JPH0771030B2 - Echo canceller - Google Patents

Description

TECHNICAL FIELD The present invention relates to an echo canceller for canceling echo signals in long-distance telephone communication lines, conference phones, and the like.

[Prior Art] Conventionally, echo cancellers have been used to control the echo of long-distance lines, loudspeakers, two-way repeaters, and the like.

However, in this echo canceller, when a disturbance such as a transmission signal or noise is superimposed on the echo signal and is input to the transmission side input, the measurement accuracy of the echo path is reduced, and the echo cancellation amount is also reduced. It has a predisposition to decrease to a value determined by the ratio of the echo signal of the transmitter side input to the disturbance signal level.

In order to prevent the reduction of echo cancellation amount due to such causes,
An echo canceller has been proposed which detects a superposed call using an undeleted signal.

An example of a conventional echo canceller of this type is shown in FIG. 3 and explained. 1 is a reception input terminal to which a reception signal is applied, 2 is a reception output terminal from which a reception output signal is obtained, and 3 is a transmission signal. The applied speech input terminal 4 is a speech output terminal from which a speech output signal is obtained. Reference numeral 5 denotes an echo canceller, which receives the subtraction circuit 6 for subtracting the output of the approximate echo signal synthesis circuit 7 from the transmission signal from the transmission input terminal 3 and the reception input signal from the reception input terminal 1 and outputs it. It is composed of an approximate echo signal synthesis circuit 7 that controls the subtraction circuit 6.

The echo canceller 5 measures the characteristics of the input and output signals of the echo path, and creates an echo path model that approximates the echo path characteristics internally based on the echo path characteristics obtained by this means. It constitutes means for erasing the actual echo signal by synthesizing the approximate echo path signal based on the path model and subtracting it from the transmitter input signal.

Reference numeral 8 is a receiver side signal level measuring circuit for measuring the signal level on the receiving side, and reference numeral 9 is a remaining signal level measuring circuit for measuring the remaining signal level. 10 inputs the output of the receiving side signal level measuring circuit 8 and the output of the remaining unerased signal level measuring circuit 9,
An attenuation amount measuring circuit for measuring an attenuation amount (sum of echo loss and echo cancellation) from these outputs, 11 is an output signal level of the receiving side signal from the receiving side signal level measuring circuit 8 and an erasure residual signal level measuring circuit 9 A superposed call detection circuit for detecting a two-way call based on the level of the residual signal to be erased and the level from the attenuation measurement circuit 10.
Is supplied to the approximate echo signal synthesis circuit 7 to control the operation of measuring the characteristics of the echo path (echo path, 2-3).

In the echo canceller thus configured, the receiving-side signal level and the remaining unerased signal level are measured by the receiving-side signal level measuring circuit 8 and the remaining unerased signal level measuring circuit 9, respectively. The sum of echo loss and echo cancellation) is measured by the attenuation measuring circuit 10. In a one-way call, the output of the remaining signal level measuring circuit 9 becomes almost equal to the output of the signal level measuring circuit 8 on the receiving side reduced by the value obtained by the attenuation measuring circuit 10. When the output of 9 greatly exceeds the value obtained by lowering the output of the reception side signal level measuring circuit 8 by the value obtained by the attenuation measuring circuit 10, it can be judged that the two-way communication state is established. The operation of measuring the characteristics of the echo path is controlled based on this determination result.

[Problems to be Solved by the Invention] However, in such an echo canceller, when the echo path (echo path, 2-3) is opened,
The reception signal input from the reception input terminal 1 passes through the approximate reverberation signal synthesizing circuit 7 and the subtraction circuit 6 and is input to the residual signal level measuring circuit 9, and its output is increased. Judge as if it was a call,
There is a drawback that the correction of the echo model of the echo canceller 5 is stopped or the correction speed is reduced, and a signal is output to the transmission output terminal like an echo for a while.

More specifically, when the echo path is open, the input signal on the transmitting side disappears, and at this time, the output signal on the transmitting side (remaining signal to be erased) becomes equal to the approximate echo signal, and the remaining signal to be erased remains. The echo is increased and output to the output of the transmitting side, resulting in deterioration of speech quality. Therefore, when the echo path is opened, the echo path model must be promptly converged in the direction of 0. However, in the above-mentioned superposed call detection, the measured value before the opening is used due to the delay in the measurement of the attenuation measurement circuit even though the attenuation amount changes due to the opening of the echo path, so that it is as if it is a superposed call. Judgment was made, and the correction of the echo path model was stopped or the speed of correction was reduced, resulting in the deterioration of the call quality.

In order to solve this problem, a method of dealing with the problem by measuring the transmission input level and detecting the open state has been considered in the past. However, in order to compare the transmission input level with a predetermined threshold level, the transmitter input If the DC component contained in the signal causes a malfunction, or if the threshold is set to remove the influence of the DC component, there is a problem that when the signal is small, the line is considered to be open and the superimposed call cannot be detected.

Therefore, in view of the above points, the present invention has been made to solve such problems and to eliminate such defects.
Its purpose is to make it possible to detect the opening of the echo path quickly, prevent malfunction of superimposed call detection, and prevent deterioration of call quality without disturbing the function of superimposed call detection in a normal state with a simple configuration. An object is to provide an echo canceller.

[Means for Solving the Problems] According to the present invention, the echo path characteristic measuring means for measuring the echo path characteristic from the input / output signals of the echo path and the echo path characteristic obtained by the echo path characteristic measuring means are provided. Based on this, an erasing means for erasing the actual echo signal by synthesizing the approximate echo path signal, an erasure residual signal level measuring means for measuring the erasure residual signal level, and a reception side signal level measurement for measuring the reception side signal level Means for measuring the amount of attenuation from the reception output end to the subtraction circuit output based on the output from the remaining signal level measuring means and the output from the receiving side signal level measuring means, The echo path characteristic measuring means for measuring the characteristic of the echo path based on the output from the residual signal level measuring means, the output from the receiving side signal level measuring means, and the output from the attenuation measuring means. In the echo canceller having a superposed call detecting means for controlling the above, the output of the transmitting side signal level measuring means for measuring the transmitting input level, the output of the remaining unerased signal level measuring means, and the receiving side signal level measurement. An echo canceller is provided which is provided with control means for controlling the attenuation amount measuring means based on the output of the means and the output of the superimposed call detecting means.

Further, according to the invention, the control means comprises a first comparing means for comparing the output of the erasure residual signal level measuring means with the output of the transmitting side signal level measuring means, and the transmitting side signal level measurement. Second comparing means for comparing the output of the means and the output of the receiving side signal level measuring means, and third comparing means for comparing the output of the receiving side signal level measuring means with a predetermined set value. An echo canceller having a judging means for judging the state of the echo path based on the outputs of the first, second and third comparing means and the output of the superimposed call detecting means. can get.

[Embodiment] FIG. 1 is a block diagram of a first embodiment of the present invention.

In FIG. 1, reference numerals 1 to 11 indicate the same constituent elements as in FIG. 12 is the signal level measuring circuit on the transmitting side, which determines the level of the signal input to the transmitting side.

The control circuit 13 determines whether or not the echo path is in the open state based on the signal level on the transmitting side, the signal level on the receiving side, and the level of the remaining signal to be erased. When the open state is determined, the control circuit 13 controls the attenuation measuring circuit 10. By controlling the value of the measured attenuation amount, the malfunction of the superimposed call detection circuit 11 is prevented. The operation of the control circuit 13 will be described according to the state of the signal input to the echo canceller. (See Fig. 2 for details of the control circuit 13) (1) No call state In this state, the echo path is open with no signal on both the receiving side and the transmitting side; the superimposed call detection circuit malfunctions. Also,
Since there is no signal, there is no particular problem. Therefore, the attenuation amount measuring circuit is not controlled.

(2) When only the speaker on the side with the echo canceller is speaking, in this state, there is no signal on the receiving side and only the transmitting side has a signal. In this state, since there is no signal on the receiving side, there is no approximate echo signal, and there is no problem even if the echo path is opened and the superimposed speech detection circuit malfunctions. Therefore, the attenuation amount measurement circuit 10 is not controlled. The relationship of each signal at this time is as follows.

Received signal level ≤ transmitted signal level Received signal level ≤ erased residual signal level Deleted signal level = transmitted signal level (3) When there is a signal on both sides In this state, there is a signal on both the receiving side and the transmitting side.

In this state, when the echo path is normal, the attenuation measurement circuit 10 is not controlled. Even when the echo path is open, the attenuation measurement of the echo path is impossible, so the attenuation measurement circuit 10 is controlled. Do not do.

The relationship of each signal in this state is as follows.

Receiving signal level ≤ Transmitting signal level + TH _α Receiving signal level ≤ Remaining erased signal level + TH _ρ Remaining erased signal level ≤ Transmitting signal level + TH _γ where TH _α , TH _ρ and TH _γ are constants for detecting echo path characteristics. Is.

(4) When only the other party on the side with the echo canceller is speaking In this state, there is a signal only on the receiving side.

The relationship of each signal when the echo path is normal in this state is as follows.

The relationship between the received signal level and the transmitted signal level is not determined. Received signal level ≥ erase remaining signal level + TH _ρ erase remaining signal level ≤ transmitted signal level + TH _{γ Since} this state is normal operation,
There is no need to control.

When the echo path is opened in this state, an approximate echo signal is output to the transmitter output, and the superimposed call detection circuit erroneously detects it as if it were in the superimposed call state. In order to prevent this erroneous detection, it is necessary to control the attenuation amount measuring circuit 10.
The relationship of each signal in this state is as follows: reception signal level ≥ transmission signal level + TH _α reception signal level ≤ erase remaining signal level + TH _ρ erase remaining signal level ≥ transmission signal level + TH _γ .

Comparing the above states, it is necessary to control the time attenuation amount measuring circuit in the next state.

When there is a received signal and the received signal level ≥ the transmitted signal level + TH _{α The} received signal level ≤ the erase remaining signal level + TH _ρ and the erase remaining signal level ≥ the transmitted signal level + TH _{γ In} the present invention, the transmission is performed to detect the above condition. Talkside level measuring instrument
12 and a control circuit 13 are provided. Fig. 3 shows the control circuit
13 is a detailed view of 13. FIG.

The present invention will be described with reference to FIGS.

The reception signal is input to the reception side signal level measuring circuit 8 and the signal level is measured. This result is the attenuation measurement circuit
10 and the superimposed call detection circuit 11 and at the same time the control circuit 13
Sent to. In the control circuit 13, the input signal level on the receiving side is set to the threshold value set by the comparator C133.
The presence or absence of the received signal is compared with TH _X.

The signal level of the receiving side is simultaneously measured by the signal level measuring circuit 12 of the transmitting side.
Which is larger by the comparator B132 having the threshold TH _α set by the value of the transmission signal measured by the above, and it is judged which is larger, the reception signal level or the transmission signal level having the threshold TH _α. .

At the same time, the transmission signal level is measured by the erasure residual signal level measuring circuit 9
Which is larger by the comparator A131 having the threshold TH _γ set with the value of the remaining unerased signal measured by, and it is determined which of the transmission signal and the remaining unerased signal level having the threshold TH _γ is larger.

The superposed call detection circuit 11 has a threshold TH _ρ and compares the levels of the received signal and the unerased signal.

The determination circuit 134 includes a comparator A131, a comparator B132, and a comparator C133.
And the output of the superimposed call detection circuit 11 are used to determine whether or not the above condition is satisfied, and the result is controlled to decrease the measured value of the attenuation measurement circuit, whereby the superimposed call detection circuit 11 malfunctions. Prevent.

[Effects of the Invention] As is apparent from the above description, according to the present invention, a transmission input level measuring circuit for measuring a transmission input level and a control for detecting an open state of an echo path are used without using complicated means. With a simple circuit configuration that includes a circuit, the opening of the echo path can be detected quickly without impairing the function of detecting a superposed call in the normal state, malfunctions of the detection of a superposed call can be prevented, and deterioration of call quality can be prevented. Therefore, the practical effect is extremely large.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an echo canceller according to the present invention, FIG. 2 is a block diagram showing a detailed view of a control circuit in FIG. 1, and FIG. 3 is an example of a conventional echo canceller. It is a block diagram shown. 1 …… Receiving input terminal, 2 …… Reception output terminal, 3 …… Sending input terminal, 4 …… Sending output terminal, 5 …… Echo canceller, 6 …… Subtraction circuit, 7 …… Approximate echo signal synthesis Circuit, 8 …… Receiving side signal level measuring circuit, 9 …… Remaining erased signal level measuring circuit, 10 …… Attenuation measuring circuit, 11 …… Superposed call detection circuit, 12 …… Sending side signal level measuring circuit, 13 ...... Control circuit, 131 …… Comparator A, 132…
… Comparator B, 133 …… Comparator C, 134 …… Judgment circuit.

Claims (2)

[Claims] 1. An echo path characteristic measuring means for measuring an echo path characteristic from an input / output signal of the echo path, and combining an approximate echo path signal based on the echo path characteristic obtained by the echo path characteristic measuring means. From the erasing means for actually erasing the echo signal, the erasing residual signal level measuring means for measuring the erasing residual signal level, the receiving side signal level measuring means for measuring the receiving side signal level, and the erasing residual signal level measuring means. Based on the output of and the output from the receiving side signal level measuring means,
Attenuation amount measuring means for measuring the amount of attenuation from the reception output end to the subtraction circuit output, output from the residual signal level measuring means, output from the receiving side signal level measuring means, and output from the attenuation amount measuring means In the echo canceller having a superposed call detecting means for controlling the echo path characteristic measuring means for measuring the echo path characteristic, the output of the transmitting side signal level measuring means for measuring the transmitting input level. And a control means for controlling the attenuation amount measuring means based on the output of the erasure remaining signal level measuring means, the output of the receiving side signal level measuring means, and the output of the superposed call detecting means. An echo canceller characterized by the above. 2. The echo canceller according to claim 1, wherein said control means compares the output of said residual signal level measuring means with the output of said transmitting side signal level measuring means. 1 comparing means, a second comparing means for comparing the output of the transmitting side signal level measuring means and the output of the receiving side signal level measuring means, and the output of the receiving side signal level measuring means. Judgment for judging the state of the echo path based on the third comparing means for comparing the set value, the outputs of the first, second and third comparing means, and the output of the superimposed call detecting means. And an echo canceller.