JPS6137826B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio multiplex signal demodulation device for receiving television audio multiplex broadcasts.

Its purpose is to detect the level of the video signal component (phase modulation component in the video signal) included in the audio signal and the audio signal level of the demodulated subchannel, and to limit the pass frequency band of the audio signal. The object of the present invention is to provide a device that can always obtain high-quality reproduction signals.

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'. Also demodulator 2
As shown in FIG.
1, an audio amplifier 12, and output terminals 5 and 5'.

The conventional example shown in FIG. 2 has the disadvantage that when demodulating a highly modulated signal at a low frequency in the sub channel, a video signal component in the audio signal generates a buzz beat, deteriorating the sound quality.

The present invention eliminates the above-mentioned conventional drawbacks, and one embodiment of the present invention will be described below with reference to FIG. 3.

In FIG. 3, 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 the low frequency component of the audio signal from a part of the sub-channel output of the demodulation circuit, and 22 is a variable passband filter inserted between the matrix circuit 11 and the audio amplifier 12. An audio signal detection circuit including detection and integration; 23 is an input terminal of a video intermediate frequency amplification circuit 24 in the television receiver 1; 25 is an output terminal; 26 is a part of the output signal of the video intermediate frequency amplification circuit 24; 27 is a video signal component level detection circuit including a detection and integration circuit; 28 is an output signal of the audio signal detection circuit 22; This is a playback band control circuit that controls the playback band of the variable passband filter 20 by controlling the output signal of the video signal component level detection circuit 27 and the switching control signal from the demodulation circuit 10.

The operation of this example will be explained with reference to FIG.

Since the proportion of the video signal in the signal appearing at the audio FM detection output terminal 4 is proportional to the magnitude of the phase modulation component of the video signal, a part of the output signal of the video intermediate frequency amplification circuit 24 is taken out and the phase A modulation component detection circuit 26 detects a phase modulation component included in the video signal. Phase modulation component detection circuit 26
The output signal is a first signal proportional to the magnitude of the video signal included in the output signal of the audio FM detection output terminal 4 which has been detected and integrated by the video signal component level detection circuit 27.
A control signal is output. Also, the sub-channel output of the demodulation circuit 10 is applied to the matrix circuit 11, but a part of it is sent from the division point 30 to the low-pass filter 21.
join. The low-pass filter 21 extracts the low frequency signal of the audio signal contained in the sub-channel output, and has the characteristics as shown in FIG. The signal obtained by the low-pass filter 21 is sent to the audio signal detection circuit 2
2, 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 28. At the same time, a switching control signal is taken out from the demodulation circuit 10 and applied to the reproduction band control circuit 28. The reproduction band control circuit 28 uses first and second control signals and switching signals to determine 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. It outputs a control signal for changing the reproduction band of the variable passband filter 20 under the control of the variable passband filter 20. The output signal of the reproduction band control circuit 28 is applied to the variable passband filter 20. The variable passband filter 20 has a characteristic as shown in FIG. 4, and changes from a to b and c in accordance with the output signal of the reproduction band control circuit 28. That is, the change in reproduction band is set to suit the content of the audio multiplexed signal. For example, when there are few video signal components in the audio multiplexed signal, the characteristics shown in a of FIG. 4 will be obtained, which will widen the reproduction band the most, and when there are many video signal components and there are few low frequency signals, the characteristics shown in b,
Moreover, when there are many low frequency signals, the characteristic shown in c is 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 video signal level in the audio signal,
Sound quality can be improved by controlling the reproduction band based on the audio signal level.

In addition, when changing the playback band, the switching control signal is used to change the playback band for only the sub channel in the case of dual broadcasting, without band limiting the main channel, and for both the L channel and R channel in the case of stereo broadcasting. . This distinction is controlled by the reproduction band control circuit 28. The dotted arrows in FIGS. 2 and 3 indicate sub-channel signal transmission lines.

As described above, according to the present invention, the levels of the video signal component included in the audio signal and the demodulated audio signal of the sub-channel are detected, and the passing frequency band of the audio signal is limited based on the detection results. Therefore, it is possible to always perform high-quality reproduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television audio multiplex broadcast receiver, FIG. 2 is a block diagram of a conventional television audio multiplex signal demodulator, and FIG. 3 is a block diagram of a television audio multiplex signal demodulator according to an embodiment of the present invention. ,
FIG. 4 is a frequency characteristic diagram of the variable passband filter of the same device, and FIG. 5 is a frequency characteristic diagram of the low-pass filter of the same device. 10... Demodulation circuit, 11... Matrix circuit,
12... Audio amplifier, 20... Pass band variable filter, 21... Low pass filter, 22... Audio signal detection circuit, 23... Input terminal, 24
...Video intermediate frequency amplification circuit, 25...Output terminal,
26... Phase modulation detection circuit, 27... Video signal component level detection circuit, 28... Reproduction band control circuit.

Claims (1)

[Claims] 1. A phase modulation detection circuit that extracts a phase modulated component in a video signal from the video intermediate frequency signal;
A video signal level detection circuit detects the output of the phase modulation detection circuit to obtain a first control signal proportional to the magnitude of the video signal, and a video signal level detection circuit extracts and detects low frequency components from the output of the sub-channel FM demodulator. and an audio level detection circuit that obtains a second control signal according to the magnitude of the audio signal, and controls the playback frequency band from the first and second control signals and a switching control signal that switches between dual broadcasting and stereo broadcasting. and a variable passband filter that varies the passband by the third control signal. , the main channel is not controlled, and in the case of stereo broadcasting, the playback band is changed for both channels, and when the video signal component in the audio multiplex signal is small, the playback band is expanded to the maximum, If there are many video signal components and few low frequency signals, lower the high frequency band of the playback band, and if there are many video signal components and low frequency signals, lower the high frequency band of the playback band. A television audio multiplex signal demodulator characterized by changing the playback band so as to lower the band to the lowest level.