JPS6137825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demodulator for television audio multiplex broadcasting.

1. Configuration of conventional example and its problems An example of a receiving apparatus for television audio multiplex broadcasting is shown in FIG. 1, and is composed of a television receiver 1, a demodulator 2, and speakers 3 and 3'. The demodulator 2 also has an audio FM detection output terminal 4, as shown in FIG.
It is composed of a demodulation circuit 10, a matrix circuit 11, an audio amplifier 12, and output terminals 5 and 5'. However, the conventional device shown in FIG. 2 has the disadvantage that when demodulating a signal with a large modulation at a low frequency in the sub channel, the video signal component in the audio signal causes buzz bead, which deteriorates the sound quality.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned conventional drawbacks, and to provide a television audio multiplex signal demodulation device that can always obtain good reproduced signals.

Structure of the Invention The present invention detects the level of a video signal component included in an audio signal and the audio signal level of a demodulated subchannel, and limits the pass frequency band of the audio signal to always obtain a high-quality reproduced signal. It is characterized by a television audio multiplex signal demodulation device that can perform the following functions.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows an embodiment of the present invention.
In the figure, 20 is a variable passband filter inserted between the matrix circuit 11 and the audio amplifier 12, 21 is a low-pass filter that extracts low frequency components of the audio signal from a part of the sub-channel output of the demodulation circuit 10, and 22 is a variable passband filter inserted between the matrix circuit 11 and the audio amplifier 12. 23 is a band filter for extracting the video signal component included in the audio FM detection output; 24 is a video signal component level detection circuit including a detection and integration circuit; 25 is an audio signal This is a reproduction band control circuit that controls the reproduction band of the variable passband filter 20 based on the output signal of the detection circuit 22, the output signal of the video signal component level detection circuit 24, and the switching control signal from the demodulation circuit 10.

In such a configuration, the signal appearing at the audio FM detection output terminal 4 is applied to the demodulation circuit 10;
A part of it is applied from the dividing point 30 to the band filter 23 for extracting video components. This band filter 23 for _{extracting the video component extracts the high frequency (2 H , 3H} ...)
Therefore, as shown in Figure 5B, _H
2H (sub-carrier frequency) in the frequency band above
It has characteristics other than . In Figure 5B, a is _H and 3 _H
The bandpass filter b is a filter that removes _2H by trapping in a band of _H or more, and the bandpass filter 23 for extracting video components can be realized by either a or b. _2H needs to be removed because it is the same as the subcarrier frequency. The video signal component obtained by the band filter 23 for video component extraction is detected and integrated by the video signal component level detection circuit 24, and the first
A control signal is output. Further, the sub-channel output of the demodulation circuit 10 is applied to the matrix circuit 11, and part of it is applied to the low-pass filter 21 from the division point 31. The low-pass filter 21 extracts the low frequency signal of the audio signal contained in the sub-channel output, and has the characteristics shown in FIG. 5A. The signal obtained by the low-pass filter 21 is sent to the audio signal detection circuit 22.
The signal is detected and integrated, and a second control signal corresponding to the magnitude of the audio signal is output. The first and second control signals are applied to the reproduction band control circuit 25. or,
At the same time, a switching control signal is taken out from the demodulation circuit 10 and applied to the reproduction band control circuit 25. The reproduction band control circuit 25 is controlled by first and second control signals according to the content of the multiplexed signal (double broadcast or stereo broadcast) and the magnitude of the low frequency component of the audio signal and the video signal component contained in the signal. and outputs a control signal for changing the reproduction band of the variable passband filter 20. The output signal of the reproduction band control circuit 25 is applied to the variable passband filter 20. This variable pass band filter 20 has characteristics as shown in FIG. 6, and changes from a to b to c in accordance with the output signal of the reproduction band control circuit 25. That is, the change in the playback band is set to suit the content of the audio multiplex signal. For example, when there are few video signal components in the audio multiplexed signal, the reproduction band will be expanded the most with the characteristic shown in a in Figure 6, and when there are many video signal components and few low frequency signals, the characteristic will be b.
If there are many low frequency signals, the characteristic shown in c will be obtained. In this way, the inclusion of the video signal in the audio signal has caused deterioration in sound quality in the high range, especially when low frequency components are included, but the playback band is controlled by the video signal level and audio signal level in the audio signal. By doing so, it is possible to improve the sound quality.

By the way, when changing the playback band, it is assumed that only the sub channel is used in the case of double broadcasting, and the band of the main channel is not limited by the switching control signal. Furthermore, in the case of stereo broadcasting, the reproduction band is changed for both the L channel (main channel) and the R channel (sub channel). This distinction is assumed to be controlled by the reproduction band control circuit 25. Second
The dotted arrows in the figures and FIG. 3 indicate sub-channel signal transmission lines.

In addition, using the block shown in FIG. 3, it is also possible to control the playback band by extracting only the video signal component contained in the audio signal.

Effects of the Invention The present invention detects the level of the video signal component included in the audio signal and the audio signal level of the demodulated subchannel, and limits the pass frequency band of the audio signal, so that it is possible to always obtain a high-quality reproduced signal. It has the advantage of being able to

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a receiving device for television audio multiplex broadcasting, FIG. 2 is a block diagram of a conventional television audio multiplex signal demodulating device, and FIG. 3 is a block diagram of a television audio multiplex signal demodulating device according to an embodiment of the present invention. Figure 4 is a spectrum diagram of the video signal included in the audio FM detection output, Figure 5A is a characteristic diagram of the low-pass filter of the same device, Figure 5B is a characteristic diagram of the band filter of the same device, FIG. 6 is a characteristic diagram of the variable pass band filter of the same device. 1... Television receiver, 2... Demodulator, 3, 3'
...Speaker, 4...Audio FM detection output terminal,
5, 5'... Output terminal, 10... Demodulation circuit, 11
... Matrix circuit, 12 ... Audio amplifier, 20 ... Pass band variable filter, 21 ... Low-pass filter, 22 ... Audio signal detection circuit,
23...Band filter, 24...Video signal component level detection circuit, 25...Reproduction band control circuit.

Claims (1)

[Claims] 1 A bandpass filter for extracting a video signal component from an audio FM detection output signal, and a first control signal that detects the output of this bandpass filter and generates a first control signal corresponding to the level of the video signal component included in the audio multiplexed signal. a video signal level detection circuit for extracting and detecting a low frequency component from the output of the sub-channel FM demodulator to obtain a second control signal corresponding to the magnitude of the low frequency component; a reproduction band control circuit that outputs a third control signal for controlling a reproduction band from the first and second control signals and an initial control signal for switching between dual broadcasting and stereo broadcasting; and an output signal of the reproduction band control circuit. In the case of dual broadcasting, the playback band of only the sub channel is changed by the above-mentioned switching control signal, and the band of the main channel is not limited, and in the case of stereo broadcasting, In addition to changing the playback band for both channels, the first and second control signals expand the playback band to the maximum when there are few video signal components in the audio multiplex signal, and when there are many video signal components, and It is characterized by a configuration in which the level of the high frequency band of the reproduction band is lowered when there are few low frequency signals, and the level of the high frequency band of the reproduction band is lowered to the lowest level when there are many video signal components and there are many low frequency signals. TV audio multiplex signal demodulation device.