JPS6226611B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an echo suppressor that is inserted into a long-distance telephone line and suppresses echo sounds, and particularly relates to a half-echo suppressor in which a control switching circuit is inserted in the sending channel and a control attenuator is inserted in the receiving channel. It is something.

With the recent advances in digital technology, digital half-echo suppressors have been developed that operate faster than conventional analog half-echo suppressors and can reduce deterioration in call quality such as disconnection at the beginning of a conversation. . The characteristics of this digital form are recommended by CCITT.
Recommended as Types B, C, and D of G.164. FIG. 1 shows a diagram of the operating range determined by the transmitting level and receiving level of the echo suppressor according to this recommendation. FIG. 2 shows an example of the configuration of a conventional echo suppressor.

To explain the configuration of FIG. 2, the 2-wire/4-wire conversion circuit 1 has a 2-wire line 11 and a transmission channel 1 of the 4-line line.
2 and the receiving channel 13 are connected, and the control suppression switch 2 is inserted into the sending channel 12,
A control attenuator 3 is inserted into the receiving channel 13 to provide a receiving loss. The signal on the input side of the control attenuator 3 is branched and input to the reception detection circuit 4, where the reception detection circuit 4 sets the reception level to the reception detection threshold T set by the reception detection level setting circuit 14.
It is compared with _xz , and if the reception level is high, it is determined that the reception has been received. The detection output of the reception detection circuit 4, the transmission level on the transmission channel 12 side of the 2-wire/4-wire conversion circuit 1, the reception level on the output side of the control attenuator 3, and the transmission detection level setting circuit 15 are set. The transmission detection threshold value T _xy is input to the area determination circuit 5, and a determination is made as to whether there is a no-call state X, a transmission state Y, a reception state Z, or a two-way communication state W in FIG. This judgment result is the control circuit 6
The control circuit 6 controls the control suppression switch 2 and the control reception attenuator 3 with a predetermined operating time and residual time.

The operation of this echo suppressor is in the no-call state
There are four states: a transmitting state Y, a receiving state Z, and a two-way communication state W, and a hysteresis state V which takes either state W or Z depending on the direction of communication. That is, in the no-call state X, the control suppression switch 2
is closed, and the receiver attenuator 3 is also removed, resulting in a common fault state for both directions. The transmitting state Y also becomes a passing state, similar to the no-calling state. In the half echo suppressor according to CCITTG.161, the receive attenuator 3 was inserted when in the Y state, but in Recommendation G.164, when transmitting,
When the receiver attenuator 3 is inserted and removed, the amplitude of the receiver noise changes and becomes harsh, so the receiver attenuator 3 is no longer inserted.

In the receiving state Z, the suppression switch 2 is opened, the signal from the receiving channel 13 leaks through the 2-wire 4-wire conversion circuit 1, and the path to the other party via the transmitting channel 12 is blocked, and in the bidirectional speaking state W, the transmitting channel is The suppression switch 2 is closed, the receiver attenuator 3 is inserted, and the echo is attenuated. When transitioning from the two-way communication state W to the suppression state, that is, the reception state Z, if the reception attenuator 3 is inserted, a hysteresis region V occurs, which slows down the suppression operation, and the transmission signal is suppressed by the reception signal. Cuts due to suppression action. This makes it difficult for so-called tipping to occur. The reception attenuator 3 may provide a constant loss (usually 6 dB) or may provide a non-linear loss that depends on the reception level.

In the above configuration, if there is an interruption from the other party (far end) while the near end talker is transmitting (Y area state) and a receive signal comes, the state changes from Y to W and the receive level is high. In this case, it becomes Z state,
The suppression switch 2 of the sending channel is activated, and the receiving signal is cut off to the other party. This state usually occurs at the boundary between V and Z in the area diagram in Figure 1 due to the reception loss that is inserted during the W state, but if the other party's interrupting call level is high, the line changes instantly from Y to Z. In other words, if the reception level is detected in a shorter time than the operation time of the control attenuator (this is the time from detecting the W state to inserting the control attenuator 3, in other words, the reception level is detected before the control attenuator is inserted). When a level is detected, the suppression operation will occur at the boundary between W and V in Figure 1 without passing through the hysteresis region, and the suppression operation will actually be more likely to occur. The suppression switch is likely to operate in response to the interrupt signal, and the so-called chopping phenomenon, in which the transmitted signal is interrupted to the other party, is likely to occur, and there is a risk that the quality of the call will be significantly degraded.

SUMMARY OF THE INVENTION An object of the present invention is to provide a half-echo suppressor in which a control attenuator is not inserted in the transmitting state, which can reduce the chopping phenomenon with a simple configuration. be.

The feature of this invention is that the transmitting state Y is detected from the relationship between the transmitting level and the receiving level, and only in this case, the receiving input after passing through the attenuator on the receiving side is provided to the area determination circuit through the attenuator that depends on the transmitting level. It is characterized by

The present invention will be explained below with reference to the drawings. FIG. 3 shows an embodiment of the present invention. The control reception attenuator 3 is considered to have a constant loss and a non-linear characteristic in which the loss increases depending on the reception level. The variable loss circuit 8 is a circuit that obtains the output of the second transmitting level detection circuit 7 and gives a loss equivalent to the receiving loss (loss caused by the control receiving attenuator 3) inserted to the receiving level corresponding to the transmitting level. In a digital echo suppressor, this can be easily realized using a table circuit using RAM (random access memory).
The output of the variable loss circuit 8 and the reception level input after passing through the reception attenuator 3 are input to the detection area determination circuit 5 through a changeover switch circuit 9 which is switched according to the Y area detection output information of the area determination circuit 5.

According to this configuration, when in the transmitting region Y, for example at point A in FIG. 1, the variable loss circuit 8 has a loss value (L in FIG. 1) determined by the receiving loss characteristic, The output of the circuit 8 is selected by the changeover switch circuit 9 based on the Y area detection output of the area determination circuit 5. In this state, when there is an interrupt signal from the far-end speaker and the region shifts from Y→W→V→Z, it is extremely short and the Z region is detected before the W region is detected and the control receiver attenuator 3 is controlled. Even when the signal is in the Y area, a predetermined receiving loss L is inserted into the receiving detection input by the loss circuit 8, so hysteresis occurs, and the point at which the signal changes to the Z area is point b in Figure 1. . This makes it difficult for the suppression operation to be performed by the width of the hysteresis, and it is possible to reduce chopping in which the transmitted signal is interrupted by an interrupt signal from the far-end speaker during transmission, thereby improving the quality of the communication. It goes without saying that the second speech level detection circuit 7 can be used in part or in whole as the speech level detection circuit in the area determination circuit 5.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the operating range of an echo suppressor, FIG. 2 is a block diagram showing the configuration of a conventional echo suppressor, and FIG. 3 is a block diagram showing an example of the configuration of an echo suppressor according to the present invention. 1: 2-wire 4-wire conversion circuit, 2: Control suppression switch, 3: Control reception loss, 4: Reception detection circuit, 5:
Area determination circuit, 6: control circuit, 7: second transmitting level detection circuit, 8: variable loss circuit, 9: changeover switch circuit, 11: two-line line, 12: transmitting channel, 13: receiving channel.

Claims (1)

[Claims] 1. A transmission channel into which a control switch is inserted;
a reception channel into which a control attenuator is inserted; a reception detection circuit that determines the presence or absence of a reception level on the input side of the control attenuator; an output of the reception detection circuit; a transmission level on the input side of the control suppression switch; an area determination circuit whose input signals are a reception level on the output side of the control attenuator and an output of a transmission detection level setting circuit that provides a threshold value for determining the presence or absence of a transmission level on the input side of the control suppression switch; , a control circuit that controls the control suppression switch and the control attenuator depending on the output signal of the area determination circuit, the echo suppressor including a control circuit that branches the input side of the control suppression switch and detects a transmitting level. a variable loss circuit that varies depending on the output of the second transmission level detection circuit; and the controlled reception attenuator that is controlled by and guided by the output of the area determination circuit. by the variable loss circuit to the reception level on the output side of the
an echo suppressor comprising a changeover switch that is controlled so as to apply attenuation only in the transmission region determined by the region determination circuit.