JP3068249B2 - Voice secret device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speech signal polarizer, and more particularly to a transmission side in which a transmission voice signal is superimposed on a periodic noise signal whose power spectrum is substantially flat within the entire frequency band of the transmission voice signal. Confidential signal is transmitted, and on the receiving side,
The present invention relates to an improvement of a privacy apparatus that extracts a transmission voice signal from a received privacy signal by referring to a reference noise signal using an adaptive echo canceller.

[0002]

2. Description of the Related Art A conventional voice privacy apparatus transmits a privacy 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 a transmission side, and a reception side. In Japanese Patent Application No. 63-156012, a voice signal is extracted from a secret signal received using an adaptive echo canceller.

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 signal is added by the circuit 103 and transmitted as a secret signal to the transmission line 111 via the output terminal 104 on the transmission side.
23, a reference noise generation circuit 122, and a cancellation amount estimation circuit 1
24, a mute circuit 125, and a level comparison between a transmission noise signal component included in a secret signal guided to the adaptive echo canceller 123 and a residual difference appearing at an output terminal of the adaptive echo canceller 123. Is used to mute the output signal of the adaptive echo canceller 123 when the canceling amount is estimated to be abnormally small by using the canceling amount estimating circuit 124 that approximately estimates the canceling amount.

[0004]

However, in this type of voice confidential device, the transmitting side masks the transmitting voice signal with a periodic noise signal whose power spectrum is substantially flat within the entire frequency band of the transmitting voice signal. . At this time, the secret signal includes a transmission noise signal having a higher level than the level of the transmission voice signal. Therefore, the transmitted voice signal level included in the transmitted confidential signal is transmitted at a relatively lower level than the voice signal level of a normal telephone. Therefore,
In normal operation, the conventional apparatus amplifies and reproduces the output signal of the adaptive echo canceller to a level that allows easy listening.

[0005] When the transmitting side or the receiving side is mounted on an automobile or the like and passes through a tunnel or the like, a secret signal to be temporarily received is greatly attenuated. After passing through the tunnel, the level of the confidential signal to be received is restored, but the adaptive echo canceller cannot follow the tap correction, and thus the sufficient amount of cancellation cannot be obtained in the adaptive echo canceller, resulting in noise as a cancellation error. There is a drawback that it appears in the output of the secret device. More specifically, in the conventional cancellation amount estimating circuit, the power between the different signals of the secret signal guided to the input terminal of the adaptive echo canceller and the reproduced voice signal appearing at the output terminal of the adaptive echo canceller is used to estimate the cancellation amount. Because of the comparison, sufficient integration time was required to obtain a more accurate estimate of the amount of cancellation.

Therefore, it has been difficult to reduce the operation start time of the mute function and to accurately obtain the estimated value of the cancellation amount at which the mute function should be operated.

Therefore, instantaneous interruptions in transmission lines, large attenuation distortion,
There is a drawback that a cancellation residual caused by the disconnection of the confidential signal due to the end of the communication on the transmitting side appears at the output terminal of the voice confidential signal via the adaptive echo canceller.

[0008] An object of the present invention is caused by a synthetic error of a pseudo echo by an adaptive echo canceller in response to a large fluctuation or instantaneous interruption of transmission loss in a transmission line, and interruption of a secret signal from a transmission side due to termination of transmission. An object of the present invention is to provide a voice confidential speech device with reduced noise.

[0009]

A transmission noise generating circuit for masking a transmission audio signal with a noise signal, a monitoring signal generation circuit for generating a gain fluctuation monitoring signal on a transmission line, and a transmission audio signal are provided on the transmission side. And a transmission noise signal and a monitoring signal are added to each other, and an addition circuit is provided for transmitting the signal as a privacy signal to the transmission line. The reception side has a gain following the level of the monitoring signal included in the received privacy signal. Variable gain amplifier circuit controlled, a bandpass filter circuit for extracting a monitoring signal from an output signal of the variable gain amplifier circuit, a level for outputting a direct current following the level of the monitoring signal extracted by the bandpass filter circuit A reproduction circuit, a reference noise generation circuit for generating the same noise signal as the transmission noise generation circuit, a multiplication circuit for obtaining a product of an output signal of the reference noise generation circuit and an output signal of the level reproduction circuit, a transmission voice included in a secret signal A low-pass filter that extracts the signal component and the transmission noise signal component, an adaptive echo canceller that extracts the audio signal from the output signal of the low-pass filter with reference to the reference noise signal, and an output signal of the low-pass filter By providing a range detection circuit that detects the level range of the signal and a mute circuit controlled by the output signal of the range detection circuit, and connecting to the output of the adaptive echo canceller, instantaneous interruption in transmission lines, significant attenuation distortion, transmission It is possible to realize a voice confidential device with a small residual error in the adaptive echo canceller even when the confidential signal is interrupted due to the end of transmission on the side.

In particular, the present invention is characterized in that a monitoring signal is superimposed on a secret signal transmitted on the transmitting side for the purpose of monitoring the attenuation of the transmission path.

[0011]

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

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

The transmission noise generation circuit 202 periodically generates a noise signal having a substantially flat power spectrum in the entire frequency band of the transmission voice signal and having the same waveform. It is more effective for this noise signal to resemble white noise in terms of the intensity of the confidential speech of the transmission voice signal.

The monitoring signal generation circuit 203 generates a sine wave signal for monitoring.

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

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

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

On the receiving side, the receiving-side input terminal 221 receives a secret signal. The bandpass filter 223 extracts only the monitoring signal from the received privacy signal.

The low-pass filter 224 extracts a transmission voice signal and a transmission noise signal component from the received privacy 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 amount of attenuation of the transmission path 211.

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

The multiplication circuit 228 includes a reference noise generation circuit 22
7 and the DC signal from the level reproduction circuit 225. In other words, the multiplication circuit 228 functions like a resistance attenuation circuit in which the amount of attenuation is controlled by an external direct current.

A general adaptive echo canceller is composed of a transversal filter that changes tap coefficients and a subtractor, and synthesizes a pseudo echo by passing a reference signal through a transversal filter. A residual is obtained from the pseudo echo and the actual echo by a subtractor, and the tap coefficient of the transversal filter is adaptively modified so that the residual is minimized. When the signals of a general adaptive echo canceler and the adaptive echo canceller 229 of the present invention are compared, the reference signal of the transversal filter is multiplied by the multiplying circuit 227 of the present invention.
Similarly, a signal corresponding to an actual echo is a transmission noise signal component included in the output signal of the low-pass filter 224.

The residual corresponds to the output of the adaptive echo canceller 229, which corresponds to the transmitted voice signal component. Actually, the output of the adaptive echo canceller 229 is a pseudo-echo combined error signal, a transmission voice signal of a transmitter, and a transmission path 2.
The mixed noise at 11 appears.

Originally, it is desirable that the residual is only a component of the transmitted voice signal. In particular, in the present invention, the time until the adaptive echo canceller 229 finishes correcting the tap coefficients of the transversal filter so as to minimize the residual is apparently reduced.

In the following, a description will be given on the assumption that a large transmission loss occurs in the transmission path 211, for example, an instantaneous interruption. Here, for easy understanding, it is assumed that the input signal and the output signal of the multiplication circuit 228 are the same (the multiplication coefficient is 1). Now, the secret signal is received on the receiving side, and the adaptive echo canceller 229 refers to the reference noise signal from the reference noise generation circuit 227 via the multiplication circuit 228 to transmit 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 audio signal is extracted. At this time, the tap coefficient of the transversal filter is corrected so as to synthesize a pseudo echo substantially equal to the echo component, and the filter is in a convergence state.
Next, due to the instantaneous interruption of the transmission path 211, the received privacy signal is abruptly attenuated momentarily, and the echo component is eliminated. At this time,
The tap coefficient of the transversal filter of the adaptive echo canceller 229 is gradually corrected to minimize the residual. However, the residual appears at the output of adaptive echo canceller 229 until the tap coefficients of the transversal filter converge to minimize the residual. In the present invention, until this convergence, the same attenuation as the echo included in the confidential signal is simultaneously applied to the reference noise signal to be referred to,
The residual is reduced without substantially changing the tap coefficient of the filter once converged. This follows a change in the amount of attenuation of the transmission line 211, in other words, a change in the level of the monitoring signal included in the secret signal, and the level reproduction circuit 22
In step 5, a DC signal proportional to the magnitude of the monitoring signal is extracted. 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 instantaneous interruption has been described above, the residual can be similarly reduced when the instantaneous interruption is recovered. The same applies to a signal interruption from the transmission side at the end of a call.
Further, when the attenuation of the transmission line 211 fluctuates slowly, the control operation via the multiplication circuit 228 and the operation for reducing the residual by the adaptive echo canceller 229 itself are simultaneously performed. In realizing the first embodiment, it should be noted that the adaptive echo canceller 229 2
This is to control the level fluctuation of two input signals so as to be the same in time. If not controlled in this way, the effects of the first embodiment will be reduced. Therefore, how much the level fluctuation of the monitoring signal from the input terminal of the band-pass filter 223 is delayed by how long the adaptive echo canceller 229
It is important that the signal appears in the reference noise signal component that is supplied to the signal. Then, the delay time needs to be as close as possible to the delay time in which the transmission noise component is given by the low-pass filter 224.

Next, a second embodiment will be described. FIG.
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 eliminates the level reproducing circuit and the multiplying circuit as compared with the first embodiment, and as shown in the figure, replaces the mute circuit 230 with the adaptive echo canceller 229. And a range detection circuit 226 is further disposed between the output terminal of the band-pass filter 223 and the mute circuit 230 between the output terminal of the bandpass filter and the reception-side output terminal 231. Range detecting circuit 226 has two thresholds, an upper limit and a lower limit, for the level of the received monitoring signal, and determines whether or not the level of the monitoring signal exists within a range given by the two thresholds. Or to detect. If the level of the monitoring signal is out of range, range detection circuit 226 controls mute circuit 230 to attenuate the output of adaptive echo canceller 229.

In this embodiment, when the level of the confidential signal becomes extremely small, even the small residual in the adaptive echo canceller 229 is reduced, the reproduced sound at the output terminal on the receiving side is made almost silent, and the receiver It has the effect of reducing discomfort.

The secret signal is extremely large and the transmission path 2
When the amount of attenuation differs from the expected attenuation at 11, the output signal of the range detection circuit 226 controls the mute circuit 230 as described above. This necessity is such that the level of the echo included in the confidential signal that originally arrives at the receiving side is always smaller than the level of the reference noise signal referred to at the receiving side. If the prerequisites are different, distortion occurs in the filter tap coefficients of the adaptive echo canceller 229, and the duplicated pseudo echo is completely different from the original one. This premise is a condition from the necessity of effectively utilizing 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 audio signal can be increased, in other words, an audio signal with less noise can be reproduced. ing. In particular, the voice privacy apparatus according to the present invention masks the originally required transmission voice signal with a noise signal and reduces the signal-to-noise ratio as a privacy signal, which is particularly necessary.

FIG. 4 shows a third embodiment in which the first and second embodiments are combined. The functions and operations of the components are as described above. When the transmitting side or the receiving side is located in a radio wave obstruction such as a tunnel or the transmission path 2
In the case of an instantaneous interruption in the eleventh embodiment, the first embodiment is a noise reduction method as described above, and the second embodiment is effective in reducing noise due to a rounding error in an operation that cannot be removed in the first embodiment. Although the example has been described in which the confidential signal cannot be received at all, if the monitoring signal exceeding the lower threshold of the range detection circuit 226 can be received, the mute circuit 230 of the second embodiment passes the extracted voice signal. The first embodiment and the second embodiment can coexist.

FIG. 5 shows a third embodiment in which a variable gain amplifier circuit 222 is provided at the input terminal on the receiving side to stabilize the level. The variable gain amplifying circuit 223 includes the bandpass filtering circuit 22.
The level of the monitoring signal from the output terminal 3 is monitored, and the output levels of the variable gain amplifier 222 and the bandpass filter 223 are kept substantially constant. This effect makes it possible to narrow the range for detection by the range detection circuit 226 and to reduce the range of the mute circuit 230.
This has the effect that the time until the start of the operation can be reduced. As a result, the time and level range at which muting is started for the extracted audio signal are narrowly limited, and an audio signal with less disconnection can be reproduced. Further, advantages such as 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, adaptive echo can be performed in response to a large fluctuation or instantaneous interruption of transmission loss on a transmission line, and a disconnection of a confidential signal from the transmission side due to transmission termination. There is an effect that it is possible to realize a voice confidential speech device in which noise caused by a synthesis error of the pseudo echo by the canceller is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional configuration.

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

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

FIG. 4 is a diagram illustrating a configuration of a third embodiment based on a combination of the first and second embodiments of the present invention.

FIG. 5 is a diagram illustrating a configuration of an embodiment in which a monitoring signal level is stabilized at a reception-side input terminal according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 201 transmission-side input terminal 202 transmission noise generation circuit 203 monitoring signal generation circuit 204 addition circuit 205 transmission-side output terminal 211 transmission line 221 reception-side input terminal 222 variable gain amplification 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 Multiplication circuit 229 Adaptive echo canceller 230 Mute circuit 231 Reception side output terminal

Continuation of the front page (56) References JP-A-61-3542 (JP, A) JP-A-3-92030 (JP, A) JP-A-5-63611 (JP, A) JP-A-5-235904 (JP) , A) JP-A-2-7636 (JP, A) Prince Oji et al., "A study of analog confidential devices", Proc. Of the 1984 IEICE Autumn National Convention, (1988), p. . B-2-180 (B302) (58) Fields investigated (Int. Cl. ⁷ , DB name) G09C 1/00-5/00 H04K 1/00-3/00 H04L 9/00 H04B 3/23

Claims (3)

(57) [Claims] A transmission noise generating circuit for masking a transmission voice signal with a noise signal, a monitoring signal generation circuit for generating a signal for monitoring a gain variation in a transmission path, a transmission voice signal and a transmission noise signal on a transmission side. And a monitoring signal are added, and an adder circuit is provided to transmit the signal as a secret signal to the transmission line. On the receiving side, a band-pass filter circuit, a low-pass filter circuit, a level reproduction circuit, a multiplication circuit, and a reference noise generation circuit are provided. , An adaptive echo canceller, guides the received confidential signal to the band-pass filter and the low-pass filter, and supplies the output signal of the band-pass filter to the level recovery circuit, generating the output signal of the level recovery circuit and the reference noise. And a circuit output signal supplied to a multiplication circuit, and the multiplication circuit output signal and the low-pass filter 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, a monitoring signal generation circuit for generating a signal for monitoring gain fluctuation in a transmission path, a transmission voice signal and a transmission noise signal on a transmission side. And a monitoring signal are added, and an adder circuit is provided for transmitting the signal as a secret signal to the transmission line. On the receiving side, a band-pass filter circuit, a low-pass filter circuit, a range detecting circuit, a reference noise generating circuit, and an adaptive type are provided. An echo canceller and a mute circuit are provided, the received secret signal is supplied to the band-pass filter and the low-pass filter, the output signal of the band-pass filter is supplied to the range detection circuit, and the output signal of the reference noise generation circuit A voice confidential speech device characterized in that an output signal of a band-pass filter is supplied to an adaptive echo canceller, and an output signal of the adaptive echo canceller and an output signal of a range detection circuit 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 monitoring signal generation circuit for generating a signal for monitoring a gain variation in a transmission path, a transmission voice signal and a transmission noise signal. And a monitoring signal are added, and an addition circuit is provided for transmitting the signal as a secret signal to the transmission line. On the receiving side, a band-pass filter circuit, a low-pass filter circuit, a level reproduction circuit, a range detection circuit, and a reference noise generator are provided. Circuit, multiplying circuit, adaptive echo canceller, and mute circuit, supply the received secret signal to the band-pass filter and the low-pass filter, and output the band-pass filter output signal to the level reproduction circuit and range detection circuit. The output signal of the level reproduction circuit and the output signal of the reference noise generation circuit are supplied to a multiplication circuit, and the output signal of the multiplication circuit and the output signal of the low-pass filter circuit are supplied to an adaptive echo canceller. A voice confidential speech device characterized in that an output signal and a range detection circuit output signal are supplied to a mute circuit.