JPH0241952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical scan type video tape recorder having at least two rotating magnetic heads and having an after-recording function. In a videotape recorder that adopts the so-called overlap method in which a period in which the data overlaps with each other, and in which after-recording can be performed during this period, the deterioration of the reproduced video signal that occurs during after-recording is reduced, and an improved reproduced signal can be obtained. This is what we are trying to do.

In a helical scan type video tape recorder, for example, two rotating magnetic heads are used to
Video signals are recorded and reproduced on a magnetic tape using recording tracks diagonal to the running direction (longitudinal direction) of the magnetic tape. Furthermore, if the helical scan type video tape recorder to be fitted uses an overlap method, the winding angle of the magnetic tape around the head drum may be increased to increase the period during which the two rotating magnetic heads are in simultaneous contact with the magnetic tape ( An overlapping period) is generated, and a time-compressed audio signal and the like is recorded separately from the video signal in an extended portion (overlap portion) of the recording track formed during this period. In such an overlap method, when one of the two rotating magnetic heads is in the extension of the recording track, that is, in the overlap region, there is no effect on the video signal recorded on the recording track. It is possible to erase and record signals without having to do so. Therefore, it is possible to provide an after-recording function for reproducing a video signal recorded on one of the two rotating magnetic heads while recording an audio signal related to the content of the video signal in the overlap area on the other.

Before explaining the embodiments of the present invention, the after-recording in the helical scan video tape recorder employing the above-mentioned overlap method will be described.The recording pattern on the magnetic tape is as shown in FIG. That is, for example, a field period part r _F in which one field's worth of video signal S _v is recorded, and an extension part in which, for example, an audio signal is recorded as a PCM signal (pulse code modulation signal) S _a . , overlap part r _L
Recording tracks consisting of are sequentially arranged diagonally parallel to the running direction of the magnetic tape. The arrow indicates the direction of movement of the rotating magnetic head. Now, assuming that the two rotating magnetic heads are the first head and the second head, the first head scans the recording track A and the second head alternately scans the recording track B, respectively. The video signal _Sv is reproduced from the field period part _rF of the recording track, and the PCM signal _Sa is recorded in the overlap part _rL . The timing in this case is as shown in FIG. 2. First, in the recording track a, the first head reproduces the video signal S _v from the field period r _F in one field period T _F , and then During the following overlap period T _L , the PCM signal S _a is recorded in the overlap part r _L . Next, in the recording track B, the second head performs a 1st recording starting from the time when the first head enters the overlap region _rL of the recording track A.
During the field period T _F , the video signal S _v is reproduced from the field period part r _F , and during the following overlap period T _L , the PCM signal S _a is reproduced from the overlap part r _L.
is recorded. Then, again by the first head,
One field period T _F starting from the time when the second head enters the overlap part r _L of recording track b
The video signal S _v is reproduced from the field period r _F of the recording track a, and the overlap portion of the recording track a is reproduced during the following overlap period _TL .
The PCM signal S _a is recorded on r _L , and this is repeated thereafter. As can be seen, in each overlap period T _L , one of the two rotating magnetic heads moves to the overlap part r _L of a certain recording track.
At the same time, the other rotating magnetic head starts reproducing _{the video signal S v from} the field period r _F of the next recording track.

After-recording is performed in this way, but since the supply of the recording signal to the rotating magnetic head and the reception of the playback signal from the rotating magnetic head are generally performed via a rotary transformer, two rotating magnetic heads It is difficult to eliminate crosstalk between signals handled by each. That is, during the overlap period _TL in which the PCM signal Sa is recorded by one of the first and second heads, the video signal Sv is reproduced by the other of the first and second heads; Generally, the PCM signal Sa as a signal and the video signal Sv as a reproduction signal are sent to the first and second heads via a pair of rotary transformer coils wound adjacent to a common magnetic core. It is difficult to prevent such a crosstalk phenomenon due to electromagnetic action between a pair of rotary transformer coils. Crosstalk occurs between the PCM signal Sa, which is the recording signal, and the video signal Sv, which is the reproduction signal, during the overlap period _TL .
Therefore, in the overlap period T _L , for example,
The initial part of the video signal S _v for one field (the shaded part in Figure 2) that is played back when the PCM signal S _a is recorded is the PCM signal to be recorded.
It is strongly influenced by S _a and deteriorates significantly, and the synchronization signal is not even reproduced during this period.
The reproduced image from the reproduced video signal containing such degraded portions should originally be displayed correctly as shown in FIG. 3A, but it becomes partially distorted and unsightly as shown in FIG. 3B. There is a problem with this. In FIG. 3B, the upper part _P1 of the image is an image noise part where the reproduced video signal has deteriorated due to the influence of the recorded signal, and the lower part P2 is the part _P2 where the reproduced video signal is degraded. Since the synchronization signal, especially the horizontal synchronization signal, is not reproduced in the deteriorated part, this is the part where image disturbance occurs until horizontal synchronization is properly applied in the subsequent period.

Therefore, the present invention aims to solve such problems.
In a helical scan video tape recorder that adopts the overlap method and is equipped with an after-recording function, this is intended to reduce the deterioration of the reproduced video signal that causes disturbances in the reproduced image during after-recording. To provide a video tape recorder capable of obtaining a reproduced signal without a degraded part by replacing a reproduced video signal which deteriorates due to a received signal with another video signal including a separately prepared synchronizing signal. Embodiments of the present invention will be described below with reference to FIGS. 4 and 5 of the drawings.

FIG. 4 shows an example of a video tape recorder equipped with an after-recording function according to the present invention. 1 and 2 are rotating magnetic heads; 3 and 4 are rotating magnetic heads;
are the recording/recording heads respectively connected to these rotating magnetic heads.
This is a playback switch. Reference numeral 5 denotes a head changeover switch for the recording system, through which the signal from the recording signal generation circuit 6 for after-recording is switched between recording/recording.
The signal is supplied to the recording side contacts R of the reproduction changeover switches 3 and 4. The recording signal generation circuit 6 generates, for example, an audio signal in the form of a PCM signal. Reference numeral 7 designates a playback system head changeover switch, through which the playback video signal, for example FM modulated, obtained at the playback side contacts of the recording/playback changeover switches 3 and 4 is sent to the amplifier circuit 8, and then to the FM The signal is supplied to the demodulation circuit 9.
The reproduced video signal SV from the FM demodulation circuit 9 is transmitted to one fixed contact 10 of the video signal changeover switch 10.
horizontal synchronization signal generation circuit 1
1. The horizontal synchronization signal generation circuit 11 is
Horizontal synchronizing signal separation circuit 12 and connected to it
PLL circuit (phase locked loop circuit)
It consists of a phase comparator circuit 13, a low-pass filter 14, a sampling/hold circuit 15, and a voltage controlled oscillation circuit 16, and a delay circuit 17 and a waveform shaping circuit 18 connected to the output terminal of this PLL circuit. has been done. The output of the horizontal synchronization signal generation circuit 11 and the output of the video information signal generation circuit 19 are supplied to an addition circuit 20, and the output
SV' is supplied to the other fixed contact 10b of the video signal changeover switch 10. A video signal output terminal 21 is connected to the movable contact of the video signal changeover switch 10.
has been derived.

In this example, the output of the FM demodulation circuit 9 is further supplied to a vertical synchronization signal generation circuit 22.
The vertical synchronization signal generation circuit 22 includes a vertical synchronization signal separation circuit 23 , an AND circuit 24 to which an output of the vertical synchronization signal separation circuit 23 and a timing signal t _d to be described later are supplied, an oscillation circuit 25 , and an output of the AND circuit 24 . The end is connected to the reset terminal, and the oscillation circuit 25
The frequency divider circuit 26 to which the output of the frequency divider 2 is supplied, and the frequency divider circuit 2
6 and a delay circuit 27 and a waveform shaping circuit 28. The output of this vertical synchronizing signal generating circuit 22 is also supplied to the adding circuit 20.

29 is a timing signal generation circuit that generates four types of timing signals t _a to t _d . These timing signals are pulses as shown in FIG. 5, where the timing signal t _a is a pulse having a width of one field period T _F and a period of two field periods, and the timing signal t _b is a pulse having a width of one field period T F and a period of two field periods. The timing signal t _a is a pulse having an opposite phase. The timing signal t _c is a pulse having a width equal to the overlap period T _L and having a period of one field period, and the timing signal t _d is a pulse having a phase opposite to that of the timing signal t _c .

Next, the operation of an example of a video tape recorder according to the present invention having the signal path as described above will be explained. First, a magnetic tape is arranged so that rotating magnetic heads 1 and 2 scan a recording track diagonal to the running direction of the magnetic tape.
In this case, the winding around the head drum is performed at a winding angle of approximately 180°, at which the rotating magnetic heads 1 and 2 alternately oppose each other, and at a winding angle of approximately 30°. This additional winding angle of about 30 DEG creates an overlap period T _L during which the rotating magnetic heads 1 and 2 are simultaneously in contact with the magnetic tape, with one rotating magnetic head scanning an extension of the recording track. The extended portion of this recording track is the overlap portion _rL . Each of the rotating magnetic heads 1 and 2 has a winding corner of about 180 degrees, and has a contact time of one field period T _F , and a field period part r _F of a recording track in which one field worth of video signal is recorded. is scanned, followed by an additional wrapping corner of approximately 30° for one overlap period.
The extended portion of each recording track, that is, the overlap portion r _L is scanned with a contact time of T _L .

During the after-recording operation, the recording/playback switch 3 is supplied with the OR output t a +t _b t _d of the timing signal t _a and the AND output _{t b} t _d of the timing signals t _b and t _d . During the period, the movable contact is connected to the playback contact P as shown in the real image diagram,
In other periods, the movable contact is connected to the recording side contact R as shown by the dotted line. On the other hand, the recording/reproduction changeover switch 4 is supplied with an AND output t _a ·t _c of the timing signals t _a and t _c , and during this period, the movable contact
As shown by the solid line, it is connected to the recording side contact R, and during other periods, the movable contact is connected to the reproducing side contact P, as shown by the dotted line. Further, a timing signal t _a is supplied to the head changeover switches 5 and 7, and during the period of this timing signal t _a , each movable contact takes the position shown by the solid line, and in other periods, each movable contact takes the position shown by the dotted line. Take the position shown. This causes the rotating magnetic head 1 to operate during a certain field period.
When a video signal is reproduced from a field period _rF of a certain recording track in T _F , in an overlap period T _L at the beginning of the field period _TF , the rotating magnetic head 2 reproduces the overlap of the previous recording track. In part _rL , there is a signal from the recording signal generation circuit 6.
After the PCM signal is recorded, the rotating magnetic head 1 finishes scanning the field period r _F of the above-mentioned certain recording track, and starts the next field period T _F scanning the subsequent overlap portion r _L.
During the overlap period TL at the beginning of this field period _TF , the rotating magnetic head 1 records the PCM signal from the recording signal generation circuit 6 in the overlap part, and the rotating magnetic head 2 records the PCM signal from the recording signal generation circuit 6 in the overlap period _TL at the beginning of this field period TF. At T _F , the video signal is reproduced from the field period r _F of the next recording track. Then, when the rotary magnetic head 2 finishes scanning the field period _rF of the next recording track and enters the next field period TF in which it scans the subsequent overlap portion _rL , the rotary magnetic head 2 scans the field period _rF of the next recording track. Then, the video signal is reproduced from the field period _rF of the next recording track, and the same operation as described above is repeated. As a result, when one of the rotating magnetic heads 1 and 2 reproduces a video signal from the field period _rF of a certain recording track, at the beginning, the other rotates from the overlap part _rL of the previous recording track. to
The PCM signal will be recorded, and after-recording will be performed.

The video signal reproduced in each field period T _F obtained at the output terminal of the head selector switch 7 is FM.
This is modulated by the amplifier circuit 8 and then demodulated by the FM demodulator circuit 9. However, in the portion corresponding to the initial overlap period of each field, the signal is degraded due to the influence of the recorded PCM signal. Also, the synchronization signal, especially the horizontal synchronization signal, is not normal. The demodulated reproduced video signal SV is supplied to the fixed contact 10a of the video signal changeover switch 10 and also to the horizontal synchronization signal generation circuit 11. Horizontal synchronization signal generation circuit 1
1, a horizontal synchronization signal is separated in a horizontal synchronization signal separation circuit 12, and a phase comparison circuit 13 of a PLL circuit is composed of a phase comparison circuit 13, a low-pass filter 14, a sampling/holding circuit 15, and a voltage controlled oscillation circuit 16. supplied to Here, the sampling/holding circuit 15 receives the timing signal t _d
is supplied, sampling is performed at a predetermined frequency during the period of this timing signal _td , that is, a period other than the overlap period _TL , and sampling is not performed during each overlap period _TL , but the value immediately before the overlap period _TL is hold. Therefore,
An overlap period during which a normal playback horizontal synchronization signal can be obtained because the playback video signal SV is not degraded.
During periods other than T _L , an oscillation output synchronized with the reproduced horizontal synchronizing signal is obtained from the voltage controlled oscillator circuit 16 of the PLL circuit, but the reproduced video signal SV deteriorates and a normal reproduced horizontal synchronizing signal cannot be obtained. During the overlap period _TL , the sampling/holding circuit 15 holds the value immediately before the overlap period _TL , and based on this, an oscillation output with a constant frequency is obtained from the voltage controlled oscillation circuit 16, and this oscillation with a constant frequency The output is synchronized with the reproduction horizontal synchronization signal just before the overlap period _TL .
The oscillation outputs of these voltage controlled oscillation circuits 16 are phase-adjusted by a delay circuit 17, and a waveform shaping circuit 18
The waveform is shaped into a horizontal synchronization signal,
It is supplied to the adder circuit 20 as the output of the horizontal synchronizing signal generating circuit 11.

In this example, the reproduced video signal SV from the FM demodulation circuit 9 is further transmitted to the vertical synchronization signal generation circuit 2.
Here, the vertical synchronizing signal is separated by a vertical synchronizing signal separation circuit 23, and the separated vertical synchronizing signal and timing signal _td are supplied to an AND circuit 24. Further, the oscillation output of the oscillation circuit 25 is frequency-divided by a frequency divider circuit 26 to obtain a signal of the vertical synchronizing signal frequency, and this frequency divider circuit 26 can be reset by the output of the AND circuit 24. Therefore, the period of the timing signal t _d ,
That is, in periods other than the overlap period T _L ,
Since the reproduced video signal SV is not degraded, the reproduced vertical synchronization signal is also obtained correctly, and an AND output is obtained from the AND circuit 24, which causes the frequency divider circuit 26
is reset, and a frequency-divided output synchronized with the reproduction synchronization signal is obtained. On the other hand, the overlap period T _L
In this case, the AND output from the AND circuit 24 cannot be obtained, so the frequency divider circuit 26 resets itself based on the reset immediately before the overlap period _TL , and synchronizes with the reproduced vertical synchronization signal immediately before the overlap period _TL . Outputs the divided frequency output. The outputs of these frequency dividing circuits 26 are phase-adjusted by a delay circuit 27,
Further, the waveform is shaped by the waveform shaping circuit 28 to form a vertical synchronizing signal, and the vertical synchronizing signal generating circuit 28 generates a vertical synchronizing signal.
2 is supplied to the adder circuit 20 as an output.

The video information signal from the video information signal generation circuit 19 is also supplied to the adder circuit 20, and from its output terminal,
A video signal SV' to which a horizontal synchronizing signal from the horizontal synchronizing signal generating circuit 11 and a vertical synchronizing signal from the vertical synchronizing signal generating circuit 22 are added is supplied to the fixed contact 10b of the video signal changeover switch 10. A timing signal t _d is supplied to the video signal changeover switch 10, and during a period of this timing signal t _d , that is, a period other than the overlap period _TL , its movable contact is switched to the fixed contact 10a as shown by the solid line.
The undegraded playback video signal SV from the FM demodulation circuit 9 is connected to the video signal output terminal 21.
In addition, during the overlap period T _L , the movable contact is connected to the fixed contact 10b as shown by the dotted line, and during this period the movable contact is deteriorated under the influence of the recorded PCM signal obtained from the FM demodulation circuit 9. Instead of the reproduced video signal SV, the video signal SV' from the adder circuit 20 is output to the video signal output terminal 21. In this way, the video signal obtained at the video signal output terminal 21 is the same as that in the reproduced video signal SV.
The parts degraded due to the influence of the recording signal are replaced with another video signal SV' that includes a separately prepared video information signal and horizontal and vertical synchronization signals, so that the degraded part of the reproduced video signal is reduced. will be reduced. Therefore, when an image is displayed based on the video signal obtained at the video signal output terminal 21, no image noise is included and no synchronization disturbance occurs. However, it is inevitable that the upper part of the image after replacing the video signal will be displayed differently from the original image, such as specific characters, codes, or patterns. However, the advantage of eliminating the unsightliness of the reproduced image, which includes image noise in the upper part and causes synchronization disturbance, is extremely large.

Note that the vertical synchronization signal is
Since it is considered that even the reproduced video signal deteriorated due to after-recording in T _L will not be easily damaged, the above-mentioned vertical synchronization signal generation circuit 22
Even in the overlap period T _L without providing
The vertical synchronization signal in the reproduced video signal SV from the FM demodulation circuit 9 may be derived to the video signal output terminal 21.

As explained above, according to the present invention, in a video tape recorder that adopts the overlap method and is equipped with an after-recording function, by replacing the degraded portion of the reproduced video signal that occurs during after-recording with another video signal,
Deterioration in the entire reproduced video signal can be suppressed to a minimum, and it is possible to eliminate the mixing of image noise and synchronization disturbance in the reproduced image display based on the obtained reproduced video signal. Furthermore, if the video information signal to be inserted for replacement is appropriately selected, there is an advantage that a special effect can be produced on the reproduced image display.

The present invention described above is not limited to the embodiments described with reference to FIGS. 4 and 5, and it goes without saying that various configurations may be adopted without departing from the gist thereof.

[Brief explanation of drawings]

1, 2, and 3 are schematic diagrams used to explain after-recording in a video tape recorder, and FIG. 4 is a block connection diagram showing an example of a video tape recorder according to the present invention. FIG. 5 is a waveform diagram used to explain the operation of the video tape recorder according to the present invention. In the figure, 1 and 2 are rotating magnetic heads, 3 and 4 are recording/reproduction changeover switches, 5 and 7 are head changeover switches, 6 is a recording signal generation circuit, 10 is a video signal changeover switch, and 11 is a horizontal synchronization signal generation circuit. , 19 is a video information signal generation circuit, 20 is an adder circuit, 21 is a video signal output terminal, 22 is a vertical synchronization signal generation circuit, and 29 is a timing signal generation circuit.

Claims (1)

[Claims] 1 At least two rotating magnetic heads for recording and reproducing signals are connected to a signal recording and reproducing circuit via a switching circuit, and there is a period in which both of them are in simultaneous contact with the magnetic tape, during which one of them is connected to the signal recording and reproducing circuit. The head is arranged to scan an extension of the recording track on the magnetic tape, and each of the two rotary magnetic heads for signal recording and reproduction scans the video from a portion other than the extension of each recording track. In addition to reproducing the signal, other information signals are also recorded on the extended portion of each of the recording tracks, and during after-recording for each of the recording tracks, one of the two rotary magnetic heads for signal recording and reproduction is During the period when the other information signals are being recorded on the extended portion of each recording track, the reproduction signal from the other of the two rotary magnetic heads for signal recording/reproduction is transferred to the other information signal from the one rotary magnetic head. 1. A video tape recorder comprising signal replacement means for replacing the information signal with another video signal synchronized with the reproduction signal immediately before the start of recording.