JPH0439248B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an echo canceling device for controlling echoes in long-distance circuits such as satellite communications, teleconferencing systems, and the like.

Conventional technology In recent years, with the rapid increase in long-distance lines, especially satellite communications, and the practical use of teleconferencing systems,
Clear and natural voice transmission is desired. Reverberation signals are a phenomenon in which a signal generated by a speaker returns to the speaker due to reflection on the receiver, but in teleconferencing systems that include long-distance lines and acoustic systems, echoes due to long delays occur. This presence causes deterioration in call quality. Recently, adaptive echo canceling devices that eliminate this echo are being put into practical use.
These are remote-operated types (identifying the echo path by the far-end speaker's voice) and must detect the presence or absence of the near-end speaker (for example, ``Two-way simultaneous conversation detection method'' (1981)). National Conference of the Institute of Electronics and Communication Engineers in 2018
589)).

The conventional echo canceling device as described above will be described below with reference to the drawings.

FIG. 7 shows the configuration of a conventional echo canceling device. In FIG. 7, 1 is a receiving side input terminal;
2 is the receiving side output terminal, 3 is the transmitting side input terminal, 4 is the transmitting side output terminal, and 5 is an echo canceler installed between each terminal to cancel the echo that returns from the receiving side output terminal to the transmitting side output terminal. do. 56 is an erased residual signal level detection section that detects the level of the erased residual signal that is the transmission output of the echo canceller 5, 57 is a receiving side signal level detection section, and 58 is an erased residual signal level.
Lsout Received signal level Lrin and threshold value used last time
A threshold updating unit calculates the threshold value Kt to be used this time from Kt, 59 is a threshold storage unit that stores the threshold value Kt sent from the threshold updating unit, and 60 is the threshold value Kt and the erased residual signal. Receiving side signal level estimator for estimating the receiving side signal level from the level, 61
is a comparison unit that compares the estimated receiving side signal level Lrin and the actual receiving side signal level Lrin to control whether or not to identify the echo path of the echo canceller.

The operation of the echo canceling device configured as described above will be explained below.

First, the far-end speaker's voice signal is supplied to the echo canceller 5 via the receiving side input terminal 1 as a receiving input Rin. In addition, the signal Rin is output from the receiving side output terminal 2.
The received signal Rout is sent to the nearer end speaker.
In the absence of a near-end speaker signal, the signal Rout enters the transmitting input terminal 3 as the transmitting input Sin through the echo path. In echo canceller 5, the transmitting side output signal
A pseudo echo path is created from the received input Rin sequence and the transmitted output Sout so that Sout (also called the cancellation residual signal) becomes zero. Although the echo signal is canceled in this way, if a near-end speaker is present, the echo path cannot be estimated successfully. Therefore, it is necessary to detect the presence of a near-end speaker signal and stop estimating the echo path. Therefore, the presence or absence of a near-end speaker is detected from the relationship between the receiving side input signal Rin and the cancellation residual signal Sout which is the transmitting side output signal. A receiving side signal level Lrin is detected by the receiving side signal level detection section 57. The erased residual signal level detection section 56 detects the erased residual signal level.
Lsout is detected. The threshold updating unit 58 receives the receiving side signal level Lrin, the erased residual signal level Lsout, the previously used threshold value Kt′ from the threshold storage unit 59, and the signal Adp indicating stopping or continuation of echo path estimation from the comparing unit 61. The threshold value Kt used this time is calculated and sent to the threshold value storage section 59. The method for updating the threshold value Kt is to set the threshold value Kt slightly larger than the previously used threshold value Kt′ so as not to exceed the convergence speed of the echo canceller when only the far-end speaker is speaking and estimation of the echo path continues. value, and gradually increase the threshold value Kt. In a two-way simultaneous conversation where the near-end speaker and the far-end speaker are speaking at the same time, the threshold value Kt is gradually reduced. The received signal level estimator 20 calculates the product of the threshold value Kt and the erased residual signal level Lsout as the received signal level estimated value Lrin. When only the far-end speaker speaks and echo path estimation continues, the received signal level Lrin/residual signal level
Lsout increases in proportion to the convergence speed of the echo canceller. Since the threshold value Kt is the expected value of the received signal level Lrin/the cancellation residual signal level Lsout, the threshold value is set gradually so as not to exceed the convergence speed of the echo canceller.
If Kt is increased, the threshold value Kt becomes slightly smaller than the actual received signal level Lrin/erasure residual signal level Lsout, so the threshold value Kt and the erasure residual signal level Lsout
The estimated receiving side signal level Lrin, which is the product of Lrin, is smaller than the actual receiving side signal level Lrin. In the case of a two-way simultaneous call, the voice of the near-end speaker is added to the cancellation residual signal, and the cancellation residual signal level Lsout increases.
Therefore, the estimated receiving side signal level Lrin, which is the product of the threshold value Kt and the erased residual signal level Lsout, becomes larger than the actual receiving side signal level Lrin. Comparison section 21
Then, if the receiving side signal level Lrin ≧ the receiving side signal level estimate Lrin, it is assumed that only the far end speaker is speaking, and the echo path estimation is executed, and the receiving side signal level Lrin < the receiving side signal level estimate Lrin In this case, it is determined that there is a simultaneous two-way call, and estimation of the echo path is stopped.

However, even if the characteristics of the echo path change, the echo canceller 5 cannot follow it instantaneously, so the cancellation residual signal level Lsout increases, and as in the case of simultaneous two-way communication, the echo canceler 5 stops estimating the echo path. Put it away.
Therefore, if it is determined that there is a two-way simultaneous call, by gradually decreasing the threshold value Kt, the estimated receiving side signal level Lrin will also become smaller, and after a while, the receiving side signal level Lrin ≧ the estimated receiving side signal level Lrin relationship established, echo canceller 5
Estimation of the echo path is restarted. In the conventional example, the amount of decrease in the threshold value Kt is controlled so that the time from when it is determined that it is a two-way simultaneous call until estimation of the echo path is restarted is within 3 seconds. This causes a change in the echo path, resulting in a delay of up to 3 seconds until the echo canceller starts tracking.

Problems to be Solved by the Invention However, with the above configuration, when holding a conference with a large number of people using a teleconference system, there is a high possibility that two-way simultaneous calls will occur for more than 3 seconds, so the decision time will be reduced. need to be longer,
This method has the disadvantage that it is slow to follow changes in the echo path.

In view of the above-mentioned problems, the present invention provides an echo canceling device that can quickly determine simultaneous two-way communication and fluctuations in the echo path.

Means for Solving the Problems In order to achieve this object, the echo canceler of the present invention includes a first echo canceler that cancels the echo signal included in the input signal on the transmitting side, and a first echo canceler that cancels the echo signal included in the input signal on the receiving side. first and second filters for extracting signals in a predetermined band from the transmitter output signal; first and second thinning means for thinning out the output signals of the first and second filters; and first thinning means. a second echo canceller whose output is the receiving side input and the output of the second thinning means is the transmitting side input; and the receiving side input signal, the transmitting side input/output signal, and the transmitting side input of the second echo canceller. It is comprised of a two-way simultaneous conversation detection means that detects the presence or absence of a near-end speaker from the output signal and controls the first and second echo cancellers.

The two-way simultaneous call detection means includes a receiving side input signal level detecting means for detecting the receiving side input signal level, and a transmitting side input signal level detecting means for detecting the first transmitting side input signal level before the echo cancellation of the first echo canceller. level detection means; a transmission side output signal level detection means for detecting a first transmission side output signal level after echo cancellation of the first echo canceller; and a transmission side output signal level detection means for detecting the first transmission side output signal level/the first transmission side a first echo cancellation effect calculation means for calculating a first echo cancellation effect which is an input signal level; and a sub-band transmission side input for detecting a second transmission side input signal level before echo cancellation of the second echo canceller. signal level detection means; sub-band transmission side output signal level detection means for detecting a second transmission side output signal level after echo cancellation of the second echo canceller; 2
a second echo cancellation effect calculation means for calculating a second echo cancellation effect which is the transmitting side input signal level; a value obtained by adding a predetermined value to the held estimated echo cancellation effect; an estimated echo-cancelling effect calculation means for comparing the estimated echo-cancelling effects and calculating the smaller one as a new estimated echo-cancelling effect, and retaining the smaller one;
a first comparing means for comparing the first echo-cancelling effect and the new estimated echo-cancelling effect; and the second
a second comparison means for comparing the echo cancellation effect of the second estimated echo cancellation effect with the new estimated echo cancellation effect; a third comparison means for comparing a predetermined threshold and the receiving side input signal level; When the input signal level is equal to or higher than the threshold value and the first comparison means determines that the first echo cancellation effect is equal to or less than the new estimated echo cancellation effect, or in the third comparison means If the input signal level on the receiving side is equal to or higher than the threshold and the second comparison means determines that the second echo cancellation effect is equal to or less than the new estimated echo cancellation effect, it is determined that there is no near-end speaker. control means for determining the echo path of the first echo canceller only when the determining means determines that there is no near-end speaker; The control means controls the echo canceller to stop identifying the echo path.

Operation With this configuration, when the far-end speaker is busy and the near-end speaker is absent, the first echo canceller identifies the characteristics of the echo path and cancels the echo signal. When the far-end speaker is talking and the near-end speaker also speaks, or when the echo path changes, the first echo cancellation effect calculated by the first echo cancellation effect calculation means increases, and the first echo cancellation effect calculated by the first echo cancellation effect calculation means increases. The second echo cancellation effect calculated by the second echo cancellation effect calculation means detection means also increases, and when the first and second echo cancellation effects become larger than the estimated echo cancellation effects, the first and second comparison means The determining means is informed that the first and second echo canceling effects have become larger than the estimated echo canceling effect, and the determining means determines that a near-end speaker is present. The control means immediately stops identifying the echo path of the first echo canceller. If a near-end speaker is present, the second echo canceller cannot identify the echo path due to the near-end speaker's voice, and the first and second echo cancellation effects are not reduced. Therefore, the determining means determines that there is a near-end speaker, and the controlling means stops identifying the echo path of the first echo canceller, so that the characteristics of the identified echo path are not disturbed. However, if this is a change in the echo path, the second echo canceller will gradually identify the echo path, and the second echo cancellation effect will decrease. When it becomes equal to the estimated echo cancellation effect, the second comparison means detects this, the determination means determines that there is a variation in the echo path, and the control means starts identifying the echo path of the first echo canceller. In this way, fluctuations in the echo path and simultaneous bidirectional communication can be determined within the convergence time of the second echo canceller.

In addition, the first and second filters and the first and second
By using the thinning means, a second echo canceller that can cancel echoes of the same length as the first echo canceller can be constructed at the same thinning ratio as the first echo canceller.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an echo canceling device in one embodiment of the present invention. 1st
In the figure, 1 is a receiving side input terminal, 2 is a receiving side output terminal, 3 is a transmitting side input terminal, 4 is a transmitting side output terminal, and 5 is a first echo canceller provided between the above terminals. The echo returning from the side output terminal 2 to the transmission side input terminal 3 is erased. The above configuration is the same as the configuration shown in FIG. These devices are realized by digital signal processing of a sampled analog signal, and in this example,
The signal is sampled at 4kHz, and the band of the first echo canceller 5 is 2kHz or less.

7 is the first filter that extracts the signal in the band from 500Hz to 1kHz of the receiving side input signal Rin1 coming in from the receiving side input terminal 1, and 8 is the first filter that extracts the signal from 500Hz of the sending side input signal Sin1 coming in from the sending side input terminal 3.
a second filter that extracts signals in the 1kHz band;
9 is a first thinning means for extracting the output signal of the first filter 7 at a rate of once every four samples;
0 is a second thinning means 6 for extracting the output signal of the second filter 8 at a rate of once every four samples;
uses the output signal Rin2 of the first thinning means as the receiving side input signal, and uses the output signal Sin2 of the second thinning means as the receiving side input signal.
is the input signal on the transmitting side, the second echo canceler has the same delay time for echo cancellation as the first echo canceller, 11 is the receiving side input signal Rin1, the transmitting side input/output signals Sin1, Sout1, and the second echo canceller. A two-way simultaneous system that detects the presence or absence of a near-end speaker and changes in the echo path after receiving the output signal Sin2 of the thinning means and the cancellation residual signal Sout2 of the second echo canceller, and controls the first and second echo cancellers. This is a call detection means.

FIG. 2 is a block diagram showing details of the two-way simultaneous call detection means. In FIG. 2, 21 is a receiving side input signal level detection means for detecting the level of the receiving side input signal Rin1, and 22 is a transmitting side input signal Sin1.
23 is a transmitting side output signal level detecting means for detecting the level of the transmitting side output signal Sout1, and 24 is detecting the level of the output signal Sin2 of the second thinning means. Sub-band transmitting side input signal level detection means, 2
5 is the cancellation residual signal Sout of the second echo canceller
Sub-band transmitting side output signal level detection means for detecting the level of 2, 26 is the receiving side input signal level Lrin1
and a predetermined threshold Th.
27 is the transmitting side input signal level LSin
1 and the transmission side output signal level Lsout1 ratio Acnc1
(Hereinafter, the ratio Acnc1 of the transmitting side output signal level Lsout1/the transmitting side input signal level LSin1 will be referred to as the first echo canceling effect). The value calculated before one sample (hereinafter referred to as the estimated echo cancellation effect)
Estimated echo cancellation in which the value obtained by adding a predetermined value (1/40000 in the example) to the first echo cancellation effect Acnc1 (referred to as Acnc1) and the first echo cancellation effect Acnc1 is adopted as the estimated echo cancellation effect Acnc1. Effect calculation means, 29 is the input signal level of the subband transmitting side
Lsin2 and subband transmitting side output signal level Lsout2
Acnc2 (hereinafter referred to as subband transmitting side output signal level
Lsout2/subband transmission side input signal level Lsin2 is called a second echo cancellation effect); 30 is a first echo cancellation effect;
A first comparison means for comparing Acnc1 and the estimated echo cancellation effect Acnc1∧, 31 is the estimated echo cancellation effect
A third comparison means for comparing Acnc1∧ and the second echo cancellation effect Acnc2, 32 is the result Cmp1, Cmp of the first, second and third comparison means 30, 31, 26.
2. Judgment means for detecting the presence or absence of a near-end speaker and changes in the echo path from Cmp3; 33 is the result of the judgment means 32;
This control means controls the continuation and stop of identification of the echo path of the first echo canceller and the maintenance and clearing of the identified echo path of the second echo canceler from noise.

Regarding the echo canceling device configured as above,
The operation will be explained below.

First, the far-end speaker's audio signal is the receiver's input signal.
It is supplied as Rin1 to the echo canceller 5 via the receiving side input terminal 1. In addition, the signal Rin1 is the receiving side output signal from the receiving side output terminal 2 to the near-end speaker.
Sent as Rout1. When there is no near-end speaker signal, the signal Rout1 passes through the echo path and enters the transmitter input terminal 3 as the transmitter input signal Sin1. In the first echo canceller 5, the transmitting side output signal Sout1
A pseudo echo path is created from the sequence of the input signal Rin1 on the receiving side and the output signal Sout1 on the transmitting side so that the value becomes zero.
Although the echo signal is canceled in this way, if a near-end speaker is present, the echo path cannot be estimated successfully. Therefore, it is necessary to detect the presence of a near-end speaker signal and stop estimating the echo path.

This will be explained below with reference to FIG. The two-way simultaneous call detection means 11 detects the presence or absence of a near-end speaker as follows. When there is no near-end speaker signal and the echo path is constant, when the far-end speaker signal is sent as the receiving side input signal Rin1, the receiving side input signal level detection means 21 detects the far-end speaker signal level Lrin1. Third
In the comparison means, when the far-end speaker signal level becomes equal to or higher than a predetermined threshold Th, the third comparison means outputs Cmp3=1 to the determination means 32 (pass 1).

Next, this far-end speaker signal returns via the echo path as the transmitting side input signal Sin1. The signal level of the transmitting side input signal Sin1, that is, the echo signal, is detected by the transmitting side input signal level detection means 22, and the signal level of the cancellation residual signal of the echo canceller is detected by the transmitting side output signal level detecting means 23, and the signal level is detected by the first echo cancellation effect calculation means. 27
At this time, the echo cancellation effect Acnc1 by the first echo canceller is calculated. The estimated echo cancellation effect calculating means 28 compares the value obtained by adding a predetermined value to the estimated echo cancellation effect of one sample before and the first echo cancellation effect Acnc1, and selects the smaller one as the estimated echo cancellation effect Acnc1∧. adopt. 1st
The comparing means compares the first echo canceling effect Acnc1 and the estimated echo canceling effect Acnc1∧, and outputs Cmp1=1 to the determining means 32 when the first echo canceling effect Acnc1 is equal to the estimated echo canceling effect Acnc1∧.
In the case of only the far-end speaker signal, the first echo canceller identifies the echo path so that the transmitting side output signal Sout1 becomes small, so the first echo cancellation effect is achieved.
Acnc1 becomes equal to the estimated echo cancellation effect Acnc1∧, and Cmp1=1 is output from the first comparing means. The determining means determines that there is no near-end speaker when Cmp1=1 and Cmp3=1 (pass 2).

When the near-end speaker speaks, the near-end speaker signal is added to the transmitting side input/output signals Sin1 and Sout1, so the first echo cancellation effect calculation means 27 calculates the
The echo cancellation effect Acnc1 becomes large, the first comparison means outputs Cmp1=0, and the second echo canceller continues to identify the echo path, but due to the near-end speaker signal, the cancellation residual output signal Sout2 does not converge, and the second echo cancellation effect Acnc2 becomes larger than the estimated echo cancellation effect Acnc1∧, and the output Cmp2 of the second comparison means becomes 0, and the determination means determines that there is a near-end speaker signal (Path 3 ).

In this case, in the control means 33, Cmp1=Cmp2
=0 period stops identifying the echo path of the first echo canceller. If the echo path changes, there will be a difference between the characteristics of the echo path identified by the first and second echo cancellers and the actual echo path.
The cancellation residual output Sout2 of the echo canceller increases, and the first and second echo cancellation effects become larger than the estimated echo cancellation effects, and the first and second comparing means 30, 3
1 output Cmp1 = Cmp2 = 0 and determination means 3
2, it is determined that there is a near-end speaker signal, but since the second echo canceller continues to identify the echo path, the second echo canceller will eventually converge and produce the second echo cancellation effect. Acnc2 becomes equal to the estimated echo cancellation effect Acnc1∧ and the second comparing means 31
outputs Cmp2=1, the determination means determines that there is no near-end speaker signal (path 4), and the control means 33 controls the first echo canceller so as to identify the echo path of the first echo canceller. Control Sera. In this way, fluctuations in the echo path and the utterance of the near-end speaker can be determined within the convergence time of the second echo canceller. The second echo canceller is only necessary to distinguish between fluctuations in the echo path and utterances of the near-end speaker, and is not required to cancel echo signals in the entire signal transmission band.

In this embodiment, the band for echo cancellation is set to 2 kHz or less, as shown in FIG. 4A. The audio signal is the 6th
As shown in the figure, there is a relatively wide range of power mainly from 300Hz to 1kHz, so it is sufficient for the second echo canceller to cancel the echo signal in this band. Therefore, as shown in FIG. 4B, the pass bands of the first and second filters 8 and 9 are set from 500 Hz to 1 kHz. Next, the signals extracted by the first and second filters 8 and 9 are processed so that the band ratio of the input and output signals of the first and second filters 8 and 9 is 4:1 as shown in FIG. Therefore, by performing the operation of extracting the signal only once every four samples by the first and second thinning means, the output signals of the first and second thinning means are as shown in FIG. 4C. The signal ranges from 0Hz to 500Hz. The sampling time of the second echo canceller is four times that of the first echo canceller, so even if the first and second echo cancellers can cancel echo signals with the same delay time, The second echo canceller requires one-fourth the hardware of the first echo canceller.

As described above, according to this embodiment, when there is no near-end speaker, the first echo canceller simulates the echo path and cancels the echo signal. When the near-end speaker or the echo path changes, the first echo cancellation effect of the first echo canceller calculated by the first echo cancellation effect calculation means decreases, and the estimated echo cancellation effect calculation means When the estimated echo cancellation effect is greater than the computed estimated echo cancellation effect, the first comparison means detects this, and the determination means immediately stops identifying the echo path of the first echo canceller. The second echo cancellation effect of the second echo canceller calculated by the effect calculation means is compared with the estimated echo cancellation effect, and when the second echo cancellation effect is equal to the estimated echo cancellation effect, it is determined that the echo path has changed. The control means then starts estimating the echo path of the first echo canceller. In cases other than the above, it is assumed that there is a two-way simultaneous conversation, and identification of the echo path of the first echo canceller remains stopped.
The band in which echo cancellation is performed by the second echo canceller is limited to the main band of the audio signal by the first and second filters, and this band is converted into a low frequency signal by the first and second thinning means. As a result, the scale of the hardware is small, and fluctuations in the echo path and simultaneous bidirectional communication can be determined at high speed (within the convergence time of the second echo canceller).

Note that in this embodiment, the band of the first echo canceller was set to 2 kHz or less, but if the band was set to 4 kHz,
The band of the second echo canceller is 500Hz to 1kHz.
In this case, the rate of thinning by the thinning means may be set to once every eight times. In this way, if the band of the second echo canceller is set to an integer fraction of the band of the first echo canceller, the bands of the first and second echo cancellers may be changed as necessary.

Also, the delay amount of the second echo canceller is
Although the echo canceller has the same delay amount as the first echo canceller, it may be an echo canceler with a delay amount smaller than the delay amount of the first echo canceller. In this case, the first
When comparing the echo cancellation effect and the second echo cancellation effect, it is sufficient to add a deterioration of the echo cancellation effect corresponding to the small amount of delay of the second echo canceller to the second echo cancellation effect. By reducing the delay amount of the second echo canceller, it is possible to further reduce the scale of the device, and the convergence speed of the second echo canceller is increased, which allows simultaneous two-way communication and fluctuations in the echo path. Judgment becomes faster.

Effects of the Invention As described above, in the present invention, when there is no near-end speaker, the first echo canceller simulates the echo path and cancels the echo signal. When the near-end speaker or the echo path changes, the first echo cancellation effect of the first echo canceller calculated by the first echo cancellation effect calculation means decreases, and the estimated echo cancellation effect calculation means When the estimated echo cancellation effect is greater than the computed estimated echo cancellation effect, the first comparison means detects this, and the determination means immediately stops identifying the echo path of the first echo canceller. The second echo cancellation effect of the second echo canceller calculated by the effect calculation means is compared with the estimated echo cancellation effect, and when the second echo cancellation effect is equal to the estimated echo cancellation effect, it is determined that the echo path has changed. The control means then starts estimating the echo path of the first echo canceller.

In cases other than the above, it is assumed that there is a two-way simultaneous conversation, and identification of the echo path of the first echo canceller remains stopped. The band in which echo cancellation is performed by the second echo canceller is limited to the main band of the audio signal by the first and second filters, and this band is converted into a low frequency signal by the first and second thinning means. As a result, the scale of the hardware is small, and fluctuations in the echo path and simultaneous two-way communication can be determined quickly (within the convergence time of the second echo canceller), and the first echo canceler always performs well. It can simulate the echo path and perform excellent echo cancellation. In particular, even when extremely large hardware is required, such as an echo canceller in an acoustic system, the scale of the second echo canceller can be made small, and it can quickly follow fluctuations in the echo path, allowing a large number of people to use the echo canceller. It can also perform excellent echo cancellation in teleconferencing systems, and its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an echo canceling device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a two-way simultaneous call detection means in the same embodiment, and FIG. 3 is a block diagram showing the configuration of a two-way simultaneous call detection means in the same embodiment. A flowchart explaining the algorithm of the detection means, FIG. 4 is a characteristic diagram showing the input/output bands of the first and second filters and the first and second thinning means, and FIG. FIG. 6 is a waveform diagram showing an example, FIG. 6 is a voice power distribution diagram, and FIG. 7 is a block diagram showing the configuration of a conventional echo canceling device. 1... Receiving side input terminal, 2... Receiving side output terminal, 3... Transmitting side input terminal, 4... Transmitting side output terminal, 5... First echo canceller, 6... Second
echo canceller, 7...first filter, 8
... second filter, 9 ... first thinning means,
DESCRIPTION OF SYMBOLS 10... Second thinning means, 11... Two-way simultaneous call detection means, 21... Receiving side input signal level detection means, 22... Transmitting side input signal level detection means, 23... Transmitting side output signal level detection means, 2
4...Subband transmission side input signal level detection means, 2
5...Subband transmitting side output signal level detection means, 2
6... Third comparison means, 27... First echo cancellation effect calculation means, 28... Estimated echo cancellation effect calculation means, 29... Second echo effect calculation means, 30...
First comparison means, 31...Second comparison means, 32
...determination means, 33...control means.

Claims (1)

[Claims] 1. Identify the characteristics of the echo path between the receiving side and the transmitting side, synthesize a pseudo echo from the identified echo path characteristics and the input signal on the receiving side, and synthesize the pseudo echo from the input signal on the sending side. a first echo canceller that cancels echo signals included in the transmitting side input signal by subtracting echoes and outputting the canceled transmitting side input signal; and a signal of a specific band from the receiving side input signal. a first filter that extracts a signal in the same band as that of the first filter from the transmitting side input signal, and thins out the outputs of the first filter and the second filter at the same ratio, respectively. first and second thinning means; a second echo canceller that constantly identifies characteristics of echo paths in bands of output signals of the first and second thinning means; The echo cancellation amount of the canceller and the presence or absence of the receiving side input signal are detected, and at least one of the echo cancellation amounts of the first and second echo cancellers is less than or equal to a predetermined value, and the receiving side input signal is detected. An echo canceling device characterized by comprising: a two-way simultaneous conversation detection means that executes the identification of the echo path of the first echo canceller when detected, and stops the identification in other cases. 2. The two-way simultaneous call detection means includes a receiving side input signal level detecting means for detecting the receiving side input signal level, and a transmitting side input signal level detecting means for detecting the first transmitting side input signal level before canceling the echo of the first echo canceller. a signal level detection means; a transmission side output signal level detection means for detecting a first transmission side output signal level after echo cancellation of the first echo canceller; and a transmission side output signal level detection means for detecting the first transmission side output signal level/the first transmission side output signal level. a first echo cancellation effect calculation means for calculating a first echo cancellation effect which is a side input signal level; and a sub-band transmission side for detecting a second transmission side input signal level before the echo cancellation of the second echo canceller. input signal level detection means; sub-band transmission side output signal level detection means for detecting a second transmission side output signal level after echo cancellation of the second echo canceller; Second
a second echo cancellation effect calculation means for calculating a second echo cancellation effect which is the transmitting side input signal level; a value obtained by adding a predetermined value to the held estimated echo cancellation effect; an estimated echo-cancelling effect calculation means for comparing the estimated echo-cancelling effects and calculating the smaller one as a new estimated echo-cancelling effect, and retaining the smaller one;
a first comparing means for comparing the first echo-cancelling effect and the new estimated echo-cancelling effect; and the second
a second comparison means for comparing the echo cancellation effect of the second estimated echo cancellation effect with the new estimated echo cancellation effect; a third comparison means for comparing a predetermined threshold and the receiving side input signal level; When the input signal level is equal to or higher than the threshold value and the first comparison means determines that the first echo cancellation effect is equal to or less than the new estimated echo cancellation effect, or in the third comparison means If the input signal level on the receiving side is equal to or higher than the threshold and the second comparison means determines that the second echo cancellation effect is equal to or less than the new estimated echo cancellation effect, it is determined that there is no near-end speaker. control means for determining the echo path of the first echo canceller only when the determining means determines that there is no near-end speaker; 2. The echo canceling device according to claim 1, further comprising a control means for controlling the echo canceller to stop identifying the echo path. 3. The echo canceling device according to claim 1, wherein the pass bands of the first and second filters are one integer fraction of the echo canceling band of the first echo canceller. 4. Claim 1, wherein the first and second thinning means thin out the signal at a ratio of the echo canceling band of the first echo canceller to the passband of the first and second filters. The echo canceller described.