JPS62287468A - Mute signal detecting method by no-signal noise - Google Patents

Abstract

PURPOSE:To make mute signal detection by no-signal noise possible by selecting high level band of no-signal noise, detecting high level noise in the band and cutting off output of a demodulator in this state. CONSTITUTION:A band pass filter 84 is a filter that takes out band of 5MHz-6 MHz, and a comparator 85 is a circuit that compares the level of high frequency noise in the band with the reference level and takes out high signal level. An integrator 86 is a CR circuit to smoothen high frequency noise of high signal level, and reset by a noise presence signal and charged after a fixed time by a no-noise signal. Accordingly, even when intermittent high frequency noise of above reference level enters input of the integrator 86, continuous signals are outputted in the output, and the continuous signals are outputted extended for a fixed time determined by a time constant.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention <Industrial Application Field> The present invention is a method for removing noise that occurs when there is no video playback output in the playback system of a VTR or electronic still camera. This invention relates to a mute signal detection method using signal noise.

<Prior art and its problems> In VTRs and electronic still cameras, the reproduction system for captured images extracts the FM modulated video No. 13 recorded on the recording medium using a magnetic head, and then demodulates it. Images are played back on a television receiver. Therefore, in a state where the video signal is not yet reproduced and no image is reproduced, the video signal is in a no-signal state, so noise appears in the image and the image quality is extremely poor. In particular, demodulation is FM
Therefore, the noise output from the demodulator when there is no signal is at a high level, resulting in an extremely unsightly screen.

For this reason, conventionally, as shown in FIG. 7, an envelope detector 4 for the modulated video signal (FM signal) is inserted after the preamplifier 2 connected to the magnetic head 1 and before the demodulator 3. A signal presence state is detected, and upon this detection, a switch 5 provided after the demodulator 3 is controlled to be turned on to cut off and mute the reproduced output of no-signal noise. That is, muting is canceled by detecting a signal presence state of a video signal, and muting is applied when there is no signal presence state.

In addition, in this method, as shown in FIG.
In models in which the preamplifier 2 and envelope detector 4 are integrated into one unit, and the demodulator RJR 3 and switch 5 are integrated into one unit, when connecting one unit to another unit, not only the video signal is played back, but also the signal status is determined. The number of connection lines increases as it is also necessary to convey information. This makes the construction of the connector and its connection complicated, even if the number of wires is only increased.

The present invention takes a different perspective from the above and adopts a novel method of detecting noise when there is no signal in the reproduced video signal instead of when there is a signal, and the present invention is different from the above-mentioned unitized separate structure. Another object of the present invention is to provide a method for detecting a mute signal using no-signal noise, which eliminates disadvantages such as an increase in the number of connection lines.

<Means for Solving the Problems> The present invention achieves the above-mentioned object by demodulating an FM modulated video signal recorded on a recording medium to obtain a video playback output. The demodulator selects a frequency band in the high range where the reproduced video signal component of the device is small and has a large difference from the noise output component when there is no signal, detects the signal level of the noise component in this band, and It is characterized by cutting off the output.

The present invention captures the phenomenon that the output signal component of an FM video demodulator exists up to about 5 MHz when there is a signal, as shown in FIG. This 5MHz~6MHz
We focus on the fact that the spectral characteristics are significantly different when there is a signal and when there is no signal around z, and we extract the level of no-signal noise in this band.

Function: Only the noise when there is no signal can be extracted reliably, so this noise can be used to control the switch and mute, making it possible to directly mute the noise.

<Example> The present invention will now be described in detail with reference to FIGS. 1 to 6. FIG. 1 shows a reproduction system, in which 1 is a magnetic head, 2 is a preamplifier, 3 is a demodulator, 6 is a de-emphasis circuit, 5 is a switch, and 7 is an amplifier. The output end of the de-emphasis circuit 6 is connected to the switch 5 as well as to a switch control circuit 8. This switch control circuit 8 is a circuit that detects only a high level of noise when there is no video signal and obtains a control output for opening the switch 5.

That is, the system detects the noise level when there is no signal and applies mute to cut out the noise. Specifically, the circuits are as illustrated in FIGS. 2 to 4.

In FIG. 2, the switch control circuit 8 connected to the output terminal of the de-emphasis circuit 6 includes a bandpass filter 81.
, an envelope detector 82, and a comparator 83. As shown in FIG.
Since the difference between the presence of a signal and the noise of a signal in the band from MHz to 6MIIZ is clearly expressed on the spectrum, this filter is used to select that band. The envelope detector 82 extracts the envelope of the high frequency noise generated by the band pass filter 81. Further, the comparator 83 is a circuit that compares the noise level extracted as an envelope with a reference level at which muting should be applied, and outputs an open signal for the switch 5 in the case of high level noise.

In FIG. 3, the switch control circuit 8 subsequent to the de-emphasis circuit 6 includes a bandpass filter 84, a comparator 85, and an integrator 86. Bandpass filter 84
is a filter that extracts the above-mentioned band from 5 MHz to 6 M+lz, a comparator 85 is a circuit that compares the level of high frequency noise in this band with a reference level and extracts a high signal level, and an integrator 86 is a circuit that extracts a high signal level above the reference level. This is a CR circuit for smoothing high frequency noise, and is reset when a noise signal is present (rising edge), and is connected for a certain period of time to be charged when there is no noise signal (falling edge).

Therefore, even if intermittent high-frequency noise above the reference level enters the human power of the integrator 86, a continuous signal will be output, and a continuous signal will be output for a certain period of time determined by the time constant. . As a result, switch 5 becomes
It is left open and muted for a certain period of time from the time the high-level noise occurs until it ends, and then for a certain period of time.

In FIG. 4, the switch control circuit 8 includes a bypass filter 875, a frequency sensitive discriminator 88, and an integrator 89. This bypass filter 87 passes a frequency band of 5 M)lz or higher, and the frequency sensitive discriminator 88 is a circuit in which the signal level for discrimination changes depending on the frequency.
Since high signal levels are discriminated as the frequency reaches higher frequencies with Hz as the boundary, the bypass filter 87 passes the frequency band of 5 MHz or more, and the frequency sensitive discriminator 88 passes the frequency band of 5Mflz to 6MIIz. In addition to the low level signals in the 6MH7 and above frequency bands, high level signals can also be removed. As the actual circuit of this frequency sensitive discriminator 88, a television synchronization separation circuit can be applied. The frequency characteristics of this synchronous separation circuit are as shown in FIG.
Since the human power signal level gradually increases after the Z plane, it cannot be compared unless it is above this level, and in the end it is 5MHz ~
Only noise at a certain level in the 6Ml1z band is discriminated. The integrator 89, like the integrator 86 described above, obtains a continuous switch control signal.

In addition, the bypass filter 87 in FIG. 4 may be replaced with a bandpass filter, and in this case, 5Ml!
Since the band from z to 6 MHz is extracted, the frequency sensitive discriminator 88 may have the same function as a simple comparator.

In FIGS. 2 to 4 described above, the switch control circuit 8 is provided after the de-emphasis circuit 6, but it may be connected before the de-emphasis circuit 6 and after the demodulator 3. In this case, since the target is a high frequency noise level that cannot be de-emphasized, the comparison level of the switch control circuit 8 must also take this into account.

<Effects of the Invention> As explained above, according to the present invention, a high level band of no-signal noise is selected, high level noise in this band is detected, and the output of the demodulator is cut off in this state. As a result, a completely new type of noise removal can be performed in which noise is muted, and the connector structure can be simplified for models that are divided into units.

[Brief explanation of the drawing]

1 to 4 show the structure for one embodiment of the present invention, FIG. 1 is a circuit block diagram, FIGS. 2 to 4 are concrete block diagrams showing three examples, and FIG. is a characteristic diagram showing the spectrum of video signal and no-signal noise, No. 6
The figure is a characteristic diagram of a synchronous separation circuit, and FIG. 7 is a block diagram of a conventional divided type. In the figure, 3 is a demodulator, 5 is a switch, 8 is a switch control circuit, old, 84 is a band pass filter, 82 is an envelope detection circuit, 83, 85. C is a comparator, 86 and 89 are integrators, 88 is a frequency sensitive discriminator, and T is a transistor.

Claims (1)

[Claims] In a video playback system that demodulates an FM modulated video signal recorded on a recording medium to obtain a video playback output, the noise output component in the high frequency range where the playback video signal component of the demodulator is small when there is a signal and when there is no signal. 1. A mute signal detection method using no-signal noise, characterized in that a frequency band in which the difference between the noise component and the noise component is large is selected, the signal level of a noise component in this band is detected, and the output of the demodulator is cut off.