JP2581922B2 - Audio signal processing device in CATV - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an audio signal processing device in CATV, and more particularly to an audio signal processing device in CATV suitable for paying for CATV.

(Conventional technology) In pay CATV, the transmitting device scrambles the TV signal of the pay channel and sends it to the subsequent stage, and the terminal device in the subsequent stage scrambles the subscriber who has contracted with CATV and paid the fee. To enable paid channel viewing. However, it is difficult to scramble the audio signal, and in the normal case, only the audio is heard without paying a fee.

Therefore, in order to prevent eavesdropping on the audio, the transmitting device divides the audio signal temporally, and transmits the signal while maintaining the polarity for one time and inverting the polarity at the other time, and paying a fee In the terminal device of the user, the polarity is restored only for the time when the above polarity is inverted.

(Problems to be Solved by the Invention) The above-mentioned conventional audio signal processing apparatus in CATV has the following problems. In other words, since the time for inverting the polarity is set at random in the transmitting device, the terminal device of the subscriber who pays for the fee reliably synchronizes with the transmitting device side and relies on the polarity of the audio signal at the above time. I have to put it back. For this reason, the configuration of the apparatus is complicated and the cost is high.

The present invention has been made in order to solve the above-described problems, and is used for a pay CATV, and can reliably prevent a voice of a pay channel from being eavesdropped on a terminal device of a non-pay CATV subscriber. It is another object of the present invention to provide a CATV audio signal processing apparatus which is simple and inexpensive.

(Means for Solving the Problems) In order to solve this object, the means as described in the claims are taken, and the operation is as follows.

(Operation) The audio signal from the audio signal generator is applied to the transmission device.
This signal is AM-modulated by the AM modulation circuit of the transmitting device to be a signal having a frequency higher than the audio frequency. This signal is sent from the sending device and sent to the terminal side via the transmission line.

In the terminal device, the selection circuit operates so as to select a signal processed by the AM demodulation circuit for a subscriber having a paid reception contract, so that the signal transmitted from the transmission device is subjected to AM demodulation. Output after Thus, the audio receiver can listen to the sound information sent from the audio signal generator as it is.

On the other hand, in a terminal device of a subscriber who does not have a paid reception contract, a selection circuit operates so as to select a signal that has been input and passed without being subjected to AM demodulation. Therefore, the audio receiver reproduces the signal outside the audible frequency band,
It is completely inaudible to human ears, preventing eavesdropping.

(Embodiment) Drawings showing an embodiment of the present application will be described below.

FIG. 1 shows a system diagram of the CATV system. 1
Receives television broadcasts that are normally broadcast on an antenna. Reference numeral 2 denotes a CATV center device, and reference numeral 3 denotes a receiving amplifier. Reference numeral 4 denotes a VTR as an audio signal generator. In addition, a video disc player can be used. 5
Denotes a video camera with a microphone as an audio signal generator, which is used, for example, when a live broadcast is sent from a studio or the like. Reference numerals 6 and 7 denote sending devices. The detailed circuit configuration will be described later. Reference numerals 8 and 9 indicate RF modulators, 8a and 9a indicate video input terminals, 8b and 9b indicate audio input terminals, and 8c and 9c indicate output terminals, respectively. As is well known, these RF modulators 8 and 9 AM-modulate an input video signal, FM-modulate an input audio signal, and add both modulated signals to output as a television signal. The channel of the output television signal (hereinafter referred to as “paid channel”) is selected as a channel not included in the output of the receiving amplifier 3. Reference numeral 10 denotes a mixer also called a channel combiner. A transmission line 11 uses a coaxial cable. 12 is a main branch amplifier, 13
Indicates tap-off. Reference numeral 14 denotes a terminal device, the detailed circuit configuration of which will be described later. 15 is a voice receiver
On the AV TV, 15a indicates a speaker.

Next, FIG. 2 is a block circuit diagram showing a specific configuration of the transmitting device. Components corresponding to those in the previous figure are denoted by the same reference numerals, and redundant description will be omitted (the same concept will be used below, and redundant description will be omitted). The VTR 4 includes a video signal generation circuit 4a and an audio signal generation circuit 4b. In the transmitting device 6, 6a is a video input terminal, 6b is an audio input terminal,
6c indicates a video output terminal, and 6d indicates an audio output terminal. Reference numeral 16 denotes a video signal processing circuit, which uses a circuit for scrambling the video signal. 17 is an AM modulation circuit, the frequency of which is, for example, 47.25 KHz
Is modulated by the audio signal applied to the audio input terminal 6b and output. The frequency of this carrier is an integral multiple of the horizontal synchronizing frequency of 15.75 KHz of the television video signal, so that unpleasant disturbing sounds due to beats are not generated in the AV television 15 as an audio receiver. This carrier frequency is selected to be one of the 30 to 50 KHz bands so that it can be processed by the subsequent RF modulator and can modulate the audio signal of up to 10 KHz from the audio signal generator 4. . Reference numeral 18 denotes a high-pass filter that blocks the audio signal from the audio signal generator 4 in the output of the AM modulation circuit 17 and passes the remaining signals.

Next, FIG. 3 is a block circuit diagram showing a specific configuration of the terminal device. In the terminal device 14, 14a is an input terminal, 14b
Indicates a video output terminal, and 14c indicates an audio output terminal. Reference numeral 19 denotes a channel selection circuit for selecting and specifying one of a plurality of television signals transmitted through the transmission line 11. Reference numeral 20 denotes a frequency conversion circuit which is used to convert a television band to an intermediate frequency band. Reference numeral 21 denotes an intermediate frequency amplifier circuit. 22 is a demodulation circuit, 22a is a video output terminal, and 22b is an audio output terminal.
Reference numeral 23 denotes a video signal processing circuit of the terminal device 14, which has a descrambling function for descrambling the video signal by the video signal processing circuit 16 of the transmission device 6 described above. 24 denotes an AM demodulation circuit, and 24a denotes an AM detection circuit. Reference numeral 24b denotes a low-pass filter for passing an audio signal up to 10 KHz out of the output of the AM detection circuit 24a. Reference numeral 25 denotes a switching circuit as a signal selection circuit. The switching circuit 25 switches to the contact X side when a control signal is applied to the control terminal 25a, and is connected to the contact Y side otherwise. Reference numeral 26 denotes a selection control circuit which outputs a control signal during operation. Note that the selection control circuit 26 is connected to various circuits (for example, a coin timer or the like) for determining whether or not the user has subscribed to pay CATV, and is configured to operate when subscribed.

Next, FIG. 4 showing a specific circuit configuration of the AM detection circuit 24a will be described. In the AM detection circuit 24a, IN indicates an input terminal, OUT indicates an output terminal, and V indicates a power supply terminal. C1 and C2 denote capacitors that pass signals up to 50 KHz including audio signals and block direct current, respectively. D1 is a diode for detection,
R1 and R2 indicate the bias resistors of the diode D1, respectively.

The operation of the CATV system having the above configuration will be described based on the signal waveform of FIG. 5 and the frequency spectrum of FIG. In FIG. 5, (A) to (E) are signal waveforms relating to time, and show signal waveforms at points A to E in FIGS. 2 and 3, respectively. 6 (a) to 6 (e) show the frequency spectrum of the signal at each of the above points A to E.

For example, an audio signal from the VTR 4 as shown in FIG. The frequency spectrum of the signal here is distributed, for example, in a band of 0 to 10 KHz as shown in FIG. In the transmitting device 6, the signal having the waveform (A) is changed to the signal having the waveform (B) by the AM modulation circuit 17. The frequency spectrum of the signal here is as shown in FIG. In the drawing, CW indicates a carrier, USB indicates an upper sideband, and LSB indicates a lower sideband. Next, the signal having the waveform (B) passes through the high-pass filter 18 and becomes a signal having the waveform (C). The frequency spectrum of the signal here is as shown in (c). The signal of the waveform (C) output from the audio output terminal 6d of the transmitting device 6 is converted into a pay channel television signal by the RF modulator 8 and mixed with other normal broadcast television signals by the mixer 10. The signal is transmitted through the transmission line 11 to the terminal device 14.

In the terminal device 14, the signal of the channel selected and designated by the channel selection circuit 19 is converted by the frequency conversion circuit 20 into an intermediate frequency band. When the pay channel signal is selected, the intermediate frequency signal is amplified by the intermediate frequency amplification circuit 21 and demodulated by the demodulation circuit 22. Audio output end
From the point 22b, a signal having the same waveform as that shown in FIG. This terminal device 14 is a paid CA
If the TV is for a non-subscriber, the switching circuit 25 is set to the contact Y
Side, the signal having the waveform (C) is applied to the AV television 15 as it is. Even if this signal is reproduced by the speaker 15a of the AV television 15, since the signal has a high frequency outside the audible frequency band, it cannot be heard by human ears, and therefore is not eavesdropped.

On the other hand, in the case of a terminal device of a receiver who has already subscribed to pay CATV, the switching circuit 25 is switched to the contact X side. Therefore, the signal from the audio output terminal 22b of the demodulation circuit 22 is AM
The signal is detected by the detection circuit 24a and output as a signal having the waveform (D). The frequency spectrum of the signal here is as shown in (d). Next, the signal having the waveform (D) passes through the low-pass filter 24b and becomes a signal having the waveform shown in (E). This is the same as the waveform shown in (A), and the frequency spectrum shown in (e) is also the same as that shown in (a). The signal from the low-pass filter 24b passes through the switching circuit 25 and is applied to the AV television 15. Normal sound is reproduced from the speaker 15a of the AV TV 15.

In the above embodiment, the carrier of the AM modulation circuit 17
A 5KHz signal is used, but if the horizontal sync signal is separated from the video signal by a horizontal sync separation circuit and the frequency is tripled and amplified to create a signal with the above frequency, the speaker
Deterioration of the sound quality in 15a can be prevented.

Next, FIG. 7 is a block circuit diagram showing a configuration of a different transmitting device. The components having the same or equivalent functions as those of the previous embodiment are denoted by the same reference numerals with the letter e added thereto, and redundant description will be omitted. The video signal processing circuit of this transmission device 6e
A trap circuit 28 is connected to a stage subsequent to 16e, and removes a frequency component around 4.5 MHz from the video signal output from the processing circuit 16e. Because of this, the carrier frequency of the AM modulation circuit 17e is 30
No matter where you set it in the ~ 50KHz band, speaker 1
With 5a, the sound can be prevented from being distorted.

(Effect of the Invention) As described above, in the present application, it is used for pay CATV,
It is possible to reliably prevent the voice of the pay channel from being eavesdropped on the terminal device of the non-pay subscriber of the pay CATV.

In addition, the apparatus has a feature that the configuration is simple and the apparatus is inexpensive.

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a system diagram of a CATV system, FIG. 2 is a block circuit diagram showing a specific configuration of a transmitting device, and FIG. 3 is a specific configuration of a terminal device. FIG. 4 is a circuit diagram showing a specific configuration of the AM detection circuit, FIG. 5 is a graph showing a signal waveform with respect to time at each point in FIGS. 2 and 3, and FIG. FIG. 7 is a graph showing the frequency spectrum at each point in FIG. 2 and FIG. 3, and FIG. 7 is a block circuit diagram showing a configuration of a different transmitting device. 4 ... Voice signal generator (VTR), 6 ... Transmission device, 11 ...
… Transmission line, 14… terminal equipment, 15… audio receiver (AV television), 17… AM modulation circuit, 24… AM demodulation circuit, 25… signal selection circuit (switching circuit).

Claims (1)

(57) [Claims] An audio signal from an audio signal generator is added to a transmitting device and subjected to signal processing. The transmitting device sends the processed audio signal to a terminal device via a transmission line, and sends the signal to the terminal device. In the audio signal processing device in CATV, which performs another signal processing on the added signal and receives it with the audio receiver, the frequency of the carrier wave of the transmitting device is set to a frequency outside the audible frequency band. In addition to having an AM modulation circuit, the terminal device selects one of a signal applied to the input of the device and a signal obtained by AM demodulation of the signal by an AM demodulation circuit, and transmits the signal to a subsequent audio receiver. An audio signal processing device in CATV, comprising a signal selection circuit.