JPH0621919A - Transmitter/receiver for privacy telephone system - Google Patents

Abstract

PURPOSE:To reduce the residual that is caused by a fact that an adaptive echo canceler is unable to follow a sudden change of attenuation value on a transmission line in a short period with a privacy telephone system which superposes the noises on the transmitted signals to transmit these signals as the privacy telephone signals through a transmitter and extracts the voice signals out of the privacy telephone signals through a receiver with reference given to the noises via the echo canceler. CONSTITUTION:A transmitter outputs the signal obtained by adding together the transmitting noise signal produced by a transmitting noise generating circuit 202, the monitoring signal generated by a monitoring signal generating circuit 204, and the transmitting voice signal via an adder circuit 204 as a privacy telephone signal. Meanwhile a receiver reproduces the level of the monitoring signal extracted by a BPF circuit 223 through a level reproducing circuit 225, multiplying the reference noise signal produced by a reference noise signal generating circuit 227 by the monitoring signal based on its level, and uses the output signal of the multiplication as a reference signal of an adaptive echo canceler 229.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice signal secret-talking device, and in particular, a secret talk in which a transmitting voice signal is superposed on a periodic noise signal whose power spectrum is largely flat in the entire frequency band of the transmitting voice signal on the transmitting side. The signal is sent out, and on the receiving side, the reference noise signal is referenced using the adaptive echo canceller,
The present invention relates to an improvement of a confidential talk device that extracts a transmission voice signal from a received secret talk signal.

[0002]

2. Description of the Related Art As a conventional voice confidential device, on the transmitting side,
The secret voice signal is generated by superimposing the transmission voice signal on a noise signal whose power spectrum is significantly flat over the entire frequency band of the transmission voice signal, and the receiving side outputs the voice from the secret voice signal received using the adaptive echo canceller. A device for extracting a signal has been proposed (see Japanese Patent Laid-Open No. 2-7636).

Further, as another conventional voice confidential communication device, a device shown in FIG. 6 has been proposed. The voice secret device is
A transmitter that secretly processes a transmitted voice signal and sends the confidential voice signal, and a voice confidential voice signal transmitted from this transmitter, receives the confidential voice signal, demodulates the transmitted voice signal, and outputs the received voice signal. And a receiving device that operates.

The transmitting apparatus comprises a transmitting side input terminal 101, a transmitting noise generating circuit 102, an adding circuit 103, and a transmitting side output terminal 104. A transmission voice signal is input to the transmission side input terminal 101. This transmitting side input terminal 10
The transmission voice signal from 1 is supplied to the addition circuit 103. The transmission noise generation circuit 102 generates a transmission noise signal. This transmission noise signal is supplied to the adding circuit 103. The adder circuit 103 adds the transmission voice signal and the transmission noise signal, and uses the added signal as a confidential signal as a transmission side output terminal 104.
To the transmission path 111 via.

The receiving device includes a receiving side input terminal 121, a reference noise generating circuit 122, and an adaptive echo canceller 12.
3, a cancellation amount estimation circuit 124, and a mute circuit 125
And a receiving-side output terminal 126. A secret signal is input to the reception-side input terminal 121 from the transmission device via the transmission path 111. This received confidential signal is supplied to the adaptive echo canceller 123 and the cancellation amount estimation circuit 124. The reference noise generation circuit 122 generates a reference noise signal. This reference noise signal is an adaptive echo canceller 12
3 is supplied. The adaptive echo canceller 123 adaptively echo cancels the received confidential signal based on the reference noise signal, and outputs the echo canceled signal. The echo canceled signal is supplied to the cancellation amount estimation circuit 124. The cancellation amount estimation circuit 124 compares the levels of the transmission noise component included in the received confidential signal and the residual difference appearing in the echo canceled signal, and approximately estimates this level difference as the cancellation amount. Mute circuit 12
5 mutes the echo canceled signal when the cancellation amount is estimated to be smaller than the expected value. The output signal of the mute circuit 125 is output from the reception side output terminal 126 as a reception audio signal.

[0006]

However, this type of voice confidential device is a transmitter that masks a transmission voice signal with a periodic noise signal whose power spectrum is substantially flat within the entire frequency band of the transmission voice signal. is doing. At this time, the confidential signal includes a transmission noise signal having a higher level than the level of the transmission voice signal. Therefore, the transmission voice signal level included in the transmitted confidential signal is transmitted at a relatively low level as compared with the voice signal level of a normal telephone. Therefore, in the process of transmitting and reproducing the audio signal in this device, the signal-to-noise ratio (S / N) of the reproduced audio signal is
Therefore, special consideration is required so that

Further, the transmitter or the receiver is mounted on a moving body such as an automobile, and when this moving body passes through a radio wave obstacle such as a tunnel, a confidential signal to be temporarily received is greatly attenuated. To do.

The mobile object passes through the radio wave obstacle (tunnel), and the level of the confidential signal to be received is restored. However, the adaptive echo canceller cannot obtain a sufficient amount of cancellation due to the followability due to the correction speed of the tap coefficient of the adaptive echo canceller. As a result, noise as a cancellation error is generated, and this noise appears in the output of the voice confidential communication device, degrading the call quality.

The situation in this respect will be described in more detail. In the conventional canceling amount estimation circuit, in order to estimate the canceling amount, a secret signal introduced to the input end of the adaptive echo canceller and a low-level reproduced voice signal appearing at the output end of the adaptive echo canceller are different in level and level. A power comparison is made between signals with large differences. Therefore, in order to obtain a more accurate estimated value of the amount of cancellation in the cancellation amount estimation circuit, a sufficient integration time was required.

Therefore, in the conventional voice confidential communication device, it is difficult to accurately obtain the estimated amount of cancellation amount by which the mute function should be operated by the mute circuit 125. As a result, in the conventional voice confidential device, it is difficult to shorten the operation start time of the mute function and stably operate the mute function.

Therefore, in the conventional voice conversation device, the cancellation residual due to the interruption of the transmission line, the great attenuation distortion, and the disconnection of the secret signal due to the end of the communication at the transmission side causes the adaptive echo canceller 123 to operate. There is a drawback that it appears at the output end of the audio confidential signal via the.

Therefore, the technical problem of the present invention is to solve the above-mentioned problems and to eliminate the residual error which occurs when the adaptive echo canceller cannot follow a rapid change in the attenuation amount in the transmission line in a short time. An object of the present invention is to provide a voice confidential talking device that can be reduced.

[0013]

According to the present invention, a transmission noise generating circuit for generating a transmission noise signal in a transmitter of a voice confidential communication device for secretly processing a transmission voice signal and transmitting the confidential voice signal; A supervisory signal generating circuit for generating;
A transmitting device of a voice confidential talk device, comprising: an addition circuit that adds a transmission voice signal, a transmission noise signal, and a supervisory signal, and outputs the added signal as a secret voice signal.

In the transmitter of the voice confidential device, the transmission noise generating circuit is a pseudo random pattern generating circuit which generates a pseudo random pattern as a transmission noise signal, and the supervisory signal generating circuit generates a digital sine wave as a supervisory signal. A sine wave generating circuit, wherein the adding circuit adds a pseudo-random pattern and a digital sine wave and outputs a digital signal obtained by adding; a digital signal converting the added digital signal into an analog signal obtained by adding; An analog conversion circuit; a variable gain amplifier circuit that outputs a variable gain amplified signal by variable gain amplification of a transmission voice signal; an analog that outputs a confidential signal by adding the added analog signal and the variable gain amplified signal It is preferably composed of an adder circuit.

The present invention also provides a receiving device for a voice confidential device which receives a voice confidential signal transmitted from the transmitting device, demodulates the transmitted voice signal from the received confidential voice signal, and outputs a received voice signal. Pertain.

According to the first aspect of the present invention, the receiving device of the above-mentioned voice confidential talk device includes a band-pass filtering circuit for band-pass filtering the received secret-talk signal and outputting the band-pass filtered signal; A level reproduction circuit that reproduces the level of the waved signal and outputs a level reproduction signal; a low-pass filter circuit that low-pass filters the received confidential signal and outputs a low-pass filtered signal; a reference A reference noise generating circuit for generating a noise signal; a multiplication circuit for multiplying a level reproduction signal and a reference noise signal and outputting a multiplied signal; adapted based on a signal multiplied to a low-pass filtered signal And an adaptive echo canceller that outputs the received echo signal as a received voice signal.

According to a second aspect of the present invention, the receiving device of the voice confidential device described above includes a band-pass filter circuit for band-pass filtering the received confidential voice signal and outputting the band-pass filtered signal; A range detection circuit that detects the range of the waved signal and outputs a range detection signal; a low-frequency filter circuit that low-pass filters the received confidential signal and outputs a low-frequency filtered signal; a reference A reference noise generating circuit that generates a noise signal; an adaptive echo canceller that adaptively cancels a low-pass filtered signal based on the reference noise signal and outputs the echo canceled signal; Muted based on the range detection signal,
And a mute circuit for outputting the muted signal as a reception audio signal.

According to a third aspect of the present invention, the receiving device of the above-mentioned voice confidential communication device includes a band-pass filtering circuit for band-pass filtering the received confidential voice signal and outputting the band-pass filtered signal; A level reproduction circuit that reproduces the level of the waved signal and outputs the level reproduction signal; a range detection circuit that detects the range of the band-filtered signal and outputs the range detection signal; A low-pass filter circuit that performs a low-pass filtered signal after performing a low-pass filter; a reference noise generation circuit that generates a reference noise signal; a signal that is obtained by multiplying a level reproduction signal and a reference noise signal An adaptive echo canceller that adaptively cancels the echo based on the signal multiplied by the low-pass filtered signal and outputs the echo canceled signal; hand Mute based on Nji detection signal, and having a mute circuit for outputting the mute signal as the received speech signal.

According to a fourth aspect of the present invention, the receiving device of the voice confidential communication device comprises: a variable gain amplifier circuit for amplifying a received confidential voice signal based on a gain control signal, and outputting the amplified signal; A band-pass filtered circuit that outputs the band-pass filtered signal to the variable gain amplifier circuit as a gain control signal and outputs the band-pass filtered signal; A level reproduction circuit that reproduces and outputs a level reproduction signal; a low-pass filtering circuit that low-pass filters the amplified confidential signal and outputs a low-pass filtered signal; a reference that generates a reference noise signal A noise generating circuit; a multiplying circuit for multiplying the level reproduction signal and the reference noise signal and outputting the multiplied signal; and an adaptive echo cancellation for the low-pass filtered signal based on the multiplied signal. , This echo can And having a adaptive echo canceller that outputs the Le signal as received voice signal.

According to a fifth aspect of the present invention, the receiving device of the voice confidential device comprises: a variable gain amplifying circuit for amplifying a received confidential signal based on a gain control signal; and a variable gain amplifying circuit; A band-pass filtering circuit that outputs the band-pass filtered signal to the variable gain amplifying circuit as a gain control signal, and outputs the band-pass filtered signal to the variable gain amplifier circuit; A level detection circuit that detects and outputs a range detection signal; a low-pass filtering circuit that low-pass filters the amplified confidential signal and outputs a low-pass filtered signal; a reference that generates a reference noise signal A noise generating circuit; an adaptive echo canceller that adaptively cancels echoes of a low-pass filtered signal based on a reference noise signal, and outputs the echo canceled signals; Mute based on the range detection signal Te, and having a mute circuit for outputting the mute signal as received voice signal.

According to a sixth aspect of the present invention, the receiving device of the voice confidential communication device comprises: a variable gain amplifying circuit for amplifying a received confidential communication signal based on a gain control signal, and outputting the amplified signal; A band-pass filtered circuit that outputs the band-pass filtered signal to the variable gain amplifier circuit as a gain control signal and outputs the band-pass filtered signal; A level reproduction circuit for reproducing and outputting a level reproduction signal; a level detection circuit for detecting the level of the band-filtered signal and outputting a level detection signal; a low-pass filter for the amplified confidential signal, A low-pass filtering circuit that outputs a low-pass filtered signal; a reference noise generating circuit that generates a reference noise signal; a multiplication circuit that multiplies a level reproduction signal and a reference noise signal and outputs the multiplied signal ; Low-pass filtered signal An adaptive echo canceller that adaptively cancels echo based on a signal multiplied by the signal and outputs the echo canceled signal; a mute based on a level detection signal for the echo canceled signal, and the muted signal Is output as a reception audio signal.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, a voice confidential device according to a first embodiment of the present invention includes a transmitter for secretly processing a transmitted voice signal and transmitting the secret signal, and a voice secret transmitted from the transmitter. A reception device that receives a signal, demodulates the transmission voice signal from the received confidential signal, and outputs the reception voice signal.

The transmitting device comprises a transmitting side input terminal 201, a transmission noise generating circuit 202, a supervisory signal generating circuit 203,
It is provided with an adder circuit 204 and a transmission side output terminal 205.

A transmission voice signal is input to the transmission side input terminal 201. The transmission noise generation circuit 202 generates a transmission noise signal whose power spectrum is substantially flat within the entire frequency band of the transmission voice signal and which has the same waveform periodically. It should be noted that it is more effective that this transmission noise signal resembles white noise in terms of the confidential level of the transmission voice signal. Supervisory signal generation circuit 20
3 generates a sine wave signal as a monitoring signal. The addition circuit 204 adds the transmission voice signal, the transmission noise signal, and the monitoring signal (sine wave signal). The added signal is sent from the transmission-side output terminal 205 to the transmission line 211. The transmission path 211 is, for example, a telephone line or a space.

The signal levels of the transmission voice signal, the transmission noise signal, and the supervisory signal at this time are selected as follows. For example, even if the confidential signal is intercepted, the transmitted voice signal is masked by 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 0% at a signal-to-noise ratio (S / N) of about -20 dB. 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 supervisory signal is selected to be a single frequency which does not overlap the transmission voice signal and the transmission noise signal on the frequency axis. Further, the levels of the transmission voice signal, the transmission noise signal, and the supervisory signal do not give non-linear distortion to the confidential signal on the transmission line 211, and accurately follow the attenuation amount change on the transmission line 211 on the receiving side. Are set so that a coefficient for multiplication described later can be obtained.

FIG. 2 shows details of the adder circuit 204 of the transmitter and its peripheral portion. The transmission noise generating circuit 202 is realized by extracting the output signals of the maximum long-period sequence generating circuit (M sequence generating circuit) and the PN pattern generating circuit which are general pseudo random pattern generating circuits. The monitor signal generation circuit 203 generates a sine wave signal which is a monitor signal as digital data. This is a read-only memory (ROM)
It is realized by reading the data of the digital sine wave signal stored in.

The addition circuit 204 adds the digital data of the transmission noise generation circuit 202, the output data of the supervisory signal generation circuit 203, and the transmission voice signal input to the transmission side input terminal 201.

The adder circuit 204 is a digital adder circuit 20.
6 and a digital / analog (D / A) conversion circuit 207
, Analog adder circuit 208, and variable gain amplifier circuit 20
9 and. The digital adder circuit 206, the digital / analog (D / A) converter circuit 207, the analog adder circuit 208, and the variable gain amplifier circuit 209 are electrical devices such as an adder, a D / A converter, an analog multiplier, and an operational amplifier. Realized with parts.

More specifically, the digital adder circuit 206 adds the pseudo-random pattern and the digital sine wave and outputs the added digital signal. Digital/
The analog conversion circuit 207 converts the added digital signal into an added analog signal. Variable gain amplifier circuit 20
Reference numeral 9 variably gain-amplifies the transmission voice signal and outputs a signal obtained by variably amplifying the gain. The analog adder circuit 208 adds the added analog signal and the variable gain-amplified signal, and outputs a confidential signal.

In this way, the signals added by the adder circuit 204 are sent out from the output terminal 205 on the transmission side as a secret signal and guided to the receiving device via the transmission line 211 (FIG. 1).

Returning to FIG. 1, the receiving device has a receiving side input terminal 221, a band-pass filter circuit 223, and a low-pass filter circuit 22.
4, the level reproduction circuit 225, and the reference noise generation circuit 22.
7, a multiplication circuit 228, and an adaptive echo canceller 22.
9 and a receiving-side output terminal 231.

A secret-speech signal is introduced from the transmission device to the reception-side input terminal 221 via the transmission path 211. The band-pass filter circuit 223 band-pass filters the received confidential signal and outputs the band-filtered signal. In other words, the bandpass filtering circuit 22
3 extracts only the supervisory signal from the received confidential signal. The low-pass filtering circuit 224 low-pass filters the received confidential signal and outputs the low-pass filtered signal. In other words, the low pass filter circuit 224 extracts the transmission voice signal and the transmission noise signal from the received confidential signal. The level reproduction circuit 225
The level of the band-pass filtered signal is reproduced and a level reproduction signal is output. In other words, the level reproduction circuit 225 outputs a DC signal proportional to the amplitude of the extracted monitor signal as a level reproduction signal. Therefore, the output terminal of the level reproduction circuit 225 outputs a DC signal that follows changes in the attenuation of the transmission line 211. The reference noise generation circuit 227 generates a reference noise signal that is substantially the same as the transmission noise signal generated from the transmission noise generation circuit 202.

The multiplication circuit 228 is a circuit for obtaining the product of two input signals. That is, the multiplication circuit 228 multiplies the level reproduction signal and the reference noise signal and outputs the multiplied signal. More specifically, the multiplication circuit 228 calculates the product of the reference noise signal generated from the reference noise generation circuit 227 input to one input terminal and the DC signal from the level reproduction circuit 225 input to the other input terminal. Ask for. The multiplication circuit 228 functions like a resistance attenuation circuit in which the amount of attenuation is controlled by the external DC level.

The adaptive echo canceller 229 adaptively performs echo cancellation based on the signal obtained by multiplying the low-pass filtered signal, and outputs the echo canceled signal as a reception voice signal.

The adaptive echo canceller 229 will be described in more detail. A general adaptive echo canceller is composed of a transversal filter having a variable tap coefficient, a subtractor, and a tap correction part.
The transversal filter synthesizes a pseudo echo through the reference signal. The subtractor obtains the residual between this pseudo echo and the actual echo. The tap correction part adaptively corrects the tap coefficient of the transversal filter so that this residual is minimized. Next, the signals of the general adaptive echo canceller and the adaptive echo canceller 229 according to the present invention are compared. The reference signal of the transversal filter corresponds to the output signal of the multiplication circuit 228 of the present invention. Similarly, the signal corresponding to the actual echo is the transmission noise signal component included in the output signal of the low pass filter circuit 224. The residual error corresponds to the output signal of the adaptive echo canceller 229, which corresponds to the transmission voice signal component.

In practice, this adaptive echo canceller 2
At the output of 29, the pseudo echo synthesis error signal, the transmission voice signal of the talker, and the mixed noise in the transmission path 211 appear. Originally, it is desirable that the residual error be only the component of the transmitted voice signal. Particularly, in the present invention, the time until the adaptive echo canceller 229 finishes correcting the tap coefficient of the transversal filter so as to minimize the residual error is apparently shortened.

In the following, when a large transmission loss occurs in the transmission line 211, the operation of the confidential signal of this embodiment will be described, assuming, for example, a momentary interruption. Here, in order to facilitate understanding, it is assumed that the input signal and the output signal of the multiplication circuit 228 are the same, that is, the multiplication coefficient of the multiplication circuit 228 is 1.

Now, in the receiving apparatus, the confidential signal is received, 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 outputs it from the low-pass filtering circuit 224. The transmission noise signal component (echo component) included in the signal is deleted and the transmission voice signal is extracted. At this time, the tap coefficient of the transversal filter is corrected so that a pseudo echo almost equal to the echo component is synthesized, and the filter is in a converged state.

Next, due to the momentary interruption of the transmission line 211, the received confidential signal is rapidly attenuated for a moment, and the echo component disappears. At this time, the tap coefficient of the transversal filter of the adaptive echo canceller 229 is gradually corrected so as to minimize the residual error. However, until the tap coefficients of the transversal filter converge to minimize the residual error, the residual error remains in the adaptive echo canceller 229.
Appears at the output end of.

In the present invention, in order to reduce the residual output until the convergence, the same attenuation as the echo contained in the secret signal is also applied to the reference noise signal to be referred, and the convergence is completed once. The residual coefficient is reduced with almost no change in the tap coefficient of the filter.

For this reason, the change in the attenuation of the transmission line 211,
In other words, the level reproduction circuit 225 follows the level change of the supervisory signal included in the confidential signal and extracts a DC signal proportional to the magnitude of the supervisory signal. Next, this DC signal is guided to the adaptive echo canceller 229 as a signal to be referred to the reference noise signal component having the attenuation applied thereto via a multiplication circuit 228 whose attenuation is controlled by a voltage. That is, the same change in the attenuation amount as the abrupt change in the transmission line 211 is applied to the reference noise signal as well, so that the filter tap coefficient of the adaptive echo canceller 229 which has already converged is maintained almost as it is. Echo canceller 229
The residual of is minimized.

The same applies to the disconnection of the signal from the transmitter at the end of the call. Further, when the attenuation amount of the transmission line 211 fluctuates 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.

Next, the characteristics of the control when the change in the attenuation amount of the transmission line 211 is abrupt or slow will be described.

The adaptive echo canceller 229 includes a transversal filter which makes a normal filter tap coefficient variable, a subtractor, and a tap correction portion. The stability and convergence time of these general systems are described. The magnitude of the residual error and the stability of the system caused by the error included in the system for modifying the tap coefficient are related to the time for modifying the tap coefficient.

In order to obtain the minimum residual and to ensure the stability, it is necessary to increase the convergence time (decrease the convergence speed) until the desired tap coefficient is obtained.

Therefore, the present invention is characterized in that the correction of the tap coefficient is carried out slowly, and the transmitted voice signal is extracted with almost no modification of the tap coefficient of the filter with respect to a sudden change in the attenuation amount in the transmission line. .

Next, in realizing the first embodiment,
Special points to note are described below.

One is the reference noise generating circuit 22 of the receiving device.
The signal generation source 7 and the signal generation source of the transmission noise generation circuit 202 of the transmission device are the same. This is because the output signal of the reference noise generating circuit 227 is the transmitter and the transmission path 211,
It is assumed that the echo is input to the adaptive echo canceller 229 as an echo with linear distortion through the low-pass filter circuit 224. Therefore, the source of these noise signals is a commonly known pseudo random pattern generation circuit, for example, P
Application of N pattern generation circuit, maximum long cycle sequence generation circuit (M sequence generation circuit), etc. would be practical.

Next, if the received confidential speech signal has non-linear distortion, the speech signal to be reproduced contains noise, which causes deterioration of speech quality. This is because when a noise signal component that should normally be an echo (in other words, a transmission noise signal component included in the received confidential signal) is given non-linear distortion, that distortion component is reproduced as noise. , Deteriorates the signal-to-noise ratio (S / N) of the reproduced transmission voice signal.
Therefore, it is necessary to pay sufficient attention to the occurrence of amplitude distortion due to overload when the transmission voice signal, the transmission noise signal, and the monitor signal are added. Therefore, it is extremely useful to employ a variable gain amplifier circuit that keeps the long-term average level of the transmitted voice signal almost constant.

Further, 2 of the adaptive echo canceller 229
It is to control the level fluctuations of two input signals so that they are the same in time. If it is not controlled in this way, the effect of the first embodiment will be diminished. Therefore, it is important how much the level fluctuation of the monitor signal from the input end of the bandpass filter circuit 223 is delayed and appears in the reference noise signal component supplied to the adaptive echo canceller 229. 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.

FIG. 3 shows a voice conversation device according to the second embodiment of the present invention. The structure of the transmitter is the same as that of the first embodiment. Compared to the first embodiment, the receiving apparatus does not include the level reproducing circuit and the multiplying circuit, and as shown in FIG. 3, the mute circuit 230 is provided to the output end of the adaptive echo canceller 229 and the receiving side output. A range detection circuit 226 is further arranged between the terminal 231 and the band-pass filter circuit 223 and between the output end and the mute circuit 230.

The range detection circuit 226 detects the range of the band-filtered signal and outputs a range detection signal. In other words, the range detection honey dew 226 has two thresholds, an upper limit and a lower limit for the level of the received supervisory signal,
It is detected whether or not the level of the supervisory signal exists within the range given by these two threshold values. If the level of the supervisory signal is out of range, range detection circuit 226 controls mute circuit 230 to attenuate the output of adaptive echo canceller 229. That is, the mute circuit 2
30 mutes the echo canceled signal based on the range detection signal and outputs the muted signal as a reception voice signal.

In the second embodiment, the adaptive echo canceller 22 is activated when the secret signal reaches a very small level.
Even the small residual at 9 is reduced, and the receiving side output terminal 231
There is an effect of reducing the uncomfortable feeling of the listener by making the reproduced voice in the substantially silent state. Also, the secret signal is extremely large,
When the amount of attenuation in the transmission line 211 is different from what it should be, the output signal of the range detection circuit 226 controls the mute circuit 230 as described above. This necessity essentially assumes that the level of the echo included in the confidential signal reaching the receiving device is always smaller than the level of the reference noise signal referred to by the receiving device. If this condition is not satisfied, the filter tap coefficient of the adaptive echo canceller 229 will be distorted, and the copied pseudo echo will be completely different from the original one. This premise is a condition based on the necessity of effectively using the dynamic range. The fact that the dynamic range of 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. There is. In particular, the voice confidential talk apparatus according to the second embodiment is particularly necessary because the originally necessary transmission voice signal is masked with a noise signal to reduce the signal-to-noise ratio to make the secret voice signal.

FIG. 4 shows a voice conversation device according to the third embodiment of the present invention. The third embodiment is a combination of the first embodiment and the second embodiment, and the functions and operations of the constituent elements are as described above. The first embodiment is the noise reduction method as described above when the transmission device or the reception device is located inside a radio wave obstacle such as a tunnel or when there is a momentary interruption on the transmission path 211. Is effective in reducing noise due to a rounding error in calculation that cannot be removed in the first embodiment.

Now, the example in which the confidential signal cannot be received at all has been taken as an example. However, if the monitor signal exceeding the lower limit threshold value of the range detection circuit 226 can be received, the mute circuit 230 of the second embodiment is extracted. The first embodiment and the second embodiment can coexist.

FIG. 5 shows a voice conversation device according to the fourth embodiment of the present invention. The fourth embodiment is different from the third embodiment in that a variable gain amplifier circuit 222 is provided at the reception signal end,
This is intended to stabilize the level. The variable gain amplifier circuit 222 amplifies the received confidential signal based on the gain control signal, and outputs the amplified signal. Bandpass filter circuit 223
Supplies the band-filtered signal to the variable gain amplifier circuit 222 as a gain control signal. That is, the variable gain amplifying circuit 222 monitors the level of the supervisory signal from the output end of the bandpass filtering circuit 223, and keeps the output levels of the variable gain amplifying circuit 222 and the bandpass filtering circuit 223 substantially constant. This effect has an effect that the range for the detection of the range detection circuit 226 can be narrowed and the time until the operation of the mute circuit 230 can be shortened. As a result, the time and level range at which the mute circuit 230 starts muting the extracted audio signal can be narrowed, and an audio signal with less disconnection can be reproduced. Further, there are advantages that the dynamic range of the level reproduction circuit 225 and the multiplication circuit 228 can be reduced, and the dynamic range of the adaptive echo canceller 229 can be effectively used.

The variable gain amplifier circuit 222 may be provided in the voice confidential communication device of the first embodiment shown in FIG. 1 or the voice confidential communication device of the second embodiment shown in FIG.

[0060]

As is apparent from the above description, according to the voice confidential signal of the present invention, the confidential signal from the transmitter is disconnected due to abrupt fluctuation of transmission loss in the transmission path, momentary interruption, or termination of transmission. In this case, it is possible to reduce the noise caused by the synthetic error of the pseudo echo generated in the process of correcting the filter tap coefficient of the adaptive echo canceller, and to realize the voice confidential communication device that copes with the slow fluctuation of the attenuation amount of the transmission line. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a voice conversation device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing details of an adder circuit of a transmitter of the voice confidential device shown in FIG. 1 and its periphery.

FIG. 3 is a block diagram showing a voice conversation device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a voice confidential device according to a third embodiment of the present invention.

FIG. 5 is a block diagram showing a voice confidential device according to a fourth exemplary embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional voice confidential device.

[Explanation of symbols]

 101 Transmitting Side Input Terminal 102 Transmitting Noise Generating Circuit 103 Adding Circuit 104 Transmitting Side Output Terminal 111 Transmission Line 121 Receiving Side Input Terminal 122 Reference Noise Generating Circuit 123 Adaptive Echo Canceller 124 Cancellation Estimating Circuit 125 Mute Circuit 126 Receiving Side Output Terminal 201 Transmission side input terminal 202 Transmission noise generation circuit 203 Monitoring signal generation circuit 204 Adder circuit 205 Transmission side output terminal 206 Digital addition circuit 207 Digital / analog (D / A) conversion circuit 208 Analog addition circuit 209 Gain variable amplification circuit 211 Transmission line 221 Receiving side input terminal 222 Variable gain amplifier circuit 223 Band-pass filter circuit 224 Low-pass filter circuit 225 Level reproduction circuit 226 Range detection circuit 227 Reference noise generation circuit 228 Multiplier circuit 229 Adaptive echo canceller 230 Mu Output circuit 231 Receive side output terminal

Claims (8)

[Claims] 1. A transmitter of a voice confidential device for secretly processing a transmitted voice signal and transmitting a secret signal, comprising: a transmission noise generating circuit for generating a transmission noise signal; a supervisory signal generating circuit for producing a supervisory signal; A transmitter of a voice confidential communication device, comprising: an addition circuit that adds a transmission voice signal, the transmission noise signal, and the monitoring signal, and outputs the added signal as the confidential voice signal. 2. The transmission noise generation circuit is a pseudo random pattern generation circuit that generates a pseudo random pattern as the transmission noise signal, and the supervisory signal generation circuit generates a digital sine wave that generates a digital sine wave as the supervisory signal. A digital adder circuit for adding the pseudo-random pattern and the digital sine wave and outputting the added digital signal; and a digital converter for converting the added digital signal into an added analog signal. / Analog conversion circuit, variable gain amplification circuit for variable gain amplification of the transmission voice signal to output a variable gain amplified signal, and the added analog signal and the variable gain amplified signal 2. The transmission of the voice confidential device according to claim 1, comprising an analog adder circuit for outputting a signal. Location. 3. A receiver of a voice confidential device which receives a voice confidential signal transmitted from the transmitter according to claim 1, demodulates the transmitted voice signal from the received confidential voice signal, and outputs a received voice signal. A band-pass filter circuit for band-filtering the received confidential signal and outputting a band-filtered signal, and a level reproducing circuit for reproducing the level of the band-filtered signal and outputting a level reproduced signal. A low-pass filtering circuit that low-pass filters the received confidential signal and outputs a low-pass filtered signal; a reference noise generating circuit that generates a reference noise signal; the level reproduction signal and the reference Multiply with the noise signal,
A multiplication circuit for outputting a multiplied signal, and an adaptive echo for adaptively echo canceling the low-pass filtered signal based on the multiplied signal, and outputting the echo canceled signal as the reception voice signal A receiver of a voice confidential device, comprising a canceller. 4. A receiver of a voice confidential device which receives a voice confidential signal transmitted from the transmitter according to claim 1, demodulates the transmitted voice signal from the received confidential voice signal and outputs a received voice signal. In the above, the band-pass filter circuit that band-filters the received confidential signal and outputs the band-filtered signal, and the range detection circuit that detects the range of the band-filtered signal and outputs the range detection signal. A low-pass filtering circuit that low-pass filters the received confidential signal and outputs a low-pass filtered signal; a reference noise generation circuit that generates a reference noise signal; and the low-pass filtered signal An adaptive echo canceller that adaptively cancels echo based on the reference noise signal and outputs the echo canceled signal, and an echo canceled signal based on the range detection signal And a mute circuit that mutes and outputs the muted signal as the received voice signal. 5. A receiver of a voice confidential device which receives a voice confidential signal transmitted from the transmitter according to claim 1, demodulates the transmitted voice signal from the received confidential voice signal and outputs a received voice signal. A band-pass filter circuit for band-filtering the received confidential signal and outputting a band-filtered signal, and a level reproducing circuit for reproducing the level of the band-filtered signal and outputting a level reproduced signal. A range detection circuit that detects the range of the band-filtered signal and outputs a range detection signal; and a low-range filter that low-pass filters the received confidential signal and outputs a low-pass filtered signal. A filtering circuit, a reference noise generating circuit for generating a reference noise signal, the level reproduction signal and the reference noise signal are multiplied,
A multiplication circuit that outputs a multiplied signal; an adaptive echo canceller that adaptively cancels the low-pass filtered signal based on the multiplied signal, and outputs the echo canceled signal; A mute circuit for muting a canceled signal based on the range detection signal, and outputting the muted signal as the received audio signal. 6. A receiver of a voice confidential device which receives a voice confidential signal transmitted from the transmitter according to claim 1, demodulates the transmitted voice signal from the received confidential voice signal and outputs a received voice signal. A gain variable amplification circuit for amplifying the received confidential signal based on a gain control signal and outputting the amplified signal, and band-pass filtering the amplified signal, and outputting the band-filtered signal. A band-pass filter circuit that supplies the band-filtered signal to the variable gain amplifier circuit as the gain control signal; a level reproduction circuit that reproduces the level of the band-filtered signal and outputs a level reproduction signal; A low-pass filter circuit that low-pass filters the amplified confidential signal and outputs a low-pass filtered signal, a reference noise generation circuit that generates a reference noise signal, the level reproduction signal, and the reference noise signal Multiply by
A multiplication circuit for outputting a multiplied signal, and an adaptive echo for adaptively echo canceling the low-pass filtered signal based on the multiplied signal, and outputting the echo canceled signal as the reception voice signal A receiver of a voice confidential device, comprising a canceller. 7. A receiver of a voice confidential device that receives a voice confidential signal transmitted from the transmitter according to claim 1, demodulates the transmitted voice signal from the received confidential voice signal, and outputs a received voice signal. A gain variable amplification circuit for amplifying the received confidential signal based on a gain control signal and outputting the amplified signal; and band-pass filtering the amplified signal to output a band-filtered signal and A band-pass filtering circuit that supplies a band-pass filtered signal to the variable gain amplifier circuit as the gain control signal; a level detection circuit that detects a range of the band-pass filtered signal and outputs a range detection signal; A low-pass filter circuit that low-pass filters the amplified confidential signal and outputs a low-pass filtered signal, a reference noise generation circuit that generates a reference noise signal, and the low-pass filtered signal The standard miscellaneous An adaptive echo canceller that adaptively cancels echo based on a sound signal and outputs the echo canceled signal; a mute based on the range detection signal for the echo canceled signal; and the muted signal And a mute circuit for outputting as a received voice signal. 8. A receiver of a voice confidential device which receives a voice confidential signal transmitted from the transmitter according to claim 1, demodulates the transmitted voice signal from the received confidential voice signal and outputs a received voice signal. A gain variable amplification circuit for amplifying the received confidential signal based on a gain control signal and outputting the amplified signal; and band-pass filtering the amplified signal to output a band-filtered signal and A band-pass filter circuit that supplies the band-filtered signal to the variable gain amplifier circuit as the gain control signal; a level reproduction circuit that reproduces the level of the band-filtered signal and outputs a level reproduction signal; A level detection circuit that detects the level of the band-pass filtered signal and outputs a level detection signal, and a low-pass filtering circuit that low-pass filters the amplified confidential signal and outputs a low-pass filtered signal When A reference noise generator circuit for generating a reference noise signal, by multiplying the level reproduced signal and said reference noise signal,
A multiplication circuit that outputs a multiplied signal; an adaptive echo canceller that adaptively cancels the low-pass filtered signal based on the multiplied signal, and outputs the echo canceled signal; And a mute circuit for muting the canceled signal based on the level detection signal and outputting the muted signal as the received voice signal.