JPH0685716A - Nonlinear processor control circuit for echo canceller - Google Patents

Abstract

PURPOSE:To eliminate the noise component of a line or the like by adopting a 1st condition for suppressing a residual signal for the level of the residual signal only. CONSTITUTION:The circuit is provided with a 1st level detection section (a level measurement circuit 7 and a level discrimination circuit 8) receiving a transmission output signal 102 (in this case, referred to as the residual signal of an echo 105), detecting a level with respect to a prescribed reference binary value and outputting a 1st switching signal and with a 2nd level detection section (a level measurement circuit 10 and a level comparator circuit 9) receiving a reception output signal 104 and a transmission output signal 106, detecting a level difference and outputting a 2nd switching signal. Then an output signal suppressed by a suppression circuit or the residual signal, that is, the transmission output signal 102 not suppressed is outputted through a switching circuit 6 as an output signal 103 based on prescribed discrimination. Thus, noise on a line or the like is eliminated and the degradation in speech quality is avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear processor control (NLP) circuit of an echo suppressor used for satellite communication or conference call.

[0002]

2. Description of the Related Art An echo suppressor is for canceling the echo of a received signal to the transmission signal side due to impedance mismatch of a hybrid transformer on the signal reception side, that is, for canceling an echo, and an NLP circuit transmits the echo suppressor body. This circuit is provided on the signal side and originally suppresses a signal that remains without being echo-cancelled by the echo canceller during single talk (there is no signal on the transmitting side), that is, a residual signal.

Conventionally, this type of echo canceller NRP is used.
The circuit has the configuration shown in FIG. In FIG. 3, the transmission signal of the transmitting-side speaker 21 passes through the hybrid transformer 22, becomes the transmission input signal 201, passes through the echo canceller main body 23, becomes the transmission output signal 202, and enters the NRP circuit side. Here, the transmission signal is through, but the residual signal of the echo is further suppressed and sent as the output signal 203 to the transmission line side.

The received input signal 204 from the transmission line side is NR
At the same time as the level is detected by the P circuit 24 and the echo canceller main body 23, it is sent to the transmitting side speaker 21 through the hybrid transformer 22. When passing through the hybrid transformer 22, a wraparound caused by impedance mismatch with the speaker 21 on the transmitting side, that is, an echo 205 is generated, and a received input signal 204 wraps around to the transmitting side. The echo suppressor main body 23 refers to the received input signal 204 and the transmitted output signal 202 to estimate this echo by the adaptive FIR type filter, and subtracts the estimated echo from the transmitted input signal 201 to cancel, but it cannot be canceled completely. The residual signal is output as the transmission output signal 202.

Next, the operation of the NLP circuit 24 will be described. First, the first step is to detect the state where single talk and echo are canceled, and the second step is to suppress the residual signal and use it as a transmission output signal in that state.
In this first step, a level-averaged level measurement of the received input signal 204 (referred to as the RIN signal) is made in the level measuring circuit 30 and there is a transmitted output signal 202, in this case the residual signal (referred to as the E signal). The level measurement circuit 27 performs time-averaged level measurement, judges each level, and
When the N signal is higher than a certain level and the E signal is lower than a certain level, it is judged by the level judgment circuits 28 and 29 that the state is single talk and echo canceled. In the second step, the switching circuit 26 switches between the suppression of the E signal by the suppression circuit 25 and transmission as the output signal 203 or the direct transmission of the E signal without suppression, based on the judgment of the first step.

[0006]

In the conventional method, the suppression of the residual signal is limited to the single talk and the echo canceling state. Therefore, for example, the line noise in the transmission input signal or the room noise from the transmitting speaker may occur. In the case where there is a component such as, the noise component becomes the transmission output signal when both the reception signal and the transmission signal are silent after the single talk and echo cancellation state. The transmission output signal changes from a signal in which the residual signal is suppressed to a signal in which a noise component remains, giving the listener an unpleasant feeling and degrading the communication quality. Further, during a two-way call (a state in which a received signal and a transmitted signal are mixed with each other), there is a case where there is a discontinuity in a single talk state and an echo canceling state, which also causes a problem that the call quality is deteriorated.

[0007]

A non-linear processor control circuit of an echo canceller according to the present invention refers to an echo in which a reception output signal spills to a transmission input signal side, refers to the reception input signal and the transmission output signal, and uses an adaptive FIR type filter. A suppression circuit that inputs the transmission output signal of an echo canceller unit that outputs a residual signal obtained by subtracting the estimated echo estimated from the transmission input signal as the transmission output signal, and suppresses the signal to a predetermined level. Of the output signal and the transmission output signal, and referring to the first switching signal and the second switching signal to output one of them as an output signal; and a predetermined reference value 2 to which the transmission output signal is input. A first that detects a level for a value and outputs the first switching signal
And a second level detection unit that inputs the reception input signal and the transmission output signal, detects a level difference between them, and outputs the second switching signal.

[0008]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of this embodiment, and FIG. 2 is FIG.
It is a characteristic diagram showing the standard of the level judgment in. In FIG. 1, the speaker 1 on the transmitting side, the hybrid transformer 2, and the echo canceller main body 3 have the same configurations as those of the conventional example shown in FIG.

The operation of the NLP circuit 4 will be described below. The level measuring circuit 7 receives the transmission output signal 102 (in this case, the residual signal of the echo 105), time-averages the levels, and outputs a level signal 106. The level determination circuit 8 compares the level signal 106 with two reference levels (TH-L, TH-H, TH-L <TH-H) to determine whether they are greater than or less than the reference level. , A switching signal of “1” when larger than TH-H, and a switching signal of “2” when TH-L to TH-H is output to the switching circuit 6. Further, the level measuring circuit 10 receives the received input signal 104, and outputs a level signal 107 obtained by time-averaging this level. The level comparison circuit 9 receives the level signal 107 and the level signal 10 of the level measurement circuit 7.
6 and the signal level difference between them (level signal 10
When the 6-level signal 107) is larger than the reference level A, the switching circuit 6 outputs a switching signal of "0", and when it is smaller, the switching signal of "1".
Output to.

The switching circuit 6 inputs these two switching signals and makes the determination shown in FIG. That is, when the decision 1 level signal 106 is smaller than TH-L, the residual signal is suppressed regardless of other decisions (NLP-O).
N).

Judgment 2 When the level signal 106 is larger than TH-H, the residual signal is not suppressed (NLP-OFF) regardless of other judgments.

Judgment 3 Level signal 106 is TH-L to TH-H
Level signal 106-level signal 107
If the difference is larger than the reference level A, NLP-ON.

If the difference between the level signal 106 and the level signal 107 is smaller than the reference level A, NLP-OFF.

Based on this judgment, the switching circuit 6 switches the output signal or the residual signal suppressed by the suppression circuit, that is, the transmission output signal 102 without suppressing it, and outputs it as the output signal 103.

[0015]

As described above, in the present invention,
Since the first condition for suppressing the residual signal is only the level of the residual signal, the residual signal is suppressed even when there is no sound in the received signal and the transmitted signal, and the noise component of the line or the like can be removed. Further, the second condition for suppressing the residual signal is that the level of the received input signal and the level of the residual signal are compared, and the difference is used as the difference, so that there is no interruption during two-way communication and the deterioration of the communication quality is eliminated. There is.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing switching conditions in FIG.

FIG. 3 is a block diagram of a conventional example.

[Explanation of symbols]

 1 Speaker on the transmitting side 2 Hybrid transformer 3 Echo canceller body 4 NLP circuit 7, 10 Level measurement circuit 8 Level judgment circuit 9 Level comparison circuit 6 Switching circuit 5 Suppression circuit 101 Transmission input signal 102 Transmission output signal (residual signal) 103 NLP output signal 104 Received input signal

Claims (2)

[Claims] 1. A residual obtained by estimating an echo, which a received output signal wraps around to a transmitted input signal side, by an adaptive FIR filter by referring to the received input signal and the transmitted output signal, and subtracting the estimated echo from the transmitted input signal. A suppression circuit that inputs the transmission output signal of the echo canceller unit that outputs a difference signal as the transmission output signal and suppresses the transmission output signal to a predetermined level.
A switching circuit which inputs the output signal of the suppression circuit and the transmission output signal and outputs one of them as an output signal by referring to the first switching signal and the second switching signal; The level for two reference values is detected to detect the first
A first level detecting section for outputting the switching signal and a second level detecting section for inputting the reception input signal and the transmission output signal, detecting a level difference between them, and outputting the second switching signal. A non-linear processor control circuit of an echo canceller characterized by comprising. 2. The first level detecting unit has a first level measuring circuit for averaging and measuring the level of the transmission output signal for a certain period of time and an output of the first level measuring circuit.
Two levels (TH-L, TH-H, but TH-L <TH-H) are compared or less than TH-L. "0" If TH-H is greater than "1" TH- A level judgment circuit that outputs the first switching signal of "2" in the case of L to TH-H, and the second level detection unit averages and measures the level of the reception signal for a certain period of time. And the output of the first level measuring circuit (LEVEL-E) and the output of the second level measuring circuit (LEVEL-R) are compared, and the LEVEL-R and LEVEL-E are compared. And a level comparison circuit that outputs the second switching signal of "1" when the difference is larger than a certain level and "0" when the difference is smaller than a certain level, the switching circuit including the first switching signal and the second switching signal. When the signals are "0", "0", "0", "1", "1" and "0", the output signal of the suppression circuit is output as an output signal,
The non-linear processor control of the echo canceller according to claim 1, wherein in the case of "1""1","2""0","2""1", the transmission output signal is output as it is as an output signal. circuit.