JPH0131731B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an echo control device for eliminating echoes in a communication circuit.

Conventionally, echo blocking devices, voice switches, echo canceling devices, etc. have been used to control echoes from long-distance lines, loudspeaker telephones, two-way repeaters, etc. The first two of these have problems such as disconnection at the beginning of the line and clicking noise when turning the line on and off. It was developed to compensate for the shortcomings of the switch. This device measures the echo path, synthesizes the echo signal and an approximate echo signal based on the measured echo path characteristics, and
This eliminates the actual echo signal, and does not have a mechanism that causes disturbances such as cutting off the beginning of speech or clicking noise.

However, in the case of this echo cancellation device, in its basic configuration, when the echo signal is superimposed with the transmission signal, noise, etc. and input to the transmission side input, the measurement accuracy of the echo path decreases, and the amount of echo cancellation decreases. It has a predisposition to decrease to a value determined by the ratio of the echo signal level of the transmitting side input to the other signal level. Therefore, in order to prevent the amount of echo cancellation from decreasing in this superimposed state, a superimposed speech detection circuit has been used in practice. However, since the detection of this superimposed call is performed by comparing the output signal level of the receiving side and the input level of the sending side, it is detected when the superimposed signal level is smaller than the echo signal level, or when the echo signal level is small. It had the disadvantage that it was impossible to detect phone calls.

Therefore, an object of the present invention is to enable the detection of a superimposed call even when the superimposed signal level is smaller than the echo signal level and when the echo signal level is small;
An object of the present invention is to provide an echo canceling device capable of preventing a decrease in the amount of echo canceling.

In order to achieve the above object, the present invention detects the level of the transmitter signal at the output level rather than at the input level, and accordingly adds necessary circuitry.

According to the present invention, the characteristics of the echo path are measured from the input and output signals of the echo path, and the approximate echo path signal is synthesized based on the obtained echo path characteristics, thereby subtracting the approximate echo signal from the actual echo signal. In an echo cancellation device that cancels an echo signal, a cancellation residual signal level measuring circuit measures the level of the cancellation residual signal, and an attenuation amount is measured from the input signal of the echo path and the level of the cancellation residual signal, and the measured result is and a cancellation residual echo level estimating section that estimates a cancellation residual echo level from the input signal of the echo path, and a comparison section that compares the output level of the cancellation residual signal level measuring circuit and the cancellation residual echo level estimating section. ,
When the output of this comparison section indicates that the value of the canceled residual echo level measuring circuit is larger than the value of the canceled residual echo level estimation value calculation circuit, the speed of modifying the characteristics of the echo path is reduced or the modification is performed. An echo canceling device is obtained, which is characterized in that it is controlled to stop.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing the circuit configuration of one embodiment of the present invention, which in this case shows that it is suitable for use in long-distance lines. In Figure 1,
Reference numerals 1, 2, 3, and 4 represent terminals for receiving input, receiving output, transmitting input, and transmitting output, respectively. Since the echo canceller 5 is also used in conventional echo cancelers, it consists of a subtraction circuit 6 and an approximate echo signal synthesis circuit 7. The level of the receiving side signal is measured by the receiving side signal level measuring circuit 8 as in the conventional case, but the level of the sending side signal is measured by the canceled residual echo on the sending output side of the subtraction circuit 6, which is different from the conventional case. The level is measured by a device 9.

The attenuation measurement circuit 10 is a circuit that measures how much the signal output from the output end of the handset is attenuated before the output of the subtraction circuit, and calculates the cancellation residual signal based on the outputs of the two measurement circuits 8 and 9. This is determined by taking the time average of the ratio of the measured value of the level measuring circuit and the measured value of the received signal level measuring circuit. This value is the sum of the echo loss, which is the amount of attenuation in the echo bus, and the cancellation, which is the amount of attenuation in the echo canceller. The value of this sum is that when there is no superimposed signal, the cancellation characteristics of the echo canceller always improves, so the cancellation always increases, and the sum of echo loss and cancellation always increases, but when there is a superimposed signal, The measurement value of the cancellation residual signal level measurement circuit becomes the sum of the superimposed signal and the cancellation signal, so it appears as if the cancellation residual echo has increased, and as a result, the sum of echo loss and cancellation has decreased. It will be perceived differently. In order to prevent malfunctions caused by this superimposed signal, the attenuation measurement circuit 10 compares the previously used attenuation value with the currently measured value, and uses the larger attenuation value to prevent the superimposed signal from being input. The correct amount of attenuation can be found without using the value when the amount of attenuation decreases. However, if the value of this attenuation amount is decreased over time, the stability of the device will be improved without requiring an excessively high attenuation amount.

The canceled residual echo level estimation value calculation circuit 11 calculates the estimated value of the canceled residual echo level from the attenuation level measured by the attenuation measurement circuit 10 and the receiving side output signal level (measured by the receiving side signal level measuring circuit 8). The estimated value of the canceled residual echo level is obtained by attenuating the level measured by the attenuation measuring circuit 10.The estimated value of the canceled residual echo level is obtained by multiplying both levels. When this estimated value is compared with the level measured by the erased residual signal level measuring section 9 by the comparator circuit 12, it is found that when there is a superimposed signal, the received signal is sent from the received signal output terminal 2 to the arithmetic unit 6 as described above. Cancellation is performed by adding a superimposed signal to a signal obtained by attenuating the received signal by the amount of attenuation from the receiving output terminal 2 to the calculator 6, with respect to the estimated value of the cancellation residual echo level estimation value calculation circuit 11, which is attenuated by the amount of attenuation. The value of the residual echo level measuring circuit 9 increases. At this time, a reduction in the amount of echo cancellation can be prevented by stopping the modification of the echo path model by the echo cancellation unit 5 or by reducing the modification speed. In addition, in this device, a receiving side signal level measuring circuit 8 and an attenuation amount measuring circuit 10 are used.
and the erased residual echo level estimation value calculation circuit 11 may be collectively named the erased residual echo level estimator 13.

FIG. 2 is a block diagram showing the structure of another embodiment of the present invention.

In this case, the device is suitable for transmitting signals and measuring line characteristics. In FIG. 2, reference numerals 1 to 13 indicate the same components as in the embodiment of FIG. 1, and 14 is a signal sending circuit for sending out a signal at a constant level. However, when using this signal sending circuit 14, the reception input terminal 1 is turned off. In an echo cancellation device that sends a signal at a constant level to the echo path and measures the echo path characteristics based on this signal, the signal level on the receiver side is constant and does not change, so the signal level on the receiver side shown in Figure 1 is Signal level measurement circuit 8 and attenuation measurement circuit 1
0 is no longer necessary, and the erased residual echo level estimator, that is, the estimated value calculation circuit 11 uses the smaller of the previous erased residual echo level estimate and the current erased residual echo level estimate as the current estimated value. do. Increasing this estimate over time improves the stability of the device. The operation of the comparator circuit 12 is similar to that of the embodiment shown in FIG.

As explained above, according to the present invention, even when the superimposed signal level is small relative to the echo level or when the echo signal level is small, the superimposed speech state can be quickly detected, and a decrease in the amount of echo cancellation can be prevented. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the invention, and FIG. 2 is a block diagram showing a second embodiment of the invention. Explanation of symbols: 1 is the 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, 5
1 is an echo cancellation section, 6 is a subtraction circuit, 7 is an approximate echo signal synthesis circuit, 8 is a receiving side signal level measurement circuit, 9 is a cancellation residual signal level measurement circuit, 10 is an attenuation measurement circuit, 11 is a cancellation residual echo level estimation value calculation circuit,
Reference numeral 12 represents a comparison circuit, 13 represents a residual echo level estimation section, and 14 represents a signal transmission circuit.

Claims (1)

[Claims] 1. Measure the characteristics of the echo path from the input/output signals of the echo path, synthesize an approximate echo path signal based on the obtained echo path characteristics, and subtract the approximate echo signal from the actual echo signal. In an echo cancellation device that cancels echo signals by a method, a cancellation residual signal level measuring circuit measures the level of the cancellation residual signal, and an attenuation amount is measured from the input signal of the echo path and the level of the cancellation residual signal. a residual echo level estimation section that estimates a residual echo level from the result and the input signal of the echo path; and a comparison section that compares the output level of the residual echo signal level measurement circuit and the residual echo level estimation section. However, when the output of the comparison section indicates that the value of the canceled residual echo level measuring circuit is larger than the value of the canceled residual echo level estimation value calculation circuit, the speed of modifying the characteristics of the echo path is reduced or An echo canceling device characterized in that it is controlled to stop correction. 2. In the echo canceling device according to claim 1, the canceled residual echo level estimator includes a receiving side signal level measuring circuit for measuring the receiving side signal level, an attenuation amount measuring circuit for calculating the sum of echo loss and cancellation, An echo canceling device comprising: and a cancellation residual echo level estimation value calculating circuit for calculating an estimated value of the cancellation residual echo level. 3. In the echo canceling device according to claim 1, the signal sending circuit used by the canceled residual echo level estimator to measure the echo path characteristics and the canceled residual echo level estimation value calculation for obtaining the estimated value of the canceled residual echo level. A reverberation device characterized by having a circuit.