Conference system, conference server, conference terminal, echo cancellation program, and echo cancellation method

Abstract

To provide a conference system capable of effectively suppressing the occurrence of howling in a web conference or the like.SOLUTION: A conference system comprises: first mixing means for outputting, to each terminal participating in a conference, a first synthesized sound signal obtained by synthesizing respective microphone input signals of terminals other than one terminal; sound detecting means for detecting any of the first synthesized sound signals includes a sound; attenuating means for attenuating a specific band of each first synthesized sound signal and outputting a synthesized output signal of each terminal; band limitation detecting means for detecting that the attenuated output signals of each terminal are included in the microphone input signals; echo detecting means for detecting that the microphone input signal includes an echo when it is detected that the microphone input signal includes the attenuated output signals of each terminal, and it is determined that the output signals include sound; and echo canceling means for canceling the echo detected by the echo detecting means from the microphone input signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a conference system, a conference server, a conference terminal, an echo cancellation program, and an echo cancellation method, and can be applied to, for example, a conference system that conducts a web conference.

Background Art

[0002] In recent years, due to the influence of the novel coronavirus, the use of remote conference systems such as web conferences and video conferences has increased in various scenarios.

[0003] In the above-mentioned remote conference systems such as web conferences, various technologies have been introduced to prevent echo and howling. For example, Patent Document 1 discloses a technique of synthesizing voice input signals from each terminal microphone within the same group and then removing echo using an adaptive filter.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the above-described prior art, when conducting a WEB conference using an information terminal such as a notebook-type portable personal computer (notebook PC) or a tablet terminal, any one of the conference participants (two or more participants) gathered in the same room could not effectively suppress the howling generated in the voice between adjacent information terminals by executing a speakerphone on the information terminal.

[0006] For example, the technology described in Patent Document 1 can only be applied to a configuration in which there is one speaker output in the same group and the microphone inputs in the same group can be combined, so it cannot be applied to a general Web conference. That is, in a Web conference, the voice input other than the own terminal is combined and output through the speaker, so the output sound is different for each terminal.

[0007] Therefore, there is a need for a conference system, a conference server, a conference terminal, an echo cancellation program, and an echo cancellation method that can effectively suppress the occurrence of howling in a Web conference or the like.

Means for Solving the Problem

[0008] The first invention is a conference system including a plurality of conference terminals each having a microphone to which a microphone input signal is input, and a conference server, comprising: (1) for each of the conference terminals, first mixer means for synthesizing the microphone input signals of other conference terminals other than its own terminal and outputting the synthesized signals as first synthesized sound signals; (2) sound detection means for detecting that any one of the first synthesized sound signals is sounding; (3) specific band attenuation means for attenuating a specific band of each of the first synthesized sound signals and outputting the attenuated signals as output signals of the respective conference terminals; (4) band limitation detection means for detecting that the output signals of the respective conference terminals after specific band attenuation are included in the microphone input signal; (5) echo detection means for detecting that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signals of the respective conference terminals after specific band attenuation are included, and it is determined by the sound detection means that there is sound; and (6) echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal.

[0009] The second invention is a conference server in a conference system including a plurality of conference terminals each having a microphone to which a microphone input signal is input, and a conference server, comprising: (1) for each of the conference terminals, first mixer means for synthesizing the microphone input signals of other conference terminals other than its own terminal and outputting the synthesized signals as first synthesized sound signals; (2) sound detection means for detecting that any one of the first synthesized sound signals is sounding; (3) specific band attenuation means for attenuating a specific band of each of the first synthesized sound signals and outputting the attenuated signals as output signals of the respective conference terminals; (4) band limitation detection means for detecting that the output signals of the respective conference terminals after specific band attenuation are included in the microphone input signal; (5) echo detection means for detecting that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signals of the respective conference terminals after specific band attenuation are included, and it is determined by the sound detection means that there is sound; and (6) echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal.

[0010] A third aspect of the present invention is a conference terminal in a conference system including a plurality of conference terminals each including a microphone to which a microphone input signal is input, and a conference server, the conference terminal including: (1) second mixer means for synthesizing the microphone input signal of the conference terminal itself with the first synthesized sound signal obtained by synthesizing the microphone input signals of other conference terminals other than the own terminal acquired from the conference server, and outputting the result as a second synthesized sound signal; (2) sound detection means for detecting that the second synthesized sound signal is a voiced sound; (3) specific band attenuation means for attenuating a specific band of the first synthesized sound signal and outputting the attenuated signal as an output signal of the conference terminal; (4) band limitation detection means for detecting that the output signal of the conference terminal after specific band attenuation is included in the microphone input signal; (5) echo detection means for detecting that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signal of the conference terminal after specific band attenuation is included, and it is determined by the sound detection means that the signal is a voiced sound; and (6) echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal.

[0011] The fourth echo cancellation program of the present invention causes a computer mounted on a conference server in a conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input and a conference server to: (1) cause each of the conference terminals to synthesize the microphone input signals of other conference terminals other than its own terminal and output the synthesized signals as first synthesized sound signals by first mixer means; (2) detect by sound detection means that any of the first synthesized sound signals is in an audible state; (3) attenuate a specific band of each of the first synthesized sound signals and output the attenuated signals as output signals of the respective conference terminals by specific band attenuation means; (4) detect by band limitation detection means that the output signals of the respective conference terminals after specific band attenuation are included in the microphone input signal; (5) when it is detected by the band limitation detection means that the output signals of the respective conference terminals after specific band attenuation are included and it is determined by the sound detection means that the signal is in an audible state, detect by echo detection means that the microphone input signal includes an echo; and (6) function as echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal.

[0012] The fifth echo cancellation program of the present invention is a computer installed in a conference terminal in a conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input and a conference server, and includes: (1) a second mixer means for synthesizing the microphone input signal of the own terminal with a first synthesized sound signal obtained by synthesizing the microphone input signals of other conference terminals other than the own terminal acquired from the conference server, and outputting the result as a second synthesized sound signal; (2) a sound detection means for detecting that the second synthesized sound signal is a voiced sound; (3) a specific band attenuation means for attenuating a specific band of the first synthesized sound signal and outputting the attenuated signal as an output signal of the conference terminal; (4) a band limitation detection means for detecting that the output signal of the conference terminal after specific band attenuation is included in the microphone input signal; (5) an echo detection means for detecting that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signal of the conference terminal after specific band attenuation is included, and when it is determined by the sound detection means that it is a voiced sound; and (6) an echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal.

[0013] The sixth aspect of the present invention is an echo cancellation method used in a conference system including a plurality of conference terminals each including a microphone to which a microphone input signal is input and a conference server, the method having first mixer means, voice detection means, specific band attenuation means, band limitation detection means, echo detection means, and echo cancellation means, and: (1) the first mixer means synthesizes the microphone input signals of other conference terminals other than its own terminal for each of the conference terminals and outputs the signals as first synthesized sound signals; (2) the voice detection means detects that any one of the first synthesized sound signals is voice; (3) the specific band attenuation means attenuates a specific band of each of the first synthesized sound signals and outputs the attenuated signals as output signals of the respective conference terminals; (4) the band limitation detection means detects that the output signals of the respective conference terminals after specific band attenuation are included in the microphone input signal; (5) the echo detection means detects that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signals of the respective conference terminals after specific band attenuation are included and it is determined by the voice detection means that there is voice; and (6) the echo cancellation means cancels the echo detected by the echo detection means from the microphone input signal.

[0014] The seventh invention is an echo cancellation method for use in a conference server in a conference system including a plurality of conference terminals each including a microphone to which a microphone input signal is input, and a conference server, the method having a first mixer means, a voice detection means, a specific band attenuation means, a band limitation detection means, an echo detection means, and an echo cancellation means, and: (1) the first mixer means synthesizes, for each of the conference terminals, the microphone input signals of other conference terminals other than its own terminal, and outputs the synthesized signals as first synthesized voice signals; (2) the voice detection means detects that any one of the first synthesized voice signals is voiced; (3) the specific band attenuation means attenuates a specific band of each of the first synthesized voice signals, and outputs the attenuated signals as output signals of the respective conference terminals; (4) the band limitation detection means detects that the output signals of the respective conference terminals after specific band attenuation are included in the microphone input signal; (5) the echo detection means detects that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signals of the respective conference terminals after specific band attenuation are included, and it is determined by the voice detection means that the signal is voiced; and (6) the echo cancellation means cancels the echo detected by the echo detection means from the microphone input signal.

[0015] An eighth aspect of the present invention is an echo cancellation method for use in a conference terminal in a conference system including a plurality of conference terminals each including a microphone to which a microphone input signal is input and a conference server, the method having second mixer means, voice detection means, specific band attenuation means, band limitation detection means, echo detection means, and echo cancellation means, and comprising: (1) the second mixer means synthesizes the microphone input signal of the conference terminal other than the own terminal acquired from the conference server with the microphone input signal of the own terminal to output a second synthesized sound signal; (2) the voice detection means detects that the second synthesized sound signal is voiced; (3) the specific band attenuation means attenuates a specific band of the first synthesized sound signal and outputs the attenuated signal as an output signal of the conference terminal; (4) the band limitation detection means detects that the output signal of the conference terminal after specific band attenuation is included in the microphone input signal; (5) the echo detection means detects that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signal of the conference terminal after specific band attenuation is included and it is determined by the voice detection means that the signal is voiced; and (6) the echo cancellation means cancels the echo detected by the echo detection means from the microphone input signal.

Advantages of the Invention

[0016] According to the present invention, the occurrence of howling in a Web conference or the like can be effectively suppressed.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiment for Carrying Out the Invention

[0018] (A) Main Embodiment Hereinafter, an embodiment of a conference system, a conference server, a conference terminal, an echo cancellation program, and an echo cancellation method will be described in detail with reference to the drawings.

[0019] Configuration of the Embodiment of (A-1) (A-1-1) Overall Configuration FIG. 1 is a block diagram showing a configuration example of a conference system according to an embodiment.

[0020] In FIG. 1, the conference system 1 includes three conference terminals 2 (2-A to 2-C) and a conference server 3. In FIG. 1, for simplicity of explanation, three conference terminals 2 (2-A to 2-C) are shown, but the number of conference terminals 2 is not particularly limited. That is, in this embodiment, the case where three conference terminals 2-A to 2-C hold one conference is exemplified, but the number of conference terminals 2 that hold one conference is not particularly limited.

[0021] Also, in FIG. 1, the connection configuration between the conference terminal 2 and the conference server 3 is not shown, but various connection configurations can be applied. In this embodiment, it is assumed that the conference terminal 2 and the conference server 3 can communicate bidirectionally via a communication line (for example, a wide area network such as the Internet, a telephone line, or a dedicated line).

[0022] The conference server 3 has a function of synthesizing voices obtained from each conference terminal 2 at a plurality of bases and converting them into conference data. The conference server 3 outputs (transmits) the conference data (synthesized voice) for each conference terminal 2 to each conference terminal.

[0023] The conference terminal 2 may be any information processing terminal that participates in the conference and has audio input / output functions (microphone, speaker) and communication functions. For example, the conference terminal 2 can be applied to a PC, a mobile terminal such as a smartphone, a tablet, a wearable device, etc.

[0024] Hereinafter, when showing each conference terminal 2 in FIG. 1, the conference terminal 2-A may also be simply referred to as "terminal A", the conference terminal 2-B as "terminal B", and the conference terminal 2-C as "terminal C". Also, the audio (audio data) input from the microphones of each of the terminals A to C and transmitted to the conference server 3 may be respectively referred to as "audio A", "audio B", and "audio C".

[0025] (A-1-2) Detailed configuration of the conference server 3 In FIG. 1, the conference server 3 includes a mixer unit 30 as a first mixer means, a bandwidth limiting unit 31, a bandwidth limiting detection unit 32, a voice detection unit 33, an echo detection unit 35, and an echo cancellation unit 36.

[0026] The conference server 3 may be realized by installing a program (an echo cancellation program according to the embodiment) on a computer having a processor, a memory, etc. However, even in this case, the conference server 3 can be functionally shown using FIG. 1. Note that part or all of the conference server 3 may be realized in hardware.

[0027] The mixer unit 30 generates audio data (a synthesized audio signal for the conference) obtained by synthesizing (mixing) the audio data (microphone input signals) supplied from each conference terminal 2, and supplies it to the corresponding conference terminal 2. For example, in FIG. 1, the mixer unit 30 outputs (1) the synthesized audio (audio B + C) of the microphone input signals of terminals B and C to terminal A, (2) the synthesized audio (audio A + C) of the microphone input signals of terminals A and C to terminal B, and the synthesized audio (audio A + B) of the microphone input signals of terminals A and B to terminal C.

[0028] The voice detection unit 33 (33-1 to 33-3) performs voice detection processing on the synthesized sound output from the mixer unit 30. The voice detection unit 33 can apply various voice detection processes. For example, the technique described in Patent Document 2 can be applied. The voice detection unit 33 provides the voice determination result to the condition determination unit 34.

[0029] The condition determination unit 34 performs a determination (OR condition) as to whether any of the determination results of each voice detection unit 33 (33-1 to 33-3) for each synthesized sound output from the mixer unit 30 is a determination result of voice. The condition determination unit 34 provides the result of the OR condition determination to the echo detection unit 35. The voice detection means is realized, for example, by the above-described voice detection unit 33 and the condition determination unit 34.

[0030] The band limiting unit 31 (31-1 to 31-3) limits (erases) a predetermined band for the synthesized sound output from the mixer unit 30 and outputs it as a signal to be output by the speaker of each conference terminal 2. For example, the technique described in Patent Document 3 is applied to limit the 2.5 to 3.0 kHz band that has little influence on the sense of hearing.

[0031] The band limiting detection unit 32 (32-1 to 32-3) detects the microphone input of the signal (the signal output by the speaker of each conference terminal 2) whose band has been limited by the above-described band limiting unit 31 for the microphone input (microphone input signal) of each conference terminal 2. The band limiting detection unit 32 provides the detection result of the band limiting (whether the signal whose band has been limited by the band limiting unit 31 of each conference terminal 2 is included in the microphone input signal of the conference terminal 2) to the echo detection unit 35. The details of the band limiting detection unit 32 will be described in the section on operations.

[0032] The echo detection unit 35 (35-1 to 35-3) detects whether an echo component is included in the microphone input (microphone input signal) of each conference terminal 2. Specifically, the echo detection unit 35 performs echo detection based on the detection result of the bandwidth limitation by the bandwidth limitation detection unit 32 and the result of the OR condition determination by the condition determination unit 34. For example, when, at each conference terminal 2, "microphone input of the bandwidth-limited signal" and "sound state in any speaker output" are satisfied, the echo detection unit 35 performs echo detection. The echo detection unit 35 gives the echo detection result to the echo cancellation unit 36.

[0033] When the echo detection result by each echo detection unit 35 indicates echo detection, the echo cancellation unit 36 (36-1 to 36-3) cancels the echo of the microphone input signal.

[0034] For example, the echo cancellation unit 36 can apply an echo suppressor. When the echo cancellation unit 36 uses an echo suppressor, the simplest method is to attenuate the microphone input signal as it is at the time of echo detection. Also, the echo cancellation unit 36 may divide the signal into bands and attenuate each band as necessary (in that case, FFT (Fast Fourier Transform) or the like may be used). When the echo cancellation unit 36 uses an echo suppressor, for example, the technique (method) described in Patent Document 4 can be applied.

[0035] Note that the echo cancellation unit 36 may use an adaptive echo canceller. For example, to realize an adaptive echo canceller, the technique (method) described in Patent Document 3 or 5 can be applied.

[0036] (A-2) Operations of the Embodiment Next, the operations of the conference system 1 according to the embodiment having the above configuration will be described. Since the conference system 1 is characterized by a process of detecting an echo (mainly, a bandwidth limitation detection process), the following will mainly focus on this point and will be described in detail with reference to the drawings.

[0037] (A-2-1) Processes of the Bandwidth Limitation Unit 31 and the Bandwidth Limitation Detection Unit 32 FIG. 2 is a block diagram showing a detailed configuration of the band limiting unit according to the embodiment.

[0038] As shown in FIG. 2, the band limiting unit 31 includes a BEF (band elimination filter) 310. The BEF 310 outputs, for example, by eliminating the 2.5 - 3.0 kHz band that has little influence on the auditory sense, the output signal (the synthesized sound output from the speakers of each conference terminal 2) from the mixer unit 30. Then, the signal in which the signal components in the specific band of 2.5 - 3.0 kHz are attenuated is transmitted to each conference terminal 2 and output from the speaker.

[0039] On the other hand, the microphone input signals from each conference terminal 2 are transmitted to the conference server 3. The conference server 3 supplies the received microphone input signals of each conference terminal 2 to each band limiting detection unit 32 (32 - 1 to 32 - 3).

[0040] FIG. 3 is a block diagram showing a detailed configuration of the band limiting detection unit according to the embodiment.

[0041] The band - pass filter (BPF) 321 passes a signal in a specific band (a signal in the 2.5 - 3.0 kHz band) of the microphone input signal. Also, the output signal from the BPF 321 is supplied to the power calculation unit 323.

[0042] The band - pass filter (BPF) 322 passes a signal in a specific band (a signal in the 2.0 - 2.5 kHz band) of the microphone input signal. Also, the output signal from the BPF 322 is supplied to the power calculation unit 324.

[0043] The power calculation unit 323 receives the output signal from the BPF 321, calculates a power value P_BPF1 obtained by averaging each sample value of the input signal, and supplies it to the band limiting determination unit 325.

[0044] Here, as a method for calculating the average power value of the input signal by the power calculation unit 323, for example, a method of calculating the power value P_BPF1 by averaging the squared values of each sample value of the input signal using an FIR filter can be applied. Note that the method by which the power calculation unit 323 calculates the average power value of the input signal is not limited to the method of squaring the sample values, and the absolute value of the sample value of the input signal may be used instead. Further, the power calculation unit 323 may use an IIR LPF having an appropriate time constant instead of the FIR filter.

[0045] The power calculation unit 324 receives the output signal from the BPF 322, calculates the power value P_BPF2 obtained by averaging each sample value of the input signal, and provides it to the band limitation determination unit 325. As a method for calculating the average power value of the input signal by the power calculation unit 324, the same method as that of the power calculation unit 323 can be applied.

[0046] The band limitation determination unit 325 determines the band limitation state (i.e., the echo state) based on the respective power values P_BPF1 and P_BPF2 from the power calculation unit 323 and the power calculation unit 324, and outputs the determination result to the echo detection unit 35.

[0047] FIG. 4 is an explanatory diagram for explaining the frequency characteristics of the microphone input signal of the conference terminal according to the embodiment. FIG. 4(A) shows the frequency characteristics of the microphone input signal when an echo is input from the microphone of the conference terminal 2, and FIG. 4(B) shows the frequency characteristics of the microphone input signal when the voice spoken into the microphone of the corresponding terminal is input.

[0048] The signals in the specific band of 2.5 to 3.0 kHz of the speaker output signals of each conference terminal 2 are attenuated by the band limitation unit 31 (31-1 to 31-3).

[0049] Therefore, when an echo is input from the microphone (for example, when terminals A and B exist in the same room and the output signal from the speaker of terminal A and / or terminal B is input to the microphone of terminal A and / or terminal B), as shown in FIG. 4(A), the microphone input signal has attenuation in the range of 2.5 to 3.0 kHz.

[0050] Therefore, the average power value P_BPF1 of the signal passing through the BPF321 that allows the specific band of 2.5 to 3.0 kHz to pass tends to be significantly attenuated compared to the average power value P_BPF2 of the signal passing through the BPF322 that allows the band outside the specific band, i.e., 2.0 to 2.5 kHz, to pass.

[0051] On the other hand, when the voice uttered into the microphone of the corresponding terminal is input, since the user of the conference terminal 2 is speaking, the user's voice is directly input into the microphone. Therefore, the microphone input signal has a large signal power in the specific band of 2.5 to 3.0 kHz.

[0052] Therefore, the power P_BPF1 in the band of 2.5 to 3.0 kHz (within the BEF stop band) does not tend to be attenuated as much as the power P_BPF2 in the band of 2.0 to 2.5 kHz (outside the BEF stop band).

[0053] Based on the frequency characteristics of the microphone input signal shown in FIGS. 4(A) and 4(B), the band limitation determination unit 325 determines that there is band limitation detection (echo detection) when the condition of the following formula (1) is satisfied, and determines that there is no band limitation detection when the condition of formula (1) is not satisfied.

[0054] P_BPF1 / P_BPF2 < TH …(1) Formula (1) is conditioned that the ratio of the average power value P_BPF1 of the signal passing through the BPF321 and the average power value P_BPF2 of the signal passing through the BPF322 is less than the threshold TH. This is to determine that the attenuation amount of the power value of the signal in the specific band of 2.5 to 3.0 kHz is small at the time of echo input, as shown in FIG. 4(A).

[0055] The band limitation determination unit 325 gives the determination result as to whether or not the condition of formula (1) is satisfied to the echo detection unit 35.

[0056] (A-2-2) Processing of the echo detection unit 35, etc. The output signal of the mixer unit 30 is detected for the presence of sound by each voice detection unit 33 (33-1 to 33-3). The condition determination unit 34 gives the echo detection unit 35 whether or not sound is detected by any one of the voice detection units 33 (33-1 to 33-3) (the result of OR condition determination).

[0057] The echo detection unit 35 detects (echo detection) band limitation in the microphone input signal by the above-described band limitation detection unit 32 (band limitation determination unit 325), and assumes that an echo is detected only when any one of the output signals of the mixer units 30 is a voice from the condition determination unit 34 (otherwise, no echo is detected).

[0058] When the echo detection unit 35 detects an echo, the echo cancellation unit 36 performs echo cancellation (limitation) processing on the microphone input signal by an echo suppressor or the like (for example, the methods described in Patent Document 3, Patent Document 4, Patent Document 5, etc. above).

[0059] (A-3) Effects of the Embodiment According to the present embodiment, in the conference system 1, voice (conference voice) with a band that does not affect the auditory sense is output from the speakers of each conference terminal 2, and by detecting the corresponding band attenuation for the microphone input signal of each conference terminal 2, it becomes possible to immediately detect an echo input.

[0060] And when an echo is detected, howling in a web conference can be prevented by canceling the echo of the microphone input signal of each conference terminal 2. Howling generated when two or more terminals participating in a web conference are in the same room (Terminal A, B,...) and any one of them is in speaker mode can be prevented.

[0061] (B) Other Embodiments Although various modified embodiments have been mentioned in the above embodiment, the present invention can also be applied to the following modified embodiments.

[0062] (B-1) In the above embodiment, the configuration for preventing howling is shown with the conference server 3 as the main body. However, as shown in FIG. 5, a configuration with each conference terminal 2 as the main body may be adopted to prevent howling. In FIG. 5, in addition to the configuration of the conference server 3 (bandwidth limiting unit 31, bandwidth limit detection unit, voice detection unit 33, echo detection unit 35, and echo cancellation unit 36) shown in FIG. 1, each conference terminal 2 has a mixer unit 21 as a second mixer means.

[0063] The mixer unit 21 adds the voice of its own terminal to the voice (synthesized voice output by the speaker for its own terminal) synthesized by the mixer unit 30 of the conference server 3.

[0064] Also, in the voice detection unit 33 of FIG. 5, voice detection determination is performed on the synthesized voice (synthesized voice of all conference terminals 2 participating in the conference) synthesized by the above-mentioned mixer unit 21. Other processes are the same (or similar) to the processes of each configuration shown in FIG. 1 above.

[0065] (B-2) As a modification, the configuration example of the conference system 1 is not limited to that shown in FIG. 1 or FIG. 5 above, and each configuration (function) may be appropriately distributed and arranged in each conference terminal 2 and conference server 3.

[0066] (B-3) In the above embodiment, assuming that each conference terminal 2 is a speaker output, bandwidth limiting is applied to the output signal of the mixer unit 30 of the conference server 3 by the bandwidth limiting unit 31. However, when it is possible to detect whether each conference terminal 2 is a speaker output or a headphone output, bandwidth limiting may be applied only to the speaker output (because the possibility of echo mixing is low in the case of headphone output).

[0067] (B-4) As a modification, when the participants (conference terminals 2) present at the same location (same room) can be identified, the application range of the above-mentioned process of detecting and canceling echo (howling prevention process) may be limited to only the conference terminals 2 present at the same location. Whether the conference terminals 2 are present at the same location may be determined by, for example, GPS (Global Positioning System).

[0068] (B-5) In the above embodiment, voice detection was performed on the voice output from the speaker of the conference terminal 2, but voice detection may be performed on the voice input by the microphone of the conference terminal 2 (microphone input signal).

[0069] (B-6) In the above embodiment, voice detection was performed before bandwidth limitation, but voice detection may be performed after bandwidth limitation.

Explanation of Signs

[0070] 1... Conference system, 2 (2-A to 2-C)... Conference terminal, 3... Conference server, 21, 30... Mixer section, 31 (31-1 to 31-3)... Bandwidth limitation section, 32 (32-1 to 32-3)... Bandwidth limitation detection section, 33 (33-1 to 33-3)... Voice detection section, 34... Condition determination section, 35 (35-1 to 35-3)... Echo detection section, 36 (36-1 to 36-3)... Echo cancellation section, 321, 322... BPF, 323, 324... Power calculation section, 325... Bandwidth limitation determination section.

Claims

1. A conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input, and a conference server, wherein each of the conference terminals includes first mixer means for synthesizing the microphone input signals of other conference terminals other than its own terminal and outputting the synthesized signals as first synthesized sound signals, sound detection means for detecting that any one of the first synthesized sound signals is in an audible state, specific band attenuation means for attenuating a specific band of each of the first synthesized sound signals and outputting the attenuated signal as an output signal of each of the conference terminals, band limitation detection means for detecting that the output signals of the respective conference terminals after specific band attenuation are included in the microphone input signal, echo detection means for detecting that an echo is included in the microphone input signal when it is detected by the band limitation detection means that the output signals of the respective conference terminals after specific band attenuation are included, and it is determined by the sound detection means that the signal is in an audible state, echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal A conference system characterized by comprising the same.

2. The band limitation detection means includes a specific band extraction section for extracting the specific band of the microphone input signal, a specific band outer extraction section for extracting a band other than the specific band of the microphone input signal, a band limitation determination section for determining that the output signals of the respective conference terminals after specific band attenuation are included when a ratio of a power value of an output signal from the specific band extraction section to a power value of an output signal from the specific band outer extraction section is less than a threshold value The conference system according to claim 1, characterized by comprising the same.

3. The conference system according to claim 1 or 2, characterized in that the specific band is a band having little influence on auditory sensation.

4. The conference system according to claim 3, characterized in that the specific band is a band of 2.5 to 3.0 kHz.

5. A conference server in a conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input, and a conference server, wherein each of the conference terminals includes first mixer means for synthesizing the microphone input signals of other conference terminals other than its own terminal and outputting the synthesized signals as first synthesized sound signals, sound detection means for detecting that any one of the first synthesized sound signals is in an audible state, specific band attenuation means for attenuating a specific band of each of the first synthesized sound signals and outputting the attenuated signal as an output signal of each of the conference terminals, band-limiting detection means for detecting that the output signal of each conference terminal after specific band attenuation is included in the microphone input signal; echo detection means for detecting that an echo is included in the microphone input signal when it is detected by the band-limiting detection means that the output signal of each conference terminal after specific band attenuation is included, and it is determined by the voice detection means that there is voice; echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal A conference server characterized by comprising the above.

6. A conference terminal in a conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input and a conference server, second mixer means for synthesizing the microphone input signal of the conference terminal other than its own terminal acquired from the conference server with the microphone input signal of its own terminal and outputting the result as a second synthesized sound signal; voice detection means for detecting that the second synthesized sound signal has voice; specific band attenuation means for attenuating a specific band of the first synthesized sound signal and outputting the attenuated signal as the output signal of the conference terminal; band-limiting detection means for detecting that the output signal of the conference terminal after specific band attenuation is included in the microphone input signal; echo detection means for detecting that an echo is included in the microphone input signal when it is detected by the band-limiting detection means that the output signal of the conference terminal after specific band attenuation is included, and it is determined by the voice detection means that there is voice; echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal A conference terminal characterized by comprising the above.

7. A computer installed in a conference server in a conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input and a conference server, first mixer means for synthesizing, for each of the conference terminals, the microphone input signals of the conference terminals other than its own terminal and outputting the result as a first synthesized sound signal; voice detection means for detecting that any of the first synthesized sound signals has voice; specific band attenuation means for attenuating a specific band of each of the first synthesized sound signals and outputting the attenuated signal as the output signal of each conference terminal; Band-limiting detection means for detecting that the output signal of each conference terminal after specific band attenuation is included in the microphone input signal; Echo detection means for detecting that the microphone input signal includes an echo when it is detected by the band-limiting detection means that the output signal of each conference terminal after specific band attenuation is included, and it is determined to be voice by the voice detection means; Echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal An echo cancellation program characterized by functioning as such.

8. A computer installed in a conference terminal in a conference system including a plurality of conference terminals each provided with a microphone for inputting a microphone input signal and a conference server, Second mixer means for synthesizing the microphone input signal of the own terminal with the first synthesized sound signal obtained by synthesizing the microphone input signals of other conference terminals other than the own terminal acquired from the conference server, and outputting the result as a second synthesized sound signal; Voice detection means for detecting that the second synthesized sound signal is voice; Specific band attenuation means for attenuating a specific band of the first synthesized sound signal and outputting the attenuated signal as the output signal of the conference terminal; Band-limiting detection means for detecting that the output signal of the conference terminal after specific band attenuation is included in the microphone input signal; Echo detection means for detecting that the microphone input signal includes an echo when it is detected by the band-limiting detection means that the output signal of the conference terminal after specific band attenuation is included, and it is determined to be voice by the voice detection means; Echo cancellation means for canceling the echo detected by the echo detection means from the microphone input signal An echo cancellation program characterized by having the above.

9. An echo cancellation method used in a conference system including a plurality of conference terminals each provided with a microphone for inputting a microphone input signal and a conference server, Having first mixer means, voice detection means, specific band attenuation means, band-limiting detection means, echo detection means, and echo cancellation means, The first mixer means synthesizes, for each of the conference terminals, the microphone input signals of other conference terminals other than the own terminal and outputs the result as a first synthesized sound signal, The voice detection means detects that any one of the first synthesized sound signals is voice, The specific band attenuation means attenuates the specific band of each of the first synthesized sound signals and outputs the attenuated signal as the output signal of each conference terminal. The band limitation detection means detects that the output signal of each conference terminal after specific band attenuation is included in the microphone input signal. When the band limitation detection means detects that the output signal of each conference terminal after specific band attenuation is included, and the voice detection means determines that there is voice, the echo detection means detects that the microphone input signal includes an echo. The echo cancellation means cancels the echo detected by the echo detection means from the microphone input signal. A method for echo cancellation, characterized by the above.

10. An echo cancellation method for use in a conference server in a conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input and a conference server, comprising first mixer means, voice detection means, specific band attenuation means, band limitation detection means, echo detection means, and echo cancellation means, The first mixer means synthesizes the microphone input signals of the other conference terminals other than its own terminal and outputs them as first synthesized sound signals to the respective conference terminals. The voice detection means detects that any one of the first synthesized sound signals has voice. The specific band attenuation means attenuates the specific band of each of the first synthesized sound signals and outputs the attenuated signal as the output signal of each conference terminal. The band limitation detection means detects that the output signal of each conference terminal after specific band attenuation is included in the microphone input signal. When the band limitation detection means detects that the output signal of each conference terminal after specific band attenuation is included, and the voice detection means determines that there is voice, the echo detection means detects that the microphone input signal includes an echo. The echo cancellation means cancels the echo detected by the echo detection means from the microphone input signal. A method for echo cancellation, characterized by the above.

11. An echo cancellation method for use in a conference terminal in a conference system including a plurality of conference terminals each provided with a microphone to which a microphone input signal is input and a conference server, comprising second mixer means, voice detection means, specific band attenuation means, band limitation detection means, echo detection means, and echo cancellation means. The second mixer means synthesizes the microphone input signal of the own terminal with the first synthesized sound signal obtained from the conference server by synthesizing the microphone input signals of other conference terminals other than the own terminal, and outputs it as a second synthesized sound signal. The voice detection means detects that the second synthesized sound signal is a voice signal. The specific band attenuation means attenuates a specific band of the first synthesized sound signal, and outputs the attenuated signal as an output signal of the conference terminal. The band limitation detection means detects that the output signal of the conference terminal after specific band attenuation is included in the microphone input signal. When the band limitation detection means detects that the output signal of the conference terminal after specific band attenuation is included, and the voice detection means determines that it is a voice signal, the echo detection means detects that the microphone input signal includes an echo. The echo cancellation means cancels the echo detected by the echo detection means from the microphone input signal. An echo cancellation method characterized by the above.

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