JPH0530082A - Voice privacy telephone equipment - Google Patents

Abstract

PURPOSE:To reduce a residual generated due to a fact that an adaptive type echo canceller cannot follow a sudden attenuation quantity in a transmission line in a short time, in the voice privacy telephone equipment for superposing a noise onto a sound signal on a transmitting side, transmitting it as a privacy telephone signal, and extracting the sound signal contained in the privacy telephone signal by referring to the noise by using the adaptive type echo canceller on a receiving side. CONSTITUTION:A transmitting side is constituted of a transmitting noise generating circuit 202, a monitoring signal generating circuit 203, and an adding circuit 204, a receiving side is constituted of a band-pass filter circuit 223, a low-pass filter circuit 224, a level reproducing circuit 225, a multiplying circuit 228, a reference noise generating circuit 227, and an adaptive type echo canceller 229, and by following magnitude of a level of a received monitoring signal, a level of a noise signal to be a reference signal of the adaptive type echo canceller 229 is varied through the multiplying circuit 228.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice signal anonymization device, and more particularly, on the transmitting side, superimposes a transmission voice signal on a periodic noise signal whose power spectrum is substantially flat within the entire frequency band of the transmission voice signal. Send the confidential communication signal, and at the receiving side,
The present invention relates to an improvement of a secret talk device that refers to a reference noise signal using an adaptive echo canceller and extracts a transmission voice signal from a received secret talk signal.

[0002]

2. Description of the Related Art A conventional voice confidential communication device transmits a confidential voice signal in which a transmission voice signal is superimposed on a noise signal whose power spectrum is substantially flat over the entire frequency band of the transmission voice signal on the transmission side, and a reception side. There is a method of extracting a voice signal from a received secret signal using an adaptive echo canceller (see Japanese Patent Application No. 63-156012).

Further, as shown in FIG. 1, a transmission noise generation circuit 102 and an addition circuit 103 are provided on the transmission side, and a transmission voice signal input to a transmission side input terminal 101 and an output signal of the transmission noise generation circuit 102 are added. The adaptive echo canceller 1 is provided to the receiving side by adding the circuit 103 and outputting the confidential signal as a confidential signal to the transmission line 111 via the output terminal 104 on the transmitting side.
23, the reference noise generation circuit 122, and the cancellation amount estimation circuit 1
24 and the mute circuit 125 are provided, and the level difference between the transmission noise signal component contained in the secret signal guided to the adaptive echo canceller 123 and the residual difference appearing at the output end of the adaptive echo canceller 123 is compared. There is a method in which the output signal of the adaptive echo canceller 123 is muted when the canceling amount is estimated to be abnormally small by using the canceling amount estimating circuit 124 which approximately estimates the canceling amount.

[0004]

However, in this type of voice confidential communication apparatus, the transmitting voice signal is masked on the transmitting side by a periodic noise signal whose power spectrum is substantially flat within the entire frequency band of the transmitting voice signal. . At this time, the confidential signal includes a transmission noise signal having a higher level than that of the transmission voice signal. Therefore, the transmission voice signal level included in the transmitted confidential signal is transmitted at a level relatively lower than the voice signal level of a normal telephone. Therefore,
In the conventional device, during normal operation, the adaptive echo canceller output signal is amplified and reproduced to a level that is easy to hear.

When the transmitting side portion or the receiving side portion is mounted on an automobile or the like and passes through a tunnel or the like, a confidential signal to be temporarily received is greatly attenuated. After passing through the tunnel, the level of the secret signal that should be received is restored, but due to the followability of tap correction of the adaptive echo canceller, a sufficient cancellation amount cannot be obtained in the adaptive echo canceller, and noise as a cancellation error occurs. There was a drawback that it appeared in the output of the confidential device. More specifically, in the conventional canceling amount estimation circuit, the power between different signals, that is, the secret signal introduced to the input end of the adaptive echo canceller and the reproduced voice signal appearing at the output end of the adaptive echo canceller, is used to estimate the canceling amount. Since this is a comparison, a sufficient integration time was required to obtain a more accurate estimated value of the amount of cancellation.

Therefore, it is difficult to shorten the operation start time of the mute function and to accurately obtain the estimated value of the amount of cancellation to operate the mute function.

Therefore, a momentary interruption in the transmission line or a large attenuation distortion,
There is a drawback that the cancellation residual due to the disconnection of the confidential signal due to the end of communication on the transmitting side appears at the output end of the confidential audio signal via the adaptive echo canceller.

An object of the present invention is caused by a large error in transmission loss on the transmission line, a momentary interruption, and a synthetic error of a pseudo echo by an adaptive echo canceller against interruption of a confidential signal from the transmitting side due to the end of transmission. An object of the present invention is to provide a voice confidential device with reduced noise.

[0009]

A transmission noise generation circuit for masking a transmission voice signal with a noise signal on a transmission side, a supervisory signal generation circuit for generating a signal for monitoring a gain variation in a transmission line, and a transmission voice signal And a transmission noise signal and a monitoring signal are added, and an adder circuit is provided for sending out to the transmission path as a confidential signal, and the receiving side gains by following the level of the monitoring signal included in the received confidential signal. Variable gain amplifier circuit that controls the output of the variable gain amplifier circuit, a bandpass filter circuit that extracts the monitoring signal from the output signal of the variable gain amplifier circuit, and a level that outputs a direct current following the level of the monitoring signal extracted by the bandpass filter circuit. A reproduction circuit, a reference noise generation circuit that generates the same noise signal as the transmission noise generation circuit, a multiplication circuit that calculates the product of the output signal of the reference noise generation circuit and the level reproduction circuit output signal, and the transmission voice included in the confidential signal Low-pass filter circuit that extracts the signal and transmission noise signal components, an adaptive echo canceller that extracts the audio signal from the output signal of the low-pass filter circuit by referring to the reference noise signal, the output signal of the low-pass filter circuit A range detection circuit that detects the level range of the, and a mute circuit that is controlled by the output signal of the range detection circuit are provided, and by connecting to the output of the adaptive echo canceller, instantaneous interruptions in the transmission line, large attenuation distortion, transmission It is possible to realize a voice secret communication device with a small cancellation residual in the adaptive echo canceller even when the secret signal is disconnected due to the end of transmission on the side.

In particular, the present invention is characterized in that the monitoring signal is superimposed on the confidential signal transmitted from the transmitting side for the purpose of monitoring the attenuation of the transmission line.

[0011]

Embodiment 1 Next, Embodiment 1 of the present invention will be described with reference to the drawings.

On the transmission side, a transmission voice signal is inputted from the transmission side input terminal 201 to the voice confidential device.

The transmission noise generation circuit 202 generates a noise signal whose power spectrum is substantially flat in the entire frequency band of the transmission voice signal and which has the same waveform periodically. It is more effective that this noise signal resembles white noise in terms of the confidential level of the transmitted voice signal.

The monitor signal generating circuit 203 generates a sine wave signal for monitoring.

The adder circuit 204 has a transmitting side input terminal 201.
The transmission voice signal input via the above, the output of the transmission noise generation circuit 202, and the output signal of the supervisory signal generation circuit 203 are added, and the output is sent to the transmission-side output terminal 205 as a confidential signal. The respective signal levels at this time are selected as follows. Even if the confidential signal is intercepted, the transmitted voice signal is masked with the transmitted noise signal to the extent that it cannot be perceptually recognized. Generally, when white noise is superimposed on a voice signal, the clarity of the voice signal is -20 dB.
The signal-to-noise ratio (S / N) is about 0%. The relative levels of the voice signal and the noise signal included in the confidential signal are selected to an allowable level based on the above-mentioned intelligibility.

On the other hand, the frequency of the monitoring signal is selected to be a single frequency which does not overlap with the transmission voice signal or the transmission noise signal on the frequency axis. Further, the level is such that a non-linear distortion is not given to the confidential signal on the transmission line 211, and a coefficient for multiplication is accurately obtained on the receiving side.

The confidential signal is sent to the receiving side via the transmission line 211. The transmission line 211 is a transmission line including a telephone line and a space.

On the receiving side, the receiving side input terminal 221 receives the confidential signal. The bandpass filtering circuit 223 extracts only the monitoring signal from the received confidential signal.

The low-pass filter circuit 224 extracts a transmission voice signal and a transmission noise signal component from the received confidential signal.

The level reproduction circuit 225 outputs a DC signal proportional to the amplitude of the extracted monitoring signal. Therefore,
A DC signal is output to the output terminal of the level reproduction circuit 225, following the change in the attenuation amount of the transmission line 211.

The reference noise generation circuit 227 generates substantially the same noise as the transmission noise generation circuit 202.

The multiplication circuit 228 is the reference noise generation circuit 22.
The product of the signal from No. 7 and the DC signal from the level reproduction circuit 225 is obtained. In other words, the multiplication circuit 228 functions like a resistance attenuation circuit in which the amount of attenuation is controlled by external direct current.

A general adaptive echo canceller is composed of a transversal filter having a variable tap coefficient and a subtractor, and synthesizes a pseudo echo by passing a reference signal through the transversal filter. The residual is obtained by the subtractor from the pseudo echo and the actual echo, and the tap coefficient of the transversal filter is adaptively corrected so that the residual is minimized. When the signals of the general adaptive echo canceller and the adaptive echo canceller 229 of the present invention are compared, the reference signal of the transversal filter is the multiplication circuit 227 of the present invention.
Of the transmission noise signal component included in the output signal of the low pass filter circuit 224.

The residual error corresponds to the output of the adaptive echo canceller 229, which corresponds to the transmission voice signal component. Actually, the output of the adaptive echo canceller 229 is the pseudo echo synthesis error signal, the transmission voice signal of the talker, and the transmission line 2.
The mixed noise at 11 will appear.

Originally, it is desirable that the residual is only the component of the transmitted voice signal. Particularly in the present invention, the adaptive echo canceller 229 apparently shortens the time until the tap coefficient of the transversal filter is corrected in order to minimize the residual.

In the following, description will be given assuming that a large transmission loss occurs in the transmission line 211, for example, assuming a momentary interruption. Here, for easy understanding, the input signal and the output signal of the multiplication circuit 228 are the same (the multiplication coefficient is 1). Now, the confidential signal is received by the receiving side, and the adaptive echo canceller 229 refers to the reference noise signal from the reference noise generating circuit 227 via the multiplying circuit 228 and refers to the transmission noise signal included in the output signal of the low-pass filtering circuit 224. The component (echo component) is deleted, and the transmission voice signal is extracted. At this time, the tap coefficient of the transversal filter is corrected so as to synthesize a pseudo echo that is almost equal to the echo component, and the filter is in a converged state.
Next, due to the momentary interruption of the transmission path 211, the received confidential talk signal is given a sudden attenuation for a moment, and the echo component disappears. This time,
The tap coefficient of the transversal filter of the adaptive echo canceller 229 is gradually modified to minimize the residual. However, the residual appears at the output of the adaptive echo canceller 229 until the tap coefficients of the transversal filter converge to minimize the residual. In the present invention, until the convergence, the same attenuation as the echo contained in the confidential signal is also given to the reference noise signal to be referred,
This is to reduce the residual error without changing the tap coefficient of the filter once converged. This follows the change in the attenuation amount of the transmission line 211, in other words, the change in the level of the monitoring signal included in the confidential signal, and the level reproduction circuit 22
At 5, a DC signal proportional to the magnitude of the monitoring signal is taken out. Next, this DC signal is realized by guiding the attenuated reference noise signal component to the adaptive echo canceller 229 as a signal to be referenced through a multiplication circuit 228 whose attenuation is controlled by voltage.

Although the above description has been made with respect to the instantaneous interruption, the residual error can be reduced similarly when the instantaneous interruption is recovered. The same applies to signal disconnection from the transmitting side at the end of a call.
Further, when the attenuation amount of the transmission path 211 changes slowly, the control operation via the multiplication circuit 228 and the operation of reducing the residual error by the adaptive echo canceller 229 themselves are simultaneously performed. In implementing the first embodiment, points to be particularly noted are 2 of the adaptive echo canceller 229.
This is to control the level fluctuations of two input signals so that they are temporally identical. If the control is not performed in this way, the effect of the first embodiment is reduced. Therefore, the adaptive echo canceller 229 is delayed by how much the level fluctuation of the monitoring signal from the input end of the bandpass filter circuit 223 is delayed.
It is important to appear in the reference noise signal component supplied to the. Then, it is necessary to make this delay time as close as possible to the delay time in which the transmission noise component is given by the low pass filter circuit 224.

Next, a second embodiment will be described. Figure 3
Shows the configuration of the second embodiment.

The configuration of the transmitting side is the same as that of the first embodiment, and the receiving side is different from the first embodiment in that the level reproduction circuit and the multiplication circuit are removed, and the mute circuit 230 is replaced by the adaptive echo canceller 229 as shown in the figure. Further, a range detection circuit 226 is further arranged between the output end of the band-pass filter circuit 223 and the mute circuit 230. The range detection circuit 226 has two thresholds, an upper limit and a lower limit, with respect to the level of the received monitoring signal, and determines whether the level of the monitoring signal exists within the range given by these two thresholds. To detect. If the level of the monitoring signal is out of range, the range detection circuit 226 controls the mute circuit 230 to attenuate the output of the adaptive echo canceller 229.

In this embodiment, when the confidential signal reaches a very small level, even the small residual in the adaptive echo canceller 229 is reduced, and the reproduced voice at the output end of the receiving side is made almost silent so that the listener can hear it. Has the effect of reducing the discomfort of.

The secret signal is extremely large and the transmission line 2
When the value of 11 is different from the original amount of attenuation, the output signal of the range detection circuit 226 controls the mute circuit 230 in the same manner as described above. This necessity means that the level of the echo originally contained in the confidential signal that reaches the receiving side is always smaller than the level of the reference noise signal referred to by the receiving side. When this precondition is not satisfied, distortion occurs in the filter tap coefficient of the adaptive echo canceller 229, and the copied pseudo echo is completely different from the original one. This premise is a condition from the necessity of effectively using the dynamic range. The fact that the dynamic range from the adaptive echo canceller 229 can be increased means that the signal-to-noise ratio (S / N) of the extracted voice signal can be increased, in other words, the voice signal with less noise can be reproduced. ing. In particular, the voice confidential communication device according to the present invention is particularly necessary because the originally required transmission voice signal is masked with a noise signal and the signal-to-noise ratio is reduced to form a secret voice signal.

FIG. 4 shows a third embodiment in which the first and second embodiments are combined, and the functions and operations of the constituent elements are as described above. When the transmitting side or the receiving side is located inside a radio wave obstacle such as a tunnel or the transmission path 2
In the case of the instantaneous interruption in 11, the first embodiment is the noise reducing method as described above, and the second embodiment is effective in reducing the noise due to the rounding error of the calculation that cannot be removed by the first embodiment. Although the example in which the confidential signal cannot be received at all is taken as an example, the mute circuit 230 of the second embodiment passes the extracted audio signal if the monitoring signal exceeding the lower limit threshold value of the range detection circuit 226 can be received. Therefore, Example 1 and Example 2 can coexist.

In FIG. 5, a variable gain amplifier circuit 222 is provided at the input end of the receiving side of the third embodiment to stabilize the level. The variable gain amplifying circuit 223 is provided in the bandpass filtering circuit 22.
The level of the monitoring signal from the output terminal of 3 is monitored, and the output levels of the variable gain amplifier circuit 222 and the bandpass filter circuit 223 are kept substantially constant. This effect makes it possible to narrow the range for detection by the range detection circuit 226 and also allows the mute circuit 230
There is an effect that the time until the start of the operation of can be shortened. As a result, it is possible to narrow down the time and level range for starting mute for the extracted audio signal, and reproduce the audio signal with less disconnection. In addition, the level reproduction circuit 225, the multiplication circuit 228, and the dynamic range can be reduced, and the dynamic range of the adaptive echo canceller 229 can be effectively used.

[0034]

As is apparent from the above description, according to the present invention, the adaptive echo is adapted to the large fluctuation of the transmission loss and the instantaneous interruption in the transmission line, and the interruption of the confidential signal from the transmitting side due to the end of the transmission. There is an effect that it is possible to realize a voice secret talking device in which noise caused by the synthetic error of the pseudo echo by the canceller is reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional configuration.

FIG. 2 is a diagram showing a configuration of a first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a third embodiment which is a combination of the first embodiment and the second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an embodiment in which a monitoring signal level is stabilized at a receiving side input end of Embodiment 3 of the present invention.

[Explanation of symbols]

201 Transmit side input terminal 202 Transmission noise generator 203 supervisory signal generation circuit 204 adder circuit 205 Transmitter output terminal 211 Transmission line 221 Input terminal on receiving side 222 Variable gain amplifier circuit 223 bandpass filter 224 Low-pass filter circuit 225 level reproduction circuit 226 Range detection circuit 227 Reference noise generator 228 Multiplier circuit 229 Adaptive Echo Canceller 230 mute circuit 231 Receiver output terminal

Claims (3)

[Claims] 1. A transmission noise generation circuit for masking a transmission voice signal with a noise signal on a transmission side, a supervisory signal generation circuit for generating a signal for monitoring a gain variation in a transmission line, a transmission voice signal and a transmission noise signal. An adder circuit that adds the three signals, the monitor signal and the monitoring signal, to the transmission path as a secret signal is provided, and the receiving side includes a bandpass filter circuit, a lowpass filter circuit, a level reproduction circuit, a multiplication circuit, and a reference noise generation circuit. , An adaptive echo canceller is installed, the received secret signal is guided to the band-pass filter circuit and the low-pass filter circuit, the band-pass filter circuit output signal is supplied to the level reproduction circuit, and the level reproduction circuit output signal and reference noise are generated. An audio secret-talking device, wherein the circuit output signal is supplied to a multiplication circuit, and the multiplication circuit output signal and the low-pass filtering circuit output signal are supplied to an adaptive echo canceller. 2. A transmission noise generation circuit for masking a transmission voice signal with a noise signal on a transmission side, a supervisory signal generation circuit for generating a signal for monitoring a gain variation in a transmission line, a transmission voice signal and a transmission noise signal. An adder circuit that adds the three signals of the monitor signal and the monitor signal and sends out as a secret signal to the transmission line is provided. On the receiving side, a band-pass filter circuit, a low-pass filter circuit, a range detection circuit, a reference noise generation circuit, an adaptive type An echo canceller and a mute circuit are provided, the received confidential signal is supplied to the band-pass filter circuit and the low-pass filter circuit, and the band-pass filter circuit output signal is supplied to the range detection circuit. An audio secret-talking device, characterized in that an output signal of a band-pass filter circuit is supplied to an adaptive echo canceller, and an adaptive echo canceller output signal and a range detection circuit output signal are supplied to a mute circuit. 3. A transmission noise generation circuit for masking a transmission voice signal with a noise signal on a transmission side, a supervisory signal generation circuit for generating a signal for monitoring a gain variation in a transmission line, a transmission voice signal and a transmission noise signal. An adder circuit that adds the three signals, the monitor signal and the monitoring signal, to the transmission path as a confidential signal is provided. On the receiving side, a bandpass filter circuit, a lowpass filter circuit, a level reproduction circuit, a range detection circuit, and reference noise generation. Circuit, multiplication circuit, adaptive echo canceller, and mute circuit are provided, the received confidential signal is supplied to the band-pass filter circuit and the low-pass filter circuit, and the band-pass filter circuit output signal is supplied to the level reproduction circuit and range detection circuit. The level reproduction circuit output signal and the reference noise generation circuit output signal are supplied to the multiplication circuit, and the multiplication circuit output signal and the low-pass filter circuit output signal are supplied to the adaptive echo canceller. An audio confidential device characterized in that an output signal and an output signal of a range detection circuit are supplied to a mute circuit.