JPS602830B2 - Video signal recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When recording a video signal on a recording medium such as a magnetic tape, the S/N ratio can be improved by performing balanced modulation on the video signal.

By the way, in this case, when performing balanced modulation on the original video signal as it is, the amplitude of the carrier wave is at its maximum in the synchronization signal part, and due to the gap between the head and the recording medium or variations in the magnetic material of the recording medium, etc. The so-called modulation noise increases as the amplitude of the carrier wave increases, so large modulation noise occurs in the synchronization signal part, deteriorating the S/N of the synchronization signal of the reproduced video signal, and clipping it at a certain level. However, when the synchronization signals are separated, the position and width of the separated synchronization signals are not constant.

Taking this into consideration, as shown in Figure 1, the synchronization signal H^ of the original video signal Y^ (A in the figure) is inverted to the white level side and amplified, and the peak of the synchronization signal day 8 is Obtain a video signal YB (B in the same figure) whose initial value is set to a level Lo between the white level and the black level, and balance-modulate this so that the amplitude of the carrier wave becomes zero at that level Lo. Modulated video signal Y.

A possible method is to obtain (C in the same figure) and record this. In this case, a pilot signal SP (D in the figure) having a constant frequency outside the band of the modulated video signal is combined with the modulated video signal in a portion corresponding to the synchronization signal, and the combined signal is recorded.

Then, during reproduction, the modulated video signal is synchronously detected, and at this time, the pilot signal SP is frequency separated, and this is amplitude-detected to obtain a pulse P^ (E in the figure) at a point corresponding to the synchronous signal. By delaying this, a pulse P8 (F in the same figure) is obtained at the back porch, and with this pulse PB, the carrier wave component Sc (G in the same figure) at the back porch of the modulated video signal, that is, at a bad level, is extracted. The phase of the synchronous detection signal is controlled, thereby demodulating a video signal YF (H in the figure) similar to the video signal Y8 before modulation.

Then, the synchronizing signal HF of the demodulated video signal YP is inverted to obtain the video signal YG (see Figure 1), and the synchronizing signal Hc of the video signal YG is clipped with an appropriate bell to generate the original video signal. obtain. According to this method, the amplitude of the carrier wave is zero at the peak value of the synchronization signal, and the amplitude of the carrier wave is reduced at the leading and trailing edges of the synchronization signal. The deterioration of S/N due to modulation noise at the synchronization signal of the signal is 4.0%, and when this is clipped at a constant level and the synchronization signal is separated, the position and width of the separated synchronization signal become stable.

The frequency relationship between the video signal and pilot signal is as follows:
For example, in the case of a color video signal, the arrangement is as shown in FIG.

That is, as the video signals Y^, Y8 (A in the same figure), components up to a constant frequency fs-fL are extracted, the video signal Y8 is balanced modulated so that the carrier frequency is f8-f, and the modulated video signal is Yc (B in the same figure) is supplied to a low-pass filter with a characteristic that the frequency decreases at fs-fL, and the mainly lower side band signal Yo (C in the same figure) is extracted, and the carrier color signal Cs is synthesized with this, and the signal is synthesized. The signal is frequency-converted to obtain a modulated video signal Y mainly in the form of an upper sideband wave with a carrier frequency of L.
8 and a carrier color signal CL (D in the figure) occupying the lower frequency side thereof is obtained.

Then, a pilot signal SP having a frequency of fs and fL is synthesized on the Takagi side of the modulated video signal YE, and the synthesized signal is recorded. During playback, the frequency conversion converts the modulated video signal Yo(
E) in the figure is obtained, and this is subjected to synchronous detection as described above. In this way, when recording is performed by lowering the carrier frequency of the modulated video signal, the S/N ratio can be further improved. By the way, when recording a video signal with balanced modulation in this way, as shown in FIG. 3, a guard band is not formed between adjacent recording tracks TR, and the recording density is increased by so-called overwriting recording. It is possible to raise it.

In this case, as shown in the figure, the recording positions Pu of the synchronization signals are aligned between adjacent tracks, the phases of the pilot signals SP are the same, and the phases of the carrier waves Jo of the modulated video signals are also the same. It is necessary to do so.

However, when increasing the frequency of the pilot signal SP as described above, it is difficult to match the phase of the pilot signal SP between adjacent tracks, and the phase changes by 180 degrees between adjacent tracks. As a result, the amplitude of the pilot signal extracted during reproduction may change significantly, and stable synchronous detection may no longer be possible.

The present invention provides a method for overcoming such disadvantages.

In the present invention, as shown in FIG. 4, the pilot signal SP is synthesized in the synchronization signal portion of every other horizontal section, and the recorded portions PH of the pilot signals SP are arranged in the middle position of each other in adjacent tracks. Make it.

A specific example will be explained below in Figure 5. Figure 5 shows an example of a recording method in which a color video signal is recorded. If the signal is supplied to the low-pass filter 12, and the original carrier frequency of the carrier color signal is fs, and the carrier frequency after low-pass conversion as described below is fL, then the components up to fs-fL are: For example, this color video signal is an NTSC signal, and fs:3. When the horizontal frequency is fH, fL: fH = o-5 Nada HZI, the luminance signal Y^( of the components up to about 2.99M) is
A) in FIG. 1 and A in FIG. 2 are taken out and sent to the correction circuit 13.
give false payment to

On the other hand, the input color video signal is supplied to the synchronization signal separation circuit 14 to extract the horizontal synchronization signal H^, which is sent to the correction circuit 1.
3, and from this, as a luminance signal, the luminance signal Y8(
Figure 1B) is obtained. This brightness signal YB is then supplied to the balanced modulator 15, while fs=3 from the fixed oscillator 16.
．． Signal of Gekimisaki Z and fL from variable frequency oscillator 17 =
supplying a 0.59 MHz signal to the frequency converter 18;
From this, two signals with frequencies of fs-fL=2.9 wind level z and fs+fL=4.17MHz are obtained, respectively.
The signal of fs-fL=2.9 z is sent to the balanced modulator 15.
The modulated luminance signal Yc (FIG. 1C, FIG. 2B) is obtained by balanced modulation with the luminance signal Y8.

This balanced modulation is such that the amplitude is zero at a level Lo intermediate between the white level and the bad level of the luminance signal Y8, and the amplitude is maximum at the white level and the bad level. Then, this modulated luminance signal Yc is supplied to a low-pass filter 19 with a characteristic that the wavelength decreases at fs - fL = 2.9 Tamagawa z, and mainly the lower sideband component YD (Fig. 2C) is extracted. , this is supplied to two synthesizers. The input color video signal is also fed to the bandpass filter 21 so that the carrier frequency is fs=3. Take out the carrier color signal Cs of $M ratio,
This is supplied to two synthesizers. Then, in the synthesizer 2, the modulated luminance signal Yo and the carrier chrominance signal Cs are frequency multiplexed, and the multiplexed signal Yo+Cs (C in FIG. 2) is supplied to the frequency converter 22 and the frequency converter 18 fs+f
Frequency conversion is performed using a signal of L = 4.17 MHz, and the carrier frequency is (fs + fL) - (fs - fL) = aL = 1.1
A modulated luminance signal YE mainly of the upper side band of Kaede mz and a carrier color signal CL of Eggmachi z whose carrier frequency is (fs+fL)-fs=f=0.5 are obtained (FIG. 2D).

These signals Y8 (7th
The multiplexed signals of FIG. A) and CL are taken out and supplied to the combiner 24. On the other hand, for example, a signal of fs+fL=4.17 MHz from the frequency converter 18 is supplied to the gate circuit 25, and a horizontal synchronization signal (FIG. 7B) from the synchronization signal separation circuit 14 is supplied to another gate circuit 26. This horizontal synchronizing signal H^ is further supplied to the flip-flop circuit 27 and inverted every horizontal interval (FIG. 7C).
This signal SF is supplied to the gate circuit 26 to obtain a horizontal synchronizing signal (FIG. 7D) for every other horizontal interval, which is then supplied to the gate circuit 25. fs+fL=4.17M in the horizontal synchronization signal part of
A pilot signal SP (FIG. 1E) of Hz is obtained and supplied to the combiner 24.

Then, a multiplexed signal (D in FIG. 2) of signals YE, CL, and SP is taken out from the synthesizer 24 and sent to the recording amplifier 24.
8 to a magnetic head for recording, for example, on a magnetic tape. In this case, the horizontal synchronization signal H from the circuit 14
^ is supplied to the phase comparator circuit 29, and fL from the variable frequency oscillator 7; 5 Cape Z signal frequency divider 3
0 and frequency-divided by 2'75 to obtain a signal of horizontal frequency fH, which is supplied to the phase comparison circuit 29, and the comparison error voltage is supplied to the variable frequency oscillator 17 to control its oscillation frequency. In this way, as shown in FIG. 4, the recorded portions P1 of the pilot signals SP are placed at intermediate positions between adjacent tracks.

FIG. 6 shows an example of a reproducing method when recording in this way, in which a multiplexed signal (D in FIG. 2) of the above-mentioned signals Y8, CL and SP reproduced by a magnetic head is loaded through a reproducing amplifier 31. V is supplied to the bus filter 32 and the signals YE and C are
L is taken out and supplied to the frequency converter 33, while fs=3. The uneven MHz signal and the fL=0.59M signal from the variable frequency oscillator 35 are supplied to another frequency oscillator 36, and the frequencies are fs+fL=4.17MHz and f3-fL=2. 9
■ Obtain two MHz signals and their fs + fL = 4.17
A MHz signal is supplied to the frequency converter 33 and the signals Y and CL are frequency-converted so that the carrier frequency is fs-fL=2.
．． Modulated luminance signal Yo of mainly lower sideband of 9 Hz
and the carrier frequency is fs=3. A carrier color signal Cs of uneven MHz is obtained (FIG. 2E). Then, the low-pass filter 37 extracts only the modulated luminance signal Yo, and the synchronous detection circuit 3
fs-fL from frequency converter 36;2.
9 Perform synchronous detection with the signal of egg field z. In this case, the modulated luminance signal Y from the low-pass filter 37. The gate circuit 39
Also, a multiplexed signal of the reproduced signals YE, CL and SP (FIG. 2D) is supplied to a pass filter 401 to extract only the pilot signal SP. When recording as shown in Fig. 4, when head 1 plays back across adjacent tracks, the horizontal synchronizing signal part of every other horizontal interval is more important than the horizontal synchronizing signal part of every other horizontal interval. Pilot signals SP (FIG. 7E) each having an amplitude above a certain value are obtained from adjacent tracks. This pilot signal SP is supplied to the amplitude detection circuit 41 for amplitude detection, and the detected pulse Pc (FIG. 7F)
is supplied to the level comparison circuit 42, and a constant pulse P is generated at a point corresponding to each horizontal synchronization signal. (G in FIG. 7) is supplied to the delay circuit 43 to obtain a pulse PE (H in FIG. 7) at the back porch, and this pulse PE at the back porch is supplied to the gate circuit 39. , modulated luminance signal Y
The component at the back porch of
The phase is compared with the signal of L=2.9 z, and the oscillation frequency of the variable frequency oscillator 35 is controlled by the comparison error voltage, and f
The phase of the synchronous detection signal of s-fL=2.9 is synchronized with the back porch component of the modulated luminance signal YD.

Therefore, the synchronous detection circuit 38 outputs a luminance signal YF of the desired polarity, that is, the same as the luminance signal YB corrected at the time of recording.
(Fig. 1H) is obtained.

The detected luminance signal YF is supplied to the correction circuit 45, and the synchronization signal HF is inverted by the pulse Po corresponding to each horizontal synchronization signal from the level comparator 42, and the luminance signal YG (see FIG. ) is obtained, and this luminance signal Y. is supplied to the clipping circuit 46, and the synchronizing signal Hc is clipped at an appropriate level to obtain the original luminance signal, which is then supplied to the synthesizer 47. Meanwhile, the multiplexed signal from the frequency converter 33 (the E) in FIG. 2 is supplied to a band pass filter 48 to extract a carrier color signal Cs with a carrier frequency fs=3.58M ratio, which is supplied to a synthesizer 47, and the original color video signal is output to an output terminal 49. obtain. Thus, according to the present invention,
When recording using a special method of balanced modulation to improve the S/N ratio, the video signal can be stably detected during playback even when guard bands are not formed between adjacent tracks in order to increase the recording density. You will be able to do this.

Note that the balanced modulation of the video signal may be performed in such a manner that the amplitude of the carrier wave is not zero but sufficiently small in the synchronization signal portion.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams for explaining the present invention, Figure 4 is a diagram showing a recording pattern according to the present invention, Figure 5 is a system diagram of an example of a recording system, and Figure 6 is a reproduction system. FIG. 7 is a waveform diagram for explaining each example. 11 is an input terminal for a color video signal, 12, 19 and 23 are low-pass filters, 13 is a correction circuit, 14 is a horizontal synchronizing signal separation circuit, 15 is a balanced modulator, 21 is a band-pass filter, 22 is a frequency converter, 25 and 26 are gate circuits, and 27 is a flip-flop circuit. Figure 3 Figure 1 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1 A video signal is balanced modulated by inverting its synchronizing signal part to the white level side and the amplitude of the carrier wave in this synchronizing signal part is zero or sufficiently small, and 1 is applied to this balanced modulated video signal. A video signal in which pilot signals of a constant frequency are synthesized in the synchronization signal portions in every horizontal section, and this synthesized signal is recorded such that the recorded portions of the pilot signals are located at intermediate positions between adjacent tracks. How to record.