JPH0418363B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a magnetic recording and reproducing apparatus such as a VTR that performs tracking control using a four-frequency pilot system. PRIOR ART In general, magnetic recording and reproducing devices having a rotating magnetic head such as a VTR cannot perform so-called splice editing, but editing can be performed by performing pause operations and the like. However, a simple pause operation will start recording the next track regardless of the track that has already been recorded, so the track arrangement may become discontinuous or the control signal may become discontinuous during playback. A problem arises in that the tracking servo becomes disconnected in this part, causing the image to become distorted. Therefore, in conventional magnetic recording and reproducing devices, the video tape is rewound while counting the control pulses already recorded on the video track from the last video track on which signal recording has already been completed.
When the count value reaches a predetermined value, the videotape is temporarily stopped, and then the videotape is run in the normal running direction to enter the playback mode. Tracking is performed during this replay mode, and the count value of the control pulse is determined. There is a device in which the reproduction mode is switched to the recording mode when the count value substantially matches the above-mentioned count value. However, in such a magnetic recording/playback device, recording must be started from a few video tracks before the final video track due to the sensitivity of the control amplifier and the accuracy of the video tape drive system. It didn't happen. As a result, a double recording portion occurs where a new signal is recorded on a video track where a signal has already been recorded, and during playback, this double recording portion generates beat noise and deteriorates the image quality. . Purpose This invention has been made in view of the above points, and it is an object of the present invention to prevent deterioration of image quality by preventing double recording from occurring during splicing, especially in a magnetic recording and reproducing device that tracks using a four-frequency pilot method. The purpose is to prevent. Configuration Therefore, the magnetic recording/reproducing apparatus according to the present invention records a pilot signal having a third or fourth frequency difference with respect to the pilot signal at the end of recording on the video track following the video track at the end of recording. In this case, when a signal with a third or fourth frequency difference is detected in the playback mode for continuous shooting, the playback mode is switched to the recording mode. Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram of essential parts showing one embodiment of the present invention. First, the pilot signal generator 1 includes an oscillator 2 that generates a signal of a predetermined frequency, and a signal from the oscillator 2 that is sequentially divided into a predetermined frequency division ratio, for example, 1/58 or 1/50, in accordance with an external control signal. , 1/36, 1/40
The automatic frequency control oscillator is composed of a frequency divider 3, etc., which divides the frequency and outputs the frequency in a circular order, and whose output and output stop can be controlled by an external control signal. That is, this pilot signal generator 1 first generates four types of pilot signals fm (f ₁ , f ₂ , f ₃ , f ₄ ). That is, between the frequencies of these pilot signals f ₁ to f ₄ , |f ₁ −f ₂ |=|f ₃ −f ₄ |=α |f ₂ −f ₃ |=|f ₄ −f ₁ There is a relationship of |=β |f ₃ −f ₁ |=γ |f ₄ −f ₂ |=δ. For example, if the pilot signals f ₁ to f ₄ are respectively f ₁ =
100KHz, _f2 =115KHz, _f3 =160KHz, _f4 =145KHz
When set to , the first to fourth frequency differences α,
β, γ, δ are respectively α=15KHz, β=45KHz, γ
= 60KHz, δ = 30KHz. This pilot signal generator 1 is controlled by a head switching pulse (switching pulse) and a pulse obtained by dividing the frequency of this switching pulse by 1/2, and converts these pilot signals f ₁ to _{f 4} into f ₁ →
Output in circular order: f ₂ → f ₃ → f ₄ → f ₁ . On the other hand, the recording end switch 5 is turned on when recording ends, for example, when a pause button or a stop button is operated. The recording end detection circuit 6 activates the pilot signal generator 1 when the recording end switch 5 is turned on.
The pilot signal fm output from the pilot signal generator 1 by switching the pilot rotation of the
is a positive switching signal indicating that the _next output of the pilot signal, _e.g. The instruction signal SA is output to the pilot signal generator 1 via the AND circuit 7. That is, the recording end switch 5 and the recording end detection circuit 6 constitute a recording order changing means. In addition, in this magnetic recording/playback device, when the switching instruction signal SA is output from the recording end detection circuit 6, the recording is possible by one video track more than the processing at the end of recording in the conventional magnetic recording/playback device. It is designed to be. The edge detection circuit 8 outputs a positive detection signal SB to the AND circuit 7 when it detects a rising edge (or a falling edge) of the switching pulse (head switching pulse) SWP. The hold circuit 9 outputs the pilot signal fm to the pilot signal generator 1 when the time required for the video head to trace one field has elapsed since the switching instruction signal SA was input through the AND circuit 7. Outputs an output stop instruction signal SC that instructs to stop. The pilot signal fm from the pilot signal generator 1 is input to an adder 12 via a low-pass filter 11, and is also input to a mixer 22, which will be described later. The adder 12 superimposes the pilot signal fm on the video signal (chroma signal and luminance signal) VD and outputs it to the recording amplifier 13 as a recording signal VA. The recording amplifier 13 receives the recording signal from the adder 12.
The head selector switch 15 is amplified by amplifying the VA, and is transferred to the head selector switch 15 via contacts a and c of the recording/playback selector switch 14.
The signal is supplied to the selected video head 16A or 16B. Note that the recording/playback switch 14 switches to the contact a side during recording and to the contact b side during playback, and the head selector switch 15 switches the switching pulse
Switches to contact a side or contact b side depending on SWP. The video heads 16A and 16B are rotating magnetic heads, which record the output signal from the recording amplifier 13 on the video tape 17, and also read and output the signals recorded on the video tape 17. The playback amplifier 20 connects the video heads 16A, 16
The backup signal from B is transferred to contact c- of head selector switch 15 and record/playback selector switch 14.
The reproduced signal VB input and amplified through
The signal is output to a demodulator for recycled yarn (not shown), and is also output to a bandpass filter 21. The bandpass filter 21 passes only the pilot signal (reproduction pilot signal) fm' (m=1 to 4) of the reproduction signal VB from the reproduction amplifier 20. The mixer 22 mixes the reproduced pilot signal fm' that has passed through the band-pass filter 21 with the pilot signal fm that is input from the pilot signal generator 1 via the low-pass filter 11, and generates the first to fourth signals.
A mixed pilot signal fmm' containing signals with frequency differences α, β, γ, and δ is output. The bandpass filter 23 passes the signal with the first frequency difference α of the mixed pilot signal fmm' from the mixer 22, and the bandpass filter 24 also passes the signal with the second frequency difference β. The detection circuits 25 and 26 each have a first frequency difference α
The levels of the signal and the signal of the second frequency difference β are detected and output to the differential amplifier 27. The differential amplifier 27 outputs a deviation signal SD corresponding to the level difference between the signal of the first frequency difference α and the signal of the second frequency difference β to the tracking servo system. On the other hand, the bandpass filter 30 is connected to the mixer 22
The third frequency difference γ signal of the mixed pilot signal fmm' from the band pass filter 31
similarly passes a signal with a fourth frequency difference δ. The detection circuits 32 and 33 each have a third frequency difference γ
The levels of the signal and the signal of the fourth frequency difference δ are detected and output to the differential amplifier 34. The differential amplifier 34 outputs a deviation signal SE to the hold circuit 35 according to the level difference between the signal with the third frequency difference γ and the signal with the fourth frequency difference δ. The hold circuit 35 holds the deviation signal SE from the differential amplifier 34. These band pass filters 30, 31, detection circuits 32, 33, differential amplifier 34, and hold circuit 35 constitute recording end position detection means. The switching circuit 36 is a mode switching means, and when the hold circuit 35 holds the deviation signal SE during playback for continuous shooting, that is, a signal with a third frequency difference γ and a signal with a fourth frequency difference δ. When a level difference occurs, the recording/playback switch 14 is switched from contact a to contact
switch to the side. Next, the operation of this embodiment configured as described above will be explained with reference to FIG. 2 as well. In addition, the second
In the figure, arrow A indicates the running direction of the videotape 17.
Arrow B indicates the direction of rotation of video heads 16A and 16B, respectively. First, the control operation of the four-frequency pilot type tracking will be explained. First, when recording, press the recording/playback switch 1.
4 has been switched to the contact a side. At this time, the pilot signal generator 1 converts the switching pulse and the switching pulse into 1/
The pilot signal is controlled by a pulse whose frequency is divided by 2.
Output fm in the circular order f ₁ →f ₂ →f ₃ →f ₄ →f ₁ . This pilot signal fm is superimposed on the video signal VD by the adder 12, and then sent to the recording amplifier 13 and the recording/recording/
Regeneration selector switch 14 and head selector switch 1
5 to a video head 16A or 16B and recorded on a video tape 17. That is, at the time of recording, as shown in _{FIG .}
Pilot signal _f2 to _T2 , pilot signal _f3 to track _T3 , pilot signal _f4 to track _T4
, the pilot signal f ₁ to track T ₅ , and so on along with the video signal VD, the pilot signal f ₁ to _{f 4}
are recorded in circular order. Next, during playback, switch the recording/playback switch 1.
4 switches to the contact b side. Then, from videotape 17 to video head 1
The reproduced pilot signal fm' included in the reproduced signal VB which is picked up alternately by the signals 6A and 16B and amplified and generated by the reproduction amplifier 20 is separated from the video signal VD by the bandpass filter 21 and input to the mixer 22. be done. At this time, the reproduced pilot signal fm' includes the pilot signal recorded on the track to be traced by the video heads 16A, 16B, as well as the pilot signal recorded on the track adjacent to that track. For example, when tracing track T ₂ shown in FIG. 2, the reproduced pilot signal fm' includes, in addition to the pilot signal f ₂ of track T ₂ , the pilot signal f ₁ of track T ₁ and the pilot signal of track T ₃ . Contains _f3 . On the other hand, during playback, the pilot signal fm of the regular track to be traced by the video heads 16A and 16B is sent from the pilot signal generator 1 to the mixer 2.
2 is input. For example, when tracing a track _T2 shown in FIG. 2, a pilot signal _f2 is input from the pilot signal generator 1 to the mixer 22. Therefore, from the mixer 22, a signal with a first frequency difference α and a signal with a second frequency difference β, which are beat signals due to crosstalk between the pilot signal of the regular track and the pilot signal of the adjacent track, are output. A mixed pilot fmm′ containing fmm′ is output. For example, when tracing the track T ₂ shown in FIG. 2, a signal with a first frequency difference α whose frequency is |f ₁ - f ₂ | and a signal with a second frequency difference β whose frequency is |f ₂ - _{f 3} | , is output at a level corresponding to the amount of deviation of the video head 16A or 16B from the track _T2 . These signals with the first frequency difference α and the signals with the second frequency difference β are filtered through the bandpass filters 23 and 2.
4, the level is detected by detection circuits 25 and 26, and input to a differential amplifier 27. At this time, if the video heads 16A and 16B are accurately tracing the regular track, the signal with the first frequency difference α and the signal with the second frequency difference β will be at the same level, but if the video heads 16A and 16B trace the regular track, 2 adjacent
If the track deviates from the desired track to any one of the tracks in the book, the level of either the first frequency difference α signal or the second frequency difference β signal increases depending on the amount of deviation. and the other level becomes smaller. For example, when tracing track T ₂ shown in Fig. 2, if the track deviates to the track T ₁ side, the level of the signal with the first frequency difference α increases, whereas the level of the signal with the second frequency difference β increases. When the level becomes small and deviates to the track _T3 side, the level of the signal of the second frequency difference β becomes large, whereas the level of the signal of the first frequency difference α becomes small. Then, the differential amplifier 27 outputs a deviation signal SD corresponding to the difference between the level of the signal of the first frequency difference α and the level of the signal of the second frequency difference β. Therefore, by applying the tracking servo so that the signal of the first frequency difference α and the signal of the second frequency difference β are at the same level, a normal track can be accurately traced. Note that during this normal reproduction, the mixed pilot signal fmm' from the mixer 22 does not include the signals of the third and fourth frequency differences γ and δ, so the differential amplifier 34 does not output the deviation signal SE. . Next, the continuous shooting operation will be explained. First, during recording, the track shown in Figure 2 is
If recording from T ₁ to Tn _-2 is completed and the recording end switch 5 is turned on while recording to track Tn _-1 , a positive switching instruction signal SA is output from the recording end detection circuit 6. Ru. At this time, if the recording system was originally supposed to process at the end of this track Tn _-1 , this magnetic recording/reproducing apparatus continues processing for one more track. Therefore, for example, if the switching pulse SWP rises to trace the track Tn, the edge detection circuit 8 detects the rising edge and outputs the positive detection signal SB, so the AND circuit 7 opens. become a state. As a result, the switching instruction signal SA from the recording end detection circuit 6 is outputted to the frequency divider 3 of the pilot signal generator 1 via the AND circuit 7, and is also outputted to the hold circuit 9. Thereby, the pilot signal generator 1 generates a pilot signal having a relationship of a third or fourth frequency difference γ or δ with respect to the pilot signal recorded on the track at the end of recording (the final track), for example, at the end of recording. A pilot signal fm next to the pilot signal originally recorded on the next track is output. In other words, for example, as shown in FIG. 2, when the pilot signal _f3 is recorded on the recording end track Tn _{-1 ,} the pilot signal after the pilot signal _f4 originally recorded on the track Tn next to this track Tn-1 is recorded. Output f ₁ . Therefore, a pilot signal having a third or fourth frequency difference γ or δ with respect to the pilot signal at the end of recording is recorded on the track following the track at the end of recording. That is, as shown in FIG. 2, for example, the pilot signal _f1 is recorded on the next track Tn after the recording end track Tn _-1 . This can be generally stated as shown in the following table assuming that the order of the pilot signals is changed at a constant rate, that is, the pilot signal that follows the original pilot signal is recorded.

[Table] Corresponding to the point in time when recording for the next track after this recording end track is completed, the hold circuit 9 outputs an output stop signal SC to stop the output of the pilot signal fm from the pilot signal generator 1. make it stop. In this way, for example, as shown in FIG.
Pilot signals f ₁ , f _{2 ,}
f ₃ , f ₄ , f ₁ . . . f ₁ , f ₂ , f ₃ , f ₁ are recorded together with the video signal VD, and the recording ends. Next, when performing splicing, the videotape is rewound by a predetermined amount, that is, by an amount necessary for tracking during playback. At this time, for example, if _the videotape is rewound to track _T1 shown in FIG. The tracking servo is applied based on the deviation signal SD from the dynamic amplifier 27 to control the rotational speed of the capstan motor (not shown), and the video head 16
Align A and 16B with the playback track (take tracking). Thereafter, the video head 16A picks up the track on which the pilot signal _f3 shown in FIG. 2 is recorded, for example.
If we trace TTn _-1 , this track
The track Tn _-2 next to Tn _-1 has a pilot signal f _2.
However, a pilot signal _f1 is also recorded on track Tn. Therefore, at this time, the mixed pilot signal fmm' output from the mixer 22 includes the signal of the first frequency difference α of |f ₃ −f ₂ | as well as the third signal of |f ₃ −f ₁ | contains signals with a frequency difference γ. Then, a signal with the third frequency difference γ is extracted from this mixed pilot signal fmm' by a bandpass filter 30, its level is detected by a detection circuit 32, and is input to a differential amplifier 34. At this time, since the mixed pilot signal fmm' does not include the signal of the fourth frequency difference δ, the deviation signal SE is output from the differential amplifier 34 and held by the hold circuit 35. Thereby, the switching circuit 36
When tracing Tn _-1 is completed, switch the record/playback switch 14 from contact b side (playback side) to contact a.
side (recording side). Therefore, the recording mode is entered and the track Tn
Recording starts from then, and at this time, the pilot signal _f4 is recorded anew on track Tn. Note that, for example, when the pilot signal f ₄ is recorded on the track at the end of recording and the pilot signal f ₂ is recorded on the next track, the mixed pilot signal fmm' contains the fourth signal of |f ₄ -f ₂ | A signal with a frequency difference δ is included. Therefore, at this time, the signal with the fourth frequency difference δ is extracted by the band pulse filter 31, and its level is detected by the detection circuit 33, and at this time, the mixed pilot signal fmm' has the third frequency difference. Since the γ signal is not included, the differential amplifier 34 outputs the deviation signal SE as well. Accordingly, at this time as well, the recording/reproduction changeover switch 14 is switched by the switching circuit 36 to switch from the reproduction mode to the recording mode. In this way, in this magnetic recording/reproducing apparatus, a pilot signal having a third or fourth frequency difference with respect to the pilot signal recorded on the track at the end of recording is recorded on the track following the track at the end of recording. However, when the third or fourth frequency difference signal is detected in the playback mode for continuous shooting, the playback mode is switched to the recording mode. As a result, recording can be reliably performed from the track following the track at the end of recording, there is no risk of double recording of image signals, and there is no deterioration in image quality due to the occurrence of beats. By the way, as a method for recording continuous shots by switching the circulation order of the pilot signals and detecting the level change of the two frequency difference signals that occurs as a result, the following is an example. I can think of many things. That is, first, the same pilot signal as the pilot signal recorded on the recording end track is recorded on the track following the recording end track. For example, if the pilot signal _f2 is recorded on the recording end track, the pilot signal _f2 is also recorded on the next track. In this way, when the recording end track is traced, if the tracking is successful,
In the above example, only the signal with the first frequency difference α of |f ₁ - f ₂ | is output, and the signal with the second frequency difference β is not output, so even though the deviation signal is tracked, reach maximum level. Therefore, if you switch from playback mode to record mode when this deviation signal reaches the maximum level,
Recording can be started from the track following the recording end track, and double recording will not occur. In this way, the bandpass filter, detection circuit, and differential amplifier for the tracking servo can be shared, so the configuration becomes simple. However, even if continuous shooting is performed in this manner, if the tracking servo is not completely locked when the recording end track is traced, there is a possibility that the joint cannot be detected. Also, if the mechanical system vibrates during continuous shooting,
Alternatively, when the tape is scratched, the output of the differential amplifier fluctuates, and there is a possibility that a part other than the joint may be detected as a joint. In contrast, according to the present invention, a joint is detected by detecting a third or fourth frequency difference signal that is different from the first and second frequency difference signals for applying the tracking servo. Therefore, even if a situation such as tracking is not completed occurs, the seam can be detected accurately. Note that in the above embodiment, an example was described in which the third frequency difference and the fourth frequency difference were separate;
Tracking can also be controlled using a four-frequency pilot method in which the third frequency difference and the fourth frequency difference are the same. Effects As explained above, according to the present invention, deterioration in image quality due to continuous shooting does not occur in a magnetic recording/playback device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a main part showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a pattern on a videotape to explain the operation of FIG. DESCRIPTION OF SYMBOLS 1...Pilot signal generator, 5...Record end switch, 6...Record end detection circuit, 12...Adder, 1
4...Record/playback switch, 15...Head switch, 16A, 16B...Video head, 3
0, 31...Band pass filter, 32, 33...Detection circuit, 34...Differential amplifier, 35...Hold circuit, 36...Switching circuit.

Claims (1)

[Claims] 1 Four types of pilot signals each having a predetermined first, second, third, and fourth frequency difference relationship are recorded on four consecutive video tracks in a circular order, and the reproduced pilot signals and The first and second frequency difference signals are detected from the mixed pilot signal mixed with the pilot signal of the video track to be traced, tracking control is performed based on the detection result, and the recording of the video track for which recording has been completed is performed. In a magnetic recording/playback device that rewinds a videotape by a predetermined amount, performs tracking in playback mode, and performs continuous shooting,
recording order switching means for recording a pilot signal having the third or fourth frequency difference with respect to the pilot signal at the end of recording on a video track following the video track at the end of recording; from the pilot signal to the third or fourth
a recording end position detecting means for detecting a signal with a frequency difference of said third or fourth frequency difference, and a mode switching means for switching from a reproduction mode to a recording mode when said recording end position detecting means detects a signal of said third or fourth frequency difference. A magnetic recording/playback device characterized by: