JPH027636A - Voice privacy call equipment - Google Patents

Abstract

PURPOSE:To prevent the stress of a voice signal from being recognized against the interception of a privacy call signal by sending a privacy call signal being the result of superimposing a transmission voice signal on a noise signal whose power spectrum is nearly flat in all frequency bands and extracting the voice signal from the privacy call signal at the reception side. CONSTITUTION:A transmission noise generating circuit 2 generating a noise signal of periodically the same waveform whose power spectrum is nearly flat in all the frequency band of a transmission voice signal and an adder circuit 3 adding the transmission noise signal and the transmission voice signal of the transmission noise generating circuit 2 are provided to the sender side. On the other hand, a reference noise generating circuit 12 having the same function as the transmission noise generating circuit 2 and an echo canceller 13 extracting the transmission voice signal from the privacy call signal while referencing the reference signal are provided to the reception side. In the addition of signals by the adder circuit 3, it is desired to select a level difference between the level of the transmission voice signal included in the privacy call signal and the level of the noise signal as nearly 20dB. Thus, even if the privacy call signal is intercepted, the content of conversation is not estimated while the stress of the voice is not recognized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an audio signal polarization device. Especially on the transmitting side, the noise signal has a roughly flat power spectrum within the entire frequency band of the transmitted audio signal.

Sends out a confidential signal superimposed with the transmitted audio signal. A voice secret speech device configured to extract a voice signal from a received secret speech signal on the receiving side, does not require the transmission and reception of synchronization signals or control signals between the transmitter and the receiver, and does not allow the intonation of the voice to be recognized from the intercepted signal. Regarding.

[Conventional technology]

The method used by conventional voice communication devices is the spectrum inversion method, in which the frequency spectrum of the entire frequency band of the audio signal is inverted and transmitted. Divide the entire frequency band of the audio signal into several subbands.

The four-sector division and swapping method transmits each divided subband output signal as a subband output signal of a different frequency.The audio signal waveform is temporally divided into several small sections and the temporal order is swapped. There was a method of transmission.

[Problem to be solved by the invention]

However, the confidential signals of these conventional methods.

In both cases, there is a correlation between the amplitude of the transmitted audio signal and the confidential conversation signal level, and if the confidential conversation signal is intercepted, the intonation of the transmitted voice can be recognized, and the content of the conversation can be inferred by analogy. There was a problem.

In view of the above-mentioned drawbacks, a technical object of the present invention is to provide a voice confidential communication device with a simple configuration that does not allow the intonation of the voice to be recognized even if the confidential voice signal is intercepted.

[Means for solving problems]

According to the present invention, the transmitting side is provided with a transmission noise generating circuit that generates a noise signal, and the adding circuit that adds the noise signal and the audio signal to send a secret signal to the transmission path, and the receiving side is provided with: a reference noise generation circuit that generates a reference noise signal that is substantially the same as the noise signal, and based on the reference noise signal,
An adaptive error canceller for extracting the audio signal from a received confidential communication signal is provided.

In other words, the voice secret communication device of the present invention allows, on the transmitting side, within the entire frequency band of the transmitted voice signal, ! The receiver includes a transmission noise generation circuit that periodically generates a noise signal with a substantially flat worst vector and the same waveform, and an addition circuit that adds the transmission noise signal of the transmission noise generation circuit and the transmission audio signal. On the side.

It has a reference noise generation circuit that has the same function as the transmission noise generation circuit, and an echo canceller that extracts the transmission voice signal from the confidential signal by referring to the reference signal.

〔Example〕

Next, two embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, 1 is a transmitting side input terminal for inputting a transmitted voice signal to the voice secret device, 2 is a transmitting noise generation circuit that periodically generates a noise signal with the same waveform, and 3 is a transmitting side input terminal 1 The transmission audio signal from the transmission noise generating circuit 2 and the noise signal from the transmission noise generation circuit 2 are added.

1 is a transmission line; 11 is an input terminal on the receiving side of the voice privacy device; 12 is a reference noise generation circuit; and 12 is a t3rti adaptive transversal filter.

14 is a receiving side output terminal of the voice secret communication device.

The operation will be explained below with reference to FIG.

FIG. 2a) shows an example of the waveform of a transmitted audio signal, and this signal is supplied to one input terminal of the adder circuit 3 via the transmitting side input terminal 1. Figure 2 a] to e) correspond to the time f) in Figure 2, with the horizontal axis representing the time and the vertical axis representing the amplitude of each signal.

Furthermore, the section from time tj-4 to time [, in Figure 2 f) is defined as the section j-1#, and each signal waveform within this section is expressed with the subscript "j-t". . Figure b) is the output signal of the transmission noise generation circuit 2.

The noise signal is generated by repeating a waveform of N in each interval, and the noise signal is approximately flat in the frequency band targeted by the audio signal (for example, from 300 Hz to 3400 Hz). It is a periodic signal. The adder circuit 3 simply adds the transmitted audio signal shown in FIG. 2a) from the transmitting side input terminal 1 and the transmitted noise signal shown in FIG. 2b).

Here, the signal appearing at the output terminal of the adder circuit 3 is called a secret signal and is shown in FIG. 2C.

When adding signals in the adder circuit 3, the level difference f between the level S (dB) of the transmitted audio signal included in the secret signal and the level N (dB) of the noise signal is 2 odB (-generally S/
It is desirable to select the value to be approximately N = -20 dB. This value allows the noise signal to mask the transmitted voice signal and maintains the monophonic intelligibility of the transmitted voice signal included in the confidential signal at 0%. In other words, the normal audio signal is S/N = -20
At dB, single tone intelligibility deteriorates to 0%.

Therefore, with ordinary interception means for intercepting this confidential signal, the noise signal within the entire band can be heard, and furthermore, it is extremely difficult to recognize the intonation of the voice signal at a low level compared to the noise signal. Furthermore, even if this private conversation signal is divided into P waves using a suitable bandpass filter, it is extremely difficult to recognize the presence of a voice signal as described above.

In FIG. 1, this secret signal is transmitted via a transmission line 10,
The signal is guided to the receiving side input terminal 11. To make it easier to understand, we will now explain the delay time and linear distortion of the transmission line.

The explanation will be made assuming that there is no frequency shift between the transmitted signal and the received signal due to modulation and demodulation of the carrier system.

The confidential signal is guided from the receiving side input terminal 11 to the input terminal of the adaptive echo canceller 13.

On the other hand, it is assumed that the relationship between the output signal of the reference noise generation circuit 12 and the output signal of the transmission noise generation circuit 2 with a repetition period of 1 hour and the frequency spectrum are also the same.

The output signal of this reference noise generation circuit 12 is supplied as a reference signal to the other input terminal of the adaptive echo canceller 13. This reference noise signal is shown in FIG. 2d). here,
The functions of a general adaptive echo canceller will be briefly described (Reference document 22 Echo Canceller Technology 61, 12.20, published by Japan Industrial Technology Center). A common adaptive echo canceller.

A transpersal filter with variable tag coefficients,
It consists of a subtractor and completely synthesizes pseudo echoes by passing the reference signal through a transversal filter. A residual is obtained from this pseudo echo using a subtractor from the actual echo, and the tag coefficients of the transversal filter are adaptively modified so that the residual between the pseudo echo and the actual echo is minimized.

The adaptive echo canceller follows changes in the characteristics of the echo path by adaptively modifying the tap coefficients of the filter to account for linear distortion occurring in the echo path and its fluctuations.

Next, a general adaptive echo canceller and the signals of each part in the present invention will be explained in correspondence with each other.

What is the reception signal of a typical adaptive echo canceller?

This is the output signal of the reference noise generation circuit 12 in FIG.

The echo signal is an echo component included in the secret signal introduced into the receiving side input terminal 11. Also, the reference noise generation circuit 1
The output signals of the transmission noise generation circuit 2 and the transmission noise generation circuit 2 are the same, and the portion generally called the echo path is the output signal of the transmission noise generation circuit 2.
This corresponds to the path from the output end of the terminal to the receiving side input terminal 11.

This is a common adaptive echo canceller.

The tap coefficient of the built-in transversal filter is adaptively adjusted so that the echo component present at its output end is minimized.

In other words, from the relationship between each part and the signal in the present invention, the adaptive echo canceller 13 adjusts the tag coefficient of the built-in transversal filter so that the transmission noise signal component present at the receiving side output terminal 14 is minimized. Adjusting adaptively.

In this way, the audio signal extracted by the adaptive echo canceller 13 is supplied to the receiving side output terminal 14 of the voice privacy device as a reproduced audio signal shown in FIG. 2e).

Several assumptions have been made above to facilitate understanding, and these points will be explained below. First, we will discuss the feed delay time as a problem with the transmission path.

If there is a delay time in the transmission path 10, the time relationship between the transmission noise signal included in the secret signal in FIG. 2C) and the reference noise signal in FIG. 2A) changes. However, regardless of the delay time, this relative time difference is at most the repetition period of the reference noise signal. Therefore, as long as the length of the filter prepared in the adaptive echo canceller 13 is longer than the repetition period of this reference noise signal, there is no problem at all. Variation in delay time in the transmission line 10, frequency shift between transmission and reception in the carrier system, two-frequency response, phase distortion, etc. are completely equivalent to linear distortion in the transmission line 10.

Therefore, these problems can be solved by adaptively modifying the tap coefficients of the transversal filter of the adaptive echo canceller 13 when minimizing the noise signal contained in the reproduced audio signal shown in FIG. Ru.

Next, the repetition period 1 hour relationship of the output signals of the transmission noise generation circuit 2 and the reference noise generation circuit 12 in FIG.
However, the deviation of the repetition period and the time relationship have the same characteristics as the linear distortion in the transmission line 10 mentioned above.There are two reasons for the difference in the zero frequency squictre that has been solved. The difference is bandwidth. If the frequency included in the transmission noise signal is not included in the frequency band of the reference noise signal, the frequency component not included appears as a residual signal in the output of the adaptive echo canceller 13, and the second
This will be mixed into the reproduced audio signal shown in Figure e]. However, it is easy to set the frequency band of the reference noise signal to be higher than the frequency band of the transmission noise signal, and there is no particular problem.

Second, the difference in frequency spectra caused by the frequency response between the reference noise signal and the transmitted noise signal is due to the
This is the same as the linear distortion at 0 and does not pose a problem. However, this frequency difference.

and the influence of the frequency response on the transmission path 10.

It goes without saying that a difference in frequency spectrum occurs between the transmitted audio signal and the configurable audio signal.

Next, we will explain the secret deciphering parameter, which is generally called a key. The key to this voice privacy device is obtained by simultaneously changing the repetition period of the transmission noise signal shown in Figure 2 b] and the reference noise signal shown in Figure 2 d), and by simultaneously changing the waveforms of the transmission noise signal and the reference noise signal. . This repetition period can be arbitrarily set within the time length of the filter of the adaptive echo canceller 13, and the waveforms of the transmission noise signal and reference noise signal can be set arbitrarily within the range that makes the frequency sheath approximately flat. It can be changed.

〔Effect of the invention〕

As explained above, according to the present invention, the transmitting side sends out a confidential signal in which the transmitted voice signal is superimposed on a noise signal whose value vector is approximately flat within the entire frequency band of the transmitted voice signal, and the receiving side Since the system is configured to extract all of the audio signals from the received secret signal, there is no need to transmit or receive synchronization signals or control signals between transmitters and receivers when transmitting audio signals.

When a confidential signal is intercepted, the intonation of the voice signal cannot be recognized,
This has advantages such as easy configuration.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of an embodiment of the present invention.
It is an example of an output signal waveform of the component of a figure. 1 is a transmitting side input terminal, and 2 is a transmitting noise generation circuit. 3 is an adder circuit, 4 is a transmitting side output terminal, 10 is a transmission line, 1
1 is a receiving side input terminal, 12 is a reference noise generation circuit, 13 is an adaptive echo canceller + 14 is a receiving side output terminal, a)
is the transmitted audio signal e b) is the transmitted noise signal e c) is the secret signal a a) is the reference noise signal + e) is the reproduced audio signal, f
] is the section and time.

Claims (1)

[Claims] 1) A transmission noise generating circuit that generates a noise signal on the transmitting side and an adding circuit that adds the noise signal and the audio signal and sends a confidential signal to the transmission path, and the receiving side includes a reference noise generation circuit that generates a reference noise signal that is substantially the same as the noise signal, and an adaptive echo canceller that extracts the voice signal from the received confidential signal based on the reference noise signal. A voice secret communication device characterized by: 2) The voice secret communication device according to claim 1, wherein the transmission noise generation circuit and the reference noise generation circuit are capable of varying the period and noise signal waveform of the noise signals that can be generated respectively.