JPS63234682A - Teletext reproducing device - Google Patents

Abstract

PURPOSE:To contrive to reduce high frequency noise of teletext additional sound without giving any effect onto the television sound by varying the cut-off frequency of a low pass filter at the pre-stage of an audio amplifier circuit. CONSTITUTION:An audio switching circuit 15 outputs either input signals in response to a control signal from a teletext demodulation circuit 13. The control signal controls the audio switching circuit 15 so as to pass an additional signal when the user selects the teletext broadcast. The output of the audio switching circuit 15 is inputted to a low pass filter 16. The cut-off frequency of the low pass filter 16 is varied as 10kHz when an additional sound signal is inputted and as 15kHz in case of an audio signal by using a control signal from the teletext demodulation circuit 13. Thus, the high frequency noise of the additional sound is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a teletext reproducing apparatus for reproducing additional sound signals.

BACKGROUND OF THE INVENTION Recently, various broadcasting stations have begun regular broadcasting of teletext broadcasts, and manufacturers are also putting on the market teletext reproduction devices and televisions with built-in reproduction devices. A teletext reproducing device reproduces an additional sound signal within a teletext demodulation circuit based on encoded music information.

On the other hand, it also demodulates conventional television broadcast audio. Both are reproduced from the same speaker via a switching circuit.

When reproducing teletext, the configuration is shown in FIG. 2.

In FIG. 2, 21 is an input terminal for the received television broadcast signal, 22 is a video intermediate frequency amplification circuit, and 23 is a teletext demodulation circuit that inputs the video composite signal from the video intermediate frequency amplification circuit 22 and outputs an additional sound signal. , 24 is an audio demodulation circuit that inputs the audio intermediate frequency signal output from the video intermediate frequency amplification circuit 22 and outputs the audio signal, and 26 inputs the additional audio signal and the audio signal, and outputs one of them.
26 is an audio amplification circuit which inputs the output of the audio switching circuit 25, and 27 is a speaker which inputs the output of the audio amplification circuit 26 and reproduces audio.

The operation of the teletext reproducing apparatus configured as described above will be described below.

First, the television broadcast signal input from the input terminal 21 is
It is processed by the video intermediate frequency amplification circuit 22 and output as a video composite signal and audio intermediate frequency signal. The video composite signal is input to the teletext demodulation circuit 23.

Teletext data is superimposed on the vertical blanking period, and this data is processed to create an additional sound code, and an additional sound signal is synthesized according to this code. On the other hand, the audio intermediate frequency signal is demodulated by the audio demodulation circuit 24 to become an audio signal. The additional sound signal and the audio signal are transferred to the audio switching circuit 26.
and is switched depending on whether the user selects television broadcasting or teletext broadcasting. The output of the audio switching circuit 26 is amplified by the audio amplifying circuit 26, and the output is sent to the speaker 2.
7, it is reproduced as a sound wave.

Problems to be Solved by the Invention However, with the above-described configuration, there is a problem in that the additional sound of teletext broadcasting that is to be repeated contains a lot of high-frequency noise. That is, since the teletext demodulation circuit is a digital circuit, digital-induced noise is generated.

In view of the above-mentioned problems, the present invention provides a teletext reproducing apparatus that reproduces additional sound with less high-frequency noise.

Means for Solving the Problems In order to achieve this object, the teletext reproducing apparatus of the present invention includes a video intermediate frequency amplification circuit, and a video composite signal outputted from the video intermediate frequency amplification circuit, and adds a teletext demodulation circuit that outputs a sound signal; an audio demodulation circuit that receives an audio intermediate frequency signal output from the video intermediate frequency amplification circuit; and an audio demodulation circuit that outputs an audio signal; inputs the additional audio signal and the audio signal; an audio switching circuit that outputs either one according to a user's control signal; and a low-pass filter that inputs the output of the audio switching circuit and changes its cutoff frequency according to the control signal. , an audio amplifier circuit that receives the output of the low-pass filter, and a speaker that receives the output of the audio amplifier circuit and outputs audio.

Effect: With this configuration, it is possible to lower the cutoff frequency of the low-pass filter only when reproducing the teletext additional sound, and it is possible to reduce high-frequency noise contained in the additional sound.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a teletext reproducing apparatus according to an embodiment of the present invention. In FIG. 1, 11 is an input terminal for a received television broadcast signal, 12 is a video intermediate frequency amplification circuit, and 13 is a character for inputting a video composite signal output from the video intermediate frequency amplification circuit 12 and outputting an additional sound signal. A broadcast demodulation circuit 14 inputs the audio intermediate frequency signal output from the video intermediate frequency amplification circuit 12 and outputs an audio signal; 14 inputs the additional sound signal and the audio signal and performs teletext demodulation. an audio switching circuit that outputs either input signal in response to a control signal from the circuit 13;
16 is a low-pass filter that receives the output of the audio switching circuit 15 and changes its cutoff frequency according to the control signal; 17;
Reference numeral 18 indicates an audio amplification circuit which inputs the output of the low-pass filter 16, and a speaker 18 which inputs the output of the audio amplification circuit 17 and reproduces audio.

The operation of the teletext reproducing apparatus configured as described above will be described below.

First, a television broadcast signal input from the input terminal 11 is processed by the video intermediate frequency amplification circuit 12 and output as a video composite signal and audio intermediate frequency f8. The video composite signal is input to the teletext demodulation circuit 13.

The teletext data is superimposed on the vertical blanking period, and the teletext demodulation circuit 13 takes out the teletext data,
Processing is performed to create additional sound codes. Then, an additional sound signal is synthesized according to the additional sound code. The range of the additional sound is A○
(27,5H2) to C8 (4188Hz).

Therefore, there are fewer high-frequency components compared to TV audio. On the other hand, the audio intermediate frequency signal is demodulated by the audio demodulation circuit 14 and becomes an audio signal. The additional sound signal and the audio signal are input to the audio switching circuit 15.

The audio switching circuit 15 outputs either one of the input signals according to the control signal from the teletext demodulation circuit 13. The control signal controls the audio switching circuit 15 so as to pass the additional sound signal when the user selects teletext. The output of the audio switching circuit 15 is input to a low pass filter 16. The low-pass filter 16 changes its cutoff frequency in response to a control signal from the teletext demodulation circuit 13. For example, when an additional sound signal is input, the cutoff frequency is 10kH2, and when an audio signal is input, the cutoff frequency is 15kHz. As mentioned above, there are few signal components in the high frequency range of the additional sound signal, and noise is the main component, so the cutoff frequency is set to 10kHz.
However, it has little effect on sound quality. Low pass filter 16
The signal that has passed through is amplified by the audio amplification circuit 17 and reproduced as a sound wave from the speaker 18.

As described above, according to this embodiment, the low-pass filter 1
By changing the cutoff frequency of No. 6, it is possible to realize a teletext reproducing apparatus that can reduce the high-frequency noise of the additional sound.

Effects of the Invention The present invention makes it possible to reduce the high-frequency noise of teletext additional sound by changing the cutoff frequency of the low-pass filter at the front stage of the audio amplification circuit, without affecting the television sound. This realizes a teletext reproducing device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a teletext reproducing apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional teletext reproducing apparatus. 11.21... Input terminal, 12.22...
...Video intermediate frequency amplification circuit, 13.23...Teletext demodulation circuit, 14.24...Audio demodulation circuit, 15.25...Audio switching circuit, 16.・・・
...Low pass filter, 17,26...Audio amplifier circuit, 18.27...Speaker.

Claims (1)

[Claims] a video intermediate frequency amplification circuit; a teletext demodulation circuit that inputs the video composite signal output from the video intermediate frequency amplification circuit and outputs an additional sound signal; and inputs the audio intermediate frequency signal output from the video intermediate frequency amplification circuit. an audio demodulation circuit that outputs an audio signal; an audio switching circuit that inputs the additional audio signal and the audio signal and outputs either one according to a control signal; and an audio switching circuit that inputs the output of the audio switching circuit and controls the Teletext broadcasting comprising: a low-pass filter that changes a cutoff frequency according to a signal; an audio amplification circuit that inputs the output of the low-pass filter; and a speaker that inputs the output of the audio amplification circuit and reproduces audio. playback device.