JPH02166667A - Recording and reproducing method - Google Patents

Abstract

PURPOSE:To further increase the increased amt. of a lower side wave component of a modulation signal in level without altering a noise level at the time of reproducing by modulating a video signal in frequency, removing a part of its upper side wave component and recording a signal obtained by strengthening further a lower side wave component to a recording medium. CONSTITUTION:The video signal is modulated in frequency by an FM modulation circuit 2, and a part of the upper side wave component of this modulated signal is removed by a filter circuit 3, and then the signal obtained with a filter circuit 4 by strengthening further the lower side wave component of the removed signal in its upper side wave component is connected by a changeover switch 6 to a side R to be recorded to the recording medium 13. By this method, the increased amt. of the level of the lower side wave component of the modulation signal can further be increased without altering the noise level at the time of reproducing.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording and reproducing method for video tape recorders and the like.

It is known that in conventional video tape recorders, the lower side wave component of an FM (frequency modulation) signal increases when it passes through a tape head system. Furthermore, it is well known that if the noise level is the same, the higher the level of the side wave component of the FM signal, the better the SN ratio (signal-to-noise ratio) will be.

Therefore, in Japanese Patent Application No. 62-248707, a part of the upper side wave component of the FM signal is removed to further increase the amount of increase in the lower side wave component of the modulated signal without changing the noise level during reproduction. The mechanism of this increase in the lower side wave component is clarified, for example, in 1988 Confucian Autumn National University C-16 and C-17.

Problems to be Solved by the Invention The method described above increases the amount of increase in the reproduced lower side wave component, but if the amount of increase in the lower side wave component further increases, the SN
Since the amount of improvement in the ratio can be increased, it is desired to further increase the lower side wave component.

Means for Solving the Problems In order to solve the above problems, the recording and reproducing method of the present invention includes:
A signal obtained by frequency modulating a video signal, removing a part of the upper side wave component of this modulated signal, and further enhancing the lower side wave component of the signal from which the upper side wave component has been removed is recorded on a recording medium. It is something to do.

Effect of the Invention With the above-described configuration, the present invention can further increase the amount of increase in the level of the lower side wave component of the modulated signal without changing the noise level during reproduction.

EXAMPLE Hereinafter, a recording and reproducing method according to an example of the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a recording and reproducing method in an embodiment of the present invention. The video signal is input to input terminal 1, and the FM
In the modulation circuit 2, for example, the frequency deviation range is 5.4 to 7.
It is converted into an FM signal of 0MHz. Next, a filter circuit 3 having filter characteristics as shown in FIG.
, the upper side wave component of the FM signal is attenuated, but the frequency corresponding to the white clip is passed through, so the carrier wave is not attenuated.The FM signal that has passed through the filter circuit 3 is as shown in Figure 3. The lower side wave component is enhanced in the next filter circuit 4 having filter characteristics. Figure 4 shows the carrier wave component J at the time of input. (6,45MHz) is the optimum recording current at that frequency and the first lower side wave component J, (1,
45M1(z) represents the J0 and J4 components of the output when the level is changed, where the horizontal axis is the ratio of J to Jo at the input, expressed in dB, and the vertical axis is the J at the output. The levels of and J are expressed in dB, and the output level when a single carrier signal is recorded is OdB. As shown in Fig. 4, by enhancing the lower side wave component with the filter circuit 4, the output level of the lower side wave component continues to increase, but in reality, the recording current of the lower side wave component becomes too large. If the output level of the carrier wave component is too high, the output level of the carrier wave component will drop.The output level of the carrier wave component will start to drop in this way at the level where the output level of the carrier wave component and the output level of the lower side wave component are equal (Figure 4). Therefore, the characteristics of the filter circuit 4 may be set so that the output level of the carrier wave component and the output level of the lower side wave component are equal. The FM signal that has passed through the filter circuit 4 is applied to a recording/reproduction changeover switch 6 via a recording amplifier 5. When the selector switch 6 is connected to the R side, the recording amplifier 5
The output signal is supplied as a recording current to the video head 11.12 via the rotary transformer 7.8, and the magnetic tape 13
recorded above. The video heads 11 , 12 are mounted on the rotating disk 10 and rotated at a predetermined speed by a motor (not shown) connected to the rotating shaft 9 .

On the other hand, the magnetic tape 13 is wound around the rotating disk 10 over 180 degrees, and is run at a predetermined speed in the direction of an arrow 14 by a magnetic tape feeding device comprising a well-known capstan, pinch rollers, etc. .

During reproduction, the signals reproduced by the magnetic heads 11 and 12 pass through the rotary disk 101 and the rotating shaft 9, and the changeover switch 6 is connected to the P side. A circuit 16 adjusts the magnitude of the lower side wave component. At this time, the magnitude of the noise also decreases according to the amount of attenuation of the lower side wave component. R
The output of the F equalizer circuit is such that the upper side wave component is attenuated by the filter circuit 17 and demodulated by the FM demodulator 18.
It is output from the output terminal 19.

Note that the FM modulation circuit 2 and the demodulation circuit 18 may include circuits commonly used in video tape recorders such as a pre-emphasis circuit (not shown) and a de-emphasis circuit (not shown).

Furthermore, the same applies even if the recording amplifier 5 includes an equalizer circuit (not shown) or the like.

Further, the filter circuit 3 and the filter circuit 4 may be realized by one filter.

Further, the order of the filter circuit 3 and the filter circuit 4 may be reversed.

FIG. 2 shows an example of the frequency characteristics of the filter circuit 3.
The figure shows an example of the frequency characteristics of the filter circuit 4.

FIG. 5 schematically shows an example of the frequency spectrum of the signals of each part in FIG. 1. 5(a) does not show the frequency spectrum of the output signal of the FM modulation circuit 2, and FIG.
In a), the frequency of the FM carrier wave (represented by Jo) is rc, and the frequency of the first lower side wave (represented by J4) is f.
. −f9, and the frequency of the first upper side wave (denoted by J.1) is f. +rp. That is, let fp be the frequency of the modulated wave (input video signal). Although only the first sideband is shown in FIG. 5(a), the following explanation holds true even when higher-order sidebands occur. FIG. 5(C) shows the spectrum of the output signal when the signal shown in FIG. 5(a) passes through the filter circuit 3 having the frequency characteristic shown in FIG. FIG. 5(e) shows the spectrum of the output signal when the signal shown in FIG. 5(C) passes through the filter circuit 4 having the frequency characteristic shown in FIG. 5(d).

FIG. 5(f) shows the frequency spectrum of the output signal from the reproduction amplifier 15 of the FM signal recorded and reproduced through the tape head system, and shows that the lower side wave component has increased. FIG. 5 (80 shows the frequency characteristics of the filter circuit 17, and FIG. 5(h) shows the frequency spectrum of the output signal when the reproduced FM signal passes through the RF equalizer circuit 16 and the filter circuit 17.

Note that although the frequency characteristics of the RF equalizer circuit 16 will be described here as being flat, in reality, it may have characteristics such as those shown as a cosine equalizer in, for example, Japan Broadcasting Corporation's 13 rVTR Technology. Fifth
Figure (i) shows the output signal when the signal shown in Figure 5 (b) passes through a limiter circuit (not shown) such as that used in a general FM demodulator in the FM demodulation circuit 1B. The upper side wave component is restored by passing through this limiter circuit, which shows the spectrum of .

In FIG. 5(f), <(To), 6), an example of the level of the conventional frequency spectrum is shown by an X mark, and an example of the level of the frequency spectrum according to the present invention is shown by an O mark.

Although noise components are not displayed in FIG. 5, it has been confirmed that the noise level does not change even if the upper sideband is attenuated and recorded.

Although the above explanation has been made regarding the case where a signal obtained by FM modulating a video signal is recorded and reproduced, it goes without saying that similar effects can be obtained in so-called color under recording methods such as the VH3 method and the β method. .

Although FIG. 5 shows an example of a low-pass filter as the filter circuit 3, a trap circuit (not shown) with frequency characteristics as shown in FIG. 6 or a band rejection filter circuit (not shown) with frequency characteristics as shown in FIG. (not shown).

Note that the O mark and the broken line indicate the position where the upper sideband exists.

Furthermore, when an Astaple multivibrator is used in the FM modulation circuit 2, harmonic components such as 3rd and 5th harmonics are generated along with the fundamental wave component, but even if these harmonic components are attenuated by the filter circuit 3, Almost the same effect can be obtained.

Alternatively, a sine wave FM circuit that provides an effect equivalent to the combination of the FM modulation circuit 2 and the filter circuit 3 may be used.

In the above explanation, it was assumed that components exceeding a predetermined frequency are attenuated by the filter circuit 3, but the modulation index!
J for smaller. A similar effect can be obtained even if the upper side wave components including , are attenuated by the filter circuit 3.

As described above, according to this embodiment, the amount of increase in the level of the lower side wave component of the modulated signal can be further increased without changing the noise level during reproduction, and as a result, the S/N ratio can be improved. can.

Effects of the Invention As described above, the present invention frequency-modulates a video signal, removes a part of the upper side wave component of the modulated signal, and further removes the lower side wave component of the signal from which the upper side wave component has been removed. By recording the resulting signal on a recording medium, it is possible to further increase the level of the lower side wave component of the modulated signal without changing the noise level during playback, and as a result, the S/N ratio can be increased. You can make it better.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a recording and reproducing method in an embodiment of the present invention, FIG. 2 is a characteristic diagram showing an example of the frequency characteristics of the low-pass filter circuit 3, and FIG. 3 is a characteristic diagram showing an example of the frequency characteristics of the filter circuit 4. Figure 4 is a graph showing the output levels of the carrier wave component and the first lower side wave component when the ratio of the level of the input carrier wave component and the level of the first lower side wave component is changed.
The figure is a schematic diagram of an example of the signal frequency spectrum of each part in Figure 1, Figure 6 is a characteristic diagram showing an example of the frequency characteristics of a trap circuit, and Figure 7 is a characteristic diagram showing an example of the frequency characteristics of a band rejection filter circuit. It is. 2...FM modulation circuit, 3...filter circuit, 4...filter circuit, 5...recording amplifier, 11.12... magnetic head, 13.
...Magnetic tape, 15...Reproduction amplifier,
16...RF equalizer circuit, 17...
・Filter circuit, 1B...FM demodulation circuit. −n → −? → Figure 1 Pida Ward 1in ← 亦−? →

Claims (4)

[Claims] (1) A signal obtained by frequency modulating a video signal, removing a part of the upper side wave component of this modulated signal, and further enhancing the lower side wave component of the signal from which the upper side wave component was removed. A recording and reproducing method characterized by recording on a recording medium and suppressing side wave components of a reproduced signal during reproduction. (2) The recording and reproducing method according to claim 1, wherein the enhancement of the lower side wave component during recording is set to such an extent that the lower side wave component after reproduction does not exceed the level of the carrier wave component. (3) The recording/reproducing method according to claim (1), characterized in that during reproduction, lower side wave components of the reproduced signal are suppressed. (4) The recording/reproducing method according to claim (1), wherein a part of the upper side wave component of the reproduced signal is removed during reproduction.