JPH04238480A - Switching pulse generating circuit - Google Patents

Abstract

PURPOSE:To provide the generating method of a head switching pulse at usual reproduction and a special reproduction in the device in which a magnetic tape is wound on almost the entire circumference of a rotary head drum of a VTR in order to make the diameter of the drum small. CONSTITUTION:Reproduction levels of a couple of video heads are compared and a switching pulse is generated in response to the result of comparison and an output of a video head in use is selected based on the pulse at usual reproduction start, field still and high speed reproduction. The expected normal reproduction and special reproduction are realized, a reproduction start time is reduced, an optional field is selected for a field still and flicker is reduced and segments of high speed search picture are made equal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a switching pulse used for selecting a video head, controlling the phase rotation direction of a chromaticity signal, etc. in a magnetic recording/reproducing device such as a camera-integrated VTR that is required to be compact and lightweight. Regarding the generation circuit of
This relates to the operation including special playback such as field still and high speed search.

0002

2. Description of the Related Art In recent years, there has been a constant demand for smaller and lighter VTRs with built-in cameras, and technological development has been progressing to reduce the diameter of the rotating head drum. Special Public Service 1986-5130
Publication No. 6 discloses a method of winding a videotape over almost the entire circumference of a rotary head drum to form a recording pattern that satisfies the standards for a standard two-head 180 degree winding type VTR.

In addition, special playback functions such as field still and high-speed search have become commonplace in VTRs, regardless of whether they are stationary or have an integrated camera. For example, Tokuho 1-5
As described in Japanese Patent No. 3958, a total of two so-called double azimuth heads, in which two video heads with different azimuth angles are mounted very close to each other, are installed 180 degrees apart on a rotating head drum. A common method is to switch the playback output accordingly.

0004

[Problem to be solved by the invention]
Publication No. 51306 discloses a recording-only device, and therefore does not mention matters regarding playback.

[0005] In Japanese Patent Publication No. 1-53958, it is possible to perform special playback such as field still and high-speed search. However, there is no mention of a method unique to this method when used in a VTR using a small head drum as described in Japanese Patent Publication No. 60-51306. In addition, since two double azimuth heads with a special structure are used, the price is high, and in the case of field still, the playback output of the two video heads is switched at one field cycle, so the output level of each video head is There is a problem in that image flickering occurs due to differences in frequency characteristics.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to improve the playback operation, especially special playback, in a VTR using a small head drum, without causing inconveniences such as flickering. An object of the present invention is to provide a switching pulse generation circuit that can perform operations.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention compares the playback levels of two video heads at least at startup during normal playback at the same speed as during recording. Then, a pulse whose polarity is determined to select the output of the video head with the higher level is generated as a switching pulse, and during field still playback, which is performed by stopping the running of the magnetic tape, the output of the two video heads mentioned above is generated. Compares both levels and generates a pulse with fixed polarity as a switching pulse so as to select the video head output with the higher level,
During high-speed searching, in which the magnetic tape is run at a faster speed than during recording, the levels of the two video heads are compared, and the polarity is adjusted so that the output of the video head with the higher level is always selected. A pulse that is inverted at any time is generated as a switching pulse.

[0008]

[Operation] By generating switching pulses as described above, VTR using a small rotating head drum
In this case, not only normal playback operation but also special playback operation can be realized.

Moreover, in normal playback operations, by using the above method, the lock-in time of the tracking servo at startup can be shortened.

[0010] During field still playback, by using the above-described method, a still image of an arbitrary field can be output, and the flicker phenomenon of the playback image can also be reduced.

[0011] During high-speed search reproduction, by obtaining a search image that does not generate noise bands, the segments of the reproduced image are equally spaced, and the sense of strangeness can be reduced.

0012

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a reproducing circuit of a VTR having a switching pulse generating circuit as an embodiment of the present invention, and FIG. 2 is a recording circuit of a VTR having a switching pulse generating circuit as an embodiment of the present invention. 3 is a plan view showing the periphery of a rotating head drum having the heads shown in FIGS. 1 and 2, and FIG. 4 is a timing diagram showing the timing of input and output signals of the time axis compression circuit shown in FIG. 2.

[0014] Here, an explanation will be given of an example in which a VHS Hi-Fi standard VTR is used among VTRs suitable for an integrated camera, but the scope of application is not limited to this. The VHS HiFi standard recording method of FM-modulating audio signals and multiplexing them into the deep layer of a magnetic tape is detailed in Japanese Patent Publication No. 2-27721.

First, FIG. 3 will be described.

In FIG. 3, the video heads 2A and 2B are mounted very close to each other at the same height, and their track widths are approximately the same, but their azimuth angles are different (VHS
+6° and -6°). Ideally, it would be desirable for both to be in exactly the same position, but since this is impossible, they are mounted with the mounting interval A in the figure set to a constant value. Also, the audio heads 33A and 33B are installed in different positions, very close to each other, at the same height, and have almost the same track width, but their azimuth angles are different (+30° for VHS Hifi). -30°)
. It is also desirable that the two be located in exactly the same position, but since this is not possible, they are attached at a fixed interval. The audio heads 33A, 33B scan the magnetic tape 1 in advance of the video heads 2A, 2B, and record and reproduce the audio FM modulation signal in the deep part of the recording track of the video signal.

Further, the rotating surface 72 of the rotating head drum rotates once in one field period (one vertical period) according to the broadcasting standard.
The above video heads 2A, 2B and audio head 3
3A and 33B perform recording or normal reproduction alternately every rotation of the rotary head drum. Therefore, assuming that the rotating surface 72 of the rotating head drum rotates in the direction of the arrow in FIG. The signal recorded with video head 2B
It is necessary to delay the signal recorded by the time corresponding to the installation interval A. The same is true between the audio head 33A and the audio head 33B.

The magnetic tape 1 has inclined pins 73A and 73B.
The position is regulated by , and it is wound almost all the way around the rotating head drum, but it is difficult to wrap it completely 360 degrees, and there is a gap only at the rotation angle α in the figure.

Therefore, the gap portion is used as the video head 2A.
, 2B, and audio heads 33A and 33B, each head cannot record or reproduce data, so during recording, it is necessary to compress the time axis of the signal by (360-α)/360 times in units of one field. During playback, it is necessary to expand the time axis at the same rate and output it.

Based on the above, the signal is processed as shown in FIG.

Assuming that the video head 2A and audio head 33A have +azimuth, and the video head 2B and audio head 33B have -azimuth, during recording, time axis compression circuits 51, 60, and 65 of FIG. 2, which will be described later, A continuous input signal as shown in (a) is compressed on the time axis by (360-α)/360 times in one field unit, and a signal recorded with a +azimuth head is recorded with a -azimuth head. It is necessary to delay the output signal by a time corresponding to the mounting interval to produce an output signal as shown in FIG. 4(b). Of course, since the mounting positions of the video heads 2A, 2B and the audio heads 33A, 33B are greatly different, the timings of the signal blank (there may be a signal since it is not recorded) in FIG. 4(b) are shifted from each other.

Furthermore, during playback, it is necessary to perform the reverse processing to the above-described processing in the time axis expansion circuits 12, 19, and 28 of FIG. 1, which will be described later.

[0023] By performing the above processing, VHS
Recording and reproducing operations can be performed in accordance with the HiFi standard.

Next, the operation during recording will be explained based on FIG.

In FIG. 2, 35 is a composite signal input terminal, 36A and 36B are a pair of input terminals, and 3
Luminance signal from 6A, (455/2)f from 36B
h [fh=4500/286kHz; horizontal synchronization frequency]
A chromaticity signal obtained by orthogonal two-phase modulation of a subcarrier having a frequency of is inputted. 61 is an input terminal for audio signals. 4
4 is the composite video signal output terminal, 45A, 45B
are a pair of output terminals, and the brightness signal from 45A is
A chromaticity signal is output from 45B. These 44, 45
A and 45B are supplied to a monitor television or a viewfinder external to the apparatus, so that the image to be recorded can be monitored. Further, from 62, an audio signal to be recorded is output for monitoring.

A composite signal such as a broadcast from the outside is connected to the input terminal 35, and a YC (luminance chromaticity) separated signal from a camera (not shown) inside the device is connected to input terminals 36A and 36B, respectively.

The switches 37, 41, 43, and 56 are connected in the direction shown when recording the signals from the input terminals 36A and 36B, and in the opposite direction when recording the signal from the input terminal 35. Ru. Therefore, the composite signal from the input terminal 35 is recorded via the YC separation circuit 40, and the YC separation signals from the input terminals 36A and 36B are recorded without passing through this. Further, the adder 42 adds the luminance signal and the chromaticity signal, and a desired signal is always output to the output terminals 44, 45A, and 45B.

The switch 39 connects the input signal to the AGC circuit 38.
The user can select whether or not to pass through the . When the camera side has an AGC circuit and gain control is not required on the VTR side, the connection is made in the direction shown in the figure, and when recording broadcasts, etc., the connection is made in the opposite direction.

A case will be described below in which video signals from the input terminals 36A and 36B are recorded without passing through the AGC circuit 38. At this time, switches 37, 39, 41, 43, and 56 are all connected in the direction shown.

The luminance signal from the input terminal 36A passes through switches 39 and 41, is band-limited by an LPF 46, and is applied to a clamp circuit 49 and a sync separation circuit 47. Synchronous separation circuit 4
Based on the timing of the synchronous separation pulse which is the output of 7,
The clamp circuit 49 clamps the tip of the synchronization signal to a constant level, and connects the nonlinear emphasis circuit 50 and the AGC.
It is added to the detection circuit 48.

The AGC detection circuit 48 adjusts the gain of the AGC circuit 38 based on the timing of this signal and the previous synchronization pulse, and controls the amplitude of the synchronization signal output from the clamp circuit 49 to be constant. The nonlinear emphasis circuit 50 is given a characteristic of relatively emphasizing a high-frequency, minute-level signal compared to a large-amplitude signal. As is well known, the purpose is to improve the S/N ratio, but as mentioned above, since the characteristics are nonlinear with respect to the signal amplitude, the maximum amplitude does not increase in proportion to the amount of emphasis for small signals, and the time axis compression in the subsequent stage It also acts to reduce quantization noise in circuit 51.

The time axis compression circuit 51 processes switching pulses (
Based on the polarity of the switching pulse that is delayed by the tack pulse delay circuit 32, the luminance signal is time axis compressed in units of one field as described above, and Every other time, the amount of delay given to the signal is switched and output for a time corresponding to the installation interval A (FIG. 3).

The linear emphasis circuit 52 is given a characteristic of uniformly emphasizing high frequency signals regardless of the level. After that, it becomes an FM modulation signal in the FM modulator 53, and the H
A PF 54 removes low-frequency components (approximately 1.5 MHz or less) and adds them to one end of an adder 55. Note that after the time axis compression circuit 51, the frequency axis is shifted by 360/(360-α), so the emphasis time constant, FM carrier frequency, etc. must be set to a higher frequency side than the standard to meet the VHS standard. It is not possible to create a recording pattern.

Next, the chromaticity signal inputted from the input terminal 36B is subjected to a BPF 57 in which out-of-band components are removed, and a chromaticity signal recording processing circuit 58 performs recording processing based on the VHS standard. In other words, ACC (Automatic Chrom
a Control) processing to keep the level of the burst signal constant, and burst emphasis processing to enhance the burst signal by 6 dB. Then, by low-frequency conversion processing, the subcarrier is phase-rotated every horizontal period to convert the frequency based on the synchronization pulse so as to comply with the VHS standard. At this time, based on the polarity of the switching pulse from the tack pulse delay circuit 32, the direction of phase rotation is switched between the field recorded by the +azimuth video head 2A and the field recorded by the -azimuth video head 2B.

The LPF 59 removes unnecessary components outside the band. Then, in the time axis compression circuit 60, based on the polarity of the switching pulse from the tack pulse delay circuit 32, the chromaticity signal is time axis compressed field by field in the same way as the luminance signal described above, and the video head is compressed every other field. The amount of delay given to the signal is switched and output by a time corresponding to the installation interval A (FIG. 3). Thereafter, it is added to one end of the previous adder 55.

Next, a microphone (
(not shown) etc. is input. After a recording noise reduction circuit 63 emphasizes a minute level signal, an LPF 64 removes out-of-band components.

The time axis compression circuit 65 compresses the time axis of the audio signal field by field based on the polarity of the switching pulse from the tack pulse generation circuit 4, and compresses the time axis of the audio signal in units of one field as described above.
The amount of delay given to the signal is switched and output for a time corresponding to the installation interval (Fig. 3).

After that, the FM modulator 66 converts the signal into an FM modulated signal with a carrier wave having a frequency 360/(360-α) times the standard carrier frequency, and the BPF 32 removes out-of-band components, and the signal is applied to the recording amplifier 69B.

This audio FM modulation signal is transmitted to the recording amplifier 69B.
Based on the polarity of the switching pulse from the tack pulse generation circuit 4, the audio heads 33A to 33B are amplified every field by the operation of the switch 70B, which switches every field (every rotation of the rotary head drum). The image is recorded into the deep part of the magnetic tape 1 prior to the image.

The luminance recording signal and the chromaticity recording signal which are the outputs of the adder 55 are amplified by the recording amplifier 69A, and then are converted to 1 based on the polarity of the switching pulse from the tack pulse delay circuit 32. By the operation of the switch 70A which is switched for each field (every rotation of the rotary head drum), the audio signal is superimposed on the previous recording pattern of the audio signal via the video head 2A or 2B for each field.
It is recorded on the magnetic tape 1. (The audio head runs on the magnetic tape in advance of the video head.) Switches 70A and 70B are used to determine which azimuth angle head is used to record a certain field of signals. Unlike a general 180-degree winding type two-head VTR, all heads are in contact with the magnetic tape except for the gap portion shown in FIG. There is no fixed relationship between the rotational phase of the rotary head drum and the rotational phase of the rotary head drum. Care should be taken so that the azimuth angle relationship between the recording track of the audio signal and the recording track of the video signal, which are superimposed on each other, conforms to the standard.

However, +azimuth heads 2A, 33A,
- For both the azimuth heads 2B and 33B, the time axis compression circuits 51, 60, and 65 switch delays (phase shifts) every other field, and the chromaticity signal recording processing circuit 58 performs subcarrier phase rotation. There is a fixed relationship between each direction.

Therefore, in this embodiment, the switching pulse (30 Hz) generated by the tack pulse generation circuit 4 drives the time axis compression circuit 65 and the switch 70B all at once. The switching pulse after being delayed by the tack pulse delay circuit 32 drives the time axis compression circuits 51 and 60, the chromaticity signal recording processing circuit 58, and the switch 70A all at once. It goes without saying that the delay time in the delay circuit 32 is determined depending on the difference in the mounting positions of the video heads 2A, 2B and the audio heads 33A, 33B in FIG. 3. The timing of switching the polarity of the switching pulse may be set when each head is not in contact with the magnetic tape 1, that is, when it reaches the gap portion (portion α in FIG. 3).

Next, the operation during reproduction will be explained using FIG. 1.

At the time of reproduction, consideration must be given not only to normal reproduction performed at the same speed as during recording, but also to special reproduction, which has become common knowledge, such as field still and high-speed search.

First, the tracking servo during normal playback will be described. (The components of this part are not shown in Figure 1.) In a conventional 180-degree winding type two-head VTR, only one head is in contact with the magnetic tape, so the video head and the recording track are connected to each other. Tracking servo must be applied to match the azimuth angle. As is well known, the VHS standard VTR servo system is CT.
L method (recording and reproducing control signals using a fixed head, and matching the recording and track tracing), in which, for example, a +azimuth video head enters the magnetic tape in response to a control signal that is reproduced every two fields. phase lock the timing.

In the apparatus of the present invention, one method is to similarly adjust the running phase of the magnetic tape 1 and the connection of the switch 6A so as to establish a certain relationship between the phase of the control signal and the video head to be selected. There is a way to specify the direction. In this case, the output pulse of the tack pulse delay circuit 32 may be used as the switching pulse applied to the switch 6A etc., as in the case of recording.

Another method is to focus on the fact that both heads are on the magnetic tape 1 at the same time and select the video head regardless of the phase of the control signal. In FIG. 1, the outputs of video heads 2A and 2B are amplified by regenerative amplifiers 3A and 3B, and then applied to one end of each of a level comparator 5 and a switch 6A. A logic signal indicating the result is output as a switching pulse. In other words, since the output of the video head is larger as the azimuth angle matches the recording track being traced, the polarity of the switching pulse output from the level comparator 5 is determined based on the azimuth angle of the recording track being traced. This indicates which video head has the same value. In the switch 6A, switching is controlled by the polarity of the switching pulse output from the level comparator 5, and the output of the video head with a higher level, that is, the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced, is controlled by the polarity of the switching pulse output from the level comparator 5. Output is selected.

In this way, the azimuth angle of the recording track that the video head happens to be in contact with at the time of starting reproduction is selected, so that the lock-in time of the tracking servo can be shortened.

Although the above explanation is only for the video head side, it is natural that the audio head side in this case changes the switching polarity in relation to the video head side. (not shown) Also, during normal playback,
Since the switching pulse is inverted every field, the polarity may be inverted in accordance with the pulse from the tack pulse delay circuit 32 after starting the regeneration in the above-described manner. (Even after the tracking servo locks in, there is no need to switch based on the comparison result of the level comparator 5.) Next, in FIG.
9. The chromaticity signal reproduction processing circuit 20 operates as follows: +azimuth video head 2A, -azimuth video head 2B.
Since the operation differs depending on which reproduction output is processed, the output of the level comparator 5, which indicates the azimuth angle of the recording track being traced, is commonly given to these as well as the switch 6A. Also, for the same reason, the tack pulse generation circuit 4 is connected between the switch 6B and the time axis extension circuit 28.
The switching pulses from the The purpose of the tack pulse delay circuit 32 and the necessary delay time are the same as in the recording described above, so the explanation will be omitted here.

Next, the operation of the signal circuit shown in FIG. 1 will be explained. The playback signal selected with the previous switch 6A is HPF.
7 and LPF18.

The HPF 7 takes out the brightness FM modulation signal, and after making it to a constant amplitude level independent of the sensitivity of the video heads 2A and 2B in the FMAGC circuit 8, it is applied to the dropout detector 16 and the FM demodulator 9.

The dropout detector 16 detects an instantaneous reproduction signal dropout period due to head clogging or the like. Originally, this dropout could only be detected in the reproduced FM signal. Therefore, since detection is performed in a compressed state on the time axis, compensation must be performed before expanding the time axis.

The reproduced signal demodulated by the FM demodulator 9 is subjected to a linear de-emphasis circuit 10 (having the opposite characteristics of the linear emphasis circuit 52 described earlier) to reduce high frequency components and to reduce the S/N.
After the signal is improved and unnecessary high-frequency components associated with FM demodulation are removed by the LPF 11, it is led to the time axis expansion/dropout compensation circuit 12.

Here, processing is performed in reverse to that of the time axis compression circuit 51 during recording to generate a signal based on the original time axis, but prior to that, the above-mentioned dropout compensation is performed. That is, when a dropout is detected at the stage of storing a reproduced signal in the internal memory, a signal from one horizontal cycle before is stored again in place of that signal.

Time axis extension/dropout compensation circuit 12
The output is passed through a non-linear de-emphasis circuit 13 and further processed in a noise clipping circuit 14 in a low noise range. As the noise clipping circuit 14, well-known circuits can be used, such as a base clipping circuit that suppresses high-frequency low-level components, and a line noise canceling circuit that utilizes correlation between lines using a delay line of one horizontal period.

The output of the noise clipping circuit 14 is outputted to the outside from the output terminal 15A, and is also applied to the adder 22 and the sync separation circuit 17.

The LPF 18 extracts a low-frequency converted chromaticity signal. The time axis expansion circuit 19 performs the reverse processing of the time axis compression circuit 60 during recording, and generates a signal based on the original time axis. The chromaticity signal reproduction processing circuit 20 (operation opposite to 58 in FIG. 2) generates subcarrier orthogonal signals similar to the broadcasting standard based on the synchronization pulse from the synchronization separation circuit 17 and the polarity of the switching pulse described above. Return to phase modulation signal. after that,
After interference components from adjacent tracks are removed by the comb filter 21, the signal is output to the outside via the output terminal 15B, and is also provided to the adder 22 at the same time. The output of the adder 22 is a composite signal, and is output from the output terminal 23 to the outside.

An audio FM modulated signal is extracted by the BPF 24 from the reproduced signal selected by the previous switch 6B, and the amplitude is made constant by the FMAGC circuit 25. Dropouts are detected by the dropout detector 31, demodulated by the FM demodulator 26, and unnecessary components are removed by the LPF 27. Time axis expansion/dropout compensation circuit 2
8, the reverse processing of the time axis compression circuit 65 at the time of recording is performed,
Although the signal is based on the original time axis, dropout compensation is performed prior to that. This dropout compensation is different from the previous luminance signal processing and is performed by approximating waveforms before and after dropout.

After that, the noise reduction circuit 29 (FIG. 2
After the S/N is improved by the reverse characteristic of 63), the output terminal 30
output to the outside.

The above is the operation during normal reproduction. next,
Operations during special playback such as field still and high-speed search will be explained.

First, when performing field still, it is best to do the following.

One method is to determine in advance which azimuth of the video head to use the output, as is done in a normal 180-degree winding two-head VTR. When the user issues a still command,
Immediately stop running the magnetic tape 1, and level comparator 5
The polarity of the switching pulse which is the output of is fixed so that a head output of a predetermined azimuth is selected. (The stop position of the magnetic tape is selected so that the video head accurately scans the recording track.) Another method is to compare which azimuth head to use by using the level comparator 5 when the still command is issued. There is a way to decide using the results. That is, when the magnetic tape 1 is stopped,
The comparison result of the level comparator 5 is used to fix the polarity of the switching pulse that is the output so that the reproduction output of the video head with the higher reproduction level is selected. This allows field still to be achieved.

Compared to the former method, the latter method can use any azimuth video head depending on the situation, and can select any field to reproduce still images. In addition, in a normal 180-degree wrap-around two-head VTR, a separate video head is used for each field period during field still, and flickering occurs in the reproduced still image due to the difference in characteristics. There is only one video head, and there is no cause for flickering. Also, when performing a high-speed search, do the following.

Immediately when the user issues a search command, the magnetic tape 1 is run at high speed, and the level comparator 5 constantly determines which of the video heads 2A and 2B has a higher reproduction output, and based on the comparison results. A switching pulse is generated so that the reproduction output with the higher level is always selected by the switch 6A. Therefore, switching of the switch 6A is performed many times during one field. In this way, it is possible to always select the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced, so that a high-speed search image without noise bands on the screen can be obtained.

[0065] Since this level comparison is performed on the time axis of the compressed signal, the switching pulse that is the result of this comparison is used to restore the phase rotation of the subcarrier (given during recording) to the original color. degree signal reproduction processing circuit 20
In order to reproduce a normal chromaticity signal, a normal chromaticity signal cannot be reproduced unless this switching pulse is applied after being time-axis-expanded at the same timing as the reproduction signal in the time-axis expansion circuit 19. (This process is not necessarily necessary because the polarity of the switching pulse does not change within one field in the normal playback and still playback described above.)
In a 0-degree winding two-head VTR, as shown in the cited example above, the +azimuth video head and the -azimuth video head usually have different track widths. This is because the double azimuth head was originally designed to be compatible with both standard mode (for example, 2-hour recording mode) and long-time mode (for example, 6-hour recording mode). In this case, due to switching of the video head during high-speed search, the intervals between segments in the vertical direction appearing on the playback screen become unequal. In this embodiment, the track widths can be set equally for the +azimuth video head 2A and the -azimuth video head 2B, so the vertical segments on the playback screen are equally spaced by switching the switch 6A. It has the characteristic of producing an image that is easy to see with little strangeness.

Furthermore, in conventional VTRs, during high-speed search, the part of the search image that appears on the screen that is played back by the +azimuth video head and the part played by the -azimuth video head are relatively vertically separated. However, in this embodiment, the time axis expansion circuit 1
If a function for shifting the time axis is further provided in sections 2 and 19, the portions reproduced by the video head 2A and the video head 2B will not be misaligned with each other.

Furthermore, the time axis expansion circuits 12 and 19 include H
When performing a high-speed search for unaligned recorded patterns,
It may also have a skew compensation effect.

Furthermore, since the audio signal is not output during special playback as described above, no special processing is necessary for this, and muting can be applied as usual.

[0069] VHS Hifi standard VTR so far
The explanation has been given using an example, but it can also be applied to other things. For example, regular VHS V that is not HiFi standard
It may be TR. In this case, since FM modulation recording of the audio signal is not performed, the audio signal processing system (including the audio head) shown in FIGS. 1 and 2 is removed.

[0070]

As explained above, according to the present invention, in a VTR using a small rotating head drum, by generating switching pulses as described above, not only normal playback operation but also special playback operation can be performed. I can make you do it.

Furthermore, in normal playback operations, the time for lock-in of the tracking servo can be shortened. During field still playback, any field can be selected, and flicker in the playback image can be reduced. During high-speed search, there are no noise bands in the image, the image segments are equally spaced, reducing strange sensations, and the vertical positional deviation of the image that occurs for each head can be corrected. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a reproducing circuit of a magnetic recording/reproducing apparatus having a switching pulse generating circuit as an embodiment of the present invention.

FIG. 2 is a block diagram of a recording circuit of a magnetic recording/reproducing apparatus having a switching pulse generation circuit as an embodiment of the present invention.

FIG. 3 is a plan view of the vicinity of the rotary head drum used in the present invention.

FIG. 4 is a timing diagram showing the timing of input and output signals of the time base compression circuit used in the present invention.

[Explanation of symbols]

1. Magnetic tape 2A. Video head 2B. Video head 3A. Regenerative amplifier 3B. Regenerative amplifier 4. Tack pulse generator5. Level comparator 6A. Switch 6B. Switch 7. HPF 8. FMAGC circuit9. FM demodulator 10. Linear de-emphasis circuit 11. LPF 12. Time axis expansion/dropout compensation circuit 13. Nonlinear de-emphasis circuit 14. Noise clip circuit 15A. Luminance signal output terminal 15B. Chromaticity signal output terminal 16. Dropout detector 17. Synchronous separation circuit 18. LPF 19. Time axis expansion circuit 20. Chromaticity signal reproduction processing circuit 21. Comb filter 22. Adder 23. Composite signal output terminal 24. BPF 25. FMAGC circuit 26. FM demodulator 27. LPF 28. Time axis expansion/dropout compensation circuit 29. Noise reduction circuit 30. Audio signal output terminal

Claims (3)

[Claims] 1. A pair of video heads mounted very close to each other with different azimuth angles of head gaps and at approximately the same height; and a pair of audio heads mounted on a rotary head drum at a position different from the video head, and a magnetic tape is wound around the rotary head drum over an angle slightly less than 360 degrees, and the rotary head drum is mounted on the rotary head drum. The configuration is such that signals are recorded and reproduced by making one rotation during one video field period, and during recording, the video and audio signals to be recorded are rotated once during one video field so as to avoid a period in which the magnetic tape is not wound around the rotating head drum. The time axis is compressed in units of periods, and the recording position on the magnetic tape is shifted due to the difference in the head gap position of the pair of video heads, and the recording position on the magnetic tape is determined due to the difference in the head gap position of the pair of audio heads. a time axis compression circuit that corrects the deviation by switching the amount of delay given to the signal for each field period; A signal is recorded on the magnetic tape via a first switch that alternately supplies a recording signal to the magnetic tape, and during playback, the output of the pair of video heads is switched every rotation of the rotary head drum, and the output of the pair of video heads is alternately and A magnetic field that reproduces and outputs the signal through a second switch that alternately takes out the output of the pair of audio heads, and a time axis expansion circuit that cancels the switching of the time axis compression applied during recording and the delay amount for each field. During recording in a recording/playback device, a switching pulse whose polarity is reversed is generated based on a tack pulse indicating the rotational phase of the rotary head drum during a period when the video head or audio head does not contact the magnetic tape. , is applied to the above-mentioned time axis compression circuit and the first switch, and when starting playback, the playback levels of both the above-mentioned pair of video heads are compared and the output of the video head with the higher level is selected. A switching pulse generation circuit generates a switching pulse to select the output of an audio head corresponding to a video head, and supplies the switching pulse to the above-described time axis expansion circuit and second switch. 2. During playback, when field still playback is performed with the magnetic tape stopped running, the playback levels of both of the pair of video heads are compared and the output of the video head with the higher level is selected. During high-speed search, in which the polarity of the switching pulse is fixed and the magnetic tape is run at a faster speed than during recording, the playback levels of both of the pair of video heads are compared, and the video with the higher level is always selected. 2. The switching pulse generating circuit according to claim 1, wherein the switching pulse generating circuit is configured to generate a switching pulse to select the head output at any time and apply it to the time axis expansion circuit and the second switch. 3. The switching pulse generated during the high-speed search reproduction is time-axis expanded by the time-axis expansion circuit at the same timing as the reproduced video signal, and is provided to the chromaticity signal reproduction processing circuit. The switching pulse generation circuit according to claim 2.