JP3466675B2 - Magnetic playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary head for recording information such as image signals recorded on tracks formed obliquely on a magnetic tape at a tape speed higher than that at the time of recording. The present invention relates to a magnetic reproducing apparatus such as a VTR for searching while reproducing. 2. Description of the Related Art In general, special reproduction in a digital VTR, particularly high-speed search, is an indispensable technique, and a technique excellent in searchability is required. FIG. 11 shows a trajectory of a rotary head for tracing a recording track recorded on a magnetic tape. Assuming that the playback tape transfer speed is M,
“a” indicates the trajectory of the head at the time of normal reproduction with M = 1, “b” indicates the trajectory of the head during the low-speed search with M = about 5 to 15, and “c” indicates the trajectory of the head at the time of high-speed search with M = about 50 to 100. At the time of a search, a head trace angle is determined according to a search speed M. The number of tracks traversed by the head in a unit scan corresponding to one recording track according to the winding angle of the magnetic tape around the rotating drum depends on the trace angle. The case where the head trace angle at the time of recording coincides with M = 1 is the pattern of the recording track itself. Under this condition, the reproducing head does not cross the recording track but traces the entire recording track. Here, D = 1 when the search direction matches the tape transport direction during recording, and D =-when the search direction is opposite.
Assuming that the number is 1, the number C of intersections between the read head and the recording track can be expressed as follows. C = | D * (M-1) | At the intersection of the read head and the recording track, the read signal level is reduced. This occurs due to a difference in guard space or azimuth angle between adjacent tracks. That is, a so-called azimuth loss occurs in tracing a guard space, which is a non-recording portion, or in tracing with a head having a reverse azimuth during recording, and the level of the detection signal decreases. As a result, as shown in FIG. 5, the reproduction level increases and decreases each time the recording track is passed, and when viewed in the time axis direction, it has a shape like an abacus ball. [0008] In the conventional VTR, there is a possibility that all the recorded information can be reproduced at the standard speed reproduction. However, as the search speed M increases, the information of the omission of detection may be reduced. However, there is a problem that the size of the liquid crystal becomes large, and finally falls short of a visual permissible limit. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a user-friendly magnetic reproducing apparatus which enables good information detection even when the search speed M increases, and has a high-speed searchability. The purpose is to do. A magnetic reproducing apparatus according to the present invention reproduces image data and an additional signal relating to the image data by tracing a magnetic tape on which a number of oblique tracks are formed by a rotating head. Reproducing means, speed setting means for setting a reproduction speed higher than the normal reproduction speed, and comparing means for comparing the reproduction speed reproduced by the reproduction means with a predetermined value according to the setting of the speed setting means. And reproducing and outputting the additional signal when the reproduction speed is higher than the predetermined value, and reproducing the image data when the reproduction speed is lower than the predetermined value, based on the comparison result of the comparing means. Output means for outputting. In the case of a VTR, a use condition in which the image quality of a search image is good and a use condition inferior to a visual permissible limit are distinguished according to the tape speed, and different search processes are performed. Will be That is, the search speed N corresponding to the allowable limit of the image quality is specified from various parameters, and a plurality of search modes are switched and controlled according to the result of comparison with the actual search speed M. Here, the parameters include, for example, a track width, a reproducing head width, a detection C / N, an azimuth angle, a data encoding method, and the like for each recording mode. Therefore, a search operation in a high-speed search is facilitated by dividing the search process into different search processes according to the tape speed, that is, an image search mode and an ID search mode. An embodiment of the present invention will be described below with reference to the drawings. FIG. 5 schematically shows a level variation of a reproduced signal detected from a reproducing head in a digital VTR. As the search speed changes from low to high, the time axis (horizontal axis) of the graph is gradually compressed, and the number of abacus balls detected per unit time increases.
Since the number of abacus balls is equivalent to the number of tracks to be traced, the number of abacus balls is the absolute value of the search speed M, expressed in the same manner as the number of intersections C with the recording track of the reproducing head. . Dependence of Head Detection Signal Level on Search Speed As an indication of how much recorded information can be detected as a reproduction output signal, an integral value of a reproduction signal level corresponding to the area of an abacus ball is calculated for each search speed. The plotted graph is shown in FIG. The reproduction speed on the horizontal axis is based on the reproduction signal level at this time with the left end at M = 1 for normal reproduction (10
0%) is indicated by a level on the vertical axis. FIG. 5 shows an alternating current centering on the zero level, so that the intersection (the boundary between the abacus balls) is a missing portion of the reproduced signal, and the center (the top of the mountain) between the intersections is the most. This is a portion where the reproduction signal level is high. Search Speed Dependency of Reproduced Data Error Rate In FIG. 5, the amplitude of the reproduced signal is equal to or higher than a predetermined level "A" as a portion where good signal detection is performed. The predetermined level “A” means that the transmission path quality corresponding to the transmission (recording / reproduction) information is secured.
For example, in a digital transmission (recording / reproducing) system, the transmission path quality is evaluated as a “data transmission error rate”. Generally, a data system for a computer requires about 10 ^-12 to 10 ^-14 , and it is said that image information should satisfy about 10 ^-4 to 10 ^-8 . Using these as indices, the predetermined amplitude level "A"
Will be set. The portion that satisfies the amplitude condition is shown by hatching in FIG. As the search speed increases, the number of good data reproduction portions that satisfy the amplitude condition decreases, and the data error rate of the entire reproduction information decreases.
This is shown in FIG. Similar to FIG. 6, the horizontal axis indicates the search speed, and the vertical axis indicates the data error rate. Raw data error rate curves b and E of the reproduced data
Data error rate curve a when error correction is performed by CC processing
The following two cases are shown. The raw data has a rapid rise in the data error rate, and the ECC processing has been delayed late. That is, when the error rate curves a and b at a predetermined image quality are compared, since the curve a has been subjected to the ECC processing, it is possible to output an image even at a higher search speed than the curve b. Regarding Search Speed Dependence of Number of Reproduction Sync Blocks The image quality of a search is determined by the number of sync blocks that can be detected from within the above-mentioned good area.
As shown in FIG. 5, as the search speed increases, a good area is compressed in the time axis direction, and the number of reproduced sync blocks, which are data detection units, decreases. FIG. 8 shows the relationship between the search speed and the number of reproduced sync blocks. As a representative example having different search speeds M, an example in which m1 and m2 sync blocks are detected by M1 on the high-speed side and M2 on the low-speed side, respectively, is shown in the lower part of FIG. That is,
During normal speed reproduction, the number of detected sync blocks is maximized. On the other hand, since the number of sync blocks required for the search is at least one, the maximum search speed is when the number of detected sync blocks is one. This is also true for the reverse rotation search. In the sync block reproduced in this way, data that has been subjected to image encoding processing (generally, compression) is stored in units of pixel blocks. This pixel block depends on the content of the image information, and in order to prevent a large deviation in the data generation amount of the variable length coding from occurring, as shown in FIG. Blocks are sequentially extracted. For this reason, unless a certain number of sync blocks are reproduced, there is a large loss of image information, and it is not possible to secure reproduction image quality sufficient for search. At the time of normal reproduction, both the inner code and the outer code of the data format shown in FIG. 10 can be used, so that good characteristics can be obtained. However, at the time of search, only the ECC processing by the inner code in the A direction of FIG. Will deteriorate. The relationship between the search speed and the quality of the reproduced information has been described based on several evaluation factors. A common characteristic of these is that as the search speed increases, the causes of deterioration of the reproduced image increase. Therefore, in the present invention, a line is drawn at a visually permissible limit, and a search speed Mth corresponding to this boundary line is set in advance. With this Mth as a boundary, a good image quality side reproduces an image, and performs a search operation based on the reproduced image. On the other hand, in an area having an image quality lower than the allowable limit, a subcode as an ID useful for various searches such as a time code is displayed rather than performing image reproduction in a short time. The operability can be further improved. For example, a time code has a capacity of 64 bits of a year, month, day, hour, minute, and second frame with 1 Block and 2B
If the lock is used, it can correspond to 90 bits of the VITC time code of SMPTE for business use. FIGS. 6, 7, and 8 show that a search is performed using an image and an ID with the above Mth as a boundary. As described above, the first capstan servo characteristic specialized for excellent image reproduction and the second capstan servo characteristic specialized for reproducing a subcode having only a narrow recording area are provided.
, And the servo characteristics can be selectively set as appropriate to realize an optimum search characteristic. An embodiment of the switching of the servo two-mode control according to the search speed according to the present invention will be described below with reference to FIG. The video and audio signals input to the digital signal processing circuit 100 can be recorded in the form of digital signals on a recording tape driven by the VTR mechanism 101. The VTR mechanism 101 includes an electromagnetic conversion system, a loading mechanism, and the like.
02. The output signal of the mechanical control servo circuit 102 is the first control mode circuit 10
3 and the second control mode circuit 104, and the switching circuit 105 appropriately switches between the two control modes. The search speed M is set by an external key input 106, and this information is input to the system controller 107 and the speed comparison circuit 108, and the optimum control mode is switched. The search speed M can be arbitrarily changed, for example, by operating a so-called “shuttle ring” of a so-called jog shuttle using a rotary angular displacement used in an editing machine. The set value N is given from the predetermined speed setting circuit 109 and input to the speed comparison circuit 108. The speed comparison circuit 108 compares the search speed M with the set value N and supplies the result to the system controller 107. The system controller 107 supplies the information of the search speed M to the digital signal processing circuit 100 and the mechanical control servo circuit 102, and supplies the comparison result to the digital signal processing circuit 100 and the switching circuit 105. The switching circuit 105 switches the control mode according to the comparison signal, and controls the mechanical control servo circuit 10 so that a low-speed search or a high-speed search is executed.
2 operates to control the VTR mechanism 101. As a result, the search processing can be arbitrarily used according to the use condition of the search image. FIG. 2 is a schematic block diagram of search speed control according to the present invention. An M-fold search speed set value is input to the system controller 110 from an operation panel (not shown).
A switching signal is input from the system controller 110 to the switching circuit 111 in accordance with the set value.
Further, a control signal of the system controller 110 is also input to the rotating drum 112 and the drum servo circuit 113 and the capstan servo circuit 114 which are mainly responsible for the steady maintenance of the capstan drive. Thus, when the search speed is, for example, M = 1 according to the value of M, normal reproduction is performed.
Control is performed such that low-speed search is performed when = 5 and high-speed search is performed when M = 50. The capstan servo circuit 114 includes a capstan motor 115 for controlling the feed speed of the recording tape 117 and a capstan FG 116 for grasping the rotation status thereof. Drum motor 118 for rotational drive and respective detectors FG1 for confirming rotational speed and rotational phase
19 and PG 120 are provided, and each rotation is controlled with reference to these detection outputs. The drum PG 120 further includes a sampling pulse generator 121 and a sampling pulse generator 122
And a timing signal corresponding to each of the ATF, subcode, audio, and video areas of the oblique track recorded on the recording tape 117 is generated. FIG. 3 shows the high and low timings of this timing signal. In the high-speed search mode (a), a sampling pulse is generated so that the pulse is high only in the subcode area, and in the low-speed search mode (b), the pulse is high only in the video area. Further, in the low-speed search of about twice the speed, the audio can be reproduced. In this case, the audio area may be set to be high in addition to the video area as shown in FIG. Such a timing signal is represented by S / S in FIG.
In the mode in which only the ID is detected at the time of search, only the subcode area uses high (a). In the mode in which the image is output during the search, only the video area uses high (b). H gate opening / closing is controlled. The gate opens when it is high and closes when it is low.
Servo control is performed using the TF pilot error signal. S
The output signals of the / H circuits 123 and 124 are input to a switching circuit 111, and the signals switched by the switching circuit 111 are input to a capstan servo circuit 114, and a high-speed search or a low-speed search is executed by controlling a motor system. Is done. A low frequency pilot multiplexed ATF tracking pilot signal is output from a signal distributor (not shown) and input to an ATF pilot detection circuit 125 and a signal processing circuit (not shown) to perform servo control. The pilot signal detected by the ATF pilot detection circuit 125 is supplied to the switching circuit 111
And S / H circuits 123 and 124. That is, in the case of a search, the signal is input to the switching circuit 111 via the S / H circuits 123 and 124, and during normal reproduction, the signal is input to the switching circuit 111 through. Then, the normal reproduction / low-speed search /
It is switched so that a high-speed search is performed. This output signal is supplied to the capstan servo circuit 114 to control the motor system so that the tape transfer speed can be changed between a low-speed search and a high-speed search as a search process, so that an image can be output or an ID search can be performed. Becomes FIG. 4 shows a procedure of mode determination at the time of search and its control. First, in step S1, a VTR search speed is set. Set value = M. Next, in step S2, a comparison is made with the predetermined value = N, and the mode branches to two modes according to the comparison result. If M ≦ N, the output search mode is set in step S3. If N <M, the ID search mode is set in step S4. In the image search mode, image data is reproduced in step S5, that is, an image that is hard to see visually is reproduced. In the ID search mode, when the ID data is reproduced in step S6, that is, when the search image is hard to see visually. This is performed based on the ID. Then, in steps S7 and S8, each data is displayed. Next, the process returns to the search speed setting in step S1 again to confirm the change, and the above routine is repeated thereafter. It should be noted that a fade effect may be provided at the boundary between the image output search mode and the ID search mode so as not to make the user visually uncomfortable. For example, when shifting from the image output search mode to the ID search mode, if the image is faded in, the screen becomes easy to see. According to the present invention, when a search is performed at a tape speed higher than the time of recording, a main signal such as an image signal is output and monitored according to the tape speed, or an ID signal or the like is output. By outputting and monitoring the sub-signal, reliable search information can be obtained even when a high-speed search is performed, and effects such as operability are significantly improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram illustrating an embodiment of a search speed control unit. FIG. 3 is a timing chart at the time of search control. FIG. 4 is a flowchart showing mode determination at the time of search and its control. FIG. 5 is a configuration diagram showing a change in the number of sync blocks according to a reproduction signal level and a reproduction speed during a search. FIG. 6 is a characteristic diagram showing a relationship between a search speed and a reproduction level. FIG. 7 is a characteristic diagram showing a relationship between a search speed and an error rate. FIG. 8 is a characteristic diagram showing a relationship between a search speed and the number of sync blocks. FIG. 9 is a configuration diagram showing the relationship between the arrangement of pixel blocks in one screen and a sync block. FIG. 10 is a configuration diagram of a sync block to which an error correction code is added. FIG. 11 is a configuration diagram showing a trajectory of a head that traces a recording track. [Description of Signs] 100 Digital signal processing circuit 101 VTR mechanism 102 Mechanical control servo circuit 103 First control mode circuit 104 Second control mode circuit 105 Switching circuit 106 Key input 107 Syscon 108 Speed comparison circuit 109 Predetermined speed setting circuit

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Claims (1)

(57) Claims 1. A reproducing means for tracing a magnetic tape on which a large number of oblique tracks are formed by a rotating head to reproduce image data and an additional signal related to the image data, Speed setting means for setting a reproduction speed higher than the reproduction speed; comparison means for comparing the reproduction speed reproduced by the reproduction means with a predetermined value according to the setting of the speed setting means; and Based on the comparison result, when the reproduction speed is higher than the predetermined value, the reproduction and reproduction of the additional signal,
Output means for reproducing and outputting the image data when the reproduction speed is lower than the predetermined value.