JP2536790B2 - Magnetic reproducing device with line noise canceller - Google Patents

Description

The present invention relates to a magnetic reproducing apparatus such as a video tape recorder (hereinafter abbreviated as "VTR") having line noise cancellation, a video tape player (reproduction-only machine), and the like. It is about.

[Prior Art] A line noise canceller is generally known as a noise canceling means used in a VTR reproducing circuit. FIG. 2 shows an example of this line noise canceller, which is composed of a 1H delay element 1 such as a CCD, a first adder 2, a limiter 3, an attenuator 4 and a second adder 5. . 6 is an input terminal, which is reproduced by a video head (not shown)
The FM demodulated luminance signal is input, and the luminance signal is supplied to the 1H delay element 1, adders 2 and 5. In the 1H delay element 1, the luminance signal is delayed by one horizontal scanning period (hereinafter abbreviated as “1H”) and the phase thereof is inverted, so that the adder 2
Is input to In this adder 2, the 1H-preceding luminance signal (phase is inverted) delayed by the 1H delay element 1 is added to the undelayed original luminance signal, but is added to the phase-inverted luminance signal. This adder 2
Acts as a subtractor.

Since it can be considered that the luminance signal has a correlation with the luminance signal of 1H before, a noise component having no correlation is obtained at the output of the adder 2. The minute level signal that can be regarded as this noise component is taken out by the limiter 3, the level is attenuated to 1/2 by the attenuator 4, and the phase is inverted. This attenuated minute level signal is input to the adder 5,
Substantially subtracted from the original luminance signal, a minute level signal which can be regarded as a noise component is removed from the original luminance signal and output from the output terminal 7 to the next stage.

[Problems to be Solved by the Invention] By the way, in the above line noise canceller, not only the noise component is canceled, but also a minute level signal component (detail signal) is subtracted to some extent, and the level becomes small.

Further, in the case of a luminance signal having exactly the same correlation as the luminance signal of 1H before, the level is not attenuated, but when the correlation is deviated, the level is reduced by the amount deviated.

A case where this correlation is exactly the same and a case where this correlation is out of order will be described with reference to FIG. 3 and FIG. A to e in FIG.
Shows the case of exactly the same correlation, where a is the original signal and b is 1H.
The previous signal. These have the same phase relationship. c shows the output of the adder 2, which is at 0 level. d is the output of the attenuator 4, which is also at 0 level. e is the output of the adder 5, and the same signal as the original signal shown in a is obtained. In FIG. 3, a1 to e1 are the case where the phase of the signal 1H before is advanced by 90 ° with respect to the original signal, and the signal and the signal 1H before are signals of a minute level that are not limited by the limiter 3. Suppose there is. a1 is the original signal, represented by sin θ, b1 is the signal 1H before, s
It is represented by in (θ + π / 2), that is, sin (θ + π / 2) = cos θ. c1 shows the output of the adder 2, and a1−b1 =
sin θ−cos θ, and according to the composition formula, Becomes d1 is the output of the attenuator 4 and has the level shown in c1.
1/2, ie It has become. e1 is the output of the adder 5, And from the composition formula It is represented by.

As described above, the level of the original signal a1 decreases by 30% in the output signal e1 and the phase advances by 45 °.

In general, a small signal has less line-to-line correlation than a large-amplitude signal. If it is a large amplitude signal, it cannot be recognized as a screen if there is no correlation for each line, but if it is a small signal, it can be recognized as a screen even if there is no correlation. As a minute signal, for example, in the case of unevenness of human skin, there is no correlation. Fourth
In the figure, a2 to e2 are cases where there is no correlation between the original signal and the signal 1H before, a2 is a convex original signal, and b2 is a flat signal 1H before. The original signal and the signal before 1H are signals of small amplitudes whose amplitude is not limited by the limiter 3. c2 shows the output of the adder 2, which is the same convex signal as the original signal. d2 is the output of the attenuator 4, which is a signal having an amplitude half that of the original signal. e2 is the output of the adder 5, which is a signal having an amplitude half that of the original signal shown in a2.

As described above, the line noise canceller has less noise, but on the other hand, the level of the detail signal is reduced to some extent, and when the correlation with the luminance signal of 1H before is deviated, the level is reduced accordingly. .

On the other hand, recently, high-grade tapes having better performance than normal tapes have been used as video tapes.
This high-grade tape provides a high-level reproduction signal and has less noise than a normal tape.

The present invention provides a magnetic reproducing apparatus in which the line noise canceller does not automatically operate by prioritizing the reproducibility of details when using a video tape or the like with less noise such as a high-grade tape. It is intended.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a reproduction FM is used.
In the luminance signal, the signal level does not change depending on the content of the video signal, for example, a means for detecting a reproduction FM signal level for sample-holding the level of the horizontal synchronization signal is provided, and the reproduction level detected by the means is higher than a predetermined level. The line noise canceller is configured not to operate when the value becomes high.

[Operation] In the magnetic reproducing apparatus having the line noise canceller of the present invention configured as described above, when the high-grade tape is used, the reproduction level detected by the means for detecting the level of the reproduced video signal is higher than the predetermined level. Becomes higher, and the line noise canceller does not work.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing an outline of a main part of a VTR reproduction system. In FIG. 1, reference numeral 8 is a video tape, and a video signal reproduced by a video head 9 from the tape is amplified by a reproduction preamplifier 10 and supplied to a reproduction level detector 11, HPF 12 and LPF 13. The reproduction level detector samples and holds the level of the video signal, for example, the horizontal synchronizing signal, and detects the level of the video signal as a direct current level. The detected DC level is input to the comparator 14 and compared with the reference voltage from the DC voltage source 15. This reference voltage is set to a value higher than the recording / reproducing level when a standard tape is used as the video tape 8. When the DC level is higher than the reference voltage, the switch 16 described later is opened, and when it is low, the switch is closed.

A luminance signal is extracted from the video signal in the HPF 12, the luminance signal is subjected to FM demodulation and the like in the luminance signal processing circuit 17, further de-emphasized in the main de-emphasis 18 and supplied to the line noise canceller 19. This line noise canceller 19 has the same 1H delay element 1, adder 2, limiter 3 and
The attenuator 4 and the adder 5 etc.
The switch 16 is provided between the switch 16 and the adder 5. When the switch 16 is closed, the signal from the attenuator 4 is supplied to the adder 5 to activate the line noise canceller 19, but when the switch 16 is opened, the adder from the attenuator 4 is opened. The signal to be supplied to 5 is cut off, and the line noise canceller 19 is deactivated.

The luminance signal that has passed through the line noise canceller 19 from the main de-emphasis 18 (without passing through the line noise canceller when the line noise canceller 19 is not operating) is supplied to the noise canceller 20. As is well known, this noise canceller separates high-frequency components in the reproduced luminance signal where noise is likely to be concentrated by a filter, further extracts low-level signal components by a slicing circuit, and converts these high-frequency and low-level signals into noise. It is configured to be considered and subtracted from the original luminance signal. The luminance signal that has passed through the noise canceller 20 is supplied to the adder 21.

The LPF 13 extracts only the color signals that have been low-frequency converted from the video signal from the reproduction preamplifier 10 and supplies them to the color signal processing circuit 22. In the color signal processing circuit 22, the low-frequency converted color signal is converted into a sub-carrier band color signal.

The color signal from the color signal processing circuit 22 and the luminance signal from the noise canceller 20 are added by the adder 21 and supplied to a CRT (not shown) or the like via an output terminal 23 to reproduce a color image.

In the above VTR, when a normal tape is used as the video tape 8, the DC level from the reproduction level detector 11 is lower than the reference voltage from the DC voltage source 15, so that the switch 16 is closed. Therefore, the line noise canceller 19 is in the operating state. On the contrary, when a high-grade tape is used, the above-mentioned DC level from the reproduction level detector 11 is higher than the reference voltage from the DC voltage source 15, and therefore the switch 16 is opened, so that the line noise canceller is opened. 19 goes inactive.

As described above, the present invention delays the luminance signal of the reproduced video signal by one horizontal scanning period,
The delayed luminance signal and the undelayed original luminance signal are subtracted by a subtractor, and only a minute level signal that can be regarded as a noise component is taken out by the limiter from the subtracted signal, and this minute level signal is extracted as described above. A magnetic reproducing device equipped with a line noise canceller that substantially cancels noise components by subtracting from the luminance signal, and in the reproducing FM luminance signal, the signal level does not vary depending on the content of the video signal, for example, the level of the horizontal synchronizing signal. Since the line noise canceller is provided with a means for detecting the reproduced FM signal level such as sample and hold, and the line noise canceller does not operate when the reproduced level detected by the means becomes higher than a predetermined level, When using a video tape with low noise such as tape, priority is given to detail reproducibility. So, it is possible to automatically line noise canceller inoperative.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention,
This figure shows an outline of the main part of the VTR playback system. FIG. 2 is a block diagram showing the configuration of a conventional line noise canceller, and FIGS. 3 and 4 are waveform diagrams for explaining the operation of the one shown in FIG. 1: 1H delay element, 2: adder, 3: limiter, 4: attenuator,
5: Adder, 8: Video tape, 9: Video head, 10: Playback preamplifier, 11: Playback level detector, 14: Comparator, 15: DC voltage source, 16: Switch, 19: Line noise canceller.

Claims (1)

(57) [Claims] 1. A reproduced luminance signal after FM demodulation is delayed by one horizontal scanning period, and the delayed luminance signal and the original luminance signal which have not been delayed are subtracted by a subtractor, and the subtracted difference signal. A magnetic reproducing apparatus equipped with a line noise canceller that extracts only a minute level signal that can be regarded as a noise component by a limiter, subtracts the minute level signal from the luminance signal, and substantially cancels the noise component. In the FM luminance signal, the signal level does not fluctuate depending on the contents of the video signal, for example, a means for detecting a reproduction FM signal level for sampling and holding the level of the horizontal synchronizing signal is provided, and the reproduction FM signal level detected by the means is The line noise canceller is configured so that the line noise canceller does not operate when the level becomes higher than a predetermined level. Magnetic reproducing apparatus having a canceller.