JPS60105975A - Dropout measuring apparatus - Google Patents

Abstract

PURPOSE:To facilitate the detection of a dropout by measuring the attenuation of a missed signal obtained from the AM detection of a reproduction signal of a magnetographic medium and the missing time thereof. CONSTITUTION:A reproduction signal 11 is detected with an AM detector 12 and compared with a preset threshold level 14 set for a comparator 13. Now when the level of the signal 11 exceeds the level 14, a counter 18 is started to count a dropout and the range of the dropout (missing time) is latched into an output latch 20. While the detection signal renews the peak of the attenuation, the maximum value thereof is memorized into a peak detector/holder 15. Subsequently, the detection signal is digitized with an A/D converter 16 and the depth (attenuation) of the dropout is latched with an output latch 17. This operation is repeated sequentially at each frame and the missing time and attenuation in the dropout is shown on a display 21.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a dropout measuring bag [K] for detecting dropout of a signal recorded on a magnetic recording medium.

[Prior art]

Missing magnetic material in magnetic recording media such as magnetic tape 9
The reproduction signal of the recorded signal may be missing due to scratches, protrusions, lumps, etc. on the surface, or the recorded signal may not be input properly.
(There are some parts that are not recorded.Especially video clips.
In the case of magnetic materials such as Tubi disks, as the recording density increases, dropouts are more likely to occur even due to minute surface defects. For this reason, drop 7
There is a demand for accurate detection of occlusions.

Figure 1 is a waveform diagram of missing signals showing an example of dropout measurement values, 18 to 1e are missing signals, 2 is the base level, which is OdB, and missing signals below this are considered dropouts, which will be described later. Measure the amount of attenuation and the time of loss. 3 is the threshold level, α is the attenuation amount, and β is the missing time.

The measurement of dropout will be explained below with reference to FIG.

Conventionally, in the DO detector used to measure drop 7 points (hereinafter referred to as Do), a certain attenuation amount α and a certain dropout time β are set respectively, and a dropout No. 46 exceeding the set values is regarded as the occurrence of Do. Since the number of such objects was only counted, the distribution of the size of Do was not uniform and the cause of DO could not be investigated.

Therefore, in order to capture the distribution of DO, it is possible to consider measuring the Dot multiple times while changing the threshold level 3, but the disadvantage is that the output of Do changes each time the vehicle runs, making it impossible to accurately measure the distribution of the size of O. There are seven.

[Purpose of the invention]

In this invention, considering the above point k, jK is also trp,
A signal to be measured such as an FM video signal is recorded on a magnetic recording medium, and this high frequency reproduction No. 18 is subjected to AM detection.The missing signal (more precisely, it is the envelope of the missing signal) obtained by this It is an object of the present invention to provide a kDO measuring device which detects DO from the obtained kDO signal (hereinafter referred to as a missing signal).

[Summary of the invention]

In order to achieve the above object, the present invention reproduces a signal under test written on a magnetic recording medium VC, performs AM detection on the reproduced No. 4a, and detects a signal that is below a preset threshold level. It is designed to measure the amount of attenuation and missing time, and detect Do in one playback.

[Embodiments of the invention]

FIG. 2 is a schematic block diagram showing an embodiment of the present invention.
11 is a reproduction signal (RF), 12 is this reproduction signal 11'l
AM detector that detects kAM, 13 is a comparator, A
It compares the detected signal of the M detector 12 with a preset t'Lf, -threshold level 14''f, and outputs an output when the detected signal is larger.

15 is a peak detection holder that updates and holds the peak value of DO; 16 is a peak detection holder n, y, which is detected by the AM detector 12;
,: an A/D converter that digitizes the FM video signal; 17 is an output latch that latches the depth of Do, that is, the attenuation amount α from the value held by the peak detection holder 15;
18 is a counter that measures the number of DOs, and the clock 19 starts counting when the output from the comparator 13 is output, stops counting when the output disappears, and outputs the count value up to that point, that is, the missing time β. do. 20 is an output latch that launches the DO width, that is, the missing time β;
21 is a display that displays the components of Do.

Next, the operation will be explained.

The reproduced signal 11 is detected by the AM detector 12 and compared with the threshold level 14 set in the comparator 13. If it exceeds the threshold level 14, an output is output, the counter 1B is activated, the DOi counter is counted, and the missing time β is calculated. Start measuring.

On the other hand, the maximum value of the AM detected signal t'I is stored in the peak detection holder 15 while updating the peak ffflv of the attenuation amount α. Subsequently, the detected signal is digitized by the A/D converter 16, and its value '&lLlcarnch 17
Latch 1C.

This operation is repeated one frame at a time, and KDO (α, β) is displayed on the display 21. As a result, among the missing signals 18 to 1e shown in FIG.
and 1d is determined to be Do. For example, 1c=DO(αle
+βle)+1d=DO(α1dllsa) It becomes possible to display two-dimensional components.

Further, in the Do detection process after AM detection according to the present invention, if noise occurs when switching between the writing and writing heads, the noise can be eliminated by the following method.

When switching the playback head, unexpected noise is superimposed on the FM video signal and it is determined that tty<I)o, so it is necessary to temporarily interrupt the DO count. Fig. 3 is a timing chart for this purpose, where a is the reproduction signal, b is the vertical synchronization signal of No. ++1 after FM detection of the reproduction signal a, C is the gate signal, and d is the reproduction head switching point. .

Head switching is performed approximately 7H before the vertical synchronization signal, so the gate signal C is applied 15H before the vertical synchronization signal falls.
(horizontal synchronization = 952μ5ec) and 10H minutes after falling (6
3s tt 5ee), it becomes 'L' or 'H' level, and the Do measurement process is stopped for this 25H.

This 71 allows precise O measurement without being affected by disturbances.

For example, the attenuation amount α is -0.2 dB to -22 dB.
It is convenient if the threshold level 3 can be set in 012 dB units between the two, and the missing time β can be measured from 5 μs to 256 μs.

In addition, in FIG. 2, the output launch 20 of the Kakunta 18
If the value is compared with a preset reference value and output is made only when this value is exceeded, then both the dropout time β and the attenuation amount α are output only when they are greater than the VC set reference value. Therefore, it is immediately clear that it is DO.

Note that as means for determining DO, the above-mentioned comparator 13 for the attenuation amount α and a comparator (not shown) that compares the missing time β with a reference value can also be controlled by a microcontroller. do not have.

Further, in the embodiment shown in FIG. 2, the digital conversion is performed after the A/D conversion, but this may be reversed and the processing performed after the A/D conversion.

〔Effect of the invention〕

As explained above, in order to detect Do of '+B' recorded on a magnetic recording medium, the present invention
Since the missing signal is obtained by detection and the attenuation amount of this missing signal and the missing time of the missing signal are measured and output, it is easy to determine whether it is Do or not from the attenuation amount and missing time of this missing fr signal. can do. In addition, it is easy to change the certification criteria for Do by changing the reference values of the missing time and the amount of attenuation, and since it can be expressed as a two-dimensional component of the reduced J￥sa and the missing time, the size of the DO can be easily changed. It is possible to estimate the distribution of

As described above, the present invention has the advantage that since the missing signal can be obtained by one measurement, it is extremely easy to determine DO, and the cause of Do can be investigated.

[Brief explanation of drawings]

Figure 1 is D OF! FIG. 2 is a schematic block diagram showing an embodiment of the present invention, and FIG. 3 is a timing chart for explaining the operation. In the figure, 18 to 1e are missing signals, 2 is the base value impe, ib,
3.14 is the threshold level, 11 is the reproduction signal, 1
2 is an AM detector, 13 is a comparator, 15 is a peak detection holder, 16 is an A/D converter, 17 is an output latch that launches the attenuation amount α, 18 is a counter, 19 is a polarizer, and 20 is a dropout time β. Output launch, 21 is display, α is attenuation? , β missing time, a is a reproduction signal, b is a vertical synchronization signal, C is a gate signal, and d is a reproduction head switching point. Figure 1a Figure 21':4 Figure 3

Claims (1)

[Claims] A dropout measuring device for detecting a temporary absence of a magnetic recording medium Ω playback signal, comprising: AM detection means for performing AM detection on the playback signal to obtain a dropout signal; and attenuation measurement means for measuring the amount of attenuation of the dropout signal. . A dropout measuring device comprising a dropout time measuring means for measuring the pulse width of the dropout signal to obtain the dropout time.