JPH0216078B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing method in a VTR (video tape recorder), and more particularly to a magnetic recording and reproducing method suitable for slow motion image reproduction in a VTR using an azimuth recording method.

In the azimuth recording method, for example, as shown in FIG. A tape 2 is spirally wound around a guide cylinder 1 containing first and second magnetic heads A and B having different angles with respect to the magnetic head, so-called azimuth angles, and runs at a predetermined speed. One field of video signals is alternately supplied to the first and second magnetic heads A and B, and as shown in FIG. The tracks b are recorded by the second magnetic head B so as to be inclined at a predetermined angle with respect to the longitudinal direction of the tape 2 and adjacent to each other.

During reproduction, the first and second magnetic heads A,
B obtains a reproduced video signal by scanning tracks a and b, respectively. At this time, the first magnetic A
Even if the magnetic head (or second magnetic head B) scans track a (or track b), no substantial reproduction output can be obtained due to azimuth loss.

Conventionally, when a tape recorded by the above-mentioned azimuth recording method is run at a speed of 1/m of the recording speed and a magnetic head is scanned to obtain a slow motion reproduced image, for example, in the case of 1/3 slow motion. The scanning trajectory of each magnetic head A, B is the second
As shown by the dotted lines in Figures A to F, the magnetic head straddles adjacent recording tracks, and the magnetic head moves from A to B to A.
→B→A→B will be scanned in this order. The shaded area in the diagram indicates the track area with head output.
The reproduction output of the magnetic head at this time is as shown in FIG.
Only the output from the track B scan is taken out from the second magnetic head B, and the two are combined to form a playback output, but the level of this playback output is not uniform, and there are parts where the level drops to 0. . Therefore, horizontal stripes called noise bars appear on the playback screen, making it very difficult to see.

The present invention has been made in view of the above points,
An object of the present invention is to provide a magnetic recording and reproducing method that can obtain good slow motion reproduced images even in a VTR using an azimuth recording method.

An embodiment of the present invention will be described below with reference to the drawings. The magnetic head arrangement used in the method of the present invention is as shown in FIG. Third and fourth magnetic heads A' and B' are arranged in the plane of rotation and near both magnetic heads A and B, respectively.
As shown in FIG. 4B, the azimuth angle of the third magnetic head A' placed near the first magnetic head A is the same as that of the second magnetic head B; The azimuth angle of the fourth magnetic head is the same as that of the first magnetic head A. Also, the distance l between the first magnetic head A and the fourth magnetic head B' and the distance l between the second magnetic head B and the third magnetic head A' on the outer periphery of the magnetic head rotation plane.
If H is the distance between horizontal synchronization signals recorded on tape 2, then l = nH (n is a positive integer, but if "H arrangement" is not formed between adjacent tracks, n
does not have to be an integer. ). This distance is l
The reason why is set to an integral multiple of H is to prevent disturbances in the interval of the horizontal synchronizing signal due to switching of the magnetic head output during reproduction. During recording, while the tape 2 is running at a predetermined speed, field signals are sequentially recorded on the tape 2 as recording tracks by the first and second magnetic heads A and B of the magnetic heads configured as described above.

When performing slow motion image playback by lowering the tape 2 scanning speed to 1/m during recording,
The first to fourth magnetic heads A, B, A', and B' sequentially scan across adjacent recording tracks on the tape 2 to obtain reproduction output. For example, in the case of 1/3 slow motion playback, the scanning locus of each magnetic head is
As shown in Figures A to F. In the figure, the shaded area indicates the track part with the head output. First, as shown in Figure A, the adjacent first and third magnetic heads A and A' scan the tape 2 from the lower right to the upper left.
The head output is switched so that the output of the first magnetic head A of both heads, that is, the output of the track a indicated by diagonal lines, is obtained. Next, as shown in Figure B, the second and fourth magnetic heads B and B' scan,
The head output is switched so that the output of the fourth magnetic head B' of both heads, that is, the output of the track a indicated by diagonal lines, is obtained. Below, in order A →
Head outputs are obtained in the order of B→A'→B→....
When these outputs are connected, the playback output is the 6th
As shown in the figure, the level increases and decreases somewhat, but there is no part where it drops significantly or becomes 0. That is, in contrast to FIGS. 2B and 2E showing the conventional example, the head output decreases when track a (or track b) is scanned by a magnetic head having an azimuth angle different from that during recording. In this case, a decrease in head output is prevented by selecting and switching the larger output of two adjacent magnetic heads having different azimuth angles.

Next, switching of each magnetic head output and phase inversion of the chroma signal will be explained. In this embodiment, switching of the magnetic head output is performed by a head switching pulse generated based on a control signal.

On the other hand, the chroma signal eliminates crosstalk between adjacent tracks during playback, so in the Beta method, for example, every other field is
It is recorded with a 180° phase inversion each time. That is,
As shown in FIG. 7, the phase of the chroma signal is inverted by 180 degrees every 1H on track a, and is recorded without phase inversion on track b. For this reason, the phase of the 4.27MHz carrier used during frequency conversion is inverted.

The above-mentioned magnetic head output switching and chroma signal phase inversion will be explained below with reference to the reproduction system circuit block diagram of FIG.

In the figure, 3 is a recording amplifier that supplies video signals to the first to fourth magnetic heads A, B, A', and B' during recording;
4, 5, 6, and 7 are first to fourth preamplifiers to which video signals from the first to fourth magnetic heads A, B, A', and B' are input during playback, and 8 is the first and second preamplifiers. A first head switching pulse generation circuit, which is composed of stable multivibrators 81, 82 and a first flip-flop 83, generates a head switching pulse based on a control signal, and controls the output of the first and third preamplifiers 4, 6. . 9 is a circuit similar to the first head switching pulse generating circuit 8 ;
A second head switching pulse generation circuit constituted by fourth monostable multivibrators 91, 92 and a second flip-flop 93;
This is a fifth preamplifier that receives the output of the preamplifier as an input. 111 is a horizontal synchronization separation circuit that separates the horizontal synchronization signal from the output of the fifth preamplifier 10, that is, the reproduced video signal; 112 is a 3.58MHz oscillator;
113 is a burst ID circuit that compares the phases of the oscillator output and the 3.58MHz chroma signal and outputs a trigger pulse when the two phases are different; 114 is a burst ID circuit that receives the burst ID circuit output and the horizontal synchronization separation circuit output; 1OR circuit, 115, is triggered by the output of the first OR circuit, and a third flip-flop, 11, outputs a horizontal pulse that is repeated in a horizontal period.
6 is a second OR circuit which takes the output of the third flip-flop as one input, SW ₁ is connected to the other input terminal of the second OR circuit 116, and the contact is closed during normal playback.
The first changeover switch SW 2 is a first changeover switch that is turned to the SD side to conduct the RF switching pulse and is turned to the contact SL side during slow motion playback, and SW ₂ is a switch that inputs the RF switching pulse to the fifth preamplifier 10 during normal playback. 2 changeover switch, 117 is an AND circuit which inputs the Q output of the first flip-flop 83 and the RF switching pulse, and 118 is the corresponding
an AND circuit 11 which receives the output of the AND circuit 117 and the Q output of the second flip-flop 93 and is connected to the SL contact of the first changeover switch _SW1 ;
9 is controlled by the output of the second OR circuit 116,
4.27MHz carrier every 1H in every other field
Carrier phase inversion switch that inverts the phase by 180°.
These constitute a chroma phase inversion circuit 11 . 1
2 is a low-pass filter for extracting low-frequency components from the reproduced video signal from the fifth preamplifier 10; 13;
is the output of the low-pass filter 12, 688KHz
This is a frequency conversion circuit that converts the frequency of the reproduced chroma signal to the original 3.58MHz chroma signal using a 4.27MHz carrier.

Next, the operation of this circuit will be explained. First, during recording, the first and second magnetic heads A and B are connected to the recording amplifier 3.
A video signal amplified by the recording amplifier 3 is supplied to both magnetic heads and sequentially recorded as recording tracks on the tape.

During reproduction, that is, during slow motion reproduction, first to fourth preamplifiers 4, 5, 6, and 7 are connected to the first to fourth magnetic heads A, B, A', and B', respectively. Each preamplifier has a built-in switcher (not shown), which is controlled by the Q and output of the first and second head switching pulse generation circuits 8 and 9 , respectively. Next, the first head switching pulse generating circuit 8 will be explained with reference to the waveform diagram of each part in FIG.
First, in the first monostable multivibrator 81,
A pulse c with a pulse width of 5.5 fields is created based on the control signal b, and a pulse d with a pulse width of 4 fields that rises in synchronization with the falling of the pulse c is obtained by the second monostable multivibrator 82. With this pulse, a Q output e and an output f are obtained in the first flip-flop 83, and these two outputs are supplied as head output switching pulses to the first and third preamplifiers 4 and 6, respectively. Similarly, in the second head switching pulse generation circuit 9 , a third monostable multivibrator 91 having a metastable period of 2.5 fields, a fourth monostable multivibrator 92 having a metastable period of 2 fields, and a second flip-flop 93 are used. Then Q output j and output K
is created and supplied to the second and fourth preamplifiers 5 and 7. Therefore, among the head outputs a, the outputs of the first and third magnetic heads A and A' are selected by the pulses e and f and become the head output g. The outputs of the second and fourth magnetic heads B and B' are selected by pulses j and k to obtain a head output l, and both head outputs g and l are combined to obtain a combined head output m. On the other hand, the Q output l of the first flip-flop 83 and the RF switching pulse n are input to the AND circuit 117, and the AND
Circuit output and Q output of the second flip-flop 93
is input to the third OR circuit 118 to obtain the chroma signal switching pulse O. Then, the first and second changeover switches SW ₁ and SW ₂ are turned to the SL side, and the chroma signal changeover pulse O is inputted to the second OR circuit 116 .
Also, in the burst ID circuit 113, 3.58MHz
Compare the phases of the reference signal and the 3.58MHz reproduced chroma signal, and if the phases differ, output a trigger pulse and input it to one terminal of the first OR circuit 114, and the other terminal receives a horizontal synchronization signal separated from the reproduced video signal. Input the signal. and the first OR circuit 114
The output triggers a third flip-flop to create a horizontal pulse with a horizontal period;
It is input to the other terminal of the 2OR circuit 116. Therefore, the second OR circuit 116 makes the horizontal pulse conductive when each magnetic head scans the track b and obtains an output, and turns on the carrier phase inversion switch 119.
input. This carrier phase reversal switch 1
19, when the horizontal pulse is input, the phase of the 4.27MHz carrier is inverted by 180 degrees every 1H, and the output is inverted in the frequency conversion circuit 13 every other field extracted by the low-pass filter 12 and every 1H. The 688KHz chroma signal whose phase is inverted is frequency-converted by the 4.27MHz carrier to the original 3.58MHz chroma signal whose phase is aligned every 1H.

In the above embodiment, the slow motion ratio is set to 1/3, but it is obvious that other slow motion ratios may be used.

As described above, according to the method of the present invention, when reproducing slow motion images, the head output is switched to select the larger of the outputs of two adjacent magnetic heads having different azimuth angles, so that the reproduction output is large. A good slow motion reproduced image can be obtained without any decrease in width.

[Brief explanation of drawings]

Figure 1A is a diagram showing the magnetic head arrangement of a VTR using the azimuth recording method, Figure 1B is a diagram showing the gap relationship of the same magnetic head, Figure 2A, B, C,
D, E, and F are schematic diagrams of the trajectory of the head during conventional slow motion reproduction, and FIG. 3 is a schematic diagram of the head output. 4 to 9 are diagrams showing one embodiment of the present invention, and FIG. 4A is a diagram showing the magnetic head arrangement;
Figure B shows the gap relationship of the magnetic head.
Figure 5 A, B, C, D, H, and F are schematic diagrams of the head trajectory during slow motion playback, Figure 6 is a schematic diagram of the head output, and Figure 7 is the phase relationship of the chroma signals of the recording track. 8 is a block diagram of a reproduction system circuit, and FIG. 9 is a waveform diagram of each part thereof. Explanation of main drawing numbers 1...Guide cylinder, 2...Tape, A, B, A', B'...1st, 2nd, 3rd and 4th magnetic head, 8 , 9 ...1st and 2nd head switching Pulse generation circuit, 11 ...Carrier phase inversion circuit.

Claims (1)

[Claims] 1 first and second magnetic heads having different azimuth angles, each arranged near the first magnetic head and the second magnetic head, and each having the same azimuth angle as the second magnetic head and the first magnetic head; A magnetic recording and reproducing method that reproduces slow motion images by scanning a recording track a plurality of times using the first, second, third, and fourth magnetic heads. The apparatus includes a head switching signal generating means for generating a head switching signal during slow motion image reproduction in response to tape running during slow motion image reproduction, and a head switching signal and RF switching pulse during slow motion image reproduction. chroma signal switching pulse creating means for creating a chroma signal switching pulse based on the chroma signal switching pulse, and phase control means for controlling the phase of the carrier signal for restoring the low frequency converted color signal in accordance with the chroma signal switching pulse, A magnetic recording and reproducing apparatus characterized in that the phase of the carrier signal is controlled in a manner different from that during normal reproduction during slow motion image reproduction.