JPH0477189A - Method for measuring skew distortion of magnetic recording medium and its measuring instrument - Google Patents

Abstract

PURPOSE:To measure a skew distortion accurately by taking horizontal synchronization of a composite video signal inputted from an input terminal, regulating an external synchronizing signal frequency and obtaining skew distortion from a deviation between the frequency of the external synchronizing signal and a reference synchronizing signal frequency. CONSTITUTION:A variable frequency synchronizing signal generator and a monitor having a video input terminal and an external synchronizing signal input terminal are connected to measure skew distortion. In this case, since an external synchronizing signal is inputted, distortion is immediately observed on a screen and a pattern is easily displayed on the screen by regulating the synchronizing signal frequency. The skew distortion is obtained from a difference between the synchronizing signal frequency and the reference synchronizing signal frequency. The skew is accurately obtained by having only to display a pattern on the screen normally. Even when skew distortion is too excessive, the measurement is easily implemented by adopting the measuring method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for measuring skew distortion of a magnetic recording medium for consumer use, broadcasting, or high-definition use, and also relates to a skew distortion measuring device using this method. It is related to.

Conventional technology Conventionally, skew distortion was measured using a TV monitor or oscilloscope to observe the discontinuous part of the horizontal synchronization signal that occurs at the head switching part, and based on the degree of deviation, the amount of skew distortion was calculated as skew distortion for one field. was calculated.

There is also a method of recording a single frequency signal and then calculating the skew distortion from the deviation of the recorded signal frequency.

Problems to be Solved by the Invention When observing skew distortion on a monitor, distortion occurs at the top of the monitor when the skew distortion reaches about 30 μsec, but the degree of skew distortion becomes even larger, and 6
When the skew reaches about 0 μsec or 70 μsec, no distortion is observed at the top of the TV monitor, and at the bottom of the TV monitor, the skew distortion starts from a few μsec to l Op.
It is observed that sec. In such cases, it is difficult to determine whether the head switching position of the synchronization signal is shifted by one scanning line or not at all, and with this measurement method, it is not even possible to tell whether the tape is extending or contracting. Similar results are obtained when observed with an oscilloscope.

Furthermore, when recording a single frequency signal, it is necessary to modify the deck so that the single frequency signal can be recorded, and in that case, normal color par signals etc. cannot be recorded.

Means for Solving the Problems The present invention allows skew distortion to be determined more accurately than skew distortion measurement using a television monitor.
It is possible to measure visually and easily.

When measuring skew distortion on a regular TV monitor,
Since television monitors are equipped with a function to correct skew distortion, the distortion that should appear on the monitor is successively corrected, and if the degree of skew distortion is small, this skew distortion will not be observed on a normal monitor.

However, even in this case, when the skew reaches about 30 μsec, correction is not performed sufficiently during the vertical retrace period, and distortion begins to occur even at the top of the screen of the television monitor.

This part usually appears at the bottom of the monitor at the head switching part and cannot be observed under normal conditions, so it can be observed by reducing the vertical amplitude of the monitor or shifting the vertical synchronization.

In this way, since the TV monitor itself has a correction function, distortion does not appear on the screen, but with a TV monitor that has an external synchronization signal input, if an external synchronization signal is used, the TV is synchronized to this external synchronization signal. The signal itself is observed distorted. Therefore, when an external synchronization signal is used, the entire screen is tilted uniformly, and the skew can be measured by observing the tilt and degree.

However, when determining the skew from the slope of the west face, it is difficult to measure it without importing it into a frame memory or taking a photo. However, by inputting the variable external synchronization signal of the present invention, Skew distortion can be easily measured by adjusting the frequency so that an object that is tilted as a whole stands up straight.

Effect: With this method, even when the skew distortion is large, it is possible to easily measure the skew distortion, and moreover, it is possible to measure the skew distortion accurately and visually in an easy-to-understand manner.

Example The present invention will be explained in detail below.

First, skew distortion will be explained. Skew distortion occurs when a signal is recorded on a magnetic recording medium and then left for a certain period of time or when it is repeatedly reproduced, causing distortion on the screen. This phenomenon is called skew distortion.

This skew distortion is a phenomenon in which the signal recorded on the magnetic recording medium itself also expands and contracts as the magnetic recording medium expands and contracts as a whole.

Therefore, when the signal is played back, the signal appears distorted, resulting in a distorted image on the television monitor. In order to prevent the phenomenon of skew distortion or jitter from appearing on the screen, television monitors are equipped with a circuit that corrects this distortion. Therefore, if the skew distortion is small, no distortion will be observed on the TV monitor.

Here, a method for measuring skew distortion using a conventional television monitor will be explained. When measuring skew distortion using a TV monitor, the skew distortion does not appear on the screen due to the TV monitor's own correction function.
This is because the change in time between one horizontal scanning line is extremely small and can be sufficiently corrected on the television side. However, even in this case, the situation is different at the head switching portion.

The head switching portion appears several eight times before the vertical synchronization signal. This corresponds to the vertical blanking period of the scanning line. Therefore, it is not observed under normal conditions.

However, this part can be observed by reducing the vertical amplitude of the television monitor or by shifting the vertical synchronization.

In this head switching portion, unlike the normal center of the screen, the total distortion of one field appears. In other words, the distortion of 256 horizontal scanning lines appears at once.9For example, the distance between horizontal scanning lines in the center of the screen is 0.
．． If there is a difference of 1 μsec, 1 field is 25
Since this corresponds to 6 horizontal scanning lines, this head switching portion results in a shift of 25.6 μsec.

Such a large time difference requires a considerable amount of time to correct on the TV. For example, the skew distortion is 30μs
When the skew becomes about ec, the amount of skew that can be corrected between 18 is limited, so the distortion cannot be completely corrected during the vertical retrace period and distortion appears up to the top of the screen.

In this way, the correction ability of IH is usually small, so the distortion extends to the top of the screen, but by taking advantage of this small correction ability, it is possible to...

It is possible to measure the skew just by observing the mode switching area.

By using a TV monitor in this way, the amount of skew distortion can be determined in a simple way, but in this case, when the skew distortion is exactly equal to the time interval of one scanning line, it is as if there is no skew distortion at all. Can be seen. In other words, there is a problem in that the skew distortion cannot be determined without prior knowledge of the extent of the skew distortion.

Furthermore, if a single frequency signal is recorded and skew distortion is determined from the frequency shift, the deck must be modified, and in this case, normal video signals cannot be recorded.

The skew distortion measurement principle of the present invention is characterized in that skew distortion is measured by connecting a variable frequency synchronization signal generator to a monitor having a video input terminal and an external synchronization signal input terminal.

The feature of this measurement principle is that an external synchronization signal can be input, so distortion can be immediately observed on the screen, and by adjusting the synchronization signal frequency, it can be easily displayed on the screen without distortion. It is something that can be done.

Skew distortion can be determined from the difference between this synchronization signal frequency and the reference synchronization signal frequency.

In this way, the skew value can be accurately determined just by displaying the image normally on the screen, and there is no need to know in advance how much skew distortion has occurred, unlike measurement using a conventional TV monitor. Unlike when recording a single frequency signal, there is no need to modify the deck.

The skew distortion measurement according to the present invention was determined using the following formula in order to correlate with that measured using a monitor or an oscilloscope.

Skew distortion of 1 field=(1/f0 1/f)×262.5μ5ecfO: Reference horizontal synchronizing signal frequency f: Sample synchronizing signal frequency The present invention will be explained in more detail below.

As a measurement deck, 5-VHS deck N manufactured by Matsushita Electric was used.
A V-FS900 was used, and a Shibaku TV monitor with an external synchronization signal input terminal was used as a monitor.

The synchronization signal generator has a variable horizontal synchronization signal frequency. In this case, a synchronization signal that also includes a vertical synchronization signal can be used as the external synchronization signal, but in this embodiment, only the horizontal synchronization signal is input, and the vertical synchronization signal is not included in the external synchronization signal.

Even if a synchronization signal that does not include a vertical synchronization signal is used as in this embodiment, there is no problem in measuring skew distortion. Further, although the monitor part and the synchronization signal generator were implemented separately, they may be integrated.

The samples used in the present invention will be explained below.

[Sample 1] After cross-dispersing the magnetic paint, it was coated on polyethylene terephthalate film A to obtain a magnetic recording medium.

[Sample 2] Sample 1, polyethylene terephthalate film B
Sample 2 was obtained in the same manner except that .

[Sample 3] Sample I, polyethylene terephthalate film C
Sample 3 was obtained in the same manner except that .

[Sample 4 and sample 1, polyethylene terephthalate film D
Sample 4 was obtained in the same manner except that .

Table 1 shows the heat shrinkage rate when the base film used for each sample was left at 150 degrees for 30 minutes.

After recording color par signals on these samples, 40
It was left in an environment of 80% RH for 10 days.

Table 1 Example 1 These samples 1 to 4 were input to a television monitor equipped with an external synchronization signal input terminal, and the synchronization signal frequency was adjusted using a prototype signal generator with variable synchronization signal frequency. The skew distortion was measured using the following method.

Comparative Example 1 Skew distortion was determined by observing the video head switching portion on a television monitor.

Comparative Example 2 Skew distortion was determined by observing the video head switching portion using an oscilloscope.

Comparative Example 3 The deck was modified to reduce skew distortion due to the difference in recording frequency during reproduction.

Table 2 shows the results measured by each of these methods.

If it is clear that measurement using a conventional monitor or oscilloscope would result in an incorrect measurement value, it is considered impossible to measure and is indicated by an x mark.

Results similar to those obtained when recording frequency signals in Table 2 could be obtained.

According to the method of the present invention, skew distortion can be accurately measured without modifying the deck, and the skew distortion can be easily understood visually. Furthermore, by using the measuring device of the present invention, skinny distortion can be determined extremely easily and accurately.

Name of agent: Patent attorney Shigetaka Awano Haka 1 Effect of invention

Claims (2)

[Claims] (1) Horizontal synchronization of composite video signals input from the video signal input terminal of the TV monitor using a synchronization signal generator that can set the synchronization signal frequency variably or a signal generator that can generate a variable continuous rectangular wave signal. The external synchronization signal frequency is adjusted to remove the distortion of the video signal on the TV monitor, and the skew distortion of the magnetic recording medium is determined from the deviation between the external synchronization signal frequency and the reference synchronization signal frequency. Method. (2) Consists of a synchronization signal generation section that can generate a variable synchronization signal frequency and a monitor section that has a terminal that can input a composite video signal, and synchronizes the composite video signal input to the video signal input terminal on the TV monitor. A synchronization signal generation section and a monitor section that remove distortion appearing on a television monitor by using a synchronization signal generated from the synchronization signal generation section, and calculate skew distortion from the deviation between the synchronization signal frequency and a reference synchronization signal frequency. A device for measuring skew distortion of a magnetic recording medium.