JPH0228954B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a magnetic recording and reproducing device for a VTR (video tape recorder), and in particular a magnetic recording and reproducing device suitable for multi-speed image reproduction such as 5x speed and 20x speed in a VTR using an azimuth recording method. It is related to. 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 and B
obtains a reproduced video signal by scanning tracks a and b, respectively. At this time, even if the first magnetic head A (or the second magnetic head B) scans the track a (track b), no substantial reproduction output can be obtained due to the azimuth loss. Conventionally, a tape recorded by the above-mentioned azimuth recording method is run at the same high speed as when rewinding or fast forwarding, and a magnetic head is scanned to obtain a multi-speed reproduction image, and an operator can view this image. When performing a so-called high-speed picture search to search for desired image information, for example, in the case of a picture search in the reverse direction, the scanning locus of the first magnetic head A scans a large number of adjacent records as shown by the dotted line in FIG. 1C. It will straddle the track. At this time, the reproduction output of the magnetic head is as shown in FIG. Only the output is taken out and both are connected to form a reproduced output, but this reproduced output has several parts within one field where the output is 0. This also applies to the forward picture search. Therefore, on the playback screen,
Multiple horizontal stripes called noise bars appeared, making it extremely difficult to see. The present invention has been made in view of the above points,
The object of the present invention is to provide a magnetic recording and reproducing device that can obtain good multi-speed reproduction images such as 5x speed and 20x speed 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 arrangement of the magnetic head used in the device of the present invention is as follows.
As shown in FIG. Third and fourth magnetic heads A' and B' are arranged near the magnetic head B, respectively. As shown in FIG. 2B, the azimuth angle of the third magnetic head A' arranged near the first magnetic head A is the same as that of the second magnetic head B;
a fourth magnetic head placed near magnetic head B;
The azimuth angle of B' is the same as that of the first magnetic head A. Also, the distance between the first magnetic head A and the fourth magnetic head B' and the distance between the second magnetic head B and the third magnetic head on the outer periphery of the rotation plane of the magnetic head.
The distance l from A' is 1=nH (n is a positive integer), where H is the distance between horizontal synchronizing signals recorded on the tape 2. The reason why this distance l is an integral multiple of H is to prevent disturbances in the interval of horizontal synchronizing signals 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 a high-speed picture search in the reverse direction while transporting the tape 2 at the same speed as when rewinding, the first to fourth magnetic heads A, B, A', and B' sequentially record information on the tape 2. Scan across the track to obtain playback output. In this case, the scanning locus of the magnetic head will be as shown in FIG. 1C, as in the conventional case. First, the first magnetic head A and the third magnetic head A' disposed close to it and having different azimuth angles sequentially scan the tape 2 from the lower right to the lower left across the recording tracks. At this time, the outputs of the first magnetic head A and the third magnetic head A' become as shown by solid lines and dotted lines in FIG. 2C. That is, when the first magnetic head A moves from track a to track b, when the head output begins to decrease due to azimuth loss, the head output of the third magnetic head A' begins to increase. As a result,
The output of one of the two heads will always be above a certain level. Therefore, by switching the outputs of both heads near the point where the outputs of both heads become the same level using a head switching pulse, which will be described later, as shown in FIG. There are no parts where the playback output becomes continuous, and continuous playback output above a certain level can be obtained. Both magnetic heads A and A' are connected to tape 2.
When the second and fourth magnetic heads B and B' start scanning, the same reproduction output is obtained as described above. You can get the playback video output. Next, switching of each magnetic head output and phase inversion of the chroma signal will be explained. In this embodiment, the reproduction output of each magnetic head is switched by detecting an increase or decrease in the output of each magnetic head and creating a head switching pulse. On the other hand, the chroma signal is recorded by inverting the phase of every other field by 180 degrees every 1H in the Beta method, for example, in order to eliminate crosstalk between adjacent tracks during reproduction. That is, as shown in FIG. 3, the chroma signal is recorded in track a with its phase inverted by 180 degrees every 1H, and in track b without being phase inverted. For this reason, the phase of the 4.27MHz carrier used during frequency conversion is inverted. The switching of the magnetic head output and the phase inversion of the chroma signal will be explained below with reference to the reproduction system circuit block diagram shown in 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 into which video signals from the first to fourth magnetic heads A, B, A', and B' are input during playback, and 8 is a third preamplifier 6.
is connected to a first envelope detection circuit 81, a first waveform shaping circuit 82, and a first flip-flop 8.
A first head switching pulse generating circuit constituted by 3 controls the outputs of the first and third preamplifiers 4 and 6. Reference numeral 9 denotes a circuit similar to the first head switching pulse generation circuit 8 , which is connected to the fourth preamplifier 7, and includes a second envelope detection circuit 91, a second waveform shaping circuit 92, and a second flip-flop 93. A switching pulse generation circuit controls the outputs of the second and fourth preamplifiers 5 and 7. 10 are the first to fourth preamplifiers 4,
This is a fifth preamplifier which receives the outputs of Nos. 5, 6, and 7 as inputs. 111 is the output of the fifth preamplifier 10, that is, a horizontal synchronization separation circuit that separates the horizontal synchronization signal from 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 outputs a trigger pulse when the two phases are different;
A first OR circuit which receives the ID output and the output of the horizontal synchronization separation circuit as input; 115 is a third flip-flop that is triggered by the output of the first OR circuit and outputs a horizontal pulse that is repeated in a horizontal period; and 116 is the output of the third flip-flop. The first input is
The 2OR circuit, SW ₁ , is connected to the other input terminal of the second OR circuit 116, and during normal playback, it is turned to the contact SD side to conduct the RF switching pulse, and during high-speed picture search, it is turned to the contact PS side. SW ₂ is a second switch for inputting the RF switching pulse to the fifth preamplifier 10 during normal reproduction; 117 is a switch for inputting the Q output of the first flip-flop 83 and the second flip-flop 93;
A switching circuit 118 controls the output of the RF switching pulse by the RF switching pulse and supplies it to the contact PS of the first changeover switch _SW1 ;
This is a chroma phase inversion switch that is controlled by the output of the 2OR circuit 116 and inverts the phase of the 4.27MHz carrier signal by 180 degrees every 1 field and every 1H, and these constitute the carrier phase inversion circuit 11 . 12 is a low-pass filter that extracts low-frequency components from the reproduced video signal from the fifth preamplifier 10, and 13 is a 688KHz reproduced chroma signal output from the low-pass filter 12, which is converted to the original 3.58MHz by a 4.27MHz carrier. This is a frequency conversion circuit that converts the frequency into a chroma signal. Next, the operation of this circuit will be explained. First, during recording, the first and second magnetic heads A and B are each connected to a recording amplifier 3, and a video signal amplified by the amplifier is supplied to both magnetic heads and recorded on the tape. During reproduction, that is, during multi-speed image reproduction, the first to fourth magnetic heads ABA'B' are connected to the first to fourth magnetic heads ABA'B', respectively.
Preamplifiers 4, 5, 6, and 7 are connected. 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. The output c of the third preamplifier 6, that is, the output c obtained by scanning the track b of the third magnetic head A', and the output d whose envelope is detected by the first envelope detection circuit 81 are converted to a fixed level, e.g., the highest level, by the first waveform shaping circuit 82. The waveform is shaped into a pulse e that is high at 50% or more of the level and low at less than that, and the first flip-flop 83 obtains a Q output f and an output g. These two outputs are used as head switching pulses to control the outputs of the first and third preamplifiers 4 and 6, respectively. Similarly, the outputs of the second and fourth preamplifiers 5 and 7 are controlled by the Q and output of the second head switching pulse generation circuit 9 . Therefore, the first to fourth preamplifiers 4, 5,
The output of either one of 6 and 7 is sequentially supplied to 5 preamplifier 10 and amplified. On the other hand, the first changeover switch _SW1 of the carrier phase inversion circuit 11 is turned to the PS side, and the Q output of the first flip-flop 83 and the One of the outputs of the two flip-flops 93 becomes one input of the second OR circuit 116, and the selection between the two outputs is determined by the switching circuit 1.
17 by an RF switching pulse. This RF switching pulse is a pulse with a field period. For example, during normal reproduction, the field period when the magnetic head scans track a in FIG. 3 is at a low level, and the field period when the magnetic head scans track b is at a high level. . Also, in the burst ID circuit 113, the 3.58MHz reference signal
Compare the phases of 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 input the horizontal synchronization signal separated from the reproduced video signal to the other terminal. do. Then, the third flip-flop 115 is triggered by the output of the first OR circuit 114 to create a horizontal pulse with a horizontal period, which is input to the other terminal of the second OR circuit 116. Therefore, the first
The 2OR circuit 116 allows each magnetic head to
While scanning and obtaining an output, the horizontal pulse is made conductive and input to the carrier phase inversion switch 118. This carrier phase reversal switch 118
Now, when the horizontal pulse is input, the phase of the 4.27 MHz carrier is inverted by 180 degrees every 1H, and the output thereof is input to the frequency conversion circuit 13. In the frequency conversion circuit 13, the 1
The phase is reversed every field and every 1H.
The 688KHz chroma signal is frequency-converted by the 4.27MHz carrier to the original 3.58MHz chroma signal whose phase is aligned every 1H. On the other hand, during normal playback, the Q output of the first and second flip-flops 83 and 93 is always high.
Since the output is low, only the first and second preamplifiers 4 and 5 are outputted and input to the fifth preamplifier 10. This fifth preamplifier 10 has a built-in switcher, and the second changeover switch SW ₂ is
By turning it to the SD side, an RF switching pulse is input, and the outputs of the first and second preamplifiers 4 and 5 are selected and amplified for each field. In addition, the first changeover switch SW ₁ is also turned to the SD side, and the RF switching pulse is transferred to the second OR circuit 116.
is supplied to the carrier phase reversal switch 118, and a horizontal pulse is supplied to the carrier phase inversion switch 118 every other field.
The phase of the Hz carrier is inverted every other field and every 1H, and the frequency conversion circuit 13 converts the frequency to 688KHz.
Frequency conversion of chroma signal to 3.58MHz chroma signal. Furthermore, the first and second waveform shaping circuits 82 and 83
The output of the horizontal pulse is ANDed with the output of the first,
By inputting the signal to the clock input terminals of the second flip-flops 83 and 93, output switching of the magnetic head can be performed within horizontal blanking, and a good reproduced image can be obtained. Further, in the above-described embodiment, multi-speed playback in which the tape runs in the opposite direction to that during recording has been described, but multi-speed playback in the forward direction is also possible. As described above, according to the present invention, during multi-speed image reproduction such as high-speed picture search, the head output is switched by selecting the larger output of two adjacent magnetic heads having different azimuth angles. , it is possible to obtain a good multi-speed reproduction image without significantly reducing the reproduction output.

[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 magnetic head, Figure 1C is a schematic diagram of the head trajectory during multi-speed image reproduction, FIG. 2 is a schematic diagram of the head output during conventional multi-speed image reproduction. Second
5 to 5 are diagrams showing an embodiment of the device of the present invention,
Figure 2A is a diagram showing the magnetic head arrangement, Figure 2B is a diagram showing the gap relationship of the magnetic heads, Figure 2C is a schematic diagram of the output of each head, Figure 2D is a diagram of the combined head output, Figure 3 This figure shows the phase relationship of the chroma signals of the recording track, FIG. 4 is a block diagram of a reproduction system circuit, and FIG. 5 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)

[Scope of Claims] 1. First and second magnetic heads having different azimuth angles, each of which is disposed near the first magnetic head and the second magnetic head, the second magnetic head and the first magnetic head and a third magnetic head and a fourth magnetic head, each having the same azimuth angle, to reproduce a multi-speed image. means for creating switching pulses for the magnetic head; phase changing means for changing the phase of the carrier signal to restore the low frequency converted color signal; and RF used for switching the reproduction output of the magnetic head during normal reproduction. means for creating a phase control signal during multi-speed playback based on the switching pulse and the switching pulse; and a horizontal synchronization signal that is separated from the RF switching pulse and playback signal during normal playback as a control signal to the phase change means. 1. A magnetic recording and reproducing apparatus, comprising a selection means for selecting a signal based on the signal, and selecting a signal based on the phase control signal and the horizontal synchronization signal during the multi-speed reproduction.