Tracking control for VTR editing employing previously recorded tracking information

A method and apparatus for editing video information from one or more video tapes onto a master tape, in which different video tape recorders can be used to produce the master tape, involves the storage of tracking information that was used in recording a segment at a position immediately preceding the desired editing point on the master tape, and also stores tracking information that was used in recording another segment at a position on the master tape some time prior to the segment next preceding the edit point. A difference value between the two stored tracking information signals is detected and compared with a predetermined value, and the comparison result is used to select one of the two stored tracking information signals to control the tracking during recording at the desired editing point, so that small head position detector errors will not accumulate over a number of edit points on the master tape.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a video tape recorder and, more 
particularly, to tracking control during an editing operation that can 
involve utilizing at least two such video tape recorders. 
2. Description of the Prior Art 
Editing recorded information typically involves the arrangement of one or 
more portions that have been previously recorded onto a single composite 
record medium, which is the so-called master tape. A master tape can be 
produced using a single source tape or a number of source tapes and such 
editing operations are referred to as assembly editing, in which the 
signal segment that is to be reproduced from one tape and subsequently 
recorded on the master tape is typically referred to as a cut. Thus, using 
assembly editing techniques, a number of cuts can be recorded sequentially 
on the so-called master tape. Therefore, assuming video information is 
involved, at least one video tape playback apparatus and at least one 
video tape recording apparatus are required to perform the assembly 
editing technique described above and, typically, these units are the 
well-known video tape recorders. Although video tape recorders are 
produced to high manufacturing standards, there are some measurable 
differences, which fall within the manufacturing tolerances, among all of 
the video tape recorders that are produced. For example, the phase of a 
video signal recorded by the rotary recording head will almost always be 
found to be slightly different than the phase of a control signal (CTL) 
that is recorded by a fixed control head. This phase difference is 
referred to hereinafter as CTL phase information. Another example of 
manufacturing discrepancies that may occur among video tape recorders is 
that the location of the head on the head mounting element, typically 
known as a dynamic tracking device (DT), can vary by a measurable amount 
even though the head locations are within manufacturing tolerances. 
Hereinafter, such differences in head mounting location that occur during 
manufacturing are referred to as head position information. Therefore, if 
assembly editing is achieved by moving the master tape from one video tape 
recorder to another video tape recorder, the differences of the CTL phase 
information or the head position information will cause an abrupt change 
in pitch between the last track of a cut and the first track of the next 
cut on the master tape, which will then adversely affect the tracking 
servo of a video tape recorder in the playback mode. The tracks in each 
individual cut will, of course, all have the same pitch and the tracking 
servo of the video tape recorder can provide correct tracking for each 
such cut. 
In order to resolve the above-described problem it has been proposed to 
control the tracking by changing either the CTL phase or the head 
position, in accordance with tracking information obtained by reproducing 
a cut located prior to the desired editing point. This operation is aptly 
termed tracking adjustment, and it is generally possible to provide a 
smooth editing-in of the cut at the desired position. Nevertheless, 
disadvantages still remain in this proposed approach. More particularly, 
although an abrupt change of the head tracking can be prevented between 
the end of one cut and the beginning of the next cut at the editing point 
using the above-described tracking adjustment, there nevertheless is 
detected a small appreciable tracking discrepancy at the editing point 
between the last track and first track of successive cuts. This tracking 
discrepancy has been found to occur whether or not tracking adjustments 
are made using CTL phase information or dynamic tracking head information 
and is thought to be due to inherent errors in the head position detector 
used in tracking control and to the fact that there are no control signal 
pulses on the tape at the location at which the next cut is to be 
recorded. Although this tracking discrepancy initially appears to be a 
minor problem and, by itself, is not a serious problem, in an assembly 
editing operation a large number of cuts will typically be recorded on the 
master tape by the same video tape recorder, maybe up to two hundred cuts. 
Even using the same tape recorder a tracking adjustment as described above 
will be necessary and since the same video tape recorder is used the head 
position detector error at each editing point, for example, can be 
considered to be substantially the same. Therefore, the tracking 
discrepancy that occurs at each editing operation will accumulate, and the 
accumulated tracking discrepancy will become appreciable so as to be 
readily noticeable and objectionable. Not only will such accumulated 
discrepancies become noticeable but in the case of a video tape recorder 
with the head mounted on a dynamic tracking element, the result will be 
that the dynamic tracking element will be driven to the limit of its 
deflection, with no travel remaining to accommodate additional tracking 
discrepancies. 
OBJECTIONS AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and apparatus 
for use in assembly editing using video tape recorders that can eliminate 
the above-noted defects inherent in the prior cut. 
Another object of this invention is to provide a video tape recorder that 
can prevent an accumulation of tracking discrepancy errors, even if the 
assembly editing process is performed repeatedly using the same video tape 
recorder. 
In accordance with an aspect of the present invention, to solve this 
problem in the case of editing a new cut a video tape recorder is 
controlled using tracking information detected by a tracking information 
detecting system from a cut that was made prior to the desired editing 
point. Such tracking information detection circuitry includes a first 
memory area to store the tracking information of the next preceding the 
edit point and a second memory area to store tracking information from 
some other cut that was made prior to that next preceding cut to be used 
as reference tracking information. One or the another of these two 
tracking information portions is selected to control the tracking, and 
thus the pitch between the last and first tracks of adjacent cuts, is 
based upon comparison of the difference therebetween with a preselected 
reference value. In this way, because the tracking information that is 
used has not been derived anew for every cut, inherent errors in the head 
position detector, for example, will not be present for every new cut and, 
thus, will not accumulate. 
The above and other objects, features, and advantages of the present 
invention will become apparent from the following detailed description of 
illustrative embodiments thereof to read in conjunction with the 
accompanying drawings, in which like references numerals represent the 
same or similar elements.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 represents a master tape that has been assembly edited following the 
previously proposed technique by changing the control phase or the head 
position in accordance with the stored tracking information, which changes 
have been referred to as the CTL phase information or head position 
information, respectively. In FIG. 1, the information that has already 
been edited-in is arranged in tracks TRB and is denoted as CUT A, which is 
located ahead of or prior to the editing point EP in relation to the 
direction of tape travel. The object is then to adjust the location of the 
beginning tracks TRE of CUT B relative to the location of the last tracks 
TRB of CUT A, which have already been recorded, so that there is no 
discernible change in track pitch between cuts when the master tape is 
played back. FIG. 1 shows this operation having been successfully 
accomplished to permit acceptable playback. Even so, there is a finite, 
detected tracking discrepancy between the end of CUT A and the beginning 
of CUT B at the editing point EP is denoted as .DELTA.T. This tracking 
discrepancy can be due to detector error or the like, as described above. 
FIG. 2 represents this tracking shift between the end of CUT A and the 
beginning of CUT B at the editing point EP as a difference .DELTA.TR, 
which is derived either from the CTL phase information or the DT head 
position information. 
Now, the problem discussed above is seen more clearly in that these 
tracking discrepancies and the head shifts necessary to correct them will 
occur at successive edit points EP and will tend to accumulate, and the 
sum will become very large. A summation of successive .DELTA.TR tracking 
shifts starting with the tracking information of a first cut, referred to 
as the base track CUT 0, is shown in FIG. 3. Thus, it is seen that with 
successive editing operations the accumulation of these tracking shifts 
becomes quite large and objectionable, when using the previously proposed 
system. 
The embodiment of the present invention of FIG. 4 provides tracking control 
in an assembly editing operation by controlling the dynamic tracking (DT) 
of the head position, yet which avoids inherent detector error by using, 
if possible tracking information that was used before instead of deriving 
new information each time. A system to obtain head position information 
for use as tracking information by reproducing a cut that is recorded 
ahead of the editing point is described in detail. A video signal PB is 
produced by a dynamic tracking head 1 from a magnetic tape 13 that has 
been wrapped in a helical fashion about guide drum 14. This reproduced 
video signal PB is fed through a playback amplifier 2 to an envelope 
detector 3. Envelope detectors are well-known in this technology, and the 
envelope signal ENV detected by envelope detector 3 is then fed to a 
dynamic tracking (DT) head drive circuit 4. Magnetic head 1 is mounted on 
a deflectable head mounting element 5, which conventionally comprises a 
bimorph leaf, and in order to determine the extent of deflection of such 
bimorph leaf, a deflection detecting device 6 is provided. Deflection 
detecting device 6 typically comprises a strain gauge and provides a 
detection signal Sl fed to a head position detector 7. Head position 
detector 7 generates a head position signal HH that indicates a position 
(head height) of the dynamic tracking head 1 and which is fed back to the 
head dive circuit 4. Head drive circuit 4 generates a head position 
correction command signal COM 1 that drives bimorph leaf 5 so that the 
output ENV of envelope detector 3 is maximized, as determined by head 
drive circuit 4. More specifically, the head position correction command 
signal COM 1 is fed to playback contact PB of switch 8 for connection 
directly to bimorph leaf 5. Operation of switch 8 is under the control of 
the control circuit 9 and during playback the head position correction 
command signal COM 1 controls the position of bimorph leaf 5 and dynamic 
tracking head 1 to be in the optimum tracking position. These detectors 
and drive circuit can all be a source of error contributing to the 
discrepancy described above. 
Control circuit 9 receives the head position signal HH from head position 
detector 7 after it has been converted to digital form (HHD) by an 
analog-to-digital converter 10. Then, digital head position signal HHD is 
fed to control circuit 9, which typically comprises a microprocessor and 
the relevant operation thereof will be explained in detail hereinbelow. 
Connected to control circuit 9 is a memory device 11 that aids in 
generating a tracking information signal used to control the head position 
in the assembly editing mode. The generated control digital signal is 
converted to an analog control signal COM 2 by passing it through a 
digital-to-analog converter 12 and then applying it through the record 
terminal (REC) of switch 8 to bimorph leaf 5. Memory unit 11, which is 
connected to control circuit 9, has two separate memory areas, MA and MB. 
Control circuit 9 operates to control the tracking operation in the 
assembly edit mode in accordance with the procedure that is shown in FIG. 
5. 
Referring now to FIG. 5, Start step SP1 commences after an assembly edit 
command signal ASED has been provided to the control circuit 9 from a 
manual keyboard (not shown) or the like. In the next operation SP2, tape 
13 is rewound by a tape drive mechanism (not shown) in order to reproduce 
the cut (CUT A) that was recorded just prior to the desired editing point 
EP. To accomplish this, switch 8 is operated to select the reproducing 
mode terminal (PB), and the digital data HHD is applied to control circuit 
9. In step SP3 the digital data corresponding to that head position is 
stored in tracking storage area MA of memory device 11. Once such storage 
has occurred, a decision is made in control circuit 9 corresponding to the 
decision at step SP4 in FIG. 5, more particularly, the absolute value of 
the difference ER between a reference head height digital data HHDR stored 
in a reference tracking storage area MB of memory device 11, which was 
used as a reference head position information for tracking control at some 
previous edit point before the cut next preceding the edit point, and the 
head height digital data HHD that was just obtained and stored in storage 
area MA is determined. The detected difference value (HHDR-HHD ) is 
compared with a predetermined value a. The predetermined value a is 
selected to be a value sufficient to determine whether the difference data 
ER depends on a detector error of the head position signal HH or on a 
compatibility problem between video tape recorders, for example, where the 
previous cut on the master tape had been recorded by a different video 
tape recorder. Although the value of a can be selected to be any desired 
value sufficient to distinguish between these two situations, a value that 
has been found to be advantageous for use corresponds to 3-4% of the track 
width. If, as a result of the comparison represented in step SP4, the 
decision is made that the difference ER is smaller than the predetermined 
value a, the operation of control circuit 9 proceeds to step SP5 and 
switch 8 is changed to the recording mode terminal REC after head 1 comes 
up to the editing point. There, the head position digital data HHDR from 
an earlier cut that had been stored in storage area MB of memory 11 is 
applied to bimorph leaf 5 through a digital-to-analog converter 12. Then 
at step SP6, the control of the microprocessor returns to the main 
routine, which forms no part of the present invention. As described 
hereinabove, dynamic tracking head 1 performs editing using tracking 
information (COM 2) that is not based upon the head position information 
obtained from the cut next preceding the editing point EP but, rather, is 
based on head position information of a cut that was recorded at least 
twice removed from the editing point. 
On the other hand, if at step SP4 the result of the comparison is NO, that 
is, the absolute value of the difference data ER is larger than the 
reference value a, control circuit 9 operates to perform an operation 
shown as step SP7. At step SP7, switch 8 is changed to the recording mode 
(REC) after the dynamic tracking head 1 comes up to editing point EP and 
then head position digital data HHD that was stored in memory storage area 
MA of memory 11 is fed to bimorph leaf 5 through digital-to-analog 
converter 12 and switch 8. Thus, the head position of dynamic tracking 
head 1 used to record CUT B is based solely on the head position 
information that was obtained from the cut immediately preceding the 
editing point EP. In other words, no change. After such head shift 
operation then, control circuit 9 performs step SP8 at which the head 
position digital data HHD that had been stored in the storage area MA is 
transferred to storage area MB in memory 11 and now becomes the new 
reference data (HHDR). After such transfer, the program then returns to 
the main routine by way of step SP6. 
Accordingly, as described hereinabove, the process of step SP5 is selected 
when the absolute value of the difference between the so-called reference 
head height value (HHDR) of a previous cut and the head height value (HHD) 
of the last cut recorded before the current edit point is smaller than the 
predetermined value a. This results in the editing in of a new cut at edit 
point EP by using the same head position information that had been used to 
record a previous cut sometime before the cut immediately preceding the 
edit point. Thus, the head shift value will be zero. In other words, by 
examining the head shift information of two cuts that both precede the 
edit point it is possible to determine if the same VTR made those cuts 
and, if so, then the head need not be shifted to record the current cut at 
edit point EP. On the other hand, when the absolute value of difference ER 
is larger than the predetermined value a, the procedures of steps SP7 and 
SP8 are followed, thereby to edit a new cut at edit point EP by using the 
head position information (HHD) that corresponds to the cut immediately 
preceding the edit point. Then, this preceding cut head position 
information becomes the reference head height data (HHDR) and is shifted 
into storage area MB of memory 11. An initial value can be set into 
storage area MB when the program is first in an initialization mode, not 
shown in FIG. 5. 
The decisional step SP4 of FIG. 5 is represented graphically in FIG. 6, in 
which it is seen that the amount of tracking shift is linearly related to 
the difference signal ER, provided the absolute value of such difference 
exceeds predetermined value a. 
The operation of the apparatus of FIG. 4 in accordance with the process 
shown in FIG. 5 is further explained using FIG. 7, in which it is seen 
that when CUT 2 is edited at a first editing position EP1 that occurs at 
the end of CUT 1, assuming that the decision result at step SP4 in the 
operating procedure of FIG. 5 is NO, because an initialize value has been 
stored in the reference tracking data storage area MB that results in the 
difference value ER being larger than the predetermined value a, CUT 2 is 
edited based on a head position information HHD1 of CUT 1 located just 
prior to editing point EPI, according to step SP7. 
In this assembly editing operation, the head will be shifted only by an 
amount .DELTA.TR1 relative to the head position before the editing point 
EP1, however, this tracking shift .DELTA.TR1 is based upon the actual 
detector error and, thus, the amount of the tracking shift is small. 
Continuing this example, the initialized value stored in the reference 
tracking storage area MB of memory 11 that was assumed to be the head 
position information HHD.sub.1 of CUT 1 is retained in storage area MB as 
the reference head position information (HHDR). Then, in the editing 
operation of a further CUT 3 at an editing point EP2, the head position 
information HHD1 of the initial CUT 1 will be compared with the head 
position information HHD.sub.2 of CUT 2 that is stored in storage area MA. 
Thus, the error value ER will be the difference between the detected head 
position information HHD.sub.2 and the head position information HHD.sub.1 
and will be equal to the detector error .DELTA.TR1. In this situation, 
because the preselected value a will be larger than the detector error 
.DELTA.TR1, the decisional result of step SP4 will be YES, and the new CUT 
3 is edited based on the head position information HHD.sub.1 that used in 
earlier CUT 1, which is now the so-called reference head position 
information (HHDR). Thus, because CUT 3 is edited using the head shift 
corresponding to the detector error .DELTA.TR1 derived from CUT 1, no new 
detector error is introduced and there should be little or no tracking 
shift relative to CUT 2. When this editing of CUT 3 has been completed, 
the head position information of initial CUT 1 will still be stored in the 
reference tracking data storage area MB of memory 11. Then, as with the 
above-described operation, editing of a subsequent CUT 4 at editing point 
EP3 will be based again on the head position information HHD.sub.1 of 
initial CUT 1, because that information HHD.sub.1 has been stored in 
storage area MB and the decisional result of step SP4 will again be YES. 
Then, when CUT 4 is edited, it will have the detected error .DELTA.TR1 
that had been provided relative to CUT 1 already included, and there will 
be little or no tracking shift relative to CUT 3. 
Therefore, it is seen the editing of a new cut is accomplished using 
information based upon the head position information HHD.sub.1 of a first 
CUT 1, when the new cut is to be edited into the same master tape using 
the same video tape recorder. In this fashion, it is possible to assembly 
edit new cuts having relatively little or no tracking shift at the 
subsequent respective editing points, for example, at edit points EP2, 
EP3, EP5 . . . . 
There are, of course, various approaches to performing editing operations 
and an example of another such editing operation is where the master tape 
is first produced using a first video tape recorder and then the editing 
process onto that master tape is continued utilizing another video tape 
recorder. In that case, because a video tape recorder cannot distinguish 
whether a master tape placed therein has been changed to another master 
tape, the difference value (ER) compared with the predetermined value a at 
step SP4 of FIG. 4 is the difference between head position information 
HHDR obtained from the first master tape before it was changed, and which 
was stored in reference tracking storage area MB, and head position 
information HHD that is detected from the second master tape after it has 
been placed in the video tape recorder and played back up to a position 
just prior to the edit point. In such situation, it has been found that 
even though the relevant characteristics of each of the two video tape 
recorders are within the specified tolerances, in most cases the 
difference value ER (.vertline.HHDR-HHD.vertline.) will be larger than the 
predetermined value a. As a result of this, the decisional result in step 
SP4 will be NO, so that the editing of a new cut is recorded using new 
head position information based upon head position information obtained 
from the cut immediately preceding the edit point on the new or second 
master tape. In this way the tracking is adjusted exactly, although there 
may exist a small tracking error at the editing position between the two 
cuts due to recorder tolerances. Nevertheless, this tracking error will be 
negligible when compared to the tracking error that would be present if 
the editing used the tracking information from the first master tape. 
Therefore, in this embodiment the dynamic head tracking can be adjusted 
exactly and upon repeated assembly editing operations the detected error 
will not be accumulated, and it is possible to avoid the situation in 
which accumulated detected tracking errors will exceed the bending limits 
of the bimorph leaf upon which the head is mounted. 
As described above, the present invention solves the problem in which a 
change in pitch between the last track of one cut and the first track of a 
subsequent cut is corrected with tracking information that includes 
detector error, such that new tracking information is not derived for each 
new cut, thereby presenting the accumulation of these detector errors. 
There are, of course, two approaches to controlling track pitch, either 
shift the head or alter the relative tape-head speed. A further embodiment 
of the present invention is shown in FIG. 8, in which the pitch of the 
tracks in an assembly editing mode is altered by controlling the speed of 
the tape, for example, by controlling the capstan drive speed. In the 
embodiment of FIG. 8, the video signal PB1 reproduced from magnetic tape 
19 using a recording and reproducing head 15, which need not be mounted on 
a bimorph leaf, is applied through a playback amplifier 16 to an envelope 
detector 17 and the resultant level signal ENV1 is fed to a control 
circuit 18, which is essentially the same as control circuit 9 of the 
embodiment shown in FIG. 4. This amplified video signal output from video 
amplifier 16 is also fed to an FM demodulator 20 and then to a vertical 
sync separator circuit 21, which separates the vertical sync signal from 
the demodulated video signal. The separated vertical sync pulses are then 
fed to control circuit 18. A control signal CON that was recorded on the 
tape 19 is picked up by a stationary control head 22 and also fed to 
control circuit 18. The control circuit 18 control operates in part to the 
drive of tape 19 by use of a capstan servo circuit 23 that provides the 
control signal for the capstan motor 24, which cooperates with a pinch 
roller (not shown) to drive tape 19. More particularly, capstan servo 
circuit 23 drives tape 19 in order to maximize the level of the detected 
envelope signal ENV1, as determined by control circuit 18. In performing 
the maximizing function, the control circuit 18 detects a phase difference 
(CTL phase information) between the phase of the control signal CON and 
the phase of the vertical sync pulses separated from the reproduced video 
signal PB1. Control circuit 18 then controls the capstan servo circuit 23 
in accordance with that phase difference information (CTL phase 
information). 
Therefore, in this embodiment, the tracking information is based on the CTL 
phase information and control circuit 18 can control the tracking 
adjustment at each assembly editing point by utilizing substantially the 
same procedure as discussed above relative to FIG. 5 and utilizing a 
memory device 23, which is connected to control circuit 18. More 
particularly, in the operation of this embodiment it is seen that the CTL 
phase information is detected by reproducing the cut just prior to the 
editing point, detecting a difference between that detected CTL phase 
information and another CTL phase information, which was used as a 
reference at a previous editing point, and then comparing the calculated 
difference with a predetermined value that is capable of distinguishing 
whether such difference depends on a detector error (.DELTA.TR) or on a 
different characteristic between two video tape recorders. Then, in the 
situation where the calculated difference is smaller than the 
predetermined value the cut is edited using the CTL phase information that 
was used at the previous editing point so that no new detector error need 
be accommodated and, where the calculated difference is larger than the 
predetermined value, tracking control is based on the newly detected CTL 
phase information. 
Therefore, the second embodiment can also avoid accumulation of tracking 
shifts even if the assembly editing is repeatedly recorded on the same 
master tape using the same video tape recorder, and it can correct for 
tracking errors when the master tape is used in a different video tape 
recorder. 
The above description is given on a single preferred embodiment of the 
invention, but it will be apparent that many modifications and variations 
could be effected by one skilled in the art without departing from the 
spirit or scope of the novel concepts of the invention, which should be 
determined by the appended claims.