JPH0550050B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a dropout counting device for measuring the number of dropouts contained in a reproduced signal from a medium recorded by a magnetic recording/reproducing device.

Conventional configuration and its problems Dropout in media is one of the very important problems in media manufacturing. In particular, with the recent trend toward high-density recording and high S/N, the surface properties of media have been greatly improved. Therefore, very minute foreign matter, dust, etc. on the surface of the medium are also detected as dropouts, which poses a problem. Therefore, measuring media dropout is very important in investigating its causes. Dropout is generally measured by a method of electrically counting dropouts in a reproduced signal. A conventional example of this dropout counting device is shown in FIG. 1 below. 1st
In the figure, 1' is a VTR (video tape recorder)
This is an envelope detection circuit that detects dropout by detecting the envelope of the RF (high frequency) reproduced signal from etc. 2' is a reference voltage generator, which is set to the average level of the input signal. R ₁ , R ₂ , R ₃ , R ₄ , and R ₅ each divide the reference voltage, and the voltages are applied to comparator circuits 3'a, 3'b, 3'c, and 3d. Respective comparator circuits 3'a, 3'b,
3'c and 3'd detect dropouts below the set voltage. A switch 4' switches the outputs of comparator circuits 3'a, 3'b, 3'c, and 3'd to select the dropout depth.
The detected dropout is converted into a pulse, and a dropout pulse longer than a set time is detected by the time constant circuit 5'. A time constant is set by C ₁ , C ₂ , C ₃ , and C ₄ and selected by switch 6' to detect the dropout time width. The detected dropouts are counted by a counting circuit 7', and the counted value is displayed on a display circuit 9'. Reference numeral 8' denotes a control section for the counting circuit, which starts and stops counting.

When measuring the number of dropouts of a medium using the dropout counting device configured as described above, only dropouts that satisfy a preset dropout depth and time width can be measured.

By the way, in order to investigate the cause of dropout, it is necessary to examine the various sizes (depth, time width) of dropout.
The number of pieces is required. It is also necessary to change the number of dropouts due to repeated playback. In order to perform such a measurement using the dropout counter described above, it is necessary to repeatedly measure by switching the dropout depth selection switch 4' and the time width selection switch 6'.
When measurements must be taken at limited locations on a medium, the medium must be repeatedly reproduced, and the number of dropouts changes during measurement due to demagnetization, deterioration, etc. of the medium. Furthermore, when measuring changes in the number of dropouts through repeated playback, the only way is to set only one type of dropout depth and time width.

Purpose of the Invention The present invention eliminates the above-mentioned drawbacks of the dropout counting device, and is capable of quantitatively measuring the depth, duration, and number of dropouts in a very short time. The purpose of the present invention is to provide a dropout counting device that can grasp the size and is effective for inspection in media development and production.

Structure of the Invention The dropout counting device of the present invention separates dropouts of various sizes in arbitrary combinations of various dropout depths and various time widths, and measures the number of dropouts for each dropout size at once. It is a dropout counting device. That is, a dropout detection means for detecting a dropout of a reproduced signal from a magnetic recording/reproduction device, a depth separation means for separating dropouts detected by the dropout detection means into multiple reference depths, and a depth separation means for separating the dropouts detected by the dropout detection means into multiple reference depths. a plurality of time width separation means for separating the dropouts of each depth separated by the means for each reference depth into each of the plurality of reference time widths, and each dropout separated by the plurality of time width separation means The apparatus includes a plurality of counting means for individually counting the number of times a time width dropout appears.

The dropout detection means in the dropout counting device of the present invention is a combination of an AGC circuit with an appropriate time constant that removes level fluctuations in the RF signal including dropouts reproduced from a recording medium, and an envelope detection circuit that extracts only the envelope of the RF signal. be. The depth separation means includes a reference level generation circuit that sets the average level of the input RF signal to 0 dB, a voltage divider circuit that attenuates the voltage in stages, and a voltage divider that uses each voltage divided in stages as a reference. This is a combination of multiple comparator circuits. The time width separation means includes a reference clock pulse generation circuit with a cycle smaller than the minimum dropout time width to be measured, a gate circuit that outputs a clock pulse only when a signal is lost due to dropout, and a dropout time width with an appropriate width. This circuit is a combination of a plurality of clock pulse number selection/separation circuits that step-by-step count and separate only a desired number of clock pulses from the clock pulses output from the gate circuit. The counting means for counting the number of dropouts includes a plurality of counting circuits that count the output pulses selected by the plurality of clock pulse number selection and separation circuits for each output, a control circuit that controls each counting circuit, and a counting circuit output selection circuit. This is a combination of a selection circuit to display the count value and a display circuit to display the count value.

Description of Examples Examples of the present invention will be described below, but the numerical values and the number of circuits are not limited to the examples.

In FIG. 2, the RF signal from the VTR has different outputs depending on the medium and also exhibits level fluctuations. Therefore, the amplification of the RF signal is automatically adjusted by AGC circuit 1 so that it becomes 2V _PP , and the amplification degree is automatically adjusted by the integrator circuit.
Removes fluctuations below 10Hz. reached a certain level
The RF signal is converted to RF by envelope detection circuit 2.
The signal component, 1 to 6 MHz, is converted to DC using a double-wave rectifier and an integrating circuit, and only the envelope containing the dropout of the RF signal is extracted. At this time, the average DC voltage envelope is 1V. 3 is a reference voltage generator that generates a constant DC voltage of 1V. 4
7 are voltage dividing circuits that divide the reference voltage, and although resistors or the like may be used, in the embodiment, a stepwise voltage is generated by a D/A converter using a logic circuit. The stepped voltages are -10 dB for voltage divider circuit 4, -14 dB for voltage divider circuit 5, -18 dB for voltage divider circuit 6, and -18 dB for voltage divider circuit 7 with respect to the reference voltage of 1V.
The logic circuit is set to generate four levels of constant voltage of 22dB. Each constant voltage and envelope signal are input to comparator circuits 8 to 11, respectively.
Comparator circuit 8 detects a dropout deeper than -10dB, and comparator circuit 9 detects a dropout deeper than -14dB.
Comparator circuit 10 detects dropouts deeper than -18 dB and comparator circuit 11 detects dropouts deeper than -22 dB. Each detected output becomes a pulse having the same time width as the dropout time width (referred to as a dropout time width pulse).
12 is a 1MHz reference clock pulse generation circuit. Reference numeral 13 denotes a time width separation circuit that separates dropouts by time width, and numeral a represents a gate circuit that gates the clock pulse based on the dropout time width pulse detected by the comparator circuit 8, and outputs a clock pulse only during the dropout time width. do. b to e are counting and separating circuits that count and separate the number of clock pulses, where b is 5 to 10, c is 10 to 20, d is 20 to 30, and e is 30 to 100. dropout detection pulses are output only when the number of clock pulses falls within each range. If b to e are time widths, b is 5 to 10 μsec, and c is 10 to 10 μsec.
20 μsec, d is 20 to 30 μsec, and e is 30 to 100 μsec, and the dropout time width pulse is detected at any of b to e. 14, 15 and 16
is the same time width separation circuit as 13.

The above circuit detects the depth and time width of dropout. The detected pulse output of the counting separation circuit b of the dropout time width separation circuit 13 is counted by the counting circuit f of the counter 17. The output of the counting separation circuit c is output by the counting circuit g,
The output of the counting/separating circuit d is counted by a counting circuit h, and the output of the counting/separating circuit e is counted by a counting circuit i. 18, 19, and 20 are the same counters as 17, and the counting separation circuits b to c of the time width separation circuits 14, 15, and 16 are connected to the counting circuits f to i of the counters 18, 19, and 20, respectively. are counted by counting circuits f to i. Reference numeral 21 denotes a selection circuit that selects the count value output of each of the counting circuits f to i, and is controlled by a control circuit 22. It also controls the counting start, stripping, and resetting of the counting circuits f to i. A display 23 displays the count value selected by the selection circuit 21.

Effects of the Invention The dropout counting device of the present invention separates dropouts by depth and further by time width, and counts each dropout individually. Combinations can be counted simultaneously, and the relationship between the depth, time width, and number of dropouts can be measured and understood in one measurement, and the cause of dropouts can be determined in a short time. Further, when the same position on the medium is repeatedly reproduced and the change in the number of dropouts is measured, the depth of the dropouts and the change in the number of dropouts depending on the time width can be measured at the same time. This is not possible in the conventional example. Furthermore, since only a desired range of dropout time widths is detected, time width separation is accurate. The dropout counting device of the present invention having the above-mentioned effects is very effective in the development of media, and allows the cause of dropouts to be ascertained in a short time.

Further, according to the present invention, by separating the size of dropouts as faithfully as possible and counting them in a short time, it is possible to minimize damage to the medium and obtain an accurate count distribution.

Next, a distribution map created using an example of dropout counts measured by the apparatus of the present invention is shown.

Figure 3 shows that the dropout duration is short and
Here is an example of a measurement of a magnetic medium in which a large number of magnetic media are generated at shallow depths.

FIG. 4 shows an example of measurements made on a magnetic medium in which many occurrences of long duration and deep depth occur.

This distribution diagram shows that the magnetic medium in FIG. 3 has many small protrusions, and the magnetic medium in FIG. 4 has many foreign substances attached to the surface.

In this way, the depth and duration of dropout can be statistically understood, and the characteristics of the magnetic medium can be seen at a glance by looking at the distribution diagram, which is an effective means for improving the quality of the magnetic medium.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional dropout counting device, Fig. 2 is a block diagram of an embodiment of the present invention, and Figs. 3 and 4 are examples of dropout counts measured by the device of the present invention. FIG. 1...AGC circuit, 2...Envelope detection circuit (dropout detection means), 3...Reference voltage generator, 4-7...Voltage dividing circuit, 8-11...Comparator circuit (depth separation means), 12 ... Reference clock pulse generation circuit, 13-16 ... Time width separation circuit, 17-20 ... Counter, 21 ... Selection circuit, 23 ... Display.

Claims (1)

[Claims] 1. Dropout detection means for detecting dropout of a reproduced signal from a magnetic recording/reproducing device; depth separation means for separating dropouts detected by the dropout detection means into multiple reference depths; and depth separation means. a plurality of time width separation means for separating the dropouts of each depth separated for each reference depth by a plurality of reference time widths; A dropout counting device comprising a plurality of counting means for individually counting the number of times a dropout appears.