JPH0435821B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention is a magnetic recording/reproducing device (hereinafter referred to as a VTR) that uses a rotating head to sequentially record and reproduce signals as inclined discontinuous recording trajectories on a magnetic tape.
The present invention relates to a detection method for automatically determining a recording mode. Conventional configuration and its problems A Hercal Scan type VTR requires one VTR.
Some VTRs allow you to record by changing the tape feed speed during recording. In such a VTR, it is desirable to automatically determine the recording mode during playback and to play back at the same speed as the recording speed during normal playback. Currently, as a method for realizing this, a method has been proposed in Japanese Patent Application No. 126942/1983 to distinguish the recording mode in a tracking method using four types of pilot signals instead of using conventional control signals. Let me explain using an example. First, a tracking method using four types of pilot signals will be explained. FIG. 1 shows a recorded magnetization locus by the four-frequency pilot signal tracking method, and FIG. 2 is a block diagram of a reproducing circuit for obtaining a tracking error signal. In Fig. 1, A ₁ , B ₁ , A ₂ , B _{2 .} . . are A heads and B heads having different predetermined azimuth angles.
Each recording track is recorded on the head magnetic tape. Arrow 1 indicates the scanning direction of the rotating head. Each recording track contains _f1 to _f4 along with the video signal.
Each pilot signal shown by is sequentially and repeatedly recorded for each field. The recording order of the pilot signals is as shown in FIG. 1, and within one field period, the frequency of one type of pilot signal is set to the value shown in Table 1, for example.

[Table] In Table 1, f _H indicates the frequency of the horizontal synchronizing signal, and 6.5f _H indicates a frequency that is 6.5 times the frequency of the horizontal synchronizing signal. The frequency difference between the pilot signals between each recording track is _fH or _3fH , as shown in FIG. When the head Ai (i=1, 2...) tracks are scanned, the frequency difference between the pilot signal of the scanning track and the pilot signal recorded on the adjacent track on the right side on the paper is always f _H
and that on the left is always 3f _H. When the head scans a Bi track, the relationship is reversed to that described above; the frequency difference between the pilot signals of the scanning track and the adjacent track on the right is always 3f _H , and that on the left is always f _H. Since the pilot signal is a relatively low frequency signal around 100 kHz, the pilot signal recorded on the adjacent track can be reproduced as a crosstalk signal without the head scanning the adjacent track. For example, the pilot signal obtained when the head on-tracks and scans the _A2 track is
It is a composite signal of f ₃ , f ₂ , and f ₄ , and f ₃ has the highest level, and then f ₂ and f ₄ are reproduced at the same level. Head slightly changes from track A ₂ to track B ₂
When reproduction scanning is performed with a shift to the side, the level of the pilot signal obtained decreases in the order of f ₃ , f ₂ , and f ₄ . Therefore, if the difference frequency signals f _H and 3f _H between the pilot signal on the main scanning track and each pilot signal recorded on both adjacent tracks are separated and extracted, and the reproduction levels of both signals are compared, The amount and direction of head deviation from the main scanning track can be known. FIG. 2 is a block diagram of a reproducing circuit for obtaining a tracking error signal. In FIG. 2, a reproduced RF signal, which is a combination of a video signal and a pilot signal, is input from a terminal 2. Circuit 3 is a low pass filter, and the regeneration
Separate and extract only the pilot signal from the RF signal. The pilot signal obtained at this time is a composite of the pilot signals recorded on the main scanning track and both adjacent tracks. Circuit 4 is a balanced modulation circuit and multiplies the above-mentioned composite signal by the reference signal supplied from terminal 5. The reference signal supplied from the terminal 5 is a pilot signal having the same frequency as the pilot signal recorded on the main scanning track. For example, in FIG. 1, when the head performs reproduction scanning on track A ₂ , the input signals to the balanced modulation circuit 4 are f ₂ ,
f ₃ and f ₄ , and the reference signal supplied from terminal 5 is f ₃ . Therefore, the output signals of the balanced modulation circuit 4 are f ₂ , f ₃ , and f ₄ . circuit 6
is a tuning circuit that tunes to the f _H signal, and circuit 7 is
This is a 3f _H tuned amplifier circuit. Circuits 8 and 9 are detection rectifier circuits, and circuit 10 is a level comparison circuit. Therefore, each pilot signal taken out as a crosstalk signal from both adjacent tracks is separated and taken out as a difference signal from the pilot signal recorded on the main scanning track, and then the level comparison circuit 10 compares the difference signal with the pilot signal recorded on the main scanning track. A signal corresponding to the level difference is extracted. When the reproduction level of _fH is higher than the reproduction level of _3fH , a positive voltage corresponding to the level difference is extracted from the signal obtained by the level comparison circuit 10. Note that this level comparison circuit 1
The signal obtained at 0 can be used as a tracking error signal because it includes information on the amount and direction of the head's tracking deviation. However, tracking error signals that are actually suitable for practical use require further processing. This is because, as is clear from Fig. 1, the relationship between the head deviation direction and the crosstalk signal (f _H or 3f _H ) obtained at that time is opposite to that of the A track and B track. be. In FIG. 2, a circuit 11 is an analog inversion circuit, and a circuit 12 is an electronic switch that switches according to the period of a head switching signal (hereinafter referred to as an H/SW signal) supplied from a terminal 13. Therefore, for example, when the head reproduces and scans the A track, the output signal of the level comparison circuit 10 is output as is, and when the head reproduces and scans the B track, the output signal of the level comparison circuit 10 is output as is. , B track is reproduced and scanned by the head, the output signal of the level comparison circuit 10 is inverted in analog form and output. Therefore, the signal obtained at the terminal 14 is always a positive potential when the head deviates to the right from the track to be scanned, and a negative potential is always output when the head deviates to the left, regardless of the A or B track. Therefore, if the signal obtained at the terminal 14 is supplied as a tracking error signal to control the tape feeding speed, the head will always scan on-track on the main scanning track. The above is an outline of the method for obtaining a tracking error signal using four types of pilot signals. When using this tracking method,
When a tape recorded in SP mode (for example, 1 hour recording) is played back in LP mode (for example, 2 hour recording), a tracking error signal of 1 /Changes at a frequency of 7.5Hz. Furthermore, when a tape recorded in the LP mode is played back in the SP mode, the tracking error signal changes at a period of 1/15 Hz as shown in FIG. 3, which is a different period from the above. In Japanese Patent Application No. 126942/1986, a detection circuit is installed to determine the period based on tracking error signals with different periods, and the recording mode is determined. Playback mode, LP recording mode
When playing in LP mode), it is essential that the tracking error signal does not change periodically. However, self-recording (e.g., A becomes
There is no problem when recording on a VTR and playing back on a VTR A), but in the case of compatible playback (for example, recording on a VTR A and playing back on a VTR different from A), the rotating head is For example, the tracking error signal is
As shown in Figure 4a, level fluctuations occur at a cycle of 60Hz. Also, the frequency of the 4-frequency pilot signal
Noise with a frequency between 6.5f _H and 10.5f _H or close to the above-mentioned frequency is mixed into the reproduced pilot signal, and the output level of the tuned amplifier circuits 8 and 9 tuned to the above-mentioned f _H and 3f _H signals is affected. When the influence is uniform, as shown in Figure 4b and c,
A tracking error signal with steps at a period of 1/60Hz or 1/15Hz is obtained. In this way, when the tracking error signal changes at the above-mentioned period even during normal playback, this method determines the recording mode based on the different periods of 1/7.5Hz and 1/15Hz.
It becomes extremely difficult to distinguish. OBJECTS OF THE INVENTION The present invention provides a method different from the above-described method for automatically determining a recording mode in a tracking method using a four-frequency pilot signal. Structure of the Invention The present invention is characterized in that during recording, a pilot signal for tracking control during playback is superimposed on the recorded television signal, and during playback, the pilot signal for tracking control during playback is superimposed on the recorded television signal, and during playback, the pilot signal for tracking control is superimposed on the recorded television signal. A tracking error signal corresponding to the level difference of the crosstalk signal of the pilot signal to be reproduced is used to control the relative position between the recording track and the reproduction scanning locus of the reproduction magnetic head, and the tracking error signal is passed through a low-pass filter ( After passing through the LPF), the head switching
SW) signal is frequency-divided by 1/2, a trigger pulse is created at the rising edge or rising edge of the 1/2 frequency-dividing circuit output, and the LPF output signal is sampled and held (S&H) using this trigger pulse. The S&H output is input to a trigger pulse generation circuit, which detects a DC change in the S&H output and generates a trigger pulse. This trigger pulse is input to an analog switch, and the two outputs of the analog switch are input to the set S side and reset R side of the R/S flip-flop circuit, respectively.
It is configured to obtain an automatic discrimination output from the output of the S flip-flop. Further, the output of the R.S flip-flop is passed through a delay circuit, and the output of the delay circuit is used to control the two outputs of the analog switch.
The configuration is such that the trigger pulse can be switched to one of the two outputs. If you play back at a speed different from the recording mode,
As mentioned above, the tracking error signal changes at a frequency of 1/7.5Hz and 1/15Hz. Also, since phase control is not applied at this time, the tracking error signal is
The phase is not synchronized with the H/SW signal and the phase shifts. The present invention is a recording mode discrimination method that uses the above-described configuration to detect the presence or absence of a phase shift in a tracking error signal and obtain a detection signal that automatically discriminates the recording mode. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention is shown in FIG. 5, and will be explained using the operational waveform diagram of FIG. 6. A tracking error signal is input from terminal 15, and the frequency is set slightly higher than 15Hz.
It is input to LPF16. By passing the signal through this LPF, relatively high frequency components superimposed on the tracking error signal can be removed, and d output is obtained from the LPF 16 output. From terminal 18, H/SW signal is divided into 1/2 frequency divider circuit 1
9, and the frequency-divided signal is input to a trigger pulse generation circuit 20 which is triggered at the rising edge or falling edge to obtain a pulse output e. This trigger pulse e
has a period of 1/15 Hz, and the output d of the LPF 16 is sampled and held in the S&H circuit 17 using this pulse. During normal playback, the tracking error signal may change as shown in Figure 4 a, b, c, but since the H/SW signal and the tracking error signal are synchronized in phase, -Even if sample-and-hold is performed using a trigger pulse e with a period of 1/15 Hz created in synchronization with the SW signal, the output of the S&H circuit 17 can be obtained as a DC-like voltage with almost no change. However, when playing back at a speed different from the recording mode, for example, when a tape recorded in SP mode is played back in LP mode, the cycle is 1/7.5Hz, and when a tape recorded in LP mode is played back in SP mode, the cycle is 1/15Hz. As the tracking error signal changes, the phase of the tracking error signal shifts out of synchronization with the H/SW signal. At this time, as shown in Figure 6d and e, H.
For example, the tracking error signal V _a →V _b →V _c →V _e ……→
By sampling and holding different voltages, it is possible to obtain output signals f having different voltages from the output of the S&H circuit 17 at a cycle of 1/15 Hz. The output signal f of this S&H circuit 17 is transmitted to a trigger pulse generation circuit 2 which detects a DC change position (for example, V _a → V _b , V _b → V _c ) and generates a trigger pulse G.
1, and the pulse output G of the trigger pulse generating circuit 21 is input to the analog switch 22. When the output of the delay circuit 25, which is input from the output terminal 24 of the R-S flip-flop 23, is at a LOW voltage, the analog switch 22 is switched so that the output is input to the S side of the R-S flip-flop 23. When the output is Hi voltage,
It is set so that it is switched so that it is input to the R side of the R/S flip-flop 23. The delay circuit 25 described above changes the output of the R-S flip-flop circuit 23 from a LOW voltage to a Hi voltage (or from a Hi voltage to a LOW voltage) with an appropriate time delay. Hi voltage (or from Hi voltage to LOW voltage)
This is a circuit that changes to In addition, the above-mentioned R-S flip-flop 23
When the trigger pulse G is input to the S side,
Output terminal 24 of R/S flip-flop circuit 23
is set to be a Hi voltage, and when a trigger pulse G is input to the R side, the output terminal 24 of the R/S flip-flop circuit 23 is set to be a Low voltage. If you play back at a speed different from the mode used for recording, for example, if the mode switching voltage used for recording is
When the voltage is LOW and the detection output obtained from the terminal 24 during reproduction becomes a HIGH voltage and is scanning, the trigger pulse G is input to the analog switch 22 as described above. Also, if the voltage at the terminal 24 is Hi voltage, the R-S flip-flop 2
The trigger pulse G is input to the R side of the R-S flip-flop 23 through the analog switch 22, and the detection output obtained from the output terminal 24 of the R-S flip-flop 23 is
Switches to LOW voltage and switches to normal playback mode. When the normal reproduction mode is entered, the trigger pulse generation circuit 21 no longer generates a pulse output, and this state is maintained. At this time, the signal is switched to the normal reproduction mode by the output of the delay circuit 25, and is then switched to be inputted to the S side of the R/S flip-flop 23 via the analog switch 22 and held. In addition, the mode switching voltage during recording is Hi voltage, and the detection output obtained from terminal 24 during playback is
When the voltage is LOW and scanning is performed, the trigger pulse G is applied to the analog switch 22 as described above.
is input to the S side of the R-S flip-flop 23 via the analog switch 22, and the detection output obtained from the output terminal 24 of the R-S flip-flop 23 is switched to Hi voltage, and the normal reproduction mode is switched. As described above, when the normal reproduction mode is entered, the trigger pulse generation circuit 21 no longer generates a pulse output, so this state is maintained. At this time, the output of the delay circuit 25 switches to the normal reproduction mode, and then is switched and held so as to be input to the R side of the R-S flip-flop 23 via the analog switch 22. The above is the operating principle of the detection circuit for determining the recording mode of the present invention. Effects of the Invention According to the present invention, in a conventional tracking method that does not use a control signal, the recording mode can be reliably determined with a relatively simple configuration even when the tracking error signal changes synchronously during normal playback. By obtaining a detection signal, it is possible to automatically switch to playback at the same tape speed as when recording.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a recording pattern on a tape in a tracking method using a four-frequency pilot signal. FIG. 2 is a block diagram showing the configuration of a reproduction processing circuit for a tracking method using a four-frequency pilot signal. FIG. 3 is a diagram showing the relationship between the tracking error signal and the H/SW signal when a tape recorded in SP mode is played back in LP mode, and when a tape recorded in LP mode is played back in SP mode.
FIG. 4 is a diagram showing changes in the tracking error signal during normal playback. FIG. 5 is a block diagram showing an embodiment of a detection circuit for determining the recording mode according to the present invention, and FIG. 6 is an operational waveform diagram of FIG. 16...Low pass filter (LPF), 17...
S&H circuit, 19...1/2 frequency divider circuit, 20, 21
...Trigger pulse generation circuit, 22...Analog switch, 23...R/S flip-flop circuit,
25...Delay circuit.

Claims (1)

[Claims] 1 A pilot signal for tracking control is superimposed on a video signal to be recorded, and it is sequentially recorded on a magnetic recording medium as an adjacent recording track, and during reproduction, the recording tracks adjacent to the recording track to be reproduced before and after the recording track to be reproduced are The relative position control between the recording track and the reproducing scanning locus of the reproducing magnetic head is performed using a tracking error signal corresponding to the level difference between pilot signals reproduced as crosstalk from adjacent recording tracks at the front and rear. In a magnetic recording/reproducing device having two types of recording modes, during reproduction, the tracking error signal is sampled at the rising or falling timing of a head switching signal synchronized with the rotation of a rotating cylinder to which a magnetic head is attached. and a means for generating a trigger pulse at the timing of the change only when a voltage change is obtained in the hold voltage, and a means for detecting whether or not this trigger pulse is generated. Mode determination method.