shown in FIG. 26A, the target positions are spaced 90.degree. apart. The target positions for the terminals TM-1, TM-2 and TM-3 are sequentially distributed at angular positions (+90.degree.)-(0.degree.)-(-90.degree.) about the listener from his left to right side. Since the teleconference Y is held among four terminals, the target positions are spaced 60.degree. apart. The target positions for sounds originated from the terminals TM-3, TM-4, TM-5 and TM-6 are sequentially distributed at angular positions (+90.degree.)-(+30.degree.)-(-30.degree.)-(-90.degree.) about the listener from his left to right side.
For comparison, consider the case where the target positions are determined using the number M of all connected terminals. Since the number M of all connected terminals is 6, the target positions are spaced 36.degree. apart, and as shown in FIG. 21C, the target positions for sounds originated from the terminals TM-1 to TM-6 are sequentially distributed at angular positions (+90.degree.)-(+54.degree.)-(+18.degree.)-(-18.degree.)-(-54.degree.)-(-90 .degree.) about the listener from his left to right side. In the embodiments of FIGS. 21A and 21B, since the combination is assigned after the processing for sound localization, the target positions cannot be independently set for each teleconference P; hence, the target position for sound originated from one terminal is fixed regardless of the combination of terminals. In such an instance, the target position distribution for the teleconference X among the terminals TM-1 to TM-3 is confined ranging from the right side (+90.degree.) of the listener to the front of him on the right (+18.degree.) as depicted in FIGS. 21A and 21B. In the teleconference Y involving the terminals TM-3 to TM-6, the target positions are distributed over the range from the front of the listener on the left (+18.degree.) to the front of him on the right (-90.degree.).
As described above, the embodiments of FIGS. 24 and 25 allow setting of the target positions for each of teleconferences. Additionally, by setting the target positions according to the number M.sub.P of terminals belonging to each combination (i.e. teleconference) P, the angular range of the distribution and the spacing of the target positions for sounds originated from each terminal can be wider than in the embodiments of FIGS. 20 and 22. Consequently, this embodiment allows the listener to identify each speaker more easily and to provide further improved intelligibility than in the embodiments of FIGS. 20 and 22.
According to the FIG. 25 embodiment, when the number of terminals participating in a teleconference changes, the target positions of sounds originated from the terminals participating can be updated accordingly. In such an instance, the target positions of sounds originated from all the conference participating terminals can be determined following a model for arrangement (a set of acoustic transfer functions H.sub.L (.theta..sub.J) and H.sub.R (.theta..sub.J)) of the target positions of sounds originated from respective terminals predetermined by the signal processing control part 20 of the audio communication control unit 100 in accordance with respective numbers of participating terminals. That is, when the number M Of conference participants changes in response to a request to leave or participate in the teleconference, the target positions to be assigned to remaining participants are renewed referring to the arrangement model according to the updated number of participants and the corresponding sets of acoustic transfer functions H.sub.L (.theta..sub.J) and H.sub.R (.theta..sub.J) are selected according to the renewed target positions and each set in one of the sound image processing parts 8-J. As an initial procedure of the teleconference, it is also possible to predetermine possible target positions according to the number of participants and allow the participants to customize those positions.
In the embodiments of FIGS. 8 and 14, it is also possible to employ an arrangement in which switches SW-1 to SW-N are connected in series to the respective channels at the output side of the utterance detection processing part 23B as indicated by the broken lines and the utterance detection processing part 23B judges utterance of each channel, and holds the switch SW-J in that channel OFF except only during the utterance period, thereby suppressing noise originated from that channel. Utterance can be judged depending on whether the integrated power of the audio signal exceeds the threshold E.sub.ON as described previously herein with reference to FIG. 8. In the embodiments of FIGS. 16, 22 and 25, too, it is possible to assign switches SW-1 to SW-N in series to the outputs of the decoding parts 23-1 to 23-N as indicated by the broken lines, judge utterance of each channel according to the audio signal on the channel, and hold the channel by the amplification factor setting part 35 ON only during its utterance period.
1. An audio communication control unit for teleconferencing which is connected via a communication network to a plurality of terminals, comprising:
a channel branching part for branching each of said input audio signals from said N input channels into two branched audio signals of branched channels;
a sound image control part for processing said two branched audio signals of said two branched channels corresponding to each of said N input channels with a corresponding one of N parameter sets each including two sound image control parameters or predetermined kind of kinds to produce sound-image controlled audio signals of two branch channels corresponding to each of said N input channels, at least one of said N parameter sets being different from the other parameters sets according to target positions of said terminals;
a mixing part for mixing said sound-image controlled audio signals of two branch channels corresponding respectively to said N terminals, for each branch channel, to thereby generate mixed audio signals of two channels;
a terminal-associated branching part for branching said mixed audio signals of two channels in correspondence with said N terminals for input into said switching part; and
signal processing control part for deciding a top-priority one of said N input audio signals as an audio signal of a principal speaker and the other remaining input audio signals as audio signals of other speakers;
wherein said channel branching part branches each of said N input audio signals fed thereto from said N input channels into first and second branch channel audio signals and outputs them as said two branched audio signals; and
said sound image control part includes a phase control part which, under the control of said signal processing control part, sets said first and second branch channel audio signals corresponding to said principal speaker's audio signal to be in-phase with each other and sets said first- and second-channel audio signals corresponding to said other speakers' audio signals to be out-of-phase with each other.
2. An audio communication control unit for teleconferencing which is connected via a communication network to a plurality of terminals, comprising:
a channel branching part for branching each of said input audio signals from said N input channels into two branched audio signals of two branched channels;
a sound image control part for processing said two branched audio signals of said two branched channels corresponding to each of said N input channels with a corresponding one of N parameter sets each including two sound image control parameters of predetermined kind or kinds to produce sound-image controlled audio signals of two branch channels corresponding to each of said N input channels, at least one of said N parameter sets being different from the other parameter sets according to target positions of said terminals;
a terminal-associated branching part for branching said mixed audio signals of two channels in correspondence with said N terminals for input into said switching part;
a speaker selecting part provided between said N input channels and said channel branching part, for selecting input audio signals to be mixed together from said input audio signals inputted through said N input channels via said switching part and for outputting said selected input audio signals;
N selected audio signals channels for applying said selected input audio signals from said speaker selecting part to said channel branching part; and
a signal processing control part for controlling said speaker selecting part so that one of said input audio signals to be processed by said at least one of said N parameter sets, is outputted to a predetermined one of said N selected audio signal channels;
wherein said signal processing control part decides a top-priority one of said N input audio signals as an audio signal of a principal speaker and the other remaining input audio signals as audio signals of other speakers;
said speaker selecting part outputs, on the basis of the results of said decision by said signal processing control part, said principal speaker's audio signal and said other speakers' audio signals to said predetermined one of said N selected audio signal channels and the other remaining selected audio signal channels, respectively, as input to said channel branching part;
said channel branching part branches each of said N input audio signals applied thereto and outputs first- and second-branch channel audio signals as said branched audio signals of said two branch channels; and
said sound image control part includes a phase control part which, under the control of said signal processing control part, sets said first- and second-branch channel audio signals corresponding to said principal speaker's audio signal from said predetermined one selected audio channel to be in-phase with each other and sets said first- and second-branch channel audio signals corresponding to said other speakers' audio signals from said other selected audio channels to be out-of-phase with each other.
3. An audio communication control unit for teleconferencing which is connected via a communication network to a plurality of terminals, comprising:
a mixing part for mixing said sound-image controlled audio signals of two branch channels corresponding respectively to said N terminals, for each branch channel, to thereby generate mixed audio signals of two channels; and
wherein said channel branching part branches each of said N input audio signal fed thereto into first and second branch channel audio signals and outputs them as said two branched audio signals;
a signal processing control part decides a top-priority one of said N input audio signals as an audio signal of a principal speaker and the other remaining input audio signals as audio signals of other speakers; and
said signal processing control part sets said N parameter sets to said sound image control part such that said sound image control part attenuates said second branch channel audio signal corresponding to said decided principal speaker's audio signal by a first value sufficiently larger than the attenuation value of said first branch channel audio signal corresponding to said decided principal speaker's audio signal and attenuates said first branch channel audio signal corresponding to said other speakers' audio signals by a second value sufficiently larger than the attenuation value of said second branch channel audio signal corresponding to said other speakers' audio signals.
4. The audio communication control unit of claims 1 or 2, wherein said sound image control part includes an attenuation part which attenuates said other speakers' audio signals to a level lower than that of said principal speaker's audio signal under the control of said signal processing part.
6. An audio communication control unit for teleconferencing which is connected via a communication network to a plurality of terminals, comprising:
a channel branching part for branching each of said input audio signals from sid N input channels into two branched audio signals of two branched channels;
N selected audio signal channels for applying said selected input audio signals from said speaker selecting pan to said channel branching part; and
wherein said signal processing control part decides a top-priority one of said N input audio signals from said N input channels as an audio signal of a principal speaker and the other remaining input audio signals as audio signals of other speakers;
said speaker selecting part outputs said principal speaker's audio signal and said other speakers' audio signals to said predetermined one of said N selected audio channels and the other remaining selected audio signal channels, respectively, for input to said channel branching part;
said channel branching part branches each of said N input audio signals applied thereto into first and second branch channel audio signals and outputs them as said two branched audio signals; and
said sound image control part includes an attenuation part which, under the control of said signal processing control part, attenuates said second branch channel audio signal from said predetermined one selected audio channel by a first attenuation value sufficiently larger than the attenuation value of said first branch channel audio signal from said predetermined one selected audio channel and attenuates each of said first-channel audio signals from said remaining selected audio channel by a second value sufficiently larger than the attenuation value of said second branch channels audio signals from said remaining selected audio channels.
7. An audio communication control unit for teleconferencing which is connected via a communication network to a plurality of terminals, comprising:
a switching part for switching audio signals received from N terminals via said communication network, N being an integer equal to or greater than 3;
a sound image control part for processing said K branched audio signals of said K branched channels corresponding to each of said N input channels with a corresponding one of N parameter sets each including K sound image control parameters of predetermined kind or kinds to produce sound-image controlled audio signals of K branch channels corresponding to each of said N input channels, at least one of said N parameter sets being different from the other parameter sets according to target positions of said terminals;
a mixing part for mixing sound-image controlled audio signals of K branch channels corresponding respectively to said N terminals, for each branch channel, to thereby generate mixed audio signals of K channels;
a terminal-associated branching part for branching said mixed audio signals of K channels in correspondence with said N terminals for input into said switching part; and
a cancelling part for cancelling from each of said K-channel mixed audio signals distributed by said terminal-associated branching part to each of said N terminals, respectively, the component of each of said K-channel sound-image controlled audio signals from said sound image control part corresponding to said each terminal.
8. An audio communication control unit for teleconferencing which is connected via a communication network to a plurality of terminals, comprising:
a channel branching part for branching each of said input audio signals from said N input channels into K branched audio signals of K branched channels, K being an integer equal to or greater than 2;
a terminal-associated branching part for branching said mixed audio signals of K channels in correspondence with said N terminals for input into said switching part;
wherein Q sets of said mixing part and said terminal-associated branching part are provided in correspondence with Q teleconferences; Q being an integer equal to or greater than 2;
said audio communication control unit further comprising a combination assignment part for applying said K-channel sound-image controlled audio signal from said sound image control part, which corresponds to each of said N terminals, to designated one or more mixing parts; and
an inter-combination mixing part for mixing together, for a corresponding one of the K channels, said K-channel mixed audio signals distributed from one or more of said terminal-associated branching parts and for outputting said channel-associated mixed audio signals to said each terminal;
said K channels being left and right channels and said sound image control parts each generating, for each terminal, a stereo audio signal of left and right channels as said sound-image controlled audio signal by convolving said branched audio signals of said left and right channels corresponding to said each terminal, respectively, with a pair of acoustic transfer functions used as said sound image control parameters, which correspond to a target position of a sound source different for each of said N terminals.
9. The audio communication control unit of claim 8, further comprising a signal processing control part which detects the number of said terminals participating in any of said Q teleconferences by detecting signals requesting to participate in the teleconferences from said terminals, determines a plurality of target positions of the same number as the number of terminals participating in the teleconferences, determines said pairs of acoustic transfer functions as said sound image control parameters corresponding to said determined target positions and provides said determined pairs of acoustic transfer functions to said sound image control parts, respectively.
11. An audio communication control unit for teleconferencing which is connected via a communication network to a plurality of terminals, comprising:
a mixing part for mixing said sound-image controlled audio signals of K branch channels corresponding respectively to said N terminals, for each branch channel, to thereby generate mixed audio signals of K channels;
wherein Q sets of said channel branching part, said sound image control part, said mixing part and said terminal-associated branching part are provided, Q being an integer equal to or greater than 2;
a combination assignment part for applying said input audio signal from each of said N terminals via said switching part to designated one or more of said channel branching parts; and
an inter-combination mixing part for mixing together, for a corresponding one of the K channels, said K-channel mixed audio signals distributed from designated one or more of said terminal-associated branching parts and outputting said channel-associated mixed audio signal to said each terminal; and
wherein said K channels are left and right two channels and said Q sound image control parts corresponding to said teleconferences each generate, for each terminal, a stereo audio signal of left and right channels as said sound-image controlled audio signal by convolving a pair of acoustic transfer functions as said sound image control parameters, which correspond to a target position of a sound source different for each of said N terminals, into said branched audio signals of said left and right channels corresponding to said each terminal, respectively.
12. The audio communication control unit of claim 11, further comprising a signal processing control part which detects the number of terminals participating in each of said teleconferences by detecting signals requesting to participate in said each teleconference from said N terminals, determines pairs of acoustic transfer functions corresponding to target positions of the same number as said detected number of participating terminals for said each teleconference and sets said determined pairs of acoustic transfer functions in that one of said sound image control parts corresponding to said each teleconference.
13. The audio communication control unit of claim 12, wherein, letting the number of terminals participating in each teleconference be represented by M.sub.P, wherein Mp is an integer equal to or greater than 2, said signal processing control part determines said target positions for all conference participating terminals to be symmetric left-right positions at intervals of 180/(M.sub.P -1) degrees.
4076966 February 28, 1978 Bovo et al.
Patent number: 5734724
Inventors: Ikuichiro Kinoshita (Yokosuka), Shigeaki Aoki (Yokosuka), Manabu Okamoto (Yokohama), Nobuo Hayashi (Yokohama)
Application Number: 8/608,082
Current U.S. Class: Pseudo Stereophonic (381/17); 379/202; Particular Technique For Combining Diverse Information Types (370/265); Using Summation Of Conferee Signals (370/266)