JPH0442635B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dropout classification method suitable for magnetic tape used as a recording medium in video tape recorders and the like. Home video tape recorder (hereinafter referred to as VTR)
As a result, so-called helical scan VTRs, which use 1/2-inch wide magnetic tape, are rapidly becoming popular. In such VTRs, the magnetic tape is housed in a cassette, making it very easy to load and remove the tape and perform other operations.Also, it is possible to record continuous programs for up to 6 hours, making it possible to record long programs. It became. In this way, it has become possible to record long programs because it has become possible to dramatically improve the recording density of magnetic tape. Explain using. In FIG. 1, 1 is a magnetic tape, 2 is a magnetic head, 3 is a recording track, 4 is a horizontal synchronizing signal,
be. The magnetic tape 1 runs in the direction of arrow A, and the magnetic head 2 scans the magnetic tape 1 in the diagonal direction of arrow B at an angle θ. For this purpose, record track 3
is formed obliquely on the magnetic tape 1 at an angle θ. Although not shown, two magnetic heads are used as the magnetic head 2, and these magnetic heads are provided at an angular interval of 180 degrees from each other on the rotating drum, and one magnetic head records every other magnetic head. The other magnetic head records or plays back every other recording track. Therefore, the recording tracks 3 are recorded or reproduced one by one alternately with different magnetic heads. On each recording track 3, a video signal is recorded one field at a time, and therefore, a video signal of 262H (H is a horizontal scanning period) is recorded. Although not shown, a vertical synchronizing signal is recorded at the end of each recording track 3, and a horizontal synchronizing signal 4 is
It is recorded every 1 hour. By the way, in general, a guard band is provided between each recording track 3 in order to prevent crosstalk between the recording tracks, but in order to increase the recording density, a so-called azimuth method is used. Each recording track 3 is made to touch each other without providing a guard band.
That is, the gap directions of the two magnetic heads mentioned above are made different, and the magnetization directions are made different between adjacent recording tracks 3. In this way, the reproduction output can be sufficiently suppressed even if the recording track 3 is reproduced and scanned by a magnetic head whose gap direction is different from the magnetization direction of the recording track 3. Therefore, during recording, it is possible to form a recording track that partially overlaps the adjacent recording track, and the width of the recording track can be made sufficiently narrow, resulting in a significant improvement in recording density. Incidentally, the width W of the recording track 3 is set to 20 .mu.m to 58 .mu.m, so that even if the magnetic head 2 partially scans the adjacent track 3, no crosstalk occurs. The length between horizontal synchronization signals 4 (the length in which 1H video signal is recorded) l _H is approximately 370 μm, and θ
is approximately 7°. The above has explained the recording tracks formed at high density on a magnetic tape. Generally, when a magnetic tape is played back and scanned, a dropout occurs in the video signal due to a defect on the magnetic tape, and a white dot or white line appears on the playback screen. noise appears, degrading the image quality. The causes of defects in magnetic tape include scratches, protrusions, and depressions on the magnetic tape, as well as dirt and dust adhering to the magnetic tape. The nature of defects caused by such causes can be classified as follows. First, there are defects that cannot be removed, such as scratches on the magnetic tape, and such defects always cause dropouts. (Hereinafter, such a dropout will be referred to as a permanent dropout). Next, if the magnetic tape is scanned by a magnetic head once due to a defect caused by dirt or dust, the dropout will occur, but at the same time the dust is removed and no dropout will occur in the next scan (hereinafter referred to as This type of dropout is called a temporary dropout). Also, although dropout does not occur during the first scan of the magnetic head, certain substances in the coating on the magnetic tape may be scraped up by the scan of the magnetic head and strongly adhere to certain positions on the magnetic tape. This is a defect due to dropouts, which appear after multiple scans (hereinafter, such dropouts will be referred to as semi-permanent dropouts). In any case, the occurrence of dropouts is not desirable because it causes deterioration of the playback image quality, but in particular, the occurrence of permanent dropouts and semi-permanent dropouts must be prevented as much as possible. In addition, in magnetic tapes that perform high-density recording for long-time recording as mentioned above, even minute defects on the magnetic tape appear as large dropouts, so it is important to minimize even the slightest defects. is necessary. Of course, such dropout can be removed by electrical means, and various inventions and ideas have been made for this purpose, but in principle, they compensate for it with a signal containing information content that approximates the dropout portion. Since dropouts are made to be visually inconspicuous, if dropouts occur frequently, the image quality will deteriorate. In the case of high-density recording, minute defects that have not had much of an effect up until now become effective as dropouts, so the frequency of occurrence of dropouts increases. Therefore, it is necessary to develop magnetic tape with even fewer defects, but to do so, it must first be possible to evaluate whether a detected dropout is a permanent, semi-permanent, or temporary dropout. . However, conventionally, the number of dropouts occurring per unit time is counted by reproducing and scanning a magnetic tape, and the results are aggregated and averaged to evaluate dropouts. However, with this method, it is not possible to identify what type of dropout the dropout is, and it is difficult to evaluate them all at once without distinguishing between permanent, semi-permanent, and temporary dropouts. This does not mean that magnetic tape has been truly evaluated. In other words, defects in magnetic tape that cause permanent dropouts are defects that originally exist in the magnetic tape, and defects that cause semi-permanent dropouts are defects that occur when actually recording and reproducing magnetic tape. Therefore, improvements must be made to magnetic tapes to address each of these defects. In the above-mentioned conventional technology, even if recording and reproduction are performed multiple times, temporary dropouts cannot be eliminated. This means that there is always dust on magnetic tape.
This is because there is a possibility that dust may adhere to it. Also, since dropouts do not always occur due to magnetic tape defects, permanent
It is also not possible to accurately determine the amount of quasi-permanent. The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
To provide a dropout classification method that allows dropout evaluation to be performed easily and accurately. In order to achieve this object, the present invention is characterized in that the occurrence pattern of dropouts caused by multiple reproductions is compared with a preset occurrence pattern. Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the dropout classification method according to the present invention;
VTR, 6 is a microcomputer (hereinafter referred to as microcomputer), 7 is a time setting timer, 8 is a vertical synchronization pulse counter (hereinafter referred to as V counter),
9 is a horizontal synchronization pulse counter (hereinafter referred to as an H counter), 10 is a dropout detector, 11 is a dropout width counter, and 12 is an oscillator. FIG. 3 is a flowchart showing the operation of FIG. 2. Next, the operation of this embodiment will be explained. In FIG. 2, a VTR 5 is controlled by a microcomputer 6. Terminals C ₁ , C ₂ , C ₃ , C ₄ of microcomputer 6
From there, command signals for each mode of recording, playback, stop, and rewind are sent to the VTR 5, and the VTR 5 operates in a mode corresponding to the sent command signals. The time setting timer 7 is used to set the time for recording and playback modes. When a reset signal is sent from the terminal C ₅ of the microcomputer 6, the time setting timer 7 starts operating, and at the same time, the time setting timer 7 starts operating when the reset signal is sent from the terminal C ₅ of the microcomputer 6. Alternatively, a command signal is sent from C ₂ and the VTR 5 enters recording or playback mode. The time setting timer 7 sends a time over signal to the microcomputer 6 when the set time has elapsed, and the microcomputer 6 sends command signals from terminals C ₃ and C ₄ to stop the VTR 5 and put it into rewind mode. When the VTR 5 is in the playback mode according to a command from the microcomputer 6, the magnetic tape 1 shown in FIG.
The video signal is reproduced from the reproduced video signal, and the vertical synchronizing pulse VS separated from the reproduced video signal is sent to the V counter 8, the horizontal synchronizing pulse HS is sent to the H counter 9, and the reproduced RF
The signals V are respectively supplied to dropout detectors 10. V counter 8 is a 16-bit counter,
Count the supplied vertical synchronization pulses VS. The H counter 9 is a 9-bit counter that counts the supplied horizontal synchronizing pulse HS and is reset by the vertical synchronizing pulse VS.
Therefore, the H counter 9 repeatedly counts the horizontal synchronizing pulses HS for each field. A dropout detector 10 detects a dropout from a decrease in the amplitude of the reproduced RF signal V, and supplies this to the microcomputer 6 as well as to a dropout width counter 11. The dropout width counter 11 is composed of an 8-bit counter, and when a dropout is supplied, it counts the pulses from the dropout period oscillator 12 and uses the counted number as the dropout width.
supply to. Therefore, the microcomputer 6 detects the dropout detector 1.
When a dropout is supplied from 0, the respective counts of the V counter 8 and H counter 9 at that time are also supplied, and the dropout width counter 11
is stored in a memory (not shown) along with the count number from . The count number of the V counter 8 represents the recording track in which a defect causing dropout exists, and the count number of the H counter 9 represents the H period in which the defect exists on the recording track. becomes an address signal representing the position of the defect on the magnetic tape. Since V counter 8 is a 16-bit counter,
2 ¹⁶ = 65536 recording tracks can be counted, and therefore 65536/60≈1090 seconds, or approximately 18 minutes of measurement is possible. 2 After counting ¹⁶ , it will be reset and the count will be repeated at this time period. Since H counter 9 is a 9-bit counter,
2 ⁹ = 512 counts and is reset by the vertical synchronization pulse VS, so in the case of the NTSC system, the count from 1 to 262 is repeated,
In the PAL and SECAM systems, counting from 1 to 315 is repeated. In addition, PAL
In the SECAM method, the repetition frequency of the vertical synchronization pulse VS is 50Hz, so 2 ¹⁶ /50≒1310 seconds,
That is, measurement can be performed in about 20 minutes. Since the dropout width counter 11 is an 8-bit counter, it can count 2 ⁸ = 256. Now, if the oscillation frequency of the oscillator 12 is 500KHz, the dropout width can be set from 2μs to 512μs with an accuracy of 2μs. This means that it is possible to detect defect widths from H/30 to approximately 8H. In the case of the magnetic tape in Figure 1, 1H≒370μm, so 370÷30
This means that it is possible to detect minute defects up to approximately 12 μm. Note that the above numerical values are merely an example.
For example, it is clear that if the oscillation frequency of the oscillator 12 is made higher, the width of a dropout, and hence the width of a defect in the magnetic tape, will be detected even smaller. The operation of each block in FIG. 2 has been described above. Next, the case of measuring defects in a magnetic tape using the flowchart in FIG. 3 will be described. First, the time to be measured is set in advance by the time setting timer 7. Then press the record button (not shown)
Press 13 to start the microcomputer 6,
14. Issue a recording command signal from the _C1 terminal to start recording on the VTR 5. At an appropriate time after the start of recording, a start audio signal is placed on one end of the magnetic tape 1 (not shown in FIG. 1).
16. At the same time, a reset signal is sent from the _C5 terminal to operate the time setting timer 7. Thereafter, when the time setting timer 7 generates a time over signal 17 indicating that the set time has elapsed, a stop button (not shown) is pressed, and the microcomputer 6 issues a stop command signal to the _C3 terminal to stop recording on the VTR 5. Next, press the rewind button (not shown) to issue a rewind command signal to the _C4 terminal to rewind the magnetic tape (not shown).
18. Next, when you press the playback button (not shown), the microcomputer 6
issues a playback command signal to the _C2 terminal, and the VTR 5 enters playback mode19. 20 and V when the start audio signal is detected while playing back the audio recording track.
A reset pulse is supplied to the counter 8, H counter 9, and dropout width counter 11 to reset them 21. Then, the V counter 8 receives the vertical synchronization pulse VS, and the H counter 9 receives the horizontal synchronization pulse.
HS are each counted as described above. Therefore, when a dropout is detected by the dropout detector 10, the microcomputer 6 detects this (hereinafter referred to as a dropout interrupt).
2. Read the counts of the V counter 8 and H counter 9 at the start of dropout, and also read the count from the dropout width counter 11 23, and store each count in the memory (not shown) of the microcomputer 6. Remember 24. At the same time, the dropout width counter 11 is reset 25. Note that the dropout width counter 11 can be reset using, for example, a pulse detected from the end of the detected dropout. When the counts of each counter 8, 9, and 11 are stored in the memory, it is determined whether the memory exceeds 26, and if it exceeds, the data stored in the memory is transferred to an external memory (not shown). Transfer to 27. Next, it is determined 28 whether or not a time over signal has been received from the time setting timer 7, and if the set time has not elapsed, preparations are made for the next dropout interrupt 22. Each time a dropout is detected within the time set by the time setting timer 7, the counts of the V counter 8, H counter 9, and dropout width counter 11 are stored in the memory. The stored data is transferred to external memory. When the time set by the time setting timer 7 has elapsed, the time setting timer 7 generates a time over signal 28, and by pressing the stop button and rewind button, the microcomputer 6 sends stop and rewind command signals to the C ₃ and C ₄ terminals, respectively. is generated to put the VTR 5 into stop mode and further into rewind mode29. At the same time, microcontroller 6
All data stored in the memory of is transferred 30 to external memory, and all measurements are completed 31. In the manner described above, the position of a defect on the magnetic tape can be measured. Therefore, the same magnetic tape is repeatedly scanned for reproduction four times, and in the manner described above, the same address signal is stored in the memory for each defect in each reproduction scan. Note that the same magnetic tape may be repeatedly recorded and reproduced four times and the address signal may be similarly stored in the memory. In this case, the start audio signal recorded on the audio recording track is not erased, but is used as a reference address for each recording/reproduction. By the way, when performing four playback scans,
As shown in FIG. 4, there are supposed to be 15 patterns of dropouts occurring from the same position on the magnetic tape. In FIG. 4, "1" indicates that dropout has occurred, and "0" indicates that dropout has not occurred. Incidentally, permanent dropout has a high probability of occurring during the first reproduction scan, and also has a high probability of occurring during two or more reproduction scans out of four reproduction scans. Therefore, among the reference patterns shown in FIG. 4, the reference pattern that is "1" in the first reproduction scan and has a plurality of "1"s is set as the reference pattern for permanent dropout (see FIG. 5A). ). Semi-permanent dropout does not occur in the first playback scan, but there is a high possibility that it will occur multiple times in the second and subsequent playback scans. A reference pattern having a value of 1" is used as a reference pattern for semi-permanent dropout. (Figure 5B). Temporary dropouts are caused by weakly adhering dust, dirt, etc., so they occur due to the adhesion of dust, dirt, etc. at each playback scan, but temporary dropouts occur at the same position on the magnetic tape during two or more playback scans. dust,
The probability that dust etc. will adhere is extremely small. Therefore, a reference pattern having only one "1" is used as a reference pattern for temporary dropout (FIG. 5C). In this way, each dropout occurrence reference pattern is set in advance, and the measured dropout occurrence pattern is compared with the set reference pattern to classify the measured dropouts. Next, the formation and classification of dropout occurrence patterns by the microcomputer 6 (FIG. 2) will be explained. FIG. 6 is a flowchart showing such operation. In FIG. 6, the V counter 8 (FIG. 2) and H counter 9 of the L-th dropout generated by the K-th playback scan of the VTR 5 (FIG. 2) are shown.
Let the addresses represented by the respective counts in (Fig. 2) be D·OADD(K,L). Therefore, when the operation is started, all the dropout addresses D・OADD(1,L) from the first playback scan are set to the predetermined address D・OADD(1,L).
Sequentially transfer to OSTOK (L), and at the same time, each D.
Corresponding to OSTOK(L), the same dropout pattern (D・OPATTEN(L)) is 2 ⁰ , i.e.
32 for storing the pattern "1, 0, 0, 0"; Therefore, first, a pattern "1, 0, 0, 0" is assigned to the dropout occurrence position detected in the first reproduction scan. Next, J=N (however, N is D・OADD(1,L)
33, it is determined whether the dropout address D.OADD(2,i) detected by the second reproduction scan is in D.OSTOK(L). 34 If D・OSTOK(L)’s D・OADD(1,L)
If D・OADD(2, i) does not match any of the above, transfer D・OADD(2, i) to the address D・OADD(J+1) following D・OADD(L), and at the same time correspond to this. Then 2 ¹ D・OPATTEN (J+
1), that is, 35 for storing the pattern "0, 1, 0, 0". On the other hand, D・OADD(2,i) is D・OSTOK(L)
If it matches any D・OADD(1,L), then D・OSTOK(L) at this time becomes D・OSTOK
(JJ), and the corresponding D・OPATTEN(L) is D・OPATTEN(JJ) as 2 ⁰ + ² 136. Through these processes 35 and 36, D・OADD
D・OPATTEN(L) of D・OADD(1,L) that matched (2, i) becomes “1, 1, 0, 0”,
D・OADD(2,i) did not match
D・OPATTEN(L) of OADD(1,L) is “1,
0, 0, 0”, and D・OADD(2,i) which did not match D・OADD(1,L).
OPATTEN (J+1) is set to "0, 1, 0, 1", respectively. Let the address where the dropout address is stored in the above manner be D・OSTOK(〓),
Also, the pattern for this is D・OPATTEN
If (〓), then from the above, D.
OPATTEN (〓) is one of 1, 1, 0, 0 1, 0, 0, 0 0, 1, 0, 0, respectively. Next, the dropout address D・OADD(3,i) by the third playback scan is D・OSTOK
Determine whether it is in (〓)34. If not, transfer D・OADD(3, i) to the new D・OSTOK(〓) and at the same time, correspondingly transfer D・OPATTEN(〓) which is 2 ² , i.e. “0, 0, 1, 0" are stored. If there is, the D.O.A.D.
D・OPATTEN (JJ) for OSTOK (JJ),
D・OPATTEN(JJ) ⁺² Set to 236 D・OPATTEN(〓) for D・OSTOK(〓) obtained in this way is 1, 1, 1, 0 1, 1, 0, 0 1, 0 , 1, 0 1, 0, 0, 0 0, 1, 1, 0 0, 1, 0, 0 0, 0, 1, 0. Next, the dropout address D・OADD(4,i) from the fourth playback scan is set to all D・OADD(4,i).
The same process was performed for OSTOK(〓), and in the end, D・OSTOK(〓) corresponding to all D・OSTOK(〓)
OPATTEN (〓) will be one of the patterns shown in Figure 4. As described above, the occurrence pattern at each dropout occurrence position is obtained.Next, D*OPATTEN(〓) is rearranged in the order of the addresses of D*OSTOK(〓)37. That is, the occurrence patterns are rearranged in the order of dropout occurrence positions. Then, each occurrence pattern is the fifth
Dropouts are classified by determining whether they match any of the reference patterns shown in Figures A, B, or C.
38 Therefore, if the occurrence pattern matches any of the reference patterns shown in FIG. 5A, the occurrence pattern is set as a permanent dropout, and if it matches any of the reference patterns shown in FIG. 5B,
The generated pattern is set as a semi-permanent pattern, and when it matches any of the reference patterns shown in Figure 5C, the generated pattern is set as a temporary dropout, and the address for each generated pattern is set as a permanent, semi-permanent, or temporary dropout. Classify each dropout. Although the dropout classification processing performed by the microcomputer 6 (FIG. 2) has been described above, similar classification processing can also be performed by a circuit. This point will be explained below. FIG. 6 is a block diagram showing a specific example of a processing circuit for classifying dropouts based on the occurrence pattern by the microcomputer shown in FIG.
9, 40, 42, 43, 44 are memories, 41
is a comparison classification circuit. In FIG. 7, the memory 39 stores the dropout occurrence pattern obtained as explained in FIG. The memory 40 also stores reference patterns classified as shown in FIG. 5A, B, and C. Therefore, first, one occurrence pattern and its address are supplied from the memory 39 to the comparison and classification circuit 41, where they are sequentially compared with the reference pattern in the memory 40. If there is a pattern match, the comparison and classification circuit 34
stores the pattern and address at that time in memory 4.
2, 43, or 44 for storage. When the pattern at that time is one of the reference patterns shown in FIG. 5A, it is stored in the memory 42 as a permanent dropout, and when it is one of the reference patterns shown in FIG. 5B, it is stored as a semi-permanent dropout. If it is one of the reference patterns shown in FIG. 5C, it is stored in the memory 44 as a temporary dropout. Therefore,
By sequentially comparing the occurrence patterns stored in the memory 39 as described above, the measured dropout can be determined as permanent, semi-permanent, or
All are categorized as temporary. FIG. 8 is a block diagram showing a specific example of the comparison and classification circuit of FIG. 7, in which 45 and 46 are input terminals;
47, 48 are registers, 49 is memory, 50, 5
1, 52, 53 are exclusive OR circuits, 54 is a NOR circuit, 55 is a read signal generation circuit, 56, 57, 58
is an AND circuit, 59, 60, and 61 are gate signal input terminals, and 62, 63, and 64 are output terminals. In FIG. 8, 4 represents the measured dropout occurrence pattern of memory 39 (FIG. 7).
Bit signal (hereinafter referred to as generation pattern signal)
and an address signal are supplied from the input terminal 45, the generated pattern signal is stored in the register 47, and the generated pattern signal and address signal are stored in the memory 49. When the generated pattern signal is stored in the register 47, a 4-bit signal representing the reference pattern (hereinafter referred to as the reference pattern signal) is stored in the register 48 from the memory 40 (FIG. 7) through the input terminal 46. Therefore, each bit signal corresponding to the pattern signal stored in each of the registers 47 and 48 is supplied to each exclusive OR circuit 50, 51, 52, and 53, and each operation result is supplied to a NOR circuit 54. Ru. Therefore, the output of the NOR circuit 54 becomes "1" when the generated pattern signal stored in the registers 47 and 48 matches the reference pattern signal.
and if they do not match, it becomes "0". The reference pattern signal is sequentially read out from the memory 40 (FIG. 7) and stored in the register 48 until it matches the generated pattern signal stored in the register 47, and is sequentially compared with the generated pattern signal in the register 47. When both the pattern signals of the registers 47 and 48 match and a "1" signal is obtained from the NOR circuit 54, the read signal generation circuit 55 generates a read signal and reads the generated pattern signal and address signal from the memory 49. , and are supplied to AND circuits 56, 57, and 58. When the reference pattern signal stored in the register 47 is the reference pattern signal for permanent dropout (FIG. 5A), the AND circuit 56 is turned on by supplying a gate signal to the gate signal input terminal 59. Similarly, by supplying gate signals to the gate signal input terminals 60 and 61, respectively, when the reference pattern signal stored in the register 48 is the reference pattern signal for semi-permanent dropout (FIG. 5B), When the AND circuit 57 is also the reference pattern signal for the temporary dropout (FIG. 5C), the AND circuit 58 is turned on. However, the generated pattern signal and the address signal read from the memory 49 are classified by passing through one of the AND circuits 56, 57, and 58 according to the reference pattern signal that matches the generated pattern signal, and then sent to the output terminal 62. , 63, 64 to one of the memories 42, 43, 44 (FIG. 7). Therefore, the detected dropout is classified and stored as either permanent, semi-permanent, or temporary. As described above, each dropout can be classified based on the four playback scans, and based on this result, the distribution of various types of dropouts (permanent, semi-permanent, temporary) on the magnetic tape, each playback scan. In addition, it is possible to know the occurrence status of various dropouts at each time, and it becomes possible to easily evaluate the magnetic tape and investigate the cause of defects in the magnetic tape. For example, from the dropout classification data obtained as described above, the number of occurrences of various dropouts per minute for each reproduction scan can be obtained, and the graph shown in FIG. 9 can be created. From such a graph, it is possible to know, for example, the tendency of semi-permanent dropout to occur, and it is useful for evaluating magnetic tapes. In the above embodiment, the reproduction scan is performed four times, but the reproduction scan is not limited to this, and any number of reproduction scans can be performed as long as it is three or more times. It goes without saying that a pattern must be established. Further, the circuit configuration shown in the above embodiment is merely an example, and it is obvious that other circuit configurations having similar functions can be employed. As explained above, according to the present invention, a dropout occurrence pattern at a position on a magnetic tape where a dropout occurs is obtained by performing reproduction scanning a plurality of times, and the dropout occurrence pattern is used as a reference pattern set in advance. Since it is compared with the conventional technology, it is possible to accurately identify and classify the type of dropouts detected, and it facilitates the evaluation of magnetic tapes and the investigation of defects in magnetic tapes. It is possible to provide a dropout classification method with excellent functionality.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a recording pattern on a magnetic tape, FIG. 2 is a block diagram showing an example of a dropout classification method according to the present invention, and FIG.
The figure is a flowchart for explaining the operation for obtaining the dropout address in figure 2,
The figure is an explanatory diagram showing the reference pattern, Fig. 5 A, B,
C is an explanatory diagram showing standard patterns for each type of dropout, FIG. 6 is a flowchart showing operations for forming and classifying dropout occurrence patterns in FIG. 2, and FIG. FIG. 8 is a block diagram showing a specific example of a processing circuit for classifying patterns. FIG. 8 is a block diagram showing a specific example of the comparison and classification circuit of FIG. 7. FIG. FIG. 2 is a graph diagram illustrating an example of how the obtained data is used. 5...VTR, 6...Microcomputer, 8...V counter,
9...H counter, 10...dropout detector,
41... Comparison classification circuit.

Claims (1)

[Claims] 1. The same area of the magnetic tape is covered n times (where n is 3
(integer greater than or equal to)) In a dropout classification method, a dropout is detected each time the magnetic tape is played back, and each dropout is classified according to the type of defect in the magnetic tape that causes the dropout. Dropouts are generated by generating the addresses above, and assigning bits indicating whether or not a dropout has occurred to each of the reproductions to the address of a defect that causes a dropout at least once in the n reproductions, and arranging them in the order of reproduction. A generation pattern consisting of n bits of an n-bit reference pattern representing a quasi-permanent dropout that occurs but does not occur on the first playback;
A reference pattern of n bits representing a temporary dropout that occurs only once in n times of playback is set in advance, and after the nth playback is completed,
Comparing the occurrence pattern stored in the memory with these reference patterns, and classifying the dropout that causes the occurrence pattern into one of a permanent dropout, a semi-permanent dropout, and a temporary dropout. Characteristic dropout classification method.