JPH0832014B2 - Video signal processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is suitable for application when a signal from a VTR (magnetic recording / reproducing device) is subjected to special reproduction such as slow reproduction or still reproduction on a monitor receiver. The present invention relates to a signal processing circuit.

[Outline of Invention]

The present invention detects a missing period of a video signal in a special reproduction state such as slow or still reproduction of a VTR, and inserts a pulse signal from a pulse generating means in the missing period of the video signal, thereby eliminating the missing period. The buzz sound generated by the noise signal is avoided, and the black sun phenomenon of the screen is prevented.

[Prior Art] When a video signal is reproduced using a rotary magnetic head device from a magnetic tape in which a video signal is recorded in a direction oblique to the traveling direction of the magnetic tape, the traveling of the magnetic tape is stopped in still reproduction. In the slow or picture reproduction, the tape speed is slower or faster than that at the time of recording, that is, in the special reproduction state as described above, the magnetic tape is made different from the speed at recording.

Then, the reproduction signal from the above-mentioned VTR is modulated by, for example, a carrier signal of 2 channels and input from the antenna terminal of the television receiver (monitor receiver), or the reproduction signal before modulation is changed to the video signal of the monitor receiver. By supplying them directly to the input terminal (of course, the audio signal is the input terminal for the audio signal), these monitor receivers allow not only normal reproduced images but also special reproduced images such as slow and still images to be viewed. ing.

FIG. 3 shows an example of the connection relationship of such a VTR and a part of the monitor receiver. Briefly explaining this, (1) is a VTR, (2) is its rotating magnetic head,
(3) is a reproduction processing circuit for the projection signal from the magnetic head,
(4) is a voice magnetic head, (15) is a voice signal processing circuit, and (6) and (7) are their output terminals. Reference numeral (8) is a modulation circuit which modulates the above-mentioned signal into a television signal of 2 channels, for example. (9) is its output terminal. The audio signal output system has a miute switch (10) which is switched to the position shown by the solid line during normal reproduction and to the position shown by the dotted line during other special reproduction so that no sound is output to the outside. .

(11) is a monitor receiver, (12) is its antenna input terminal, and (13) is a high-frequency system connected to the next stage.
AGC circuit, (14) next stage demodulator circuit, (15) video signal input terminal, (16) select video signal from this input terminal (15) or demodulation circuit (14) A switch for switching, (17) is an AGC circuit connected to the next stage of this switch (16), (18) is a separation circuit for the luminance signal S _Y and the color signal S _C , and the luminance signal S _Y is a clamp circuit. It is supplied to the sync separation circuit (20) through (19) to obtain the horizontal sync signal S _H and the vertical sync signal S _V, and the horizontal sync signal S _H is fed to the AGC circuit (1
It is designed to be returned to 7).

The high frequency output terminal (9) of the VTR (1) is connected to the antenna terminal (12) of the monitor receiver (11), or
Video output terminal (6) of VTR (1) is monitor receiver (11)
It is used by being connected to the video signal input terminal (15) of.

[Problems to be Solved by the Present Invention]

In such a structure, when special reproduction is performed in the above-mentioned VTR (1), the magnetic head (2) of the rotating magnetic head device scans the recording locus of the video signal on the magnetic tape diagonally across the recording locus. In particular, when a guard band is provided between recording tracks, when the magnetic head (2) crosses this guard band, the video signal is lost and noise occurs. ,
It is biased toward the white level side of the video signal. This is to give the amplifier circuit for the signal reproduced from the rotary magnetic head a reproduction characteristic of raising the white level side of the video signal to its black level side (sync chip side) in order to improve the image quality. It is because there is.

When such a video signal is supplied to the modulation circuit (8) of the VTR (1) and is modulated, the output thereof has a carrier level in the noise portion, that is, in the video signal missing period T, as shown in FIG. 4A. It will be small. When such a modulated signal is input to the antenna of the monitor receiver (11), the high frequency system AGC circuit (13) has a predetermined gain in the video signal period as shown in FIG. 4B. In the video signal dropout period T, a sufficiently high gain is obtained in an attempt to increase the low level signal. And this missing period T
Immediately after the end of, that is, immediately after eliminating the noise, the high frequency AGC circuit (13) is at full gain, and when the modulated video signal is input to the high frequency AGC circuit (13), it becomes The carried audio signal carrier itself is saturated during this full gain period, that is, the audio signal carrier is crushed, which causes a problem that a bass sound is generated.

In addition, even if the video signal of the VTR (1) is directly input (without modulation) from the video input terminal (15) of the monitor receiver (11) for monitoring, the following problems Occurs.

That is, in the AGC circuit (17) connected after the demodulation circuit (14) in the monitor receiver (11), peak A is generally generated.
Since the GC is applied, as described above, when the noise signal is biased toward the white level side of the video signal in the video signal missing period T, the black level component as a whole disappears in this period, and AGC circuit (1
7) works to suppress the white level component, which causes a problem that the entire screen is blackened (the entire screen becomes dark).

Further, due to the deviation of the noise signal toward the white level side, the level of the sync chip within this period T also changes, so that the separation of the sync signal is also uncertain, and there is a problem that sync disturbance is likely to occur. .

 The present invention solves these problems.

[Means for solving problems]

According to the present invention, when a magnetic tape having a video signal recorded in a direction oblique to the running direction of the tape is reproduced by using the rotary head (2) at a tape speed different from that at the time of recording, the video signal is predetermined. A clamp circuit (24) that clamps to the voltage value, a detection means (21) that detects the missing period of the video signal, and a pulse signal (P) that is synchronized with the horizontal sync signal ( _SH ) of the video signal by the AFC circuit. Pulse signal generating means (22) and a DC voltage source (26) of a predetermined level
Is connected to the clamp circuit (24) and switches the clamp circuit output and the DC voltage source output by the logical product output of the output (S _C ) of the missing period detection means (21) and the pulse signal (P). A pulse signal (P) in the horizontal synchronizing signal ( _SH ) period in the small level signal reproduced in the video signal missing period (T).
And a means (23) for inserting a DC signal of a predetermined level based on the video signal processing circuit.

[Action]

As a result, the pulse signal, which is the black level component of the video signal, is inserted within the missing period T of the video signal.
As a result, the circuit (13) or (17) is not operated at the so-called full gain even within the missing period T, and is always operated at an almost appropriate gain, so that the above-mentioned buzz sound is generated, It is possible to avoid the occurrence of blackening of the screen.

〔Example〕

An example of the video signal processing circuit according to the present invention will be described below with reference to FIG. 1. (2) and (3) are the above-described rotary magnetic head and video signal reproduction processing circuit.

The video signal (including the luminance signal, the chrominance signal and the sync signal) separated in the reproduction processing circuit (3) is supplied to the clamp circuit (24), while the horizontal signal separated in the reproduction processing circuit (3). sync signal S _H is also supplied to the clamp circuit (24), Shinkuchitsupu video signal described above is herein are clamped to a predetermined DC level.

A horizontal sync signal S _H mentioned above is supplied to the AFC circuit (22), the pulse signal P in synchronism with the horizontal synchronizing signal S _H in the reproduction processing circuit (3) wherein is obtained. The pulse signal P is the so-called flywheel effect of AFC circuit (22), also in the omission period T of the above-mentioned video signal, obtained with a period synchronized with the horizontal synchronizing signal S _H. Therefore, this AFC circuit (22) serves as the pulse signal generating means in the present invention.

Further, in the present invention, as described above, the detection means (21) for detecting the missing period T of the video signal is provided, which is generally provided with the dropout compensation circuit in the VTR. Similarly, the present invention has means for detecting the missing period of the video signal, and when the missing period is detected by this means, a signal of one horizontal period immediately before that is inserted and interpolated, so that the present invention Then, the means for detecting the missing period of the video signal in the dropout compensation circuit can be used.

However, in this case, since the dropout compensation circuit is generally provided for compensating the video signal in the period of 1H, that is, one horizontal period, the output from the detection means of the video signal missing period is also in the 1H period. Therefore, a switching switch (27) is provided in this example, and the time constant of the means (21) is 1H in the switching state of the switching switch (27) in the solid line and several H in the dotted line state. Controlled as. Then, the switch (27) is switched to the solid line side in the normal reproduction state and to the dotted line side in the special reproduction state.

The signal S _C from the detection means (21) for such a missing period T
And the pulse signal P from the above AFC circuit (22) are supplied to the AND circuit (25), and when both signals become "1", the switching circuit (23) is switched to the dotted line side.

The switching-circuit (23) are those in which the output signal S _a of from the clamp circuit (24) described above, adapted to supply to the output terminal (3a) by switching a DC voltage of the DC voltage source (26) , Is always in the switching position shown by the solid line. or,
The DC voltage of the DC power supply (26) is selected as the level of the sync tip of the video signal clamped by the clamp circuit (24).

With such a configuration, in the normal reproduction state, the magnetic head (2) of the rotary magnetic head device normally scans the video signal recording track on the magnetic tape, so that no signal is output from the missing period detecting means (21). The switching circuit (23) remains in the state shown by the solid line, so that a normal video signal is obtained at the output terminal (3a). In this case, the switch (27) is in the solid line switching state.

Next, in the special reproduction state described above, the magnetic head crosses the guard band on the magnetic tape, and a video signal dropout period T occurs. FIG. 2A shows the output signal S _a from the clamp circuit (24) in this case, and the period T is the above-mentioned missing period. The reproduction processing circuit (3) a horizontal synchronizing signal S _H obtained from but missing in the missing period T as shown in FIG. 2 B, since it is supplied to the AFC circuit (22), the AFC circuit (22 ) than, as shown in FIG. 2 D, synchronized with the horizontal synchronizing signal S _H, yet successive pulse signals P are obtained.

On the other hand, the missing period detection means (21) of the reproduction processing circuit (3)
More specifically, as shown in FIG. 2C, the signal S _C is obtained in the missing period T. For this trick play, switch (27)
Is in the dotted line switching state, the period of this signal S _C is several H, which corresponds to the missing period T.

Therefore, except during the video signal dropout period T, the switching circuit (23) is in the solid line switching position, and the dropout period T
In the inside, when the pulse signal P is on, that is, "1", an output is obtained from the AND circuit (25), so that the switching circuit (23) is switched to the dotted line position in synchronization with the pulse signal P. When switched to this dotted line position, the voltage of the DC power supply (26) is applied to the output terminal (3a), but this voltage is the same value as the sync tip level of the video signal obtained from the clamp circuit (24). Therefore, according to the present invention, during the missing period T, a pulse which is synchronized with the pulse signal P, that is, the horizontal synchronizing signal S _H , and whose level is the same as the sync tip of the video signal is selected. As a result, the signal S _e shown in FIG. _2E is obtained at the output terminal (3a).

By thus inserting the pulse signal also in the video signal dropout period T, the black level component is mixed in the signal in this period, and as described above with reference to FIG. Since the component does not decrease and there is no white level component, the AG on the monitor receiver side
The C circuit also operates almost as usual, and problems such as a buzzing noise or a blackout of the screen are solved.

Moreover, the level of the pulse signal inserted into the missing period T is selected equal to the sync multichip level of the video signal obtained by the clamp circuit (24), as further pulse signal is synchronized with the horizontal synchronizing signal S _H Since it is done, the synchronization disorder can be avoided.

〔The invention's effect〕

According to the present invention described above, in the special reproduction state of the VTR, it is possible to avoid the occurrence of the buzz sound as described at the beginning, and the screen becomes a black sunken state, which causes a problem of synchronization disturbance. It has a feature that can avoid.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an example of a video signal processing circuit according to the present invention, FIG. 2 is a waveform diagram explaining its operation, FIG. 3 is a connection diagram of a conventional VTR and a monitor receiver, and FIG. It is a wave form diagram explaining this operation. (3) is a video signal reproduction processing circuit, (21) is a video signal reproduction processing circuit, and (22) is an AFC circuit.

Claims (1)

[Claims] 1. When reproducing a magnetic tape on which a video signal is recorded in a direction oblique to the running direction of the tape using a rotary head at a tape speed different from that at the time of recording, the video signal is supplied with a predetermined voltage. A clamp circuit that clamps to a value, a detection unit that detects the missing period of the video signal, a pulse signal generation unit that generates a pulse signal that is synchronized with the horizontal synchronization signal of the video signal by the AFC circuit, and a DC voltage of a predetermined level. Source and the clamp circuit, and switches between the clamp circuit output and the DC voltage source output by a logical product output of the output of the detection means in the missing period and the pulse signal, and within the missing period of the video signal. Means for inserting a direct current signal of a predetermined level based on the pulse signal into the horizontal synchronizing signal period in the reproduced small level signal. No. processing circuit.