JPS6359240A - Digital voice reception equipment - Google Patents

Abstract

PURPOSE:To protect a speaker equipment by attenuating a voice signal in response to a cryptographic level in reproducing the cryptographic voice signal by a pseudo random code series without decoding so as to prevent excess voice output. CONSTITUTION:An analog voice signal is inputted to a variable attenuation means 15 and attenuated by a predetermined quantity in response to a cryptographic level signal. In case of the signal not subject to encroption, the voice signal is passed through without attenuation depending on the content of the cryptographic level signal representing no encryption. An attenuation inhibition switch 19 is acted reversely with the switch 16 and closed for the receiver for an uncontracted person. In case of a contracted person, since the cryptographic voice signal is decoded in a gate 13 correctly, it is not required to attenuate the amplitude and the switch 19 is opened to stop the function of the attenuation means 18. For example, if the pseudo random code series with multiple rate of 100%, the attenuation of nearly 15dB is preferred.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a receiving device for a digital audio signal with confidential speech.

2. Description of the Related Art Digital systems are increasingly being adopted for transmitting audio signals in satellite broadcasting, CATV, and the like. It goes without saying that the playback quality is improved, but another major feature of this digital system is that it is suitable for pay broadcasting. In paid broadcasting, we take precautions to ensure that normal video and audio are not provided to viewers other than subscribers.
Usually, the transmitted signal is scrambled. When a signal is transmitted in an analog manner, signal quality deterioration occurs during the polarization and decoding process, but when a signal is transmitted digitally, this quality deterioration does not occur, which is a major advantage.

To polarize a digital audio signal, a method of multiplying (adding) a pseudo-random code sequence (often called a PN sequence) to the digital audio signal in a -C manner is used.

The configuration is shown in FIG. 2, in which each serially input signal is added by an exclusive OR gate 1, and a polarized audio signal is obtained from the output.

In addition, since it is often convenient for operation to change the degree of confidential information, for example, the Interim Report of the Telecommunications Technology Council Satellite Television Paid System Committee (1986)
(April 2015), ``The scrambling effect is controlled by changing the duty ratio of the gate of the PN signal (
(sic). ” have been proposed. As shown in FIG. 3, a pseudo-random code sequence is first input to a multiplication ratio controller 2, outputted at a ratio corresponding to a confidential speech level signal, and multiplied with a digital audio signal. This makes it possible to provide secret speech in several stages, from a level where the content cannot be heard at all to a level where a slight amount of noise is mixed into the normal playback signal.

Problems that the invention aims to solve If a polarized audio signal multiplied by a pseudo-random code is played back as is without decoding it, a noise similar to white noise will be played loudly, making it difficult for the listener to hear the problem. Not only does this cause discomfort, but it can also damage the voice coil of the speaker device. If the level of the confidential conversation is simply two states, ie, presence and absence, it is not a big problem to simply stop (muting) the audio output during the confidential conversation. This is because the content of the playback sound during the secret conversation is unclear even if asked. However, as mentioned above, when there are several levels of privacy, broadcast operators often prefer to play back the privacy voice at intermediate levels. Audio that is mixed with noise but can be understood is thought to have the effect of encouraging unsubscribed listeners to subscribe to paid listening contracts. However, even though the multiplication ratio has decreased,
Since I played it as is, the above problem still remains.

Means for Solving the Problems In order to solve the above problems, the present invention uses a confidential speech level signal included in a transmitted signal, and adjusts the amplitude of the reproduced audio output according to the confidential speech level indicated by this confidential speech level signal. This enables the playback of polarized audio while stabilizing the listening volume level. In order to control the amplitude of the audio signal, a variable attenuation means that obtains an amount of attenuation depending on level information is used. Here, for a high confidential story level, the attenuation amount is set to be large.

Effects: As the multiplication ratio of pseudo-random code sequences to digital audio signals increases on the transmitting side and the level of confidentiality increases, the bit error rate during transmission will increase if the receiving side does not decode it (i.e. in the case of a non-subscriber's receiver). The result is similar to that of an increase in the noise energy in the reproduced sound (
Straight line (a) in Figure 4). In contrast, the straight line (b
By realizing a characteristic that lowers the amplitude of the reproduced audio signal when the confidential conversation level becomes uniform, as in l, it is possible to prevent the volume value of the audio output ultimately output from the receiving device from becoming extremely large. Can be done. Although the characteristics in Figure 4 are shown as a continuous straight line, in reality the secret level takes several values in steps, so fa) and (bl are shown in ascending and descending steps, respectively. By the way, in order for the receiver of a subscribed listener to properly polarize the conversation, it is necessary to transmit a confidential level signal, so the transmitted signal includes the confidential level signal.The receiving device of a non-contracted listener Then, by knowing the current confidential conversation level from this confidential conversation level signal, it is possible to set an appropriate amount of attenuation of the amplitude of the audio signal.

Embodiment Hereinafter, an embodiment of the digital audio receiving device of the present invention will be described with reference to the drawings.

First, FIG. 5 shows an example of the configuration of a transmitter that generates a transmission signal, which is the object of the present invention. The analog audio signal is converted into a digital audio signal by the A/D converter 4. On the other hand, the output of the pseudo-random code sequence generator 3 is set to a predetermined multiplication ratio by the multiplication ratio controller 2 based on the secret level signal, and then multiplied by the digital audio signal at the exclusive OR gate 1. The polarized audio signal output from the gate 1, the polarized level signal, and the synchronization signal are combined by a multiplexer 5, and an appropriate correction code is added by an error correction code adder 6. Finally, the modulator 7 modulates the carrier wave and sends it out as a transmission signal. When the secret story is not applied, the multiplication ratio in the multiplication ratio controller 2 may be set to zero.

FIG. 1 shows the configuration of a digital audio receiving device according to an embodiment of the present invention. A transmission signal from the transmitting device is first inputted to the demodulator 10 via a tuner (not shown) if necessary. Here, the serial digital signal is taken out, and then subjected to necessary processing in a synchronization and error correction circuit 11, and then separated into a polarized audio signal and a privacy level signal in a separator 12.

exclusive OR gate 13, multiplication ratio controller 14,
The original image random code sequence generators 15 are the same as 1 and 2.3 in FIG. 5, respectively. The decryption prohibition switch 16 is a symbolic representation of a decryption prohibition means for non-subscribers, and in the non-subscriber's receiving device, the switch 16 is in an open state, and the combination for decryption cannot be executed. It is shown that. The output of gate 13 is D
/A converter 17 converts the signal into an analog signal. The analog audio signal is input to the variable attenuation means 18 and is attenuated by a predetermined amount depending on the confidential conversation level signal. When confidential speech is not applied, settings are made so that the audio signal is passed through without attenuation, depending on the content of the confidential speech level signal indicating this. The attenuation prohibition switch 19 is the switch 1
6, and is closed when the non-subscriber's receiver (g device).In the case of a subscriber, the polarized voice signal is correctly decoded in game 1-13, so it is necessary to attenuate the amplitude. Therefore, the switch 19 is opened to stop the function of the variable attenuation means 18.

How much attenuation is appropriate for each secret level is a design issue, but for example, if a pseudorandom code sequence with a multiplication ratio of 100% is used, the attenuation should be around 15 dB. I think the amount of attenuation is preferable.

In the configuration shown in FIG. 1, the variable attenuation means 18 is used for analog signals, so it can be easily realized by changing the voltage division ratio using resistors or by switching the input resistance of an operational amplifier.

FIG. 6 shows a case where a digital variable attenuation means 20 is used in place of the variable attenuation means 18 shown in FIG. 1, and only the portion immediately before the final output is shown. The variable damping means 20 is D/
It is installed before the A converter 17 and attenuates the audio signal in the digital signal state. If you want to do it seriously,
It is appropriate to use digital multipliers to switch the multiplication coefficients. However, there are usually several levels of confidential information, and the amount of attenuation in the attenuation means 20 does not need to be exact, so a simple method is sufficient. In other words, attenuation can be easily achieved by shifting the bits downward (in the direction of LSB) for each digital audio data. Polarity bit (MSB)
If the other focus points are shifted one bit lower, the attenuation will be 6 dB. For example, for a transmitted signal with four types of confidentiality levels, including the state in which confidentiality is not applied, OdB,
Four types of attenuation can be prepared: 6dB, 12dB, and 18dB.

Effects of the Invention As described above, the present invention is capable of reproducing an audio signal polarized by a pseudo-random code sequence without decoding it during pay broadcasting of a digital audio signal (or a digital audio signal multiplexed with a video signal). By attenuating the audio signal in accordance with the polarization level, it prevents excessive audio output and protects the speaker device, etc., while at the same time maintaining and providing an appropriate volume to the listener. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a configuration example of a digital audio receiving device according to the present invention, FIG. 2 is an explanatory diagram showing how to multiply pseudo-random code sequences, and FIG. 3 is a block diagram showing a configuration example of a digital audio receiving device according to the present invention. An explanatory diagram showing how to multiply random code sequences, Fig. 4 is a graph showing the relationship between the secret level, noise energy, and necessary attenuation characteristics, Fig. 5 is a block diagram showing an example of the configuration of a transmitting device, and Fig. 6 FIG. 2 is a block diagram showing another example of the configuration of the digital audio receiving device according to the present invention. 1.13...Exclusive OR gate, 2,14...
...Multiplication ratio controller, 3,15...
・Pseudo-random code sequence generator, 4...A/D
Converter, 17...D/A converter, 16...
...Decoding prohibition switch, 19...Attenuation prohibition switch, 18...Variable attenuation means (analog), 2
0...Variable attenuation means (digital). Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2, Figure 3I2I, Figure 4, Figure 6.

Claims (1)

[Claims] Generating a polarized audio signal in which a plurality of privacy levels can be set by changing the multiplication ratio of the pseudo-random code sequence when multiplying a digital audio signal and a pseudo-random code sequence, When a transmission signal is configured to include at least this polarized audio signal and a privacy level signal indicating the privacy level, if the polarization audio signal is not decoded during reception of this transmission signal, the Based on the secret level signal,
1. A digital audio receiving device comprising variable attenuation means that attenuates the amplitude of a reproduced audio signal as the confidential conversation level increases.