KR100354748B1 - Tilt detection method of optical disc drive - Google Patents

Abstract

A method of compensating the effect of defocus in a method of detecting a tilt component using a header signal in an optical disc drive for recording and reproducing a recordable disc having a pre-pitted header for discriminating a physical sector. It is about.

A tilt detection method according to the present invention is a tilt detection method of an apparatus for reproducing an optical disc having synchronization signal regions in which at least a synchronization signal is recorded up and down at a track center line, the tilt detection method comprising: detecting in a synchronization signal region recorded above the track center line When the magnitude of the detected signal is referred to as V1, and the magnitude of the signal detected in the sync signal area recorded above the track center line is referred to as V3, the amount of tilt is changed by V1-V3 which is the difference between V1 and V3 at two different points of focus. Detecting (Kt1, Kt2) and defocusing amount (d1, d2); And determining the tilt amount by calculating a ratio of the change amount of the tilt amount and the change amount of the defocus amount detected at the two points.

The tilt method according to the present invention has an advantage that the tilt correction can be more stably performed by compensating for the effects of defocus in detecting the tilt and detrack amounts using the sync signal recorded in the header area on the disk. have.

Description

Tilt detection method of optical disc drive

The present invention relates to a method of detecting a tilt component using a header signal in an optical disc drive for recording and reproducing a recordable disc having a pre-pitted header for determining a physical sector. It is about how to compensate for the impact.

In addition to playback-only discs such as DVD-ROMs, as well as recordable discs such as DVD-RAMs, as the recording density increases, signal quality deterioration due to the disc tilt increases.

In the recordable disc, if the tilt is present during recording, the recording quality is deteriorated due to the influence thereof, and if the tilt is present even when the corresponding part is played back, the quality of the reproduction signal is increased, causing data error.

Tilts often occur depending on the state of the disk or driver, and a method and apparatus for adjusting / removing these two components are required.

A method of detecting the tilt component using the header signal recorded on the disc is used. This method detects the magnitude difference of the reproduced signals in the headers arranged up and down at the centerline of the track. Even if the tracking of the disc is maintained correctly, the distribution of the laser beam is distributed according to the tilt when the disc is tilted. Therefore, the intensity of the laser beam irradiated to the headers arranged up and down at the center line of the track changes according to the tilt, and the tilt amount can be detected by detecting the degree of the change.

However, the intensity of the laser beam irradiated onto the headers can also be changed by focus, so a method must be devised to compensate or eliminate the effects of focus.

An object of the present invention is to provide a method for compensating the influence of defocus in a method of detecting a tilt component of an optical disk drive, which is devised to meet the above requirements.

FIG. 1A shows the physical shape of the land track, and FIG. 1B shows the waveform of the push-pull signal in the land track.

2A shows the physical shape of the groove track, and FIG. 2B shows the waveform of the push-pull signal in the groove track.

3 is an enlarged view of the header area illustrated in FIGS. 1A to 2A.

4A and 4B show a push-pull signal and a sum signal obtained when the laser spot passes through the header section of the groove track, respectively, in FIG. 3.

FIG. 5 shows the configuration of a device for obtaining the push-pull signal shown in FIG. 4.

6 shows various signals and timings for detecting the magnitude of the synchronization signal.

7 shows the configuration of a device for measuring V1 and V3.

8 shows various signals and timings for detecting the magnitude of a mirror signal.

9 is a graph showing the relationship between the radial tilt and the balance value K. FIG.

10 is a graph showing a relationship between defocus and a balance value K. FIG.

11 is a block diagram showing the configuration of a conventional radial tilt correction device.

12 is a block diagram showing a detailed configuration of the radial tilt adjustment unit shown in FIG.

13 is a flowchart illustrating an embodiment of a tilt detection method according to the present invention.

14 is a flowchart illustrating another embodiment of a tilt detection method according to the present invention.

15 is a flowchart illustrating still another embodiment of the tilt detection method according to the present invention.

One embodiment of the tilt detection method according to the present invention to achieve the above object

A tilt detection method of an apparatus for reproducing an optical disc having at least a synchronous signal region in which a synchronous signal is recorded up and down at a track center line, the tilt detection method comprising: adjusting the defocus of the optical disc to be minimum; And V1 and V3 when the magnitude of the signal detected in the synchronization signal region recorded on one side of the track center line is V1, and the magnitude of the signal detected in the synchronization signal region recorded on the other side of the track center line is V3. It characterized in that it comprises a step of detecting the amount of tilt by V1-V3 which is the difference of.

Another embodiment of the tilt detection method according to the present invention which achieves the above object is a tilt detection method of an apparatus for reproducing an optical disc having synchronization signal regions in which at least a synchronization signal is recorded up and down at the track center line. V1 is the difference between V1 and V3 when the magnitude of the signal detected in the synchronization signal region recorded on one side of the track is V1, and the magnitude of the signal detected in the synchronization signal region recorded on the other side of the track center line is V3. Detecting the amount of tilt by V3; And compensating for V1-V3 by the defocus amount.

Still another embodiment of the tilt detection method according to the present invention to achieve the above object

A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, wherein the magnitude of the signal detected in the sync signal region recorded above the track center line is V1. When the magnitude of the signal detected in the sync signal area recorded above the track center line is V3, the tilt amount (Kt1, Kt2) and the defocus due to V1-V3 which is the difference between V1 and V3 at two different points of focus. Detecting the amounts d1 and d2; And determining the tilt amount by calculating a ratio of the change amount of the tilt amount and the change amount of the defocus amount detected at the two points. Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

In a DVD-RAM disc, information is recorded in a track, and the track is composed of a land track and a groove track, and the land track and the groove track intersect with each revolution of the disc. The reason why the land track and the groove track intersect in a DVD-RAM disc is to provide a tracking guide initially, and also to reduce crosstalk between adjacent tracks in a high density narrow track.

The track is composed of sectors divided into constant lengths. As a means for enabling physical division of such sectors, the header area is pre-pitted at the time of disc manufacture. The physical address of the sector is recorded in this header area.

That is, each sector is largely composed of a header area and a data area in which physical address information (hereinafter referred to as PID) is recorded.

1A shows the physical shape of the land track in a DVD-RAM disc, and FIG. 1B shows the waveform of a push-pull signal in the land track.

The header area is repeatedly arranged in a predetermined section (sector) of the track, and the so-called Complementary Allocation of Pit Address method in which four PIDs (PID1 to PID4) having the same value are alternately arranged from the center of the track to one header area is arranged side by side. Is recorded. That is, in order to accurately read the PID even when the laser spot 22 is out of the center of the track, PID1 and PID2 are arranged a certain amount out of the center of the track, and PID3 and PID4 are arranged in the opposite direction from the center of the track. do. In the land track and groove track, the arrangement of PID1, 2 and PID3, 4 is reversed. In the land track, a push-pull signal as shown in Fig. 1B can be obtained. In FIG. 1B, the large rectangles correspond to PID1 to PID4 from the left side, and PID1 and 2 are located at the bottom of the track center line (bottom header), and therefore have a low DC value and PID3 and 4 are upwards from the track center line. It has a high DC value because it is located at (peak header).

2A shows the physical shape of the groove track in the DVD-RAM disc, and FIG. 2B shows the waveform of the push-pull signal in the groove track. In FIG. 2B, the large rectangles correspond to PID1 to PID4 from the left side, and PID1 and 2 are located at the top of the track center line (peak header), and therefore have a high DC value and PID3 and 4 are lower from the track center line. It has a low DC value because it is located at (bottom header).

3 is an enlarged view of the header area illustrated in FIGS. 1A to 2A. In the structure of the header area, PID1,2 and PID3,4 are arranged to be shifted by a certain amount from side to side with respect to the track center, and each PID has an ID representing a physical address of a sector and a vfo signal of the same frequency for synchronization for ID detection. The signal is recorded. The vfo signal has a recording pattern of 4T (where T is the basic length of the recording signal).

As shown in Fig. 3, the header areas include vfo1 33 and ID1 34 (more than PID1), vfo2 35 and ID2 36 (more than PID2), vfo3 37 and ID3 38 (more than PID3). ), And vfo4 39 and ID4 40 (above PID4).

In FIG. 3, when the laser spot 32 passes through the header section of the groove track, the push-pull signal RF_pp as shown in FIG. 4A and the sum signal RF_sum as shown in FIG. 4B may be obtained. 4A and 4B, the vfo1 signal 42 corresponds to the vfo1 signal region 33 of FIG. 2, and the vfo3 signal 43 corresponds to the vfo3 signal region 37.

FIG. 5 shows the configuration of a reproduction signal generator for obtaining the push-pull signal RF_pp shown in FIG. 4A and the sum signal RF_sum shown in FIG. 4B. In Fig. 5, reference numeral 50 denotes a four-part photodetector, 52 and 54 are adders, and 56 denotes a calculation unit.

The apparatus shown in Fig. 5 is a sum signal I1, I2 of the radial pairs B and C, A and D of the light receiving elements A to D of the quad split photodetector, and the difference signal I2 of I1 and I2. Outputs the push-pull signal RF_pp which is -I1) and the sum signal RF_sum which is the sum signal of I1 and I2 (I1 + I2).

6 shows various signals and timings for detecting the magnitude of the synchronization signal. The detection output of header12 and the detection output of header34 of FIG. 6 are generated for the header section, and the enable 12 and enable 34 of FIG. 6 are generated for the synchronization signal section.

When enable 12 in FIG. 6 becomes "high", V1 is detected, and when enable 34 becomes "high", V3 is detected.

FIG. 7 illustrates the configuration of a device for measuring V1 and V3. Signals input to the enable terminal of FIG. 7 are enable 12 and enable 34 of FIG. 6.

The device shown in FIG. 7 outputs V1 when enable 12 is input, and outputs V3 when enable 34 is input.

When the laser spot crosses the center line of the track, the magnitude V1 of the vfo1 signal and the magnitude V3 of the vfo3 signal coincide, but when the radial tilt occurs, one side becomes larger when the other becomes larger.

This is because the intensity of light reflected from the signal planes of PID1, 2 and PID3, 4 arranged to be different from each other is different. When tilting and detracking occur, the intensity of the light reflected by the upper header (peak header) becomes larger than that reflected by the lower header (bottom header).

Accordingly, the ratio between the magnitude V1 of the vfo1 signal and the magnitude V3 of the vfo3 signal is changed. The ratio between the magnitude V2 of the vfo2 signal and the magnitude V4 of the vfo4 signal is similarly different.

Therefore, the tilt amount and the detrack amount can be detected by detecting the ratio (balance) between the magnitude V1 of the vfo1 signal and the magnitude V3 of the vfo3 signal.

Where the balance value K is

It is calculated | required as K = (V1-V3) / (V1 + V3).

Where (V1 + V3) is a term for normalization.

Although the balance value was calculated using V1 and V3 in Equation 1, it is also possible to use the magnitude of the synchronization signal detected in the vfo2 and vfo4 regions. It is also possible to use a value obtained by the combination of the synchronization signals detected in the vfo1 and vfo2 regions and a value obtained by the combination of the synchronization signals detected in the vfo3 and vfo4 regions. However, vfo1 and vfo3 are easier to detect than vfo2 and vfo4.

If the value without the tilt is referred to as K value and the value of K when tilt occurs as K1, the difference Kt between the two values is defined as follows.

Kt = Ko-K1

That is, the direction and magnitude of the tilt can be known according to the value and sign of Kt.

Here, Ko may be a value measured in the absence of tilt, a default value determined by the system controller of the recording / reproducing apparatus, or a value measured in a reference state determined by the system.

Since the positions of PID1,2 and PID3,4 are inverted in the land track and groove track, the polarity of K1 must be changed from track to track in order to calculate the correct Kt.

Using Kt, the radial tilt value Rt in the actual system is calculated as follows.

Rt = a * Kt

Here, a is a proportional constant having a constant value.

The tilt correction mechanism is operated or the recording / playback signal is changed in accordance with the direction and magnitude of the detected radial tilt value Rt. When the tilt correction mechanism is operated, the value of Kt or Rt is controlled to be zero. Rt is applied when changing the recording / playback signal. At this time, the proportionality constant a has a constant value which is determined according to the characteristics of the recording / reproducing apparatus and the method of manufacturing the disc.

Another example for tilt detection is to change the normalization method shown in Equation 1 by using the signal size of the mirror area immediately after the header section as follows.

K = (V1-V3) / I0

Here, Io is a term for normalization and is the magnitude of the sum signal RF_sum in the mirror region.

In this case, Io may be obtained by applying the sum signal RF_sum to the input of FIG. 6 using the mirror interval detection signal and enable 5 shown in FIG. 8.

9 is a graph showing the relationship between the radial tilt and the balance value K. FIG. In FIG. 9, the vertical axis represents the radial tilt value, and the horizontal axis represents the balance value K. In FIG. In FIG. 9, the graph indicated by ▲ shows the case where the sum signal RF_sum and the balance value according to Equation 1 are used, and the symbol indicated by ▼ shows the case where the sum signal RF_sum and the balance value according to Equation 4 are used. Denoted by the push-pull signal RF_pp and the balance value according to the equation (4), and denoted by ■ shows the case of using the push-pull signal RF_pp and the balance value by the equation (1).

As shown in FIG. 9, the best showing the radial tilt is a case in which the push-pull signal RF_pp and the balance value according to Equation 1 are used as indicated by s.

In addition, it can be seen that the mark indicated by ● shows a linear result for the radial tilt although the slope is small even when the push-pull signal RF_pp and the balance value according to Equation 4 are used.

In addition, when the push-pull signal RF_pp and the balance value according to the equation (1) are used as shown in FIG. 9, the radial tilt is almost linearly affected, and thus it is very suitable for detecting the radial tilt. Able to know.

11 is a block diagram showing the configuration of a conventional tilt adjustment device. The apparatus shown in FIG. 10 includes a header section signal generator 142, a first synchronous signal level detector 144, a second synchronous signal level detector 146, a mirror section signal generator 150, a mirror level detector 152, A balance calculator 154, a comparator 156, a land / groove detector 158, and a polarity inverter 160 are provided.

An operation of adjusting the radial tilt in the apparatus shown in FIG. 11 will be described.

The header section signal generator 152 generates a header section signal (header section signal 12, header section signal 34) indicating a header region from the push-pull signal RF_pp generated by the reproduction signal generator 130. Here, the header section signal 12 is a signal indicating the PID1, 2 areas, and the header section signal 34 is a signal indicating the PID3, 4 areas. Since the header region has a larger envelope than the data region, a header section signal representing the header region can be obtained using an envelope detector and a comparator for detecting the envelope of the reproduction signal.

The first synchronous signal level detector 144 detects the magnitude V1 of the vfo1 signal shown in FIG. 6 in synchronization with the header section signal 12 generated by the header section signal generator 142. Specifically, after generating the first enable signal enable 12 having a predetermined interval and a predetermined width from the start point of the header interval signal 1, gating the push-pull signal RF_pp by the first enable signal enable 12 V1 is detected by detecting a peak-peak value of the gated reproduction signal.

The second synchronous signal level detector 146 detects the magnitude V3 of the vfo3 signal shown in FIG. 6 in synchronization with the header section signal 34 generated by the header section signal generator 142. In more detail, a second enable signal enable 34 having a predetermined interval and a predetermined width is generated from the start point of the header section signal 34, and the gate pull signal RF_pp is gated by the second enable signal enable 34, and then gated. V3 is detected by detecting the peak-peak value of the reproduction signal. The first synchronous signal level detector 144 and the second synchronous signal level detector 146 are implemented with the apparatus shown in FIG.

The balance calculator 154 calculates a ratio between V1 detected by the first synchronous signal level detector 144 and V3 detected by the second synchronous signal level detector 146 as shown in Equation 1. Here, the balance calculator 154 may output an average value of balance values obtained from several consecutive sectors.

The comparison unit 156 compares the balance value K1 calculated by the balance calculation unit 164 with the predetermined reference value Ko as shown in Equation 2, and outputs the difference Kt between the two values. Here, Ko may be a value measured in the absence of a detrack, a default value determined by the system controller of the recording / playback apparatus, or a value measured in a reference state determined by the system.

The land / groove detector 158 introduces RF_pp to detect whether the current track is a land track or a groove track. As shown in Fig. 1B, the push-pull signal RF_pp in the land track is larger than the size of PID3,4, and in the groove track, the size of PID1,2 is smaller than the size of PID3,4. The land / groove detector 138 uses the same to determine a land / groove track.

The polarity inversion unit 160 inverts the polarity of the difference value Kt output from the comparator 156 according to the result detected by the land / groove detector 158.

The radial tilt adjustment unit 134 adjusts the radial tilt according to the polarity inverted difference value Kt output from the polarity inversion unit 160. Since the sign and magnitude of the difference value Kt represent the direction and magnitude of the radial tilt, the tilt is adjusted by feeding it back.

The mirror section signal generator 150 generates a mirror section signal representing the mirror area from the sum signal RF_sum generated by the reproduction signal generator 130. In the case of the push-pull signal RF_pp, since the mirror signal becomes zero, the mirror section signal cannot be obtained by the push-pull signal RF_pp.

Since the mirror signal has a very low envelope compared to the data region and the header region, the mirror signal may be generated by the envelope detector and the comparator.

The mirror signal level detector 152 detects the level of the mirror signal from the sum signal RF_sum based on the mirror section signal generated by the mirror section signal generator 150. The mirror signal level detector 152 generates a third enable signal enable 5 having a predetermined section and a predetermined width by the mirror section signal generated by the mirror section signal generator, and by the third enable signal enable 5. The sum signal RF_sum is gated and the peak-peak value of the gated sum signal RF_sum is detected. The mirror signal level detector 152 is implemented with the apparatus shown in FIG. 7.

The balance calculator 154 may include the level V1 of the vfo1 signal detected by the first synchronous signal level detector 144, the level V2 of the vfo3 signal detected by the second synchronous signal level detector 156, and the mirror signal level detector 162. Based on the detected mirror signal level I0, a balance value K1 as shown in equation (4) is calculated. Here, the balance calculator 164 may output an average value of balance values obtained from several sectors consecutive in the tangential direction.

Instead of the sum signal RF_sum, the sum signals I1 and I2 of the radial pair may be used. In this case, I1 is input to the first synchronous signal level detector 144 and I2 is input to the second synchronous signal level detector 146.

FIG. 12 is a block diagram illustrating a detailed configuration of the radial tilt control unit illustrated in FIG. 11. The apparatus shown in FIG. 12 includes a radial tilt servo 170, a radial tilt driver 172, and an equalizer controller 174.

10 is a graph showing the relationship between the defocus amount d and Kt when RFpp is used to calculate the balance value. In FIG. 10, the solid line in the center shows the case where the radial tilt is zero, the solid line in the upper side shows the case where the radial tilt is 0.5, and the solid line in the lower side shows the case where the radial tilt is -0.5.

As shown, it can be seen that Kt varies linearly with the amount of defocus. Therefore, it is necessary to correct Kt according to the defocus amount.

13 is a flowchart showing a tilt component detection method according to the present invention.

First, the defocus amount d is adjusted to be minimized (S1300). The point at which defocus is minimized is set to a point where the focus error signal is minimized, for example, to zero.

The next Kt is detected. (S1310) The detection of Kt can be detected by the method described in equations (1) to (6).

14 is a flowchart illustrating another embodiment of a method of detecting a tilt component according to the present invention.

First, Kt is detected. (S1400) Detection of Kt can be detected by the method disclosed in Equations 1 to 6.

The next defocus amount d is detected (S1410). The defocus amount is detected by the magnitude of the focus error signal.

Kt is corrected by the defocus amount d (S1420).

Correcting Kt by the defocus amount d is determined by the following equation.

Kc = t

Here, Kc is the amount of radial tilt in which the influence due to defocus is compensated.

Since defocus amount d and Kt have a linear relationship, Equation 7 can be modified as follows.

Kc = t

Where a is a proportionality constant.

Since the defocus amount d and Kt have a linear relationship, Equation 8 can be modified as follows.

Kc = t

Where b is a threshold.

15 is a flowchart illustrating still another embodiment of the tilt detection method according to the present invention. Unlike the method shown in Figs. 13 to 14, the method shown in Fig. 15 determines the amount of tilt by detecting a difference in the amount of tilt detected at two points with different focus.

First, the tilt amount Kt1 at a certain point is measured. (S1500

The defocus amount at this time is called d1.

Next, the tilt amount Kt2 at another point is measured. (S1510

The defocus amount at this time is called d2.

Next, the tilt amount is determined by the change value of the tilt amount and the change value of the defocus amount. (S1520) The correction equation is as follows.

Kc = t1t212

As described above, the tilt method according to the present invention can perform the tilt correction more stably by compensating the effect of defocus in detecting the tilt and detrack amounts using the sync signal recorded in the header area on the disk. There is an advantage to that.

Claims (17)

A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, the apparatus comprising: Adjusting defocus of the optical disk to a minimum; And When the magnitude of the signal detected in the synchronization signal region recorded on one side of the track center line is V1, and the magnitude of the signal detected in the synchronization signal region recorded on the other side of the track center line is V3, A tilt detection method comprising the step of detecting the amount of tilt by the difference V1-V3. The tilt detection method of claim 1, wherein the adjusting of the defocus is minimized so that the size of the focus error signal is substantially zero. A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, When the magnitude of the signal detected in the synchronization signal region recorded on one side of the track center line is V1, and the magnitude of the signal detected in the synchronization signal region recorded on the other side of the track center line is V3, Detecting the amount of tilt by the difference V1-V3; And Tilt detection method comprising the step of compensating the V1-V3 by the defocus amount. The process of claim 3, wherein the process of compensating by the defocus amount Kc is the amount of radial tilt compensated for by the defocus, Kt is the amount of detected detrack, and d is the amount of defocus. Kc = t Tilt detection method, characterized in that 4. The method of claim 3, wherein Kc is a radial tilt amount compensated for by defocus, Kt is a detected detrack amount, d is a defocus amount, and a is a proportional constant. Kc = t Tilt detection method characterized in that it is determined. 4. The method of claim 3, wherein Kc is a radial tilt amount compensated for by defocus, Kt is a detected detrack amount, d is a defocus amount, a is a proportional constant, and b is a threshold. when doing Kc = t Tilt detection method characterized in that it is determined. The tilt detection method according to claim 4 to 6, wherein d is a defocus amount detected from a focus error signal. A tilt detection method of an apparatus for reproducing an optical disc having sync signal regions in which at least a sync signal is recorded above and below a track center line, the apparatus comprising: When the magnitude of the signal detected in the synchronization signal region recorded on the upper side of the track center line is V1, and the magnitude of the signal detected in the synchronization signal region recorded on the upper side of the track center line is V3, two points of different focus are provided. Detecting the amount of tilt (Kt1, Kt2) and the defocus amount (d1, d2) by V1-V3, which is the difference between V1 and V3; And And a tilt amount is determined by calculating a ratio of a change amount of the tilt amount and a change amount of the defocus amount detected at the two points. The method according to claim 8, wherein Kc is the amount of radial tilt compensated for by the defocus effect. Kc = t1t212 Tilt detection method characterized in that it is determined. The process of claim 3, wherein the detecting of V 1 -V 3 is performed. A tilt and detrack control method, characterized by normalizing V1-V3 to V1 + V3. The process of claim 3, wherein the detecting of V 1 -V 3 is performed. A method for tilt and detrack control, characterized in that V1-V3 is normalized to the magnitude I0 of the mirror signal detected from the mirror area where no pit is recorded. The process of claim 3, wherein the detecting of V 1 -V 3 is performed. And a tilt amount is detected from the push-pull signal reproduced in the synchronization signal region. The process of claim 3, wherein the detecting of V 1 -V 3 is performed. And a detrack amount from the sum signal reproduced in the synchronization signal region. The process of claim 3, wherein the detecting of V 1 -V 3 is performed. A tilt detection method characterized by detecting an average value of V1-V3 detected from a plurality of adjacent synchronization signal regions. 4. The tilt and detrack control method according to claim 3, wherein the disc is a DVD-RAM disc. 16. The method of claim 15, further comprising inverting the polarity of V1-V3 for each land / groove track. The recording area is divided into sectors, each sector having a header indicating an address, the header having a first header and a second header which are recorded staggered from side to side at the center point of the track, and the first header and the second header have the address of the sector. A tilt and detrack detection method of an apparatus for reproducing an optical disc having an address area in which is recorded and a sync signal area in which a sync signal for detecting address signals recorded in the address area is recorded When the magnitude of the signal detected in the synchronization signal region in the first header is referred to as V1 and the magnitude of the signal detected in the synchronization signal region in the second header is referred to as V3, the difference between V1 and V3 is V1-V3. Detecting the amount of tilt by; And Tilt detection method comprising the step of compensating the V1-V3 by the defocus amount.