JPS6055886B2 - Magnetic recording and reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotary head type magnetic recording and reproducing apparatus (hereinafter referred to as a VTR) that sequentially records video signals as discontinuous recording trajectories on a magnetic recording medium using a plurality of rotary heads. , it is intended to enable recording and reproduction of audio signals even if the moving speed of the magnetic recording medium becomes sufficiently low.

Conventionally, VTRs have been configured such that video signals are sequentially recorded by a rotary head as a recording locus inclined with respect to the longitudinal direction of a magnetic tape, and audio signals are recorded at an end of the magnetic tape by a fixed head. In such VTRs, the recording secrecy of video signals has significantly improved due to improvements in magnetic tapes and heads, advances in signal processing technology, improvements in mechanical precision, and advances in control technology.

For example, if we take a VHS system (4-hour recording) VTR, it is about 92 times as much as a broadcast VTR (2-inch tape, 4-head type), and about 11 times as much as an EIAJ pure-1 type VTR.
The recording density has been doubled.

Note that in the VHS system VTR mentioned above, a tape with a width of 112 inches is used, and the tape running speed is 1.65 cm/
It is marked as S. VTRs with high-density recording
The characteristics of tapes and heads are also improving.
The trend is for higher density recording to continue in the future. If we were able to double the recording density from now, then 11
When using 2 inch tape, the tape speed is approx.
The speed becomes slow as /S. Days like this,
As the speed decreases, it becomes extremely difficult to record audio signals with good sound quality using the conventional fixed head recording method for the following reasons. (a) When the speed becomes low, the recording wavelength becomes short, making it difficult to record and reproduce high frequencies, making it impossible to obtain a sufficient audio band (10 KHz or more) (at a tape speed of 1C)
71/S, the limit of current technology is about 5 KHz. )
. (b) As the speed decreases, the playback head output decreases.
/N deteriorates and becomes more susceptible to hum. (c) As the speed becomes lower, the dynamic range of the signal recording level becomes narrower and distortion becomes more likely to occur. (d) There is a limit to the degree of mechanism, and wow and flutter become large. Based on the various conditions mentioned above, while there is plenty of room for higher density for video signals, factors are occurring that are hindering higher density for audio signal recording. Recognize.

One way to increase the tape speed even if the recording density of the video signal is increased is to narrow the tape width to 114 inches or 118 inches.
If the tape length is narrowed to 14 inches, the tape length will be twice that of a 112 inch tape (assuming the recording density is constant, the shape of the tape cassette will be slightly thinner (the thickness of the case, the thickness of the reel hub) However, since the space between the reel and the case remains the same, the surface area will not be halved but will be around 213).The surface area will be larger, and for a cassette that can record for 2 hours, it will be 1'
This has the disadvantage that it becomes extremely large compared to the cassette shape when 2-inch tape is used, resulting in an unbalanced product.

If the tape width is further narrowed to 118 inches, the tape speed can be increased, but the surface area becomes even larger and the cassette shape becomes extremely unbalanced. Apart from this shape problem, there are also problems when recording and reproducing video signals.
If the tape width is narrowed, skew distortion (temporal discontinuity of the signal at the head switching position) due to expansion and contraction of the tape will occur more easily, and the tilt angle of the video track (with respect to the tape running direction) will become smaller. Being easily affected by waping and making compatible playback difficult;
Furthermore, the air film formation between the rotating cylinder and the tape is insufficient, resulting in poor tape running stability.
It is well known that a wider tape width is advantageous from the viewpoint of recording and reproducing video signals, as there are problems such as the occurrence of jitter. As mentioned above, the bottleneck in trying to further improve the recording density of TR and maintain the desired shape of the cassette lies in the recording and playback of audio signals, which cannot be solved using conventional fixed head recording and playback methods. I understand. One way to solve this problem is to record and play back the FM-modulated audio signal by multiplexing it on the low frequency side outside the band of the FM-modulated video signal, for example, as is used in video discs. is possible.

If the audio signal is frequency-multiplexed with the video signal and recorded, it becomes impossible to re-record only the audio signal (hereinafter referred to as after-recording). Although it may be possible to use a playback-only device such as a video disc, it is a fatal flaw that dubbing cannot be performed on a device that can record and play back, such as a VTR. In view of the above-mentioned problems, the present invention provides an audio signal recording method that is suitable for high-density recording and is also capable of dubbing. This will be explained below using a specific example. FIG. 1 is a diagram for explaining the tape recording state of a conventional two-rotation, head type helical scan VTR.

The magnetic tape 1 is approximately 18 discs (180 degrees + 2
α) The tape is wound, and the video signals are sequentially recorded on the tape as a diagonal discontinuous recording trajectory 3 by the rotary heads H^, HB. An audio signal is recorded on the upper end of the tape by a fixed audio head 4. Further, a control signal as a reference signal during reproduction is recorded by the control head 5 at the lower end of the tape. In contrast to such conventional methods, in the present invention, as shown in the specific example of FIG. 2, audio signals are recorded by a rotating head without providing a fixed head for audio signals. The magnetic tape 1 is wound around a rotary head cylinder 2 by θ more than the conventional method (that is, by 180+2α+0), and the audio signal is compressed and recorded on the upper end 6 of the tape corresponding to the θ portion. Next, a specific circuit configuration for realizing the above recording method will be explained with reference to FIGS. 3 and 4.

Note that FIG. 5 is a timing diagram to supplement FIGS. 3 and 4. In FIG. 3, a video signal to be recorded is inputted to a terminal 7, and is converted into an FM wave by a frequency modulator (FM modulator) 8.

This FM wave is gated by gate circuits 9 and 10 and by pulses from a gate pulse generator 15. This gate pulse generator 15 is configured to generate various timing pulses based on the output signal of the detector PG that detects the rotational phase of the rotary heads HA and HB.
That is, as shown in FIG. 5, with respect to the vertical synchronization signal of the input video signal A, the timing of the PG pulse control is configured to occur at a position that is advanced by, for example, seven horizontal synchronization periods (denoted as 7H) from the vertical synchronization signal. The pulses for gating the gate circuits 9 and 10 are given as shown in FIGS. 3 and 2, respectively, with pulses whose stop periods substantially overlap each other, with reference to the pulse width of the gate period. That is, gated FM waves are obtained as shown in FIG.
Guided by 12. On the other hand, the audio signal input to the terminal 16 becomes a time-compressed signal by the time compression circuit 17, and its output is guided to the FM modulator 19.

Note that a synchronization signal separated from the input video signal by a synchronization separation circuit 18 is introduced to the time compressor 17. This time compression circuit will be described in detail later. The audio signals compressed and converted into FM waves in this way are guided to gate circuits 20 and 21, gated by gate pulses of chi and ri, respectively, and gated FM waves of null and ru, respectively.
The waves are guided to adders 11 and 12 as M waves, respectively.
The audio FM signal is added to the video signal, and the video signal and the audio signal are added. The pulses 1 and 2 are created, for example, by driving a monostable multi at the falling edge of the pulses 3 and 2. The outputs of the adders 11 and 12 are sent to the recording amplifier 13,
Data is recorded on the magnetic medium in the form shown in FIG. 2 through the single recording/reproducing changeover switches SW1 and SW2 rotary magnetic heads HA and H8, respectively.

When reproducing the composite signal recorded as described above,
The signals reproduced by the magnetic heads HA and HB pass through switches SWl and SW2, respectively, and are sent to preamplifiers 22 and 2.
3 respectively.

The outputs of the preamplifiers 22 and 23 are each connected to a gate circuit 24.
, 25 and 29, 30. A pulse E created by driving a flip-flop circuit with a PG pulse low is guided to the gate circuit 24, and the Hi period of the pulse E is outputted to the reproduced FM video signal. Further, a pulse having a polarity opposite to that of E is applied to the gate circuit 25, and the reproduced FM video signal of V is gated for a Hi period. and gate circuit 24
, 25 are added by an adder 26 to produce continuous reproduction FM.
A video signal is obtained. On the other hand, gate circuits 29, 30
1 and 2 pulses are added as gate pulses to the output signals, respectively, and null and null FM audio signals are obtained as the outputs, and the two outputs are added together in an adder circuit 31 and guided to an FM demodulation circuit 32.

The FM video signal output from the adder circuit 26 is led to an FM demodulator 27, and a reproduced video signal is obtained at its output terminal 28. On the other hand, the compressed audio signal demodulated by the FM demodulator 32 is led to a time axis expansion circuit 33, where it is time expanded using the output of the synchronization signal separation circuit 34 as a reference, and a continuous reproduced audio signal is obtained at the output terminal 35. It will be done.

Note that the time expansion circuit 33 will be described later. Next, the audio signal time compression circuit 17 will be explained with reference to FIG. The audio signal input to the terminal 16 is guided to two systems of memory circuits 36 and 37. On the other hand, the output of the sync separation circuit 1.8 is led to the input terminal 1'' in FIG. 4, and is led to the horizontal sync signal separation circuit 38 and the vertical sync signal separation circuit 39, respectively.

The output of the horizontal synchronization signal separation circuit 38 is guided to a write clock generator 40 and a read clock generator 45. The write clock generator 40 generates a clock having, for example, twice the horizontal synchronizing signal frequency FH, that is, approximately Fw=32 KHz. With this clock signal of 2fH=32KHZ, it is possible to write into each memory an audio signal having a frequency component up to approximately half the clock frequency, that is, approximately 1000 kHz. On the other hand, the output of the vertical synchronization signal separation circuit 39 is led to the flip-flop circuit 41,
In the case of the C signal, gate pulses Q and Q of 25 Hz in the case of the PAL signal are obtained.

The gate pulses Q and Q gate the write clock gate circuits 43 and 44, respectively, and apply the write clock to the memory circuits 36 and 37 alternately every field period, thereby inputting the input audio signal. Memorize them alternately. In this case, the number of storage bits of the memory is 525 bits (NTSC). That is, the input audio signal Al in Figure 5
, A2 portions are stored in the memory 36, for example, as the force Al, A2 portions, and the B1, B2 portions of the input voice are stored in the memory 37 as the “W” Bl, B2, . . . portions. The signals thus stored in the memory are read out by the clock of the read clock generator 45. For example, if this read clock pulse is selected to be 4 fH of the horizontal synchronizing signal frequency FH = 40fH, then the audio signal τ9/20j11 written during the period τ, = 1/Fv (F9 is the vertical scanning frequency)
It will be read out in 8 seconds. That is, the information of Al, A2, .
・Information B read out and stored in the memory 37
i, B2... are B″1, B″2, etc. in Figure 5.
... is compressed and read out in a period of 1/20. Then, the read compressed audio signal is obtained as an output of the adder circuit 48 in the form shown in the figure. Now, the timing of creating this read clock pulse can be configured as follows, for example.

That is, the gate pulse generator 42 generates a gate pulse corresponding to 525 read clocks using the leading edge of the vertical synchronization signal separated by 39 as a reference, and the gate pulse generator 42 generates a gate pulse corresponding to 525 read clocks.
6 and 47, the read clock is gated alternately every field.

Further, the timing of the gates 46 and 47 is controlled by a gate pulse generator 42 using the output of the flip-flop 41 so as to be synchronized with the timing of the flip-flop 41. be done. In addition,
In order to match the width of the generated pulses of 42 to 525 read clocks, it is reliable to count the read clocks, but in the case of recording, the pulse width does not necessarily have to match 525; it is slightly more than that. There is no problem even if it is a wide pulse.

The thus compressed audio signal is obtained at the terminal 49, and this signal is turned into an FM wave by the FM modulation circuit 19 in FIG. 3 and gated by the gate circuits 20 and 21. In this case, the gate timing is as described in 1 above. It is gated wider than the period in which the compressed signal YO exists. By doing so, it is possible to prevent noise caused by transients generated when switching carriers during FM demodulation from interfering with the audio signal. Next, the expansion circuit 33 during reproduction will be described.

The reproduction side decompression circuit can also have the same configuration as the recording side compression circuit. The only difference is that the write clock generator 40 during recording shown in FIG. Vertical sync pulse (39 outputs)
Instead of being driven by the dotted line, it may be configured to be triggered by the trailing edge of the write pulse (during reproduction) generated by the gate pulse generator 42, as shown by the broken line. In addition,
In order to determine the polarity of the flip-flop 41, it is necessary to reset the pulse flip-flop 41 generated by. Compressed signals reproduced in this manner B''., A''1, B''1, A''2,, B'' in Fig. 5
2... is expanded to BIO, A″1, B11,
A″2, BI2, etc., and the output terminal of the decompression circuit has approximately one field worth of video signal (
A continuous audio signal delayed by approximately 16 msec) is obtained. Generally, if the delay time difference between the video signal and the audio signal is less than about 50 n1 sec, it will not be detected, so the deviation of about 16 msec in this case is not a problem at all.

Now, in the above explanation, the memory element is assumed to be an analog memory element such as a BBDl capacitor memory or a CCD, but if an A/D converter is provided in front of the memory element in the above explanation, the memory can be a digital memory. It is clear that it is possible to use

In this case, by providing a D//A at the memory output to restore the compressed analog signal, the subsequent processing will be exactly the same. Now, let's consider the frequency band of the audio signal when it is compressed.

When an audio signal of about 15 KHz is time-compressed 20 times as described above, its frequency band becomes 300 KHz.

300KHz frequency band is video signal band approximately 3M
When FM is still sufficiently narrow with respect to Hz, the carrier can be set arbitrarily between several hundred K pressure and several MHz, and recording and reproduction with a sufficiently good S/N can be performed.

This means that the degree of audio compression is not just 1/20, but approximately 1/20.
This shows that it is possible to record even when compressed to about 0.
It also shows that it is possible to perform frequency-division recording by frequency modulating different carriers with two or more signals.
In addition, in the case of the above-described specific example, the angle 0 at which the tape is wound more than the conventional one in FIG. 2 may be made slightly larger, approximately 1800/20?9, and the effect on tape runnability can be ignored.

Although the method of recording a compressed audio signal by FM modulation has been described, it is clear that phase modulation, amplitude modulation, and other methods may be used instead of FM modulation. Now, in the explanation of the specific example above, when a compressed and recorded audio signal is expanded by an expansion circuit during playback, a method was described in which the starting point when writing to memory is the leading edge of the playback vertical synchronization signal. Another method for accurately determining the memory write timing during reproduction without using the reproduction vertical synchronization signal will be described with reference to FIG.

FIG. 6A shows the waveform of the video signal in the vicinity of vertical synchronization, and V indicates the vertical synchronization signal.

6 and 6 are signals FM-modulated by the video signal O in FIG. are recorded in an overlapping manner. On the other hand, the audio signal is compressed as described above, and becomes as shown in a in Fig. 6, 2. A burst signal P made from a clock signal, for example, is inserted immediately before a, and this burst signal P is terminated at the time of playback. It is possible to start writing to the memory after a certain period of time from the point (which may be (a)).

The second signal is FM modulated and gated for a wider period before and after the second signal to obtain an FM wave like E. Ho's F
The M wave is added to the FM wave of the mouth to form a composite signal such as .A sound FM signal is recorded on a part of the magnetic tape with a winding angle of 0 by a rotating magnetic head. In addition, as a method to prevent crosstalk interference even if tracking deviation occurs during playback, the FM of the audio signal FM circuit is
It is also possible to adopt a method in which carrier frequencies are changed so that their bands do not overlap with each other.

For this purpose, for example, the FM carrier shown in FIG.
After 0, a bandpass filter corresponding to each FM carrier may be provided. As a method of removing crosstalk interference from adjacent tracks, it is also effective to use azimuth recording, which is also used in HS system VTRs, to reduce the playback signal from adjacent tracks, as shown in Figure 7. It is.

That is, by tilting the inclination angles of the gaps between the rotating magnetic heads HA and HB in opposite directions, crosstalk from adjacent tracks can be reduced by taking advantage of the fact that azimuth loss increases when reproducing adjacent tracks. . In the above explanation, a specific example was described in which the control signal is recorded at the bottom end of the tape, and the audio signal is compressed and recorded at the top end of the tape. Place it on the top edge (depending on your system, a control track may not be necessary)
, the audio signal is compressed and recorded at the bottom of the tape. Although the timing relationship in the circuit configuration in this case changes slightly, it can be configured based on the same concept as in the specific example described above. In this case, the excess angle 0 of the wrapping angle of the tape in FIG. 2 may be increased by wrapping the tape more toward the head entry side (left side in the figure). In the present invention, a case has been described in which an audio signal is compressed and recorded with a rotary head in a two-head helical scan VTR. It can be applied to various devices.

Therefore, it can be used not only for tape-shaped recording media but also for devices that record on card-shaped recording media. As described above, according to the present invention, it is possible to record an audio signal regardless of whether the tape speed becomes slower as the density of TR becomes higher in the future, and has the following features.

(1) The 15K ratio of the audio band can be secured regardless of the tape speed.

(2) Almost unaffected by wow and flutter.

In other words, the rotational unevenness of a VTR is extremely small, and the wow and flutter components of tape running are caused by V, assuming that the tape speed is V, and the rotational peripheral speed of the bend is VH.
/ Becomes VH. And normally Vt/VH is 1/100 or less. (b) By recording with a rotating head, wow and flutter in the audio signal are reduced to a negligible level.

(3) A fixed head for audio recording and playback is no longer necessary, and a rotating head for video recording can be shared.

(4) Although this method records and reproduces both video and audio signals using a rotating magnetic head, it is possible to perform after-recording of the audio signals.

In other words, it is possible to erase the end of the tape corresponding to the audio recording part with a fixed erasing head and re-record it, or
Re-recording on top of a recorded audio signal erases the previously recorded signal and leaves behind a new signal. This is possible because the audio signal is modulated at a high frequency and recorded at a short wavelength. (5) When re-recording on top of a previously recorded audio signal, the recording level of the audio signal to be re-recorded is relative to the video head playback level of the video signal monitored during audio re-recording (after-recording). Since the signal is large, the re-recorded audio signal mixes with the reproduced video signal using a rotary transformer, etc., resulting in noise.However, if the time-compressed audio signal recording position is at the beginning of each track, as in the case of Fig. 8, The noise position on the monitor screen is at the bottom edge of the screen, so it is not very noticeable.An even more important feature is that no noise occurs during the vertical blanking period, and the vertical synchronization of the monitor screen is not disturbed (especially during post-recording). The screen also has the advantage of being stable.

[Brief explanation of the drawing]

Fig. 1A is a side view showing an outline of a conventional video tape recorder, and Fig. 2A is a side view showing an outline of the video tape recorder of the present invention.
The figure is a block diagram for explaining a concrete example for realizing the present invention, Figure 4 is a block diagram of a concrete example of the time compression (expansion) circuit in Figure 3, and Figure 5 shows the operation of Figure 3. FIG. 6 is a waveform diagram for explaining another specific example of determining the writing timing to the memory circuit during playback. FIGS. 1 and 8 are timing and waveform diagrams for explaining other examples of the present invention. It is a figure which shows the recording pattern on the tape in an Example. 7...Video signal input terminal, 8, 19...
...FM modulator, 9, 10, 20, 21, 24, 25,
29, 30... Gate circuit, 16...
Audio signal input terminal, 17... Time compression circuit, 2
7, 32...FM demodulator, 33...Time expansion circuit, HA, HB...Rotating head.

Claims (1)

[Claims] 1 A plurality of rotating magnetic heads are used to sequentially record a television signal in discontinuous recording trajectories in units of one field. When recording on a medium, the angle at which the magnetic medium is wound around the cylinder for the rotating magnetic head is set at an angle greater than the winding angle normally required to record a television signal, on the side where the head and the magnetic medium begin to come into contact. On the extension of each recording locus where the television signal is recorded, the time is compressed in units of one field period to the part before the recording position of the vertical synchronization signal recorded at the beginning of the stop of each recording locus. 1. A magnetic recording and reproducing method characterized in that a television signal is recorded using the rotating magnetic head, and the reproduced audio signal is time-expanded to obtain a continuous reproduced audio signal.