JPS62277867A - Video signal recording system - Google Patents

Abstract

PURPOSE:To suppress the generation of overmodulation by lowering a white clip level at an over-record (over-REC) in comparison with as conventional recording. CONSTITUTION:The white clip level of a white clip section 21 is set to a level P at normal recording and since the level P is set comparatively higher, almost no white clip is applied to an emphasis recording video signal 200. On the other hand, since an over REC signal 50 is inputted to a level switch seciton 22 at the over REC state, a white clip level of the white clip section 21 is Q. Since the white clip level Q is set lower than the white clip level P, the highest voltage inlcuded in a recording video signal 300 modulated by a frequency modulation circuit 3 is lwoer than that at the normal recording. Thus, the generation of ver-modulation at the over REC is suppressed.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention is directed to a video signal that is used when overwriting a video signal on a portion that has already been recorded on a video tape recorder. Regarding the recording method.

(Prior Art) When recording a new video signal on a tape that has already been recorded, a so-called overlapping process is performed in which the new video signal is recorded on top of the already recorded video signal from the erasing head to the writing start point. A writing part occurs.

In this overwritten portion, the low frequency conversion color signal component already recorded on the tape cannot be completely erased at the normal recorded video signal level.

Therefore, when this part is played back, the already recorded color signal and the newly recorded color signal are reproduced at the same time, causing so-called color haze noise on the playback screen, making the screen blurry. There was a drawback. Therefore, an over-record (hereinafter referred to as over-REC) VJ operation is performed to temporarily increase the frequency modulated luminance signal level of the newly recorded video signal in the overwritten portion described above, which is performed on the overwritten portion of the video signal that has already been recorded on the tape. The new color signal components are recorded while completely erasing the existing color signal components, resulting in a clean overlapping screen.

However, when this over-REC is performed, there is a drawback that so-called over-modulation is likely to occur.

(Problem to be solved by the invention) Tape and head systems are usually standardized and designed so that when a video signal is recorded on tape at the optimum current (normal recording level), the maximum envelope output can be obtained during playback. Designed. However, at over R60, a current approximately 1.5 times the optimum current value for the head at maximum is supplied to increase the level of the recording frequency modulated video signal. 6th
The figure shows the recording/reproducing output level with respect to the recording current of each frequency f1 to f4 of the recorded video signal, where A indicates the optimum current point during normal recording, and A indicates the maximum current point at an over REC value. FIG. 7 is a rewritten version of FIG. 6, and is a diagram showing the recording/reproducing output level of each frequency f1 to f3 of the video signal for each case of optimum current A and over REC.

Compared to when the optimum current is set, the recording/playback output level of especially high frequency signal components becomes lower during the over-REC time.
There is a drawback that a black-out phenomenon (overmodulation) tends to occur when the transition from black to white occurs on the so-called playback screen.

Therefore, the present invention eliminates the above-mentioned drawbacks and
An object of the present invention is to provide a video signal recording method that suppresses the occurrence of overmodulation during FC.

[Structure of the Invention (Means for Solving Problems)] The video signal recording system of the present invention is provided with a white clip level variable means for changing the white clip level of the recording signal in the video signal recording system, and when over R60, A configuration is adopted in which control is performed to lower the white clip level compared to when recording.

(Function) In the video signal recording method of the present invention, by lowering the white clip level of the recorded video signal at the time of over R60, and by lowering the highest frequency included in the frequency modulated video signal to be recorded, at the time of over RFC. The drop in the level of the reproduced frequency modulated video signal can be made smaller than that during normal recording, and overmodulation during over-RFC can be made less likely to occur.

(Example) An example of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing an embodiment of a video signal recording/reproducing circuit to which the present invention is applied.

1 is an emphasis circuit that emphasizes the high frequency component of the recorded video signal 100; 2 is a white clip level variable circuit that changes the white clip level of the emphasized recorded video signal; 3 is a frequency modulation circuit that frequency modulates the recorded video signal; Reference numeral 4 denotes a recording/playback head that records a frequency-modulated recording video signal on the tape 5 and also plays back the frequency-modulated video signal recorded on the tape 5; 6 a playback frequency-modulated video that is played back from the recording/playback head 4; A video signal reproducing circuit processes the signal, 7 is an FM demodulation circuit that demodulates the reproduced frequency modulated video signal, and 8 is a de-emphasis circuit that suppresses high-frequency components of the demodulated reproduced video signal.

FIG. 2 is a block diagram showing a detailed configuration example of the white clip level variable circuit 2 shown in FIG. 1. The white clip level variable circuit 2 includes a white clip section 21 that determines the white clip level of the emphasized recording video signal 200, and a level switch section 22 that determines to what value the white clip level of the white grip section 21 is set. In addition, the level switch section 2
2 assumes that the switch operation is performed by the over REC signal 5° generated during the over RFC operation.

Next, the operation of this embodiment will be explained. Recorded video signal 1
00 becomes an emphasis recording video signal 200 whose high frequency components are emphasized by the emphasis circuit 1. This recorded video signal 200 becomes a recorded video signal 300 whose white clip level is adjusted by the white clip level variable circuit 2.

This recorded video signal 300 is frequency modulated by the frequency modulation circuit 3 to become a frequency modulated video signal 400, which is recorded on the tape 5 by the recording/reproducing head 4. Further, the frequency modulated video signal recorded on the tape 5 is played back by the recording/playback head 4, and the video signal playback circuit 6
The amplified reproduction frequency modulated video signal 500 is amplified to a predetermined level by the FM demodulation circuit 7. The demodulated playback video signal is converted into a playback video signal 800 in which high-frequency components are suppressed by the de-emphasis circuit 8.
is output.

Here, the operation of the white clip level variable circuit 2 will be described in detail. First, during normal recording when the over RFC signal 50 is not input to the level switch section 22,
The white clip level of the white clip section 21 is set to level P. At this level P, the white clip level of the emphasis recorded video signal 200 shown in FIG. 3 (A>) is suppressed to the white clip level P shown in FIG. 3 (B). However, this level P is relatively high. Since it is set, emphasis recording video signal 20
0 has almost no white clip.

FIG. 4(A) shows the signal level of the recorded video signal 300 frequency modulated by the frequency modulation circuit 3 and the frequency modulation signal 40.
This is a diagram showing the relationship with frequencies included in 0. That is,
Frequency modulation is performed such that the higher the signal level of the recorded video signal 300, the higher the frequency of the frequency modulated video signal 400. Therefore, the highest frequency f3 of the frequency modulated video signal 400 at the white clip level P is near the white clip level. White clip level P like this
Reproduced frequency modulated video signal 500 output from the video signal reproducing circuit 6 when reproducing the recorded frequency modulated video signal 400 during normal recording recorded with white clipping.
has a frequency characteristic as shown in FIG. 4(B).

Here, when over R20, over RFC signal 50
is input to the level switch section 22, so the white clip level of the white clip section 21 becomes Q. For this reason, the white clip portion 21 is used as shown in FIG. 3(B).
A white clip is applied to the emphasis recorded video signal 200 as shown in FIG. This white clip level Q
is set lower than the white clip level P, so the maximum voltage included in the recorded video signal 300 modulated by the frequency modulation circuit 3 during over-RFC is lower than that during normal recording. Therefore, the highest frequency included in the frequency modulated video signal output from the frequency modulation circuit 3 is smaller than f3 shown in FIG. When a frequency modulated video signal recorded in 1 is reproduced, the level difference in the frequency characteristics of the reproduced frequency modulated video signal output from the video signal reproducing circuit 6 is smaller than that during normal recording.

FIG. 5 is a circuit diagram showing a specific example of the white clip level variable circuit 2 shown in FIG. When the over REC signal 50 is not input, the transistor TR is turned off, a bias is applied to the base of the transistor TR1 via the resistors R1 and R2, and the white clip level by the transistor TR1 is set to P. Next, when the over RFC signal 50 is input, the transistor TR2 is turned on, and the base bias voltage of the transistor TR1 is determined by the resistors R1, R2 and the resistor R3, and the white clip level by the one transistor TR1 is set to Q. When the emphasis recording video signal 200 of a level higher than the set white clip level is applied to its emitter, the transistor TR1 performs an operation of making the voltage higher than the level a constant voltage.

According to this embodiment, when over R20, the frequency modulation circuit 3
This can be done by suppressing the level of the highest frequency included in the frequency modulated video signal output from the For this reason, over R
It is possible to reduce the level drop in the high frequency component of the reproduction frequency modulation signal reproduced from the recording/playback head 4 during FC compared to normal recording, suppress the occurrence of overmodulation, and produce a clear reproduced image. can be obtained.

[Effects of the Invention] As described above, according to the video signal recording method of the present invention,
By lowering the white clip level of the recorded video signal during over RFC compared to that during normal recording,
It is possible to suppress the occurrence of overmodulation when over R60 occurs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a video signal recording/reproducing system to which the present invention is applied; FIG. 2 is a block diagram showing a detailed example of the white clip level variable circuit shown in FIG. 1; Fig. 3 is a waveform diagram showing an example of the operation of the white clip level variable circuit, Fig. 4 is a diagram showing frequency modulation operation waveforms during normal recording and an example of frequency characteristics of a frequency modulated reproduced video signal, and Fig. 5 is a diagram showing an example of the frequency modulation operation waveform during normal recording. Figure 2 is a circuit diagram showing a specific example of the white clip level variable circuit shown in Figure 6. Figure 6 is a characteristic diagram showing the relationship between the recording current supplied to the recording head and the recording/reproducing output level of the video signal. FIG. 7 is a characteristic diagram showing the relationship between the frequency of the recording frequency modulated video signal and the recording/reproducing output level of the video signal. 1... Emphasis circuit 2... White clip level variable circuit 3... Frequency modulation circuit 6... Video signal reproduction circuit 7... FM demodulation circuit 8... Dien 7792 circuit 21... White Clip part 22...Level switch department agent Patent attorney Nori Chika Ken Shu Canshu Hiroshi Uji Figure 1 Figure 2 (A) (B) Figure 4

Claims (1)

[Claims] A video signal recording system of a video tape recorder is provided with a white clip level variable means for changing the white clip level of the recorded video signal, and the level of the luminance signal component of the recorded video signal is higher than normal and recorded on the tape. A video signal recording method characterized in that, when performing a video signal recording method, the white clip level of the luminance signal component is controlled to be lower than normal.