JPH02282965A - Tracking device for reproduction of three layer recording signal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a tracking device for reproducing 3N recorded signals,
In particular, it is suitable for use in a three-layer recording type video tape recorder that is capable of deep recording an FM audio signal and a PCM audio signal together with a video signal.

[Summary of the invention]

When tracing a recording medium recorded in three layers, the tracking is performed by almost evenly correcting the trace deviation for each track of the two deep recording signals, and the deep recording is corrected by the deviation in the installation height of each signal head. 31! Compensates for the drop in signal playback output and increases compatibility between recording/playback devices! ! This is a tracking device for reproducing recorded signals.

[Conventional technology]

A video tape recorder that uses a 1/2-inch wide magnetic tape, such as a VH3 video tape recorder, performs two-layer recording, with an F signal between the luminance signal Y and the chroma signal C.
M-modulated audio signal (hereinafter referred to as AFM signal).

) are recorded.

In such a recording/reproducing method, by performing deep recording by modulating digital signals with, for example, 0-QDPSK (offset 4-phase PSK), it is possible to record and reproduce PCM audio signals while maintaining complete compatibility with conventional AFM hi-fi. It is proposed to do so.

Figure 6 is a frequency distribution diagram when such recording is performed, where Y is an FM-modulated luminance signal, C is a low-frequency converted chroma signal, AFM is an FM-modulated audio signal,
PCM is a pulse code modulated audio signal.

FIG. 7 is a schematic explanatory diagram of a three-layer recording system, where 1 is a video head, 2 is an AFM head, and 3 is a PCM head, VT is a video signal track, A is an AF signal track, and P is a PCM head. (Shows No. 8 truck.

In the case of deep recording, especially in three-layer recording as shown in Figure 7, there are severe restrictions on the size of the recording current during recording.
A very large playback output cannot be obtained from deep recording signals. Therefore, when reproducing deeply recorded signals, it is necessary to minimize the S/N reduction due to track deviation.

[Problem to be solved by the invention]

As shown in the track explanatory diagram of FIG. 8, in 3N recording, the AFM signal and P
CM signal recording tracks A, , PA are formed. In the case of conventional two-layer recording, assuming that the width of the video head I in FIG. 7 is 58 μm and the width of the SA FM head 2 is 28 μm, the width of each recording track in FIG. 8 is VtW, A.
To is 58 μm and 28 μm, respectively. in this case,
In the conventional AFM high-fidelity specifications, the AFM signal recording trunk A is placed in the center of the video track V, 108
m or more. Furthermore, it is said that the recording layer should not be formed protruding outside the video track VT. That is, as shown in FIG. 8, the center of the video trunk ■. The left and right recording widths A+ and Az are as follows: 10,c+msA+ ≦29μm 10μm5Az≦29. crm, and a certain degree of tolerance is allowed. This is because each signal track is unavoidably shifted relative to each other due to a difference in the height at which the video RAD 1 and the AFM RAD 2 are attached.

In this way, even if there is a certain tolerance range, there is no problem because trunk shift does not occur in the case of self-recording/playback. However, when playing back a tape recorded with another video tape recorder, video track V.

When tracking is performed at the center of
M's recording trunk A, JPPCM's recording track P? A large deviation may occur. For example, in FIG. 9 for explaining trunk displacement, width A
It is assumed that an AFM signal recording trunk A is formed with +=18 μm and width At=10 am. In this case, AFM
Head 2 is located on the left side of the center VC of the video trunk.
When reproduced with a width of 0 μm, the AFMI-rack A7 is traced by the AFM head 2 with a width of only 20 μm. Therefore, in this case, 201og20
/28 to -3 (dB), and the reproduction S/N is lowered by about 3 (dB)i.

A S/N reduction of about 3 dB does not seem to be a big problem. However, since the S/N of the deep signal in deep recording, especially in three-layer recording, is inherently poor, a 3 dB reduction causes a large adverse effect. In particular, with respect to PCM signals, it becomes difficult to reproduce the carrier, resulting in a large error rate, and there is a possibility that a high-quality audio signal may not be obtained.

Figure 10 shows C/N deterioration characteristics during deep recording and playback, and Figure 11.
The figure shows the C of a PCM signal in a 0-QDPS modulation system.
/N versus error rate characteristics. Note that in FIG. 1O, characteristic A shown by a broken line represents a video signal, and characteristic B shown by a solid line represents a deep recording signal (AFM signal, PCM signal). When performing such deep recording, by adjusting the recording current of the AFM signal and the recording current of the PCM signal, it is possible to set the C/N of AFM and PCM to be almost the same during deep recording and reproduction. Figure 10 shows the characteristics in such a state. In addition, in this characteristic diagram, 2J!
The data at 1 is data of a video signal + AFM signal or a video signal + PCM signal.

As is clear from FIG. 10, between the 2Iw recording and reproduction and the three-layer recording and reproduction, the C/N of the deep recording signal is approximately 4 dB<< worse in the three-layer recording.

For this reason, for example, the C/N during two-layer recording in FIG.
If is 54 (dB), in 3jW recording, it deteriorates by 4 (dB) to 50 (dB). In this way, C/N is 54
(dB) to 50 (dB), the bit error rate of the PCM signal becomes 10 (dB), as is clear from Figure 11.
It changes from -4 to 1o-3, becoming about one order of magnitude worse.

In PCM, error correction can be performed using the signal processing system, but in three-layer recording, when the C/N decreases as much as this, the margin for error correction decreases, and error correction may not be possible. .

Therefore, when considering the institutional compatibility of media when the recorder and playback device are different, three-layer recording has extremely strict conditions, and the current playback performance compatible with 21 recording does not allow practical recording/playback compatibility. It turned out that I couldn't get it. Therefore, attempts are being made to improve the S/N ratio by using high-quality magnetic tape, and by increasing the precision of head installation during manufacturing to reduce track misalignment that occurs between recorders and playback machines. However, there is a problem that the media and equipment are expensive.

In view of the above problems, it is an object of the present invention to improve the tracking conditions in the three-layer recording method, thereby achieving sufficient institutional compatibility.

[Means to solve the problem]

The tracking device for reproducing three-layer recorded signals of the present invention is a tracking device for reproducing a recording medium 5 on which a video signal and first and second deep recording signals are layered and recorded sequentially from the surface layer, Detection means (peak detector 22 and system controller 32) for determining a first tracking point corresponding to the track center of the head that reproduces the deep recording signal, and corresponding to the track center of the head that reproduces the second deep recording signal. A detecting means (peak detector 31 and system controller 32) that determines a second tracking point for each recording layer and a common tracking point for the three playback heads 1.2.3 corresponding to each recording layer for the first and second tracking points. It is equipped with a tracking control circuit (system controller 32 and tracking circuit 35) that is set between points.

[Effect]

Even if the first and second deep recording signal tracks are formed with deviations in directions opposite to each other, and the playback positions of the corresponding playback heads are further shifted in the direction opposite to the deviation of the tracks, the optimal Reproduction tracing is performed in an intermediate state using the tracking point as a reference so that the reproduction S/N ratio of both sides does not drop extremely. Therefore, even if the manufacturing precision of head attachment is low, compatibility between devices can be improved.

〔Example〕

FIG. 1 is a block diagram of essential parts of a video tape recorder showing an embodiment of the tracking device of the present invention.

The first channel video signal and the second channel video signal recorded on the magnetic tape 5 are transferred to the first and second video drums attached to the rotary head drum 4.
Reproduced by a, lb.

The one-channel video signal reproduced by the first video controller 1a is taken out to the signal processing circuit via the rotary transformer coil 6a, and the channel switcher 7
The signal is applied to the reproducing amplifier 8 through the terminal a. Further, the two-channel video reproduced by the second video head 1b is supplied to the reproduction amplifier 8 through the coil 6b of the rotary transformer and the terminal of the channel switcher 7.

The video signal of each channel is amplified by a reproducing amplifier 8, passed through a bypass filter 10 to a 2M demodulator 12, and passed through a bandpass filter 11 to a frequency converter I3. Therefore, an FM demodulated luminance signal is obtained from the 2M demodulator 12, and 688K
A chroma signal returned to a frequency of 3.58M11z from l(z is obtained from the frequency converter 13. Both of these signals are combined in a mixer 14, and a reproduced video signal V i d
e. and is led out to the video output terminal.

The PCM signal deeply recorded in the second layer of the magnetic tape 5 is reproduced into the first and second PCMs by the rads 3a and 3b. The reproduction signals from each PCM head 3a, 3b are applied to terminals a, b of a channel switcher 15 via coils 6c, 6d of a rotary transformer, respectively, and then supplied to a reproduction amplifier I6 through a switch 15.

The reproduced PCM signal amplified by the reproduction amplifier 16 passes through the equalizer 17 to the carrier wave recovery circuit 20 and the 0-QD PCM signal.
The data is applied to the KuI modulator 21 and decoded, and the decoded data is written from the error correction circuit 23 to the memory 24. The error correction circuit 23 corrects errors caused by deterioration of reproduction S/N, etc., based on the error correction code of the PCM data written in the memory circuit 24. The error-corrected data is converted back into an analog signal by the D/A converter 25 and output as a PCM audio signal PCM.

Further, the output of the equalizer 17 is given to the peak detector 22 to detect the magnitude of the RF output of the reproduced PCM signal, and the detected value is used as the peak detection signal Sl to the system controller 32.
Output to.

The AFM signal is deeply recorded at the 3Nth position of the magnetic tape 5, and is reproduced by the first AFM head 2a and the second AFM head 2b. These reproduction signals are applied to terminals asb of the channel switcher 26 via coils 5e and 6f of the rotary transformer, and are supplied to the reproduction amplifier 27 through the switcher 26.

The amplified output of the reproduction amplifier 27 is given to the FMuI modulator 3o and the peak detector 31, and the output of the FM demodulator 3° is led out to the audio circuit as a reproduction AFM signal. Further, the output of the peak detector 31 is given to the system controller 32 as a peak detection signal S2.

The system controller 32 is composed of a microcomputer, and the system controller 32 controls the driving of each part of the video tape recorder.

That is, for example, the switching operation of the channel switcher 7.15.26 is controlled by the channel switching signal S output from the system controller 32.

The video tape recorder of the embodiment performs tracking correction using a capstan servo.

That is, the control signal CTL reproduced by the CTL head 33 is amplified by the amplifier 34, and then the control signal CTL is reproduced by the tracking circuit 35.
to the phase servo circuit 36 to generate a phase error signal.

On the other hand, the output of the frequency generator FC is given to the speed servo circuit 37 to generate a frequency error signal. These phase error signals and frequency error signals are added by an adder 38 and provided to a capstan drive circuit 40. The capstan drive circuit 4o controls the rotation of the capstan motor M based on the output of the adder 38. Therefore, tracking is performed to correctly trace the center (2) of the recording track (2) of the video signal recorded on the magnetic tape 5.

The above is a commonly used tracking system, but in this embodiment, AFM signals recorded deep and PC
Tracking is corrected so that the reproduction output of the M signal is as large as possible. That is, the peak detector 22.31
The system controller 32 determines the final tracking point at which the magnetic tape 5 is actually traced based on the peak detection signals St and Sz given from the respective peak detection signals St and Sz. Then, trace the determined tracking point. A necessary correction signal S4 is generated and output to the tracking circuit 35. As a result, the tracking point is corrected, and even when the AFM signal and PCM signal tracks are formed offset from the center of the video signal track V1, the playback S/N of the deep recording signal is prevented from being extremely deteriorated. Prevented.

When tracking correction is performed to increase the AFM signal and PCM signal, trunk deviation occurs with respect to the recording track V of the video signal. However, since the width of the video signal recording trunk v7 is generally larger than the track width of the signal to be recorded deep, the influence on the video signal is minimal.

That is, for example, if the recording trunk width of the video signal is 58μ
m, and the recording track width of the deep signal is 28 μm. As mentioned above, there is a possibility that a track deviation of up to 8 μm may occur in the deep signal, and the playback output can be up to -3 (d
B) It gets worse.

On the other hand, when tracking is corrected for deep signals,
The amount of correction becomes the tracking deviation with respect to the video signal. Therefore, by correcting the deep signal, the reproduction output of the video signal may be reduced by 201og50/58 to -1.3 (dB) at the maximum. This decrease is less than half of that of the deep signal, and since the reproduction output of the video signal is originally large, correcting the tracking of the deep signal has almost no adverse effect.

By the way, as mentioned above, the specification of the audio trunk for AFM signals is that it should be formed extending at least 10 μm from the center VC of the video track. Therefore, we decided to change the specifications of the PCM (No. 2 truck) to the AFM.
If deep recording is performed in the same way as a signal trunk, things like the ones shown in the trace explanatory diagrams of FIGS. 2 and 3 may occur. That is, in FIGS. 2 and 3, the video track v
Width W+ of 7 = 58. un, AFM signal track AT and PCM signal track W! =39 μm. Each deep signal trunk At, Py is a video track center ■. Trunk widths W1 and W4 are formed on both left and right sides of the trunk. In this case, each track width W1, W4 is Ws = 1
0 μm-, W4 = 29 +um. Figures 2 and 3 show AFM signal tracks AT and PCM.
This shows an example in which the signal track P7 is formed most shifted in the opposite direction.

Each track V,,A? formed in this way? and P are reproduced by the recording head in FIG. That is, FIG. 2 shows the case of self-recording and playback, in which the video signal, AFM
Maximum reproduction output can be obtained for both signals and PCM signals. On the other hand, in the case of FIG. 3, there is no problem in tracing video track v7 and AFM signal trunk Aa, but there is no problem in tracing PCM signal track Pa.
The heft 3 can trace only a width of 20 .mu.m, so in the case of FIG. 3, it becomes 201og20/39 to -6 (dB), which significantly reduces the reproduction output. In the embodiment, as described above, tracking points are set so that the reproduction output of deep-recorded AFM signals and PCM signals does not decrease significantly.

Next, the procedure for determining the tracking point will be explained according to the flowchart shown in FIG.

In Fig. 4, the first half indicated by step PI”Pl& is A
The procedure for determining the tracking point (track center) TA for obtaining the maximum point vAMAX of the FM signal is shown. Also, step PI? ~The second half indicated by P32 is P
The procedure for determining the tracking point (track center) TP for determining the maximum points Vl and MAX of the CM signal will be shown, and these procedures are exactly the same.

First, initial values are set in steps P1 to P. That is, in step P1, the initial value 0 is set at the tracking point 8T, and the reproduced output at the tracking point ΔT-0 is set as the comparison reference value VaO for tracking error detection.

Also, the number of times N of detecting the playback output in step P
Set the initial value to 0.

Next, in step P, the number of detections N is increased by 1, and in step ps, 1 is added to the tracking point ΔT, and the tracking position is shifted to the right by 1 unit step amount. Next, the tracking set in step P% Step P the playback output V□ at the point
, and the comparison reference value ■ detected in step Pg. . Step P? Compare in.

As can be seen from the tracking characteristic diagram in Figure 5,
The tracking point ΔT set in step P is
If the AFM l-rack is shifted to the left of the center TA, the playback output after shifting the tracking point 8T to the right by 1 unit step amount is larger than the playback output before shifting, that is, the step The comparison in P7 is V.

<VAI. Therefore, in step Pt
,. When it is determined that the tracking point ΔT is shifted to the right, the maximum point VAMAX can be detected. In this case, proceed to step P, and step Ph
Compare the playback output VAI detected with the reference value■^. Close and set, and step P4 to P.

Repeat the process.

By repeating the process of steps P4 to P8, eventually the tracking point ΔT and the track center TA
matches. At this time, the reproduction output V at the tracking point ΔT.

becomes the maximum point VAMAX. Therefore, since the tracking point (ΔT+1) shifted to the right by one unit step is shifted to the right of the trunk center TA, the playback output after the shift is smaller than the playback output before the shift. Therefore, in this case step P
Since the determination in step 7 is No, steps P1 to P
, proceed to .

Note that if the tracking point ΔT set in step P is shifted to the right side of the track center TA, the determination in step P will be No from the beginning, so step P will be performed without passing through step P. Proceed to. In this case, the number of detections N=1.

In step P, the tracking point ΔT is shifted to the left by one unit step amount.

Therefore, when proceeding to step P after repeating the routine of steps P and ~P8, the maximum point VA MA
X is returned to the tracking point from which it was obtained. Also,
When proceeding to step P without passing through step P, the tracking point is returned to the initially set tracking point in step P.

Next, the process proceeds to step P1°, and the number of detections N of the playback output is 2.
It is determined whether or not the value is greater than or equal to the value. Therefore, step P
, it is determined to be Yt3, and if step P8 is not passed, it is determined to be N6. Step PI
Y at 0. If it is determined that
T is read as the trunk center T.

Further, if the determination is No at step P1°, the process proceeds to step P, and the tracking point is shifted to the left by one unit step amount. That is, steps P4 to P
"Then, we performed the mountain climbing method to find the maximum point vAMAX while shifting the tracking point to the right, but in step P
+ + "' The P + a routine performs a mountain climbing method to find the maximum points V and MAX while shifting the tracking point to the left. Then, in step P+1, when it is determined that the peak of the mountain, that is, the maximum point ■AMAX has been exceeded. Proceed to step pis, return to the tracking point where the maximum point VAMAX was obtained, and proceed to step Pl&.

After finding the maximum point vAMAX of the AFM signal in this way, the process proceeds to step PI7. Step PIT~P3
The process □ is the maximum point V of the PCM signal.

This is to find MAX, and as described above, this is the same operation as steps P1 to P0. Therefore, in step P3K, the center T2 of the PCM (verbal trunk) is obtained.

Next, proceed to step p, I:+ to determine the final trunking point ΔT. This decision is ΔT= (1
-α)TA+αT2 (where 0<α<1), the tracking points in each track are weighted and added (averaged).

In the embodiment, the tracking points are determined in this way, so this method is applicable regardless of the width of the AFM head 2 and the PCM head 3, or the deviation of the track center of each signal. be able to.

Therefore, even if the heads for recording/reproducing deep recording signals are mounted at different heights, it is possible to eliminate the inconvenience that the reproduction S/N of deep recording signals deteriorates drastically, and good compatibility can be obtained. .

Note that the above is a case where PCM audio and FM audio are played simultaneously, but when the user selects either the PCM signal or the AFM signal, the weighting can be done by setting the coefficient α to 1 or 0. , a tracking point is set where the RF output of the selected deep recording signal becomes maximum. In this case, if the tracking point is switched to the one that maximizes the reproduction output of the AFM signal or the one that maximizes the reproduction output of the PCM signal according to the user's selection, there is no need to calculate weighting. .

Note that when only one of the deep recording signals is recorded, the optimal tracking point for that signal is selected.

〔Effect of the invention〕

As described above, the present invention sets the tracking points for reproducing a recording medium recorded using the three-layer recording method between the optimal tracking points of each signal trunk deeply recorded on the recording medium. . Therefore, even if the recording head and the playback head are different, and the tracking deviation with respect to the track where the deep layer signal is recorded is large, the tracking point is corrected and the reproduction S/N of one of the deep layer signals is drastically reduced. You can prevent it from happening. This makes it possible to improve compatibility between devices when reproducing a recording medium in which a video signal is recorded on the surface layer of the recording medium and an FM audio signal and a PCM audio signal are recorded in the deeper layer.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a video tape recorder showing an embodiment of the tracking device for reproducing three-layer recorded signals of the present invention;
Figure 2 is an explanatory diagram of the trace in case of self-recording and reproduction, Figure 3 is P
An explanatory diagram of the trace when the deviation with respect to the CM signal trunk is maximum, Fig. 4 is a flowchart showing the procedure for finding the tracking point, Fig. 5 is a characteristic diagram showing the relationship between tracking deviation and detection output, and Fig. 6 is The frequency distribution diagram of each signal recorded in three layers, Figure 7, is 31i! ! A schematic explanatory diagram of the recording method, FIG. 8 is a diagram explaining the allowable range of positional deviation between the shallow recording track and the deep recording track, FIG. 9 is a diagram explaining the permissible range of tracking deviation of the deep recording track, and FIG. FIG. 10 is a characteristic diagram showing the difference in C/N between the two-layer recording method and the three-layer recording method, and FIG. 11 is a characteristic diagram showing the relationship between C/N and bit error rate. In addition, in the symbols used in the drawings, 1. --A
FM head 3-・・・・・・・−・−・−・−・
・−PCM head 22 ・−・・・・〜・−・−・・・
----Peak detector 31...-----
・・・−・・〜・・・−・−Beak detector 32 ・・−
・−・・−・−＝〜・・・・−・・・System controller 33−・−・−・−・・−・・・・・・・・・−
CTL head 35 ・−・・〜・−・・・・・・・・・・−・
−・・Tracking circuit 36 ・・−・−・−・−・・
・・・−・・−・Phase servo circuit 37−・−・・・・・
・−・・−・−−１−−−・Speed servo circuit 40
...
...--Beak detection signal S2 This is a peak detection signal tracking correction signal. Agent Masaru Tsuchiya Figure 5 Figure 6 3rd layer 231 Table C Kanki Kincha → Tsu 2 Figure 8

Claims (1)

[Claims] 1. A tracking device for reproducing a recording medium in which a video signal and first and second deep recording signals are layered sequentially from the surface layer, which reproduces the first deep recording signal. a detection means for determining a first tracking point corresponding to the track center of the head; a detection means for determining a second tracking point corresponding to the track center of the head for reproducing the second deep recording signal; A tracking device for reproducing a three-layer recording signal, comprising a tracking control circuit that sets a common tracking point for three corresponding reproducing heads between the first and second tracking points. 2. The three-layer recording signal according to claim 1, wherein the common tracking point is set at a position obtained by weighting each of the first tracking point and the second tracking point and averaging them. Tracking device for playback. 3. When either the first deep recording signal or the second deep recording signal is selected to be reproduced, the first tracking point or the second tracking point is selected depending on the selection. 2. The tracking device for reproducing a three-layer recorded signal according to claim 1, wherein the common tracking point is set at one of the points.