Magnetic recording and reproducing apparatus having multiple magnetic heads

A magnetic recording and reproducing apparatus for recording and reproducing a video digital signal suitable to a narrowed track pitch having two magnetic heads with the same azimuth angle arranged with an overlapped area to reproduce the same track, and a tracking servo executing phase control such that a center of a reproducing track is brought to a center of the overlapped area of the two magnetic heads. Reproduced signals of the two magnetic heads are compared so that the reproduced output of the magnetic head having a good on-track condition is always selected to improve a tracking margin without increasing crosstalk disturbance from adjacent track.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic recording and reproducing 
apparatus which records and reproduces digital signals (video signals and 
audio signals) and is useful for narrowing track pitches. 
2. Description of the Related Art 
A recording pattern in a prior art magnetic recording and reproducing 
apparatus, used in a home VTR or the like, is defined to record data 
without a guard band in order to increase recording density, and to 
conduct aximuth record in order to reduce cross-talk between adjacent 
tracks. The data is reproduced by a reproducing head having a wider head 
width than a track pitch, while taking deviation due to curvature of 
tracking into consideration. 
Tracking errors are detected by recording a pulse, representing a rotation 
phase of a head drum, as a control signal in a control track of a magnetic 
tape. The control track is located along longitudinal direction of the 
magnetic tape, separately from a video track for recording a video signal. 
In a reproduction mode, by comparing a phase of the reproduced control 
signal from the control track with a phase of the rotation pulse of the 
head drum tracking error may be detected. (See, for example, VTR 
Technology, by R. Takahaski, NHK, Oct. 20, 1980.) 
On the other hand, in 8 mm video technologies, four low frequency tracking 
pilots of different frequencies are generated, and one of them is 
azimuth-recorded for each video track by frequency-multiplexing them with 
the video signal without a guard band. In the reproduction mode, a 
reproducing head having a wider head width than the track pitch is used 
and two low frequency pilots recorded on the two adjacent video tracks are 
detected for inspection of cross-talk from the adjacent video tracks, and 
the amplitude levels of the two low frequency pilots are compared to 
detect tracking error. (For example, as disclosed in "8 mm Video (1)" by 
A. Hirota, Technical Report of the Institute of Television Engineers of 
Japan, VR61-1, pp. 1-6 Feb. 23, 1984)). 
However, in a recent apparatus which converts a video signal to a digital 
signal and records and reproduces it on and from a magnetic tape, a 
reduction of the track pitch is intended in order to reduce the size and 
the weight of the apparatus and extend the recording time. 
Accordingly, when the prior art apparatus is applied to such a narrow track 
pitch apparatus, the following problems arise. 
For example, in the above two examples of the prior art, the magnetic head 
width Tw is usually designed to be approximately 1.5 Tp, where Tp is the 
track pitch. Accordingly, a tracking margin is usually 0.5 Tp. As Tp is 
narrowed, the absolute value of the tracking margin reduces. As a result, 
expansion of the tracking margin or improvement of the tracking precision 
is required. 
Where Tw is set to 2Tp to give a greater tracking margin, the tracking 
margin is expanded, but the magnetic head width which crosses the adjacent 
tracks increases. As a result, when the data is azimuth recorded and 
reproduced in the above two examples of the prior art, a disturbance 
signal from adjacent cross-talk increases and a higher signal-to-noise 
ratio (S/N) is required. 
Where interoperable reproduction between apparatus having a very large 
track curvature is required, a variation of the tracking error increases 
and there is a risk that a next track to the adjacent track on which data 
has been azimuth-recorded may be reproduced. In this case, an azimuth loss 
may not be expected, and a disturbance signal by the cross-talk of the 
next track to the adjacent track increases and a further higher S/N is 
required. 
Accordingly, it is not possible to widen the magnetic head width more than 
an appropriate width, and the tracking margin cannot be simply expanded. 
In a tracking error detector which uses the prior art control track, the 
control reference signal is recorded on a control track, which is 
different from the video track. Accordingly, the linearity (curvature) of 
the video track cannot be detected and it is very difficult to improve the 
detection precision of the tracking error. 
SUMMARY OF THE INVENTION 
In the light of the above, it is an object of the present invention to 
provide a magnetic recording and reproducing apparatus which has strong 
resistance against an adjacent crosstalk disturbance signal or a second 
adjacent crosstalk disturbance signal which poses a problem when the track 
pitch is narrowed, or a magnetic recording and reproducing apparatus which 
has strong resistance against a track curvature and has a large tracking 
margin, or a magnetic recording and reproducing apparatus which has a high 
tracking control precision. 
A first embodiment of the present invention comprises two multi-structure 
magnetic heads having the same azimuth angle for reproducing one track 
with a overlap of one track pitch, a comparator for comparing the numbers 
of errors of digital signals reproduced by the two magnetic heads, and a 
selector for selecting one of the two reproduced output signals in 
accordance with an output of the comparator. The comparator detects the 
output signal of the magnetic head having a smaller number of errors of 
the reproduced digital signal, and the selector selects the output signal 
of the magnetic head having the smaller number of errors in accordance 
with the output of the comparator. 
A tracking error is detected by a tracking error detector which compares 
amplitude levels of the two reproduced digital signal outputs from the two 
magnetic heads for detecting a tracking error signal. 
By selecting one of the reproduced outputs of the two multi-structure 
magnetic heads, a tracking margin can be expanded up to Tp where Tp is a 
track pitch and a head width Tw of each magnetic head is 1.5 Tp. Since the 
head width of each magnetic head remains Tw=1.5 Tp, the disturbance by the 
adjacent crosstalk does not increase by the expansion of the tracking 
margin and disturbance by the second adjacent crosstalk is unlikely to 
occur. 
Further, since the signal recorded on one track is used to detect the 
tracking error signal, the detection is not affected by the level 
variation in recording and the accuracy of the tracking error detection is 
improved. 
A second embodiment of the present invention comprises two multi-structure 
magnetic heads having the same azimuth angle for reproducing one track 
with an overlap of one track pitch, a delay circuit for correcting time 
axis errors of the digital signals reproduced by the two magnetic heads, a 
comparator for comparing the output levels of the reproduced digital 
signals having the time axis errors thereof corrected, a selector for 
selecting one of the two reproduced output signals in accordance with an 
output of the comparator, and a synchronous detector for detecting a 
selection timing of the selector based on an output of the selector. 
The tracking error is detected by a tracking error detector which compares 
amplitudes of the two reproduced digital signal outputs having the time 
axis errors thereof corrected to detect a tracking error signal. 
Like the first embodiment, the second embodiment selects one of the 
reproduced outputs of the two multi-structure magnetic heads. Accordingly, 
the tracking margin can be expanded without increasing the disturbance by 
the adjacent crosstalk and without substantial disturbance by the second 
adjacent crosstalk, and the accuracy of the tracking error detection is 
improved. 
In the second embodiment, since the time axis errors of the reproduced 
digital signals are corrected and the output levels of the reproduced 
signals are compared for selection, an analog circuit may be used for 
implementation and a circuit scale can be reduced. 
A third embodiment of the present invention comprises two multi-structure 
magnetic heads having the same azimuth angle for reproducing one track 
with an overlap of one track pitch, a delay circuit for correcting time 
axis errors of digital signals reproduced by the two magnetic heads, and a 
signal adder for adding the two reproduced digital signals having the time 
axis errors thereof corrected. Like the second embodiment, the tracking 
error is detected by a tracking error detector which compares amplitudes 
of the two reproduced digital signal outputs of the two magnetic heads 
having corrected on the same time axis to detect a tracking error signal. 
In the third embodiment, since the two reproduced digital signals having 
the time axis errors thereof corrected are added by the signal adder, a 
main signal which is reproduced by overlapping is doubled, and a signal 
reproduced without overlap, primarily a noise component including the 
adjacent crosstalk is multiplied by a factor of .sqroot.2. Accordingly, 
the affect by the disturbance by the adjacent crosstalk is relieved. 
Further, since the magnetic heads are arranged in the same manner as that 
of the first embodiment, the tracking margin is expanded. 
A fourth embodiment of the present invention is a magnetic recording and 
reproducing head for recording signals on oblique tracks on a magnetic 
tape of magnetic heads which comprises two magnetic heads having a 
head-to-head interval different from a recording track pitch for 
reproducing signals from two different tracks substantially 
simultaneously, a tracking error detector for detecting a tracking error 
from a difference between levels of the reproduced output signals of the 
two magnetic heads, and a tracking servo for controlling the tracking in 
accordance with the tracking error. Since the interval of the magnetic 
heads is different from the recording track width, phases of variations of 
the signal levels reproduced by the two magnetic heads relative to the 
tracking error are different. Accordingly, the tracking error can be 
defined. Therefore, the tracking error including the linearity of the 
recording track can be detected, and the accuracy of the tracking error 
detection is improved without increasing the number of magnetic heads 
relative to the number of tracks.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiments of the present invention are now explained with reference 
to the drawings. 
FIG. 1 shows a block diagram of a principal portion of a first embodiment 
of the magnetic recording and reproducing apparatus of the present 
invention. 
Numeral 1 denotes a magnetic tape on which signals are recorded. As shown 
in FIG. 2, one-track data of the signal recorded on the magnetic tape 1 
comprises a preamble (Pr), a signal data area (D0) and a post-amble (Ps). 
The signal data area (D0) comprises at least one synchronous block which 
includes a synchronous pattern (SD) indicating a bit reference, ID data 
(ID) indicating a data position, signal data (such as a video signal) (D1) 
and an error correction code (P) (such as a code generated by a 
Reed-Solomon coding algorithm). 
Returning to FIG. 1, numerals 2 and 3 denote two multi-structure magnetic 
heads for reproducing the signals recorded on the magnetic tape 1. FIG. 3 
shows an arrangement of record tracks on the magnetic tape 1 and the 
multi-structure magnetic heads 2 and 3. A head width Tw of the magnetic 
heads 2 and 3 is larger than a record track width Tp, and an overlap of 
the magnetic heads is equal to the record track pitch Tp. The magnetic 
heads 2 and 3 have the same azimuth angle (in FIG. 3, they have the same 
azimuth angle as that of a track and the reverse azimuth with respect to 
tracks 1 and 3) and are arranged to reproduce one record track (track 2 in 
FIG. 3) with an overlap. 
In FIG. 1, signals reproduced by the magnetic heads 2 and 3 are supplied to 
equalizers 4 and 5 and a tracking error detector 12. Each of the 
equalizers and 5 comprises a cosine equalizer and a PLL circuit, and 
corrects a frequency characteristic of the reproduced signal, generates a 
reproducing clock and supplies it to a synchronous detector 6 or 7. 
Each of the synchronous detectors 6 and 7 detects the synchronous pattern 
SD to reproduce word synchronization, converts it to a standard 8-bit word 
data, detects address information from the ID data and sends them to an 
error detector 8 or 9 at a minimum unit of one synchronous block. 
Each of the error detectors 8 and 9 calculates the number of errors from an 
error correction code for each synchronous block which is the minimum 
unit, supplies it to a comparator 10 and supplies a digital decoded 
digital signal to a selector 11. 
The comparator 10 compares the numbers of errors of synchronous blocks 
having the same ID address and supplies the comparison result to the 
selector 11. The selector 11 selects the synchronous block having a 
smaller number of errors in accordance with the output signal of the 
comparator 10 for each synchronous block. 
The tracking error detector 12 compares amplitude levels of principal 
signals of the reproduced signals of the multi-structure magnetic heads 2 
and 3, that is, the amplitude levels of the signals reproduced from the 
track 2 of FIG. 3, and supplies an amplitude level difference to a 
tracking servo 13 as a tracking error signal. 
Assuming that detracking occurs in FIG. 3 so that a head position is 
shifted to the right by a small distance with respect to the record track, 
an area of the track 2 which is reproduced by the magnetic head 2 does not 
change, but an area of the track 2 which is reproduced by the magnetic 
head 3 changes. Namely, the amplitude level of the reproduced output of 
the magnetic head 3 is lower than that of the magnetic head 2. The 
amplitude level difference is detected as the tracking error and the 
tracking servo 13 controls to render the tracking error to zero, that is, 
to move the head leftward. 
Conversely, when the head position is shifted leftward by a small distance 
with respect to the record track, the area of the track 2 which is 
reproduced by the magnetic head 3 does not change but the area of the 
track 2 which is reproduced by the magnetic head 2 changes. In a similar 
manner, the tracking servo 13 controls to move the head rightward. 
In this manner, the tracking error is detected and the tracking servo 
controls the phase so that the track 2 is traced by the center of the 
multi-structure magnetic heads 1 and 2 shown in FIG. 3. 
In the present embodiment, since the reproduced signal of the magnetic head 
having the smaller number of errors is selected, the reproduced signal of 
the magnetic head which has good on-track condition can be always 
selected. In the arrangement of the magnetic heads shown in FIG. 3, a 
total magnetic head width is equivalent to MTw and the tracking margin is 
improved. 
As shown in FIG. 3, the head width Tw of each of the magnetic heads may 
usually be equal to that in the reproduction mode, and even if the 
tracking margin is expanded as described above, the disturbance signal by 
the adjacent crosstalk is equal to that in the prior art and it is not 
necessary to increase the S/N required to detect the reproduced digital 
signal. 
Even if the tracking error increases and the magnetic heads reproduce the 
second adjacent track having data recorded at the same azimuth, only one 
magnetic head reproduces the second adjacent track because of the 
arrangement of the magnetic heads as shown in FIG. 3. Thus, since the 
reproduced output of the other magnetic head does not reproduce the second 
adjacent track, the crosstalk disturbance from the second adjacent track 
can be eliminated. 
Further, since the output amplitudes of the reproduced outputs from the 
same track are detected, the affect by the amplitude variation in the 
recording mode is eliminated and the accuracy of detecting the tracking 
error can be improved. Further, since the tracking error is detected from 
the video track under reproduction, the tracking error including the 
linearity (tracking curvature) of the video track can be detected and more 
accurate tracking error detection is attained. 
As a modification 1--1 of the first embodiment of the present invention, a 
configuration to completely eliminate the adjacent crosstalk disturbance 
is explained. The modification 1--1 of the magnetic recording and 
reproducing apparatus has the same configuration as that of the first 
embodiment shown in FIG. 1 except that the structure of the magnetic 
heads, which is explained below. 
FIG. 4 shows an arrangement of record tracks and the multi-structure 
magnetic heads of the modification 1--1. The head width of each of the 
multi-structure magnetic heads 2 and 3 is smaller than the record track 
width, and the magnetic heads 2 and 3 are arranged such that the double of 
the head width less the overlap of the magnetic heads is equal to the 
record track pitch. Accordingly, even if the tracking deviates slightly, 
either the magnetic head 2 or 3 is in the on-track state in the record 
track. For example, when the tracking error occurs in FIG. 4 so that the 
head is shifted to the right by a small distance with respect to the 
record track, the magnetic head 2 is totally included in the record track 
and the area of the track 2 which is reproduced by the magnetic head 2 
does not change, but the area of the track 2 which is reproduced by the 
magnetic head 3 decreases. In this case, the number of errors of the 
reproduced output of the magnetic head 3 is larger than that of the 
magnetic head 2. Accordingly the selector 11 selects the output signal of 
the error detection circuit 8 for the reproduced output of the magnetic 
head 2. Similarly, when the head is shifted to the left by a small 
distance with respect to the record track, the selector 11 selects the 
output signal of the error detection circuit 9 for the reproduced output 
of the magnetic head 3. Thus, in accordance with the magnetic head 
structure shown in FIG. 4, the reproduced signal is produced free from the 
crosstalk disturbance signal from the adjacent track. 
As a modification 1-2 of the first embodiment of the present invention, the 
frequency multiplication of the tracking pilot signal in a low frequency 
band is explained. 
The modification 1-2 uses a tracking error detection circuit with an 
additional components to the first embodiment. In the modification 1-2, 
the primary signal of the recorded signal is frequency-multiplexed with 
low frequency tracking pilot signals on a digital signals comprising a 
synchronous block as a minimum unit which consists of a synchronous 
pattern, ID data, signal data and an error correction code as shown in 
FIG. 2. 
FIG. 5 shows an arrangement of record tracks on the magnetic tape 1 and the 
multi-structure magnetic heads 2 and 3. Tracking pilot signals (f1, f2 and 
f3 in FIG. 5, which are continuous signals of single frequency and have 
different frequencies from each other) and primary signals are recorded on 
the tracks 1, 2 and 3. The multi-structure magnetic heads 2 and 3 have the 
same azimuth angle as that of the track 2 (but they have reverse azimuth 
angle to those of the track 1 and 3 in FIG. 5) and they are arranged to 
reproduce the track 2 with an overlap. 
FIG. 6 shows a configuration of the tracking error detection circuit 12 in 
the modification 1-2. The magnetic head 2 reproduces f2 have the principal 
signal track as the tracking pilot and reproduces f1 as the adjacent 
crosstalk. Similarly, the magnetic head 3 reproduces f2 and f3. 
A pilot amplitude detector 121 limits a band for the tracking pilot signal 
(f2) reproduced from the magnetic head 2, detects an amplitude level of f2 
reproduced from the principal signal track 2, and supplies it to a level 
comparator 123. 
A pilot amplitude detector 122 limits a band for the tracking pilot signal 
(f2) reproduced by the magnetic head 3, detects an amplitude level of the 
reproduced tracking pilot signal (f2) and supplies it to the level 
comparator 123. 
The level comparator 123 compares the output levels of the pilot amplitude 
detectors 121 and 122 to detect a tracking error signal. 
In the modification 1-2, since the tracking error is detected by using the 
tracking pilot signals recorded on the record tracks, the tracking error 
including the linearity of the record track (track curvature) can be 
detected. Further, since the pilot signals of single frequency are 
detected, the band limitation can be made by the pilot amplitude detectors 
121 and 122. Thus, the S/N for the tracking error detection is improved. 
In addition, since the pilot signals recorded on the same track are used, 
the affect by the level variation of the pilot signals between the tracks 
is eliminated and the accuracy of detecting the tracking error is 
improved. 
In a modification 1-3 of the first embodiment of the present invention, the 
tracking pilot signal is reproduced as an adjacent crosstalk from the 
adjacent track in order to detect the tracking error. 
A block diagram of a principal portion of the modification 1-3 is identical 
to that of the modification 1-2 except that, in the tracking error 
detection circuit 12 shown in FIG. 6, the pilot amplitude detector 121 
limits a band for the tracking pilot signal (f1) reproduced by the 
magnetic head 2 as the adjacent crosstalk, detects an amplitude level of 
the tracking pilot signal (f1) and supplies it to the level comparator 
123. 
Similarly, the pilot amplitude detector 122 detects the amplitude level of 
the tracking pilot signal (f3) reproduced by the magnetic head 3 as the 
adjacent crosstalk and supplies it to the level comparator 123. 
The level comparator 123 compares the amplitude levels of the outputs of 
the pilot amplitude detectors 121 and 122 to produce the tracking error 
signal. 
In the modification 1-3, since the multi-structure magnetic heads 2 and 3 
are arranged as shown in FIG. 5, the reproduction width of the adjacent 
track reproduced by each of the magnetic heads is expanded compared to the 
prior art where one magnetic head is used. For example, in the prior art, 
assuming that the head width of the magnetic head is 1.5 Tp, the 
reproduction width for one side adjacent track under an ideal condition 
with the tracking servo (the center of the magnetic head is on the center 
of the track pitch of the reproducing track) is 0.25 Tp (where Tp is the 
track pitch). In the modification 1-3, assuming that the magnetic head 
width is same as the above and under the ideal condition with the tracking 
servo, the reproduction width is 0.5 Tp. Accordingly, the output level of 
the tracking pilot signal rises and dynamic range can be expanded. 
In a modification 1-4 of the first embodiment of the present invention, the 
tracking error is detected by preventing the reproduction of the reverse 
azimuth by using the tracking pilot signal. 
FIG. 7 shows a block diagram of a principal portion of the magnetic 
recording and reproducing apparatus in the modification 1-4. The like 
elements to those shown in the first embodiment of the present invention 
are designated by the like numerals. 
The magnetic tape 1 and the multi-structure magnetic heads 2 and 3 are 
identical to those shown in FIG. 5, and the magnetic heads 2 and 3 have 
the same azimuth angle and are arranged to reproduce the same record track 
with an overlap. The signals recorded on the magnetic tape 1 are digital 
signals having the tracking pilot signals added thereto. 
The tracking error detector 12 has the same configuration as that of the 
first embodiment, and compares the amplitude levels of the principal 
signals reproduced by the magnetic heads 2 and 3 (the signals reproduced 
from the track 2 of FIG. 5) and supplies an amplitude level difference to 
a tracking servo 42 as the tracking error signal. The tracking error servo 
42 executes the tracking control such that the tracking error is rendered 
to zero. 
However, in the tracking error detection circuit 12 described above, where 
signals are azimuth-recorded at different azimuth angle for each record 
track, the reproduced amplitude level difference is zero even if the 
reverse azimuth track is reproduced. Therefore, the tracking control may 
be executed to trace the reverse azimuth track (reverse azimuth 
reproduction). 
In the modification 1-4, a pilot detector 42 shown in FIG. 7 is added. The 
signal reproduced by the magnetic head 3 is applied to a pilot detector 
41, which detects the tracking pilot signal added to the digital signal to 
determine whether a proper track is being reproduced or an improper track 
is being reproduced. If the proper track is not being reproduced, a 
control signal is sent from the pilot detector 41 to the tracking servo 42 
which drives the multi-structure magnetic heads 2 and 3 by one track. In 
this manner, the reproduction of the reverse azimuth track is prevented 
and correct tracking is attained. 
FIG. 8 shows a block diagram of a principal portion of a second embodiment 
of the magnetic recording and reproducing apparatus of the present 
invention. The like elements to those of the first embodiment of the 
present invention are designated by the like numerals. 
The magnetic tape 1 and the multi-structure magnetic heads 2 and 3 are 
arranged as shown in FIG. 3. A record format of the magnetic tape 1 is 
shown in FIG. 9. Signals recorded in one track comprises a preamble (Pr), 
digital signal data (including an audio signal (A), a video signal (V) and 
a control signal (S) indicating VISS and VASS, and a minimum unit is one 
synchronous block as shown in FIG. 2) and a post-amble (Ps). A first edit 
gap (Ed 1) and a second edit gap (Ed 2) are provided at boundaries of 
data. 
Since the direction of reproduction of the magnetic heads 2 and 3 is from 
the bottom to the top and the magnetic heads 2 and 3 are arranged as shown 
in FIG. 3, the magnetic head 2 reproduces the signal faster than the 
magnetic head 3 does when the signal at the same position on the tape is 
to be reproduced. Namely, the time axis of the reproduced signal of the 
magnetic head 2 is not equal to that of the magnetic head 3. Accordingly, 
a delay circuit 21 delays the reproduced signal of the magnetic head 2 to 
correct the time axes of the reproduced signals of the multi-structure 
magnetic heads 2 and 3 into the same time axis. 
A comparator 22 compares the output amplitude level of the delay circuit 21 
and the output amplitude level of the magnetic head 3 to compare the 
reproduced levels and supplies a comparison output to a selector 23, which 
selects a larger one of the output of the delay circuit 21 and the output 
of the magnetic head 3 in accordance with the output of the comparator 22. 
The switching of the signals is carried out at the first edit gap (Ed 1) or 
the second edit gap (Ed 2). The timing of the first edit gap and the 
second edit gap is determined by a timing signal generated from the 
synchronous signal detected by the synchronous detector 25 and the address 
information of the ID data. An equalizer 24 comprises a cosine equalizer 
and a PLL circuit as it does in the first embodiment and corrects the 
frequency characteristic of the output of the selector 23 and a 
reproducing clock, which are supplied to the synchronous detector 25. The 
synchronous detector 25 detects a synchronization pattern to reproduce the 
word synchronization, converts it to a normal 8-bit word data, detects the 
address information from the ID data, generates the first and second edit 
gap timing, supplies it to the signal selector 23, and supplies the 
reproduced digital signal to the succeeding block. 
The tracking error detector 12 compares the amplitude level of the output 
signal of the delay circuit 21 and the amplitude level of the signal 
reproduced from the magnetic head 3 to detect the tracking error and 
supplies it to the tracking servo 13, as it does in the first embodiment. 
The tracking servo 13 executes the tracking control in accordance with the 
output signal of the tracking error detection circuit 12 to attain the 
correct tracing of the magnetic heads 2 and 3 shown in FIG. 3. 
In the second embodiment of the present invention, the same effect as that 
of the first embodiment is attained although the chance of signal 
selection is lower. Compared to the first embodiment, the signal selection 
may be made in an analog area of the reproduced signal. As a result, the 
delay circuit 21, the comparator 22 and the signal selector 23 may be 
implemented by analog circuits and the circuit scale can be reduced. 
The reduction of the chance of the signal selection is not significant 
because of the fact that the track curvature is substantially linear 
(characteristic of a semi-elliptic curve). Like the first embodiment, the 
second embodiment is not essentially affected by the adjacent crosstalk, 
can increase the total head width MT of the magnetic heads and expand the 
tracking margin. 
FIG. 10 shows a block diagram of a principal portion of the third 
embodiment of the magnetic recording and reproducing apparatus of the 
present invention. The like elements to those of the first embodiment are 
designated by the like numerals. 
The magnetic tape 1 and the multi-structure magnetic heads 2 and 3 are 
arranged as shown in FIG. 5, and the digital signal recorded on the 
magnetic tape 1 has the record format of the data format shown in FIG. 2 
and low frequency tracking pilot signals are frequency-multiplexed 
thereto. 
A delay circuit 31 delays the reproduced signal of the magnetic head 2 to 
correct the time axes of the reproduced signals of the multi-structure 
magnetic heads 2 and 3 into the same time axis. 
A signal adder 32 adds the output of the delay circuit 31 and the output of 
the magnetic head 3, which have the equal time axis, and supplies a sum 
output to the equalizer 4. 
The equalizer 4 has the same configuration as that of the first embodiment, 
and supplies the output of the signal adder 32 having the frequency 
characteristic thereof corrected and a reproducing clock to the 
synchronous detector 6. The synchronous detector 6 is of the same 
configuration as that of the first embodiment, and decodes the digital 
signal, reproduces the word synchronization from the synchronization 
pattern, generates 8-bit word data, detects the address information from 
the ID data and supplies it to a succeeding block. 
The tracking error detector 12 is of the same configuration as that shown 
in FIG. 6. The pilot amplitude detector 121 limits a band for the tracking 
pilot signal (f2) reproduced by the magnetic head 2, detects the amplitude 
level of the tracking pilot signal (f1) and supplies it to the level 
comparator 123. 
Similarly, the pilot amplitude detector 122 limits a band for the tracking 
pilot signal (f2) reproduced by the magnetic head 3, detects the amplitude 
level of the tracking pilot signal (f2) and supplies it to the level 
comparator 123. The level comparator 123 compares the output levels of the 
pilot amplitude detectors 121 and 122 and supplies the tracking error 
signal to the tracking servo 13. 
The tracking servo 13 executes the tracking control in accordance with the 
output signal of the tracking error detection circuit 12 to attain the 
correct tracing of the magnetic heads 2 and 3 shown in FIG. 5. 
In the present embodiment, since the output of the delay circuit 31 and the 
output of the magnetic head 3, which are corrected for the time axis, are 
added by the signal adder 32, the signal level of the signals reproduced 
from the primary signal track is doubled by the addition, while the 
disturbance signal of the adjacent crosstalk reproduced from the adjacent 
track is multiplied by a factor of .sqroot.2 by the addition of the 
components reproduced from the separate tracks. Accordingly, S/N is 
improved. Further, the random noise generated in the reproduction process 
of the magnetic heads 2 and 3 is also multiplied by the factor of 
.degree.2 by the factor of .sqroot.2 by the addition. Thus, S/N is further 
improved. 
Further, because of the arrangement of the multi-structure magnetic head 
shown in FIG. 5, the total magnetic head width is equal to MTw. As a 
result, the tracking margin is expanded, the affect by the disturbance 
signals of the adjacent crosstalk and the second adjacent crosstalk is 
relieved by the signal addition so that the reduction of the track pitch 
is enhanced. 
A modification 3-1 of the third embodiment of the present invention which 
detects the tracking error from the output signal of the signal adder by 
using the tracking pilot signal is now explained. 
FIG. 11 shows a block diagram of a principal portion of the magnetic 
recording and reproducing apparatus in accordance with the modification 
3-1. The like elements to those of the first and third embodiments of the 
present invention are designated by the like numerals. 
The modification 3-1 is identical to the third embodiment of the present 
invention except for the configuration of the tracking error detection, 
which is explained below. 
The magnetic tape 1 has recorded thereon single-low frequency tracking 
pilot signals having different frequencies f1, f2 and f3 for the track 1, 
2 and 3, respectively, which are frequency-multiplexed to the digital 
signal which is a primary signal. The multi-structure magnetic heads 2 and 
3 have the same azimuth angle and reproduce the same track (track 2 in 
FIG. 5) with an overlap equal to one track pitch. 
Turning back to FIG. 11, the reproduced signal of the magnetic head 2 is 
delayed by the delay circuit 31 to correct the time axes of the reproduced 
signals of the multi-structure magnetic heads 2 and 3 into the same time 
axis. The signal adder 32 adds the output of the delay circuit 32 and the 
output of the magnetic head 3, which have the same time axis, and supplies 
a sum output to the tracking error detection circuit 33. 
Unlike the third embodiment, the output of the signal adder 32 is applied 
to the tracking error detection circuit 33. 
The tracking error detection circuit 33 is of the same configuration as 
that shown in FIG. 6. The pilot amplitude detector 121 limits a band for 
the output of the signal adder 32, detects the amplitude level of the 
tracking pilot signal (f1) reproduced from the track 1 as the adjacent 
crosstalk, and supplies it to the level comparator 123. 
Similarly, the pilot amplitude detector 122 limits a band for the output of 
the signal adder 32, detects the amplitude level of the tracking pilot 
signal (f3) reproduced from the track 3 as the adjacent crosstalk, and 
supplies it to the level comparator 123, which compares the outputs of the 
pilot amplitude detectors 121 and 122 to detect the tracking error. 
In the modification 3-1, the multi-structure magnetic heads 2 and 3 have 
the same azimuth angle as shown in FIG. 5 and are arranged to trace the 
same track (track 2 in FIG. 5) with the overlap of one track pitch, and 
the reproduced signals of the magnetic heads 2 and 3 are added with the 
equal time axis and the tracking error is detected from the sum signal. 
Accordingly, if the tracking error occurs, for example, if the magnetic 
head is shifted toward the track 1 in FIG. 5, the tracking pilot signal 
(f1) recorded on the track 1 is reproduced by the magnetic heads 2 and 3 
as the adjacent crosstalk which has a larger signal amplitude than that 
reproduced by one magnetic head. On the other hand, the tracking pilot 
signal (f3) recorded on the track 3 is reproduced by only the magnetic 
head 3 as the adjacent crosstalk, which has the same signal amplitude as 
that reproduced by one magnetic head. Accordingly, the error signal 
produced by the tracking error detection circuit 33 changes more greatly 
than it does when one magnetic head is used. Conversely, if the tracking 
is shifted toward the track 3 in FIG. 5, the tracking pilot signal (f3) 
recorded on the track 3 is reproduced by the magnetic heads 2 and 3 as the 
adjacent crosstalk which has a larger amplitude level than that reproduced 
by one magnetic head. On the other hand, the tracking pilot signal (f1) 
recorded on the track 1 is reproduced by only the magnetic head 2 as the 
adjacent crosstalk which has the same amplitude level as that reproduced 
by one magnetic head. Accordingly, the error signal produced by the 
tracking error detection circuit 33 changes more largely than it does when 
one magnetic head is used. 
Accordingly, by detecting the tracking error from the output signal of the 
signal adder 32, the sensitivity characteristic of the tracking error 
detection can be made more abrupt than the prior art and the accuracy of 
tracking error detection is improved. 
FIG. 12 shows a tracking error detection circuit 50 in a fourth embodiment 
of the magnetic recording and reproducing apparatus of the present 
invention. 
Numeral 51 denotes a magnetic tape on which signals are recorded. Numerals 
52 and 53 denote magnetic heads for reproducing the signals recorded on 
the magnetic tape 51. 
The magnetic tape 51 and the magnetic heads 52 and 53 are arranged as shown 
in FIG. 13. Tp denotes a record track pitch, and Tw denotes a head width 
of the magnetic heads 52 and 53. In the present embodiment, Tw is equal to 
1.5 Tp. 
Record tracks A1, A2, A3, . . . have signals recorded thereon by a magnetic 
head having the same azimuth angle as the magnetic head 52, and record 
tracks B1, B2, . . . have signals recorded thereon by a magnetic head 
having the same azimuth angle as the magnetic head 53. 
The magnetic heads 52 and 53 are arranged to reproduce from two adjacent 
record tracks substantially simultaneously. However, in order to detect 
the tracking error from the reproduced signals of the magnetic heads 52 
and 53, the magnetic heads 52 and 53 are arranged such that the 
head-to-head interval Hp is not equal to the track pitch (Hp=1.25 Tp in 
the present embodiment.) 
In FIG. 12, envelope detectors 54 and 55 detect reproduced signal levels of 
the magnetic heads 52 and 53, respectively. The output of the envelope 
detectors 54 and 55 are supplied to a differentiator 56, which detects a 
difference between the outputs of the envelope detectors 54 and 55 to 
produce the tracking error signal. A tracking servo 57 executes the 
tracking control to render the tracking error signal to zero. 
An operation of the tracking error detection is explained with reference to 
FIG. 14. 
FIG. 14(a) shows an output signal level of the signal reproduced from the 
record track A1 for the tracking position of the magnetic head 52 and 
detected by the envelope detector 54. Since the head width Tw is equal to 
1.5 Tp, the magnetic head 52 is in a completely on-track state for the 
track Al between -Tp/4 and +Tp/4 and produces a voltage Vp. When the 
tracking is shifted by .+-.3Tp/4, the on-track factor is 50%. FIG. 14(b) 
shows an output signal level reproduced from the record track B1 for the 
tracking position of the magnetic head 3 and detected by the envelope 
detector 55. The output level for the tracking shift is same as that of 
FIG. 14(a), but since the head-to-head interval of the magnetic heads 52 
and 53 is equal to 1.25 Tp, the tracking shift comparing with that of the 
magnetic head 52 is equal to Tp/4. 
FIG. 14(c) shows a tracking error signal generated by subtracting the 
signals of FIGS. 14(a) and 14(b) by the differentiator 56. When the 
tracking shift of the magnetic head 52 is between 0 and -Tp/4, the 
magnetic heads 52 and 53 are complete on-track for the tracks A1 and B1, 
respectively, and the tracking error signal is zero. When the tracking 
shift of the magnetic head 52 is between -Tp/4 and -Tp/2 and between 0 and 
Tp/4, the sensitivity of the tracking error signal for the tracking shift 
is equal to Vp/Tp and the tracking error signal is produced. When the 
tracking shift of the magnetic head 52 is between -Tp/2 and -3Tp/4, the 
tracking error signal of -Vp/4 is produced, and when the tracking shift is 
between Tp/4 and Tp/2, the tracking error signal of Vp/4 is produced. 
The tracking control is effected by the tracking servo 57 to render the 
tracking error signal to zero by using the tracking error signal, and 
highly accurate tracking including the control of the linearity of the 
record track (track curvature) is attained. In addition, since the 
tracking pilot signals which are frequency-multiplexed to the primary 
signal are not used, there is no risk of disturbance to the principal 
signal. 
Compared to the first, second and third embodiments, only one magnetic head 
is required to reproduce one track. 
In the present embodiment as well as the first, second and third 
embodiments, the two multi-structure magnetic heads are used, although the 
number of the multi-structure magnetic head may be N (N is an integer 
which is not smaller than 2). In this case, further improvement is 
expected. 
While not specifically mentioned in the first, second, third and fourth 
embodiments, since the multi-structure magnetic heads are used and the 
tracking is phase-controlled to realize the condition shown in FIG. 3, a 
function to record reproduced data, for example, an after-recording 
function of an audio signal, and an insert function of a control signal 
(viss or bass) can be readily attained. 
In the modification 1-4 of the first embodiment, the tracking pilot signal 
is detected to prevent the reverse azimuth reproduction. Alternatively, by 
including the information representing the normal track position as well 
as the address information representing the signal position in the ID data 
of the signal data, the tracking servo may be controlled to trace the 
normal track by detecting the ID data. 
When the reverse azimuth track is reproduced, the signal reproduced by the 
magnetic head is of lower level than that reproduced from the normal track 
because of an azimuth loss. Accordingly, the tracking servo may be 
controlled to trace the normal track by detecting a difference between the 
reproduced amplitude levels. 
In the fourth embodiment, the tracking error detection circuit is 
constructed for the head-to-head interval of the magnetic heads equal to 
1.25 Tp and the head width of the magnetic head equal to 1.5 Tp, although 
the head width may be other than 1.5 Tp or the head widths of the two 
magnetic heads are not equal, so long as the head widths of the two 
magnetic heads are not equal to the record track pitch Tp.