Copy-proof recording medium and device for adding copy-proof interference signal

A copy-proof interference signal or signals is/are added to the composite color video signal to be recorded on a recording medium in the vicinity of the horizontal synchronous signal. The interference signal comprises a pulse having a narrow width compared to the width of the horizontal synchronous signal pulse. A negative going pulse may also be added to the front porch of the horizontal synchronous signal so as to compensate for area-decrease of the horizontal synchronous signal due to the addition of an interference signal. The interference signal may be added to the videl signal region which is close to the leading edge of the horizontal synchronous signal so that the interference signal does not cause the occurrence of noises or distortion in a reproduced picture. When the interference signal-added composite color video signal is directly applied to a monitor TV, satisfactory color pictures can be obtained as usual. However, when the signal reproduced from the recording medium is once recorded by a video tape recorder (VTR), only nonpractical color pictures can be obtained with the signal from the VTR because the phase-restoring operation of chromatic signal on reproduction is disturbed by the interference signal.

BACKGROUND OF THE INVENTION 
This invention generally relates to prerecorded recording media, such as 
video disks, video tapes and the like, from which the recorded information 
is copied by a video tape recorder, and to a device for adding a 
copy-proof interference signal, which will prevent copying from the 
recorded recording media, to a composite color video signal to be recorded 
on the media. 
Recently, various types of recording/reproducing systems have been proposed 
for recording and reproducing various information signals at a high 
density. Magnetic recording/reproducing apparatus, such as a video tape 
recorder (VTR) utilizing a magnetic tape as a recording medium; a color 
VTR using so called phase shift method (PS method) as described in detail, 
for instance, in Japanese Patent Provisional Publication No. 52-48919; a 
color magnetic video recording/reproducing device using so called phase 
invert method (PI method) as described in detail, for instance, in 
Japanese Patent Provisional Publication No. 50-34419; or the like are 
being popularized as home use magnetic video recording/reproducing devices 
(which will be referred to as home-use VTRs hereinbelow) throughout the 
world. As a high density recording/reproducing system using a disk-like 
recording medium, various systems have been developed; for instance, one 
in which reproduction is performed magnetically, one in which reproduction 
is performed optically, one in which reproduction is performed by 
detecting the variation in electrostatic capacitance, one in which 
reproduction is performed by using a piezoelectric element and others. 
Among other things, one in which reproduction is performed optically and 
one in which reproduction is performed by detecting the variation in 
electrostatic capacitance have reached a step which is expected to be 
greatly progressed to practical use. 
A problem in connection with the popularization of home-use VTRs is that 
the recording contents of a recorded recording medium is readily copied or 
duplicated by a home-use VTR since a reproduced signal from a recorded 
recording medium, such as a recorded magnetic tape, a video disk or the 
like, can be easily recorded by a home-use VTR because of the fact that a 
home-use VTR per se has a recording function. 
It is apparent that if the present circumstances allowing free copying, 
duplicating or stealing of the recording contents of a recorded recording 
media by home-use VTRs are left as they stand, it will cause serious 
damages to the production and selling industries, authors, and other 
relating parties. However, copyright law does not prohibit copying for 
private use by prescribing as to copying for private use as, "A work which 
is an objective of copyright, can be copied by a user if he intends to use 
it personally or at home or in a limited scope similar to such purposes." 
Therefore, it is inevitable that the recorded contents of recorded 
magnetic tapes or video disks are stolen on a limited scale. Therefore, it 
can be readily predicted that the same problem as the fact that authors, 
musicians, producers, phonograph record industry are influenced seriously 
by personal steal-copying which has been a problem in connection with 
phonograph records, will arise in connection with recorded magnetic 
recording tapes and video disks. Thus it can be predicted that video disk 
players, which do not have a recording function, cannot compete with 
home-use VTRs having a recording function, and therefore, popularization 
and development of video disks will be seriously affected. 
In this way, the fact that copies are produced by readily stealing the 
contents of recorded media by VTRs will seriously damage various relating 
industries and relating persons. It is well known that an effective 
countermeasure has been desired, for this reason, for making it impossible 
to make copies by stealing the contents of recorded recording media. 
It is also well known that many proposals have been made hitherto, in order 
to make it difficult to steal the contents of a recorded medium, from the 
viewpoint that a normal picture can be obtained when a reproduced signal 
from a recorded medium is directly applied to a monitor image receiver, 
and on the other hand, when the reproduced signal from the recorded medium 
is once recorded by a VTR, a satisfactory reproduced picture will not be 
imaged on the monitor image receiver with the reproduced signal from the 
VTR. 
It is often experienced, in connection with the information contents, that 
in the case that an information signal recorded on a recorded medium is a 
composite color video signal, its value is appreciated only when it is 
imaged on a monitor image receiver as a color TV image, and if the signal 
is imaged as a black and white image on a monitor image receiver, it is of 
no value. In such a case, steal-copying is invalidated by making sure that 
a clear color TV picture is imaged on a monitor image receiver when the 
reproduced signal from the recorded medium is directly applied to the 
monitor image receiver, and on the other hand, when the reproducing signal 
from the recorded medium is once recorded by a VTR, and is applied to the 
monitor image receiver after being reproduced, only a black and white 
picture is imaged on the monitor image receiver. Furthermore, invalidation 
of steal-copying can be satisfactorily achieved if it is arranged such 
that when the reproduced signal from the recorded medium is once recorded 
by a VTR, and is applied to a monitor image receiver after being 
reproduced, the original normal colored TV picture is not imaged on the 
monitor image receiver but a color TV picture of scrambled or confused 
colors is imaged on the monitor image receiver. 
In some conventional prerecorded video tapes, the magnitude of the vertical 
synchronous signal of the composite color video signal has been made 
relatively small so that vertical synchronization would not be 
satisfactorily obtained when the reproduced signal of the tape is once 
recorded by another VTR. Although such conventional method could prevent 
the contents of video tapes from being copied to other tapes when copying 
is made by a VTR, the conventional method has suffered from a fatal 
problem that vertical synchronization is apt to be lost when it is 
intended to directly reproduce the recorded information by a monitor TV. 
Furthermore, because of great progress in circuit techniques in VTRs in 
recent years, most VTRs now on the market are not affected by such a 
conventional copy-proof technique. Namely, the above-mentioned 
conventional copy-proof technique is not effective against recent VTRs. 
SUMMARY OF THE INVENTION 
The present invention has been achieved in order to remove the drawbacks 
and disadvantages inherent to the conventional copy-proof technique. 
It is, therefore, an object of the present invention to provide a recording 
medium carrying information which is substantially prevented from being 
copied by a VTR, and a device for producing a copy-proof interference 
signal which will be added to the composite color video signal recorded on 
such a medium. 
According to a feature of the present invention, one or more interference 
signals in the form of a pulse are added to the horizontal synchronous 
signal of the composite color video signal, where the position and 
magnitude of the pulse to be added are controlled so that the contents of 
the recording medium can be satisfactorily reproduced by a monitor TV and 
cannot be satisfactorily reproduced when reproduced from a VTR in the case 
that the contents are once recorded by the VTR. 
In accordance with the present invention there is provided a copy-proof 
recording medium carrying a composite color video signal to which a 
copy-proof interference signal has been added, characterized in that said 
interference signal has a pulse width considerably smaller than the pulse 
width of the horizontal synchronous signal of said composite color video 
signal, and in that said interference signal is added at least one 
particular place, within or close to the horizontal synchronous signal, at 
a position which precedes the trailing edge of the horizontal synchronous 
signal and does not appear in the reproduced picture of an image receiver. 
In accordance with the present invention there is also provided a device 
for adding at least one copy-proof interference signal to a composite 
color video signal, comprising: (a) first means responsive to the 
horizontal synchronous signal of said composite color video signal for 
producing a first pulse; (b) second means for defining the width of said 
first pulse; and (c) third means for adding said first pulse, whose width 
has been defined by said second means, to said composite color video 
signal, said first pulse having a pulse width considerably smaller than 
the pulse width of said horizontal synchronous signal, said first pulse 
being added at least one particular place, within or close to the 
horizontal synchronous signal, at a position which precedes the trailing 
edge of the horizontal synchronous signal and does not appear in the 
reproduced picture of an image receiver.

DETAILED DESCRIPTION OF THE INVENTION 
As is briefly described in the above, according to the present invention 
one or more interference signal are added to the horizontal synchronous 
signal of the composite color video signal which will be recorded on a 
master disk or tape, from which video disks or tapes are produced, in a 
particular manner as will be described hereinbelow. As a result, although 
the reproduced signal from a recording medium including such an 
interference signal can image a clear color TV picture on a monitor image 
receiver if the reproduced signal is directly applied to the monitor image 
receiver, in the case the reproduced signal from the recorded recording 
medium is once recorded by a home-use VTR and is then reproduced to be 
applied to the monitor image receiver, only black and white image, or a 
confused or scrambled color reproducing picture or image is obtained on 
the monitor image receiver. 
Referring now to FIG. 1, a schematic block diagram of an embodiment of the 
device, according to the present invention, for adding the above-mentioned 
copy-proof interference signal to the composite color video signal is 
shown. In FIG. 1, the reference numeral 1 is a composite color video 
signal source, and a composite color video signal of FIG. 2(a) is emitted 
from this signal source 1. 
The signal source 1 may be any device as long as it is capable of emitting 
a composite color video signal having a given form, and therefore, the 
signal source 1 may be a video disk player. The composite color video 
signal of FIG. 2(a) emitted from the signal source 1 is applied to an 
interference signal adding circuit SP which is shown by a dotted line 
frame. By adding a given interference signal, which will be described 
later, at a given place in the horizontal synchronous signal, a composite 
color video signal which has been added with an interference signal Ps1 or 
an interference signal Ps2 respectively shown by FIG. 2(e) and FIG. 2(h) 
may be obtained at an output terminal 2. 
The interference signal adding circuit SP shown in FIG. 1 comprises a 
synchronizing separation circuit SEP, monostable multivibrators MM1 
through MM4, level adjusters 3 and 4, and a mixer-amplifier MA, and is 
arranged to emit a composite color video signal to which an interference 
signal having a given pulse width and amplitude is added at a given time 
position on the basis of a time position of the horizontal synchronous 
signal of the composite color video signal. 
The above-mentioned synchronizing separation circuit SEP is employed for 
producing a pulse train signal synchronous with the horizontal synchronous 
signal. However, if the video signal to be recorded is separated from the 
horizontal synchronous signal so that the video signal and the horizontal 
synchronous signal are separately processed as in some recording 
apparatus, such a synchronizing separation circuit SEP is not required. 
The composite color video signal of FIG. 2(a) is applied to the 
mixer-amplifier MA and to the synchronizing separation circuit SEP, and a 
horizontal synchronous pulse P1 of FIG. 2(b) is separated to be applied to 
the monostable multivibrators MM1 and MM3. The monostable multivibrators 
MM1 and MM3 are triggered at the instant of falling of the synchronous 
pulse P1, and the monostable multivibrator MM1 produces a pulse P2 of FIG. 
2(c) which will be applied to the monostable multivibrator MM2, while the 
monostable multivibrator MM3 produces a pulse P4 of FIG. 2(f) which will 
be applied to the monostable multivibrator MM4. 
The monostable multivibrator MM2 is triggered at the instant of falling of 
the above-mentioned pulse P2 to emit a pulse P3 of FIG. 2(d) and when it 
is applied via the level adjuster 3 to the mixer-amplifier MA, a composite 
color video signal, to which an interference signal Ps1 has been added in 
the horizontal synchronous signal Ph, is emitted such as shown in FIG. 
2(e). The monostable multivibrator MM4 is triggered at the instant of 
falling of the above-mentioned pulse P4, to emit a pulse P5 such as shown 
in FIG. 2(g), and this is applied via the level adjuster 4 to the 
mixer-amplifier MA. As a result, a composite color video signal, to which 
an interference signal Ps2 has been added to the front porch of the 
horizontal synchronous signal Ph, is emitted such as shown in FIG. 2(h). 
The position of addition of the interference signal Ps1 is defined by the 
output pulse P2 of the monostable multivibrator MM1, whereas the pulse 
width of the interference signal Ps1 is defined by the output pulse P3 of 
the monostable multivibrator MM2. Namely, the pulse widths of the pulses 
Ps1 and p2 may be changed by respectively varying the time constants of 
the monostable multivibrators MM1 and MM2. Furthermore, the amplitude of 
the interference signal Ps1 may be freely set by the adjustment of the 
level adjuster 3. In the same manner the position of addition, the pulse 
width and amplitude of the interference signal Ps2 may be freely set by 
varying the pulse widths of the output pulses P4 and P5 of the monostable 
multivibrators MM3 and MM4, and by the adjustment of the level adjuster 4. 
A condition of adding an interference signal Ps1 of FIG. 2(e) is obtained 
when the output pulse P5 of the monostable multivibrator MM4 is not 
applied to the mixer-amplifier MA by the adjustment of the level adjuster 
4, and a condition of adding an interference signal Ps2 of FIG. 2(h) is 
obtained when the output pulse P3 of the monostable multivibrator MM2 is 
not applied to the mixer-amplifier MA by the adjustment of the level 
adjuster 3. In the case that both the output pulse P3 of the monostable 
multivibrator MM2 and the output pulse P5 of the monostable multivibrator 
MM4 are applied to the mixer-amplifier MA as of a given amplitude, it is a 
matter of course that a composite color video signal, to which the 
interference signals Ps1 and Ps2 have been added, will be obtained. 
In this way, in the interference signal adding circuit SP of FIG. 1, it is 
possible to add one or two interference signal(s) having given pulse width 
and amplitude to the horizontal synchronous signal Ph at one or two places 
indicative of given time positions. In the case of adding three or more 
interference signals to each horizontal synchronous signal pulse of the 
composite color video signal, it will be readily understood that all 
required is to add a monostable multivibrator to be triggered by the pulse 
P1 for determining the position of the interference pulse, a monostable 
multivibrator to be triggered by the output pulse of the above-mentioned 
position-determining monostable multivibrator for determining the width of 
the interference pulse, and a level adjuster for adjusting the amplitude 
of the output pulse of the above-mentioned pulse width-determining 
monostable multivibrator. 
Although the interference signal adding circuit SP having a structure shown 
in FIG. 1 is arranged to add one or a plurality of separate pulses, as 
interference signal(s) to the composite color video signal, it may be 
possible to add several continuous pulses having a given high repetition 
frequency, as interference signals to the composite color video signal. In 
this case, it may be arranged such that the output pulse of a pulse 
width-determining monostable multivibrator, such as MM2, MM4 or the like, 
may be applied to a locked oscillator (not shown) so that a plurality of 
continuous output pulses, which have been oscillated in the locked 
oscillator within an interval of the pulse width of the above-mentioned 
output pulse, may be supplied via a level adjuster to the mixer-amplifier 
MA. 
In the case of using the output pulse of the locked oscillator as an 
interference signal in this way, it is necessary to adjust the pulse width 
of the output pulse from the pulse width-determining monostable 
multivibrator. 
FIGS. 3(b) through (j) are waveform charts showing typical examples of 
condition of adding interference signal which is added to the composite 
color video signal in the device for adding the interference signal 
according to the present invention. FIG. 3(a) is a waveform chart of a 
horizontal synchronous signal pulse included in the original composite 
color video signal, which is illustrated as a reference for clear 
understanding of the positions and conditions of addition of the 
interference signals shown in and after FIGS. 3(b). 
In FIGS. 3(a) through (j), the reference Ph is a horizontal synchronous 
signal; Pb, a color burst; Ps1, Ps2 . . . , interference signals, and the 
above-mentioned interference signals Ps1, Ps2 . . . are added in at least 
one particular place in a portion which precedes the trailing edge "b" of 
the horizontal synchronous signal, where the interference signal has a 
pulse width considerably smaller than the pulse width of the horizontal 
synchronous signal Ph of the composite color video signal, and a level 
which does not project greatly beyond the peak portion of the horizontal 
synchronous signal Ph. 
Since the interference signal(s) is added to the composite color video 
signal in the vicinity of each horizontal synchronous signal pulse, the 
interference signal(s) does not cause the occurrence of noises or 
distortion in the reproduced picture on the monitor image receiver. 
In an example of the waveform chart shown in FIG. 3(b), the interference 
signal Ps1 is a pulse added at a time position which is retarded slightly 
(for instance, 0.5 to 1.5 microseconds) from the time position of the 
leading edge "a" of the horizontal synchronous signal Ph, and the pulse 
has a width (for instance, 0.5 to 1.5 microseconds) considerably smaller 
than approximately 4.8 microseconds of the pulse width of the horizontal 
synchronous signal Ph, and is arranged to project to the pedestal level 
side, having its base at the peak, i.e. the lower portion of the negative 
going pulse in the diagrams, of the horizontal synchronous signal Ph. 
In FIG. 3(b), although the interference signal Ps1 is shown as its peak is 
projecting upwardly from the pedestal level, the interference signal may 
be arranged such that the peak level of the pulse is substantially equal 
to the level of the pedestal level. Namely, it is preferable that the 
amplitude of the above-mentioned copy-proof interference pulse(s) may be 
substantially equal to or greater than (such as 1 to 1.5 times) the height 
of the horizontal synchronous signal Ph so that the interference pulse(s) 
is securely catched by a VTR when the composite color video signal 
including the interference signal is applied to the VTR. 
In the example of the waveform chart of FIG. 3(c), the interference signal 
Ps1 is a narrow pulse (for instance, 0.5 to 1.5 microseconds) where its 
leading edge is coinciding with the leading edge "a" of the horizontal 
synchronous signal Ph, while another narrow negative going pulse Ps2 (for 
instance 0.5 to 1.5 microseconds), whose peak substantially corresponds to 
the peak of the horizontal synchronous signal, is added to the front porch 
portion. 
The negative going pulse Ps2 of FIG. 3(c) is added in order to compensate 
for the decrease in the area of the horizontal synchronous signal pulse Ph 
caused by the addition of the positive going pulse Ps1. With this 
arrangement, the total energy of each horizontal synchronous signal pulse 
is substantially the same as that of normal horizontal synchronous signal 
pulse of FIG. 3(a). Such compensation by adding the negative going pulse 
Ps2 is a preferred embodiment, and similar effects will be obtained by the 
addition of the negative going pulse Ps2 even if the adding position of 
the interference signal Ps1, which is added in the horizontal synchronous 
signal Ph, is other than the position shown in FIG. 3(c). 
The peak value of the pulse Ps1 in the case of FIG. 3(c) may be selected to 
1 to 1.5 times the peak value of the horizontal synchronous signal Ph in 
the same manner as in the embodiment of FIG. 3(b). 
Shown by an example of the waveform chart of FIG. 3(d) is one that a narrow 
negative going pulse Ps3 (0.5 to 1.5 microseconds), which rises at an 
instant slightly preceding (0.5 to 1.5 microseconds) the time position of 
the leading edge "a" of the horizontal synchronous signal Ph, is added to 
the front porch, and the above-mentioned pulse Ps3 is arranged such that 
its peak substantially corresponds to the peak of the horizontal 
synchronous signal Ph. As a result, a positive going pulse, which 
functions as a copy-proof interference signal, is left. 
Shown by an example of a waveform chart of FIG. 3(e) is one that a narrow 
negative going pulse Ps4 (0.5 to 1.5 microseconds), which rises at an 
instant preceding the time position of the leading edge "a" of the 
horizontal synchronous signal Ph by 4 to 5 microseconds, is added to the 
front porch, and the above-mentioned pulse Ps4 is arranged such that its 
peak substantially corresponds to the peak of the horizontal synchronous 
signal Ph. 
The pulse Ps4 shown in FIG. 3(e) is added to a video signal region which 
does not appear in the reproduced picture on the monitor image receiver. 
Since the last part of the video signal does not appear in the reproduced 
picture, the presence of the pulse Ps4 does not give any undesirable 
influences to the reproduced picture. 
Shown by an example of a waveform chart of FIG. 3(f) is one in a condition 
that a pulse Ps4 is added at a time position in the same manner as in FIG. 
3(e), while the video signal between the pulse Ps4 and the front porch is 
cancelled. 
Shown by an example of a waveform chart of FIG. 3(g) is one in a condition 
that the above-described pulse Ps1 of FIG. 3(b) and the pulse Ps4 of FIG. 
3(e) are combined. Shown by an example of a waveform chart of FIG. 3(h) is 
one in a condition that the above-described pulse Ps1 of FIG. 3(b) and the 
pulse Ps4 of FIG. 3(f) are combined. Furthermore, shown by an example of a 
waveform chart of FIG. 3(i) is one in a condition that the above-described 
pulses Ps1 and Ps2 of FIG. 3(c) and the pulse Ps4 of FIG. 3(e) are 
combined. Furthermore, shown by an example of a waveform chart of FIG. 
3(j) is one in a condition that the above-described pulses Ps1 and Ps2 of 
FIG. 3(c) and the pulse Ps4 of FIG. 3(f) are combined. 
FIGS. 3(b) through 3(j) show typical examples of the adding condition of 
the interference signals, and in practicing the present invention, one or 
more pulses may be used as (an) interference signal(s) at least one given 
place in a portion which precedes the trailing edge "b" of the horizontal 
synchronous signal Ph and does not substantially occur in the reproduced 
picture of the image receiver, where the pulse has a pulse width (0.5 to 
1.5 microseconds) considerably smaller than the pulse width (approximately 
4.8 microseconds) of the horizontal synchronous signal Ph, and an 
amplitude substantially equal to or greater than the height of the 
horizontal synchronous signal. The lower level of the interference signal 
is arranged such that it does not greatly project downwardly from the 
negative peak level of the horizontal synchronous signal. The interference 
signal is added at least one particular place in a portion which precedes 
the trailing edge of the horizontal synchronous signal and does not appear 
in the reproduced picture. 
Although it has been described that one or more copy-proof interference 
signals are added to the composite color video signal in the vicinity of 
the horizontal synchronous signal in such a manner that at least one 
interference pulse is added to each horizontal synchronous signal pulse, 
similar results will be obtained by adding such an interference signal to 
some of the horizontal synchronous signal pulses. For instance, 
interference signal addition may be effected in connection with horizontal 
synchronous signal pulses of odd or even field. 
FIG. 4 is a block diagram showing an example of a recording apparatus which 
is used for recording the above-described copy-proof interference 
signal(s) together with a composite color video signal, as well as an 
audio signal attached to the composite color video signal and a given 
tracking control signals etc. In FIG. 4, the reference numeral 5 is a 
turntable, and this turntable 5 is rotated at a given rotational speed by 
an unshown motor and is transversely shifted by an unshown shifting 
mechanism. 
On the turntable 5, is fixed a grooveless master disk D which is formed by 
depositing a photoresist layer on a substrate (for instance, a glass 
plate) having a flat surface. Recording is effected by making two laser 
light beam spots, which have been amplitude modulated respectively by an 
information signal and have given cross-sectional shapes, on the 
photoresist layer formed on the master disk D. 
In FIG. 4, the reference numeral 6 is a laser light source; 7, a mirror; 8, 
an optical modulator for adjusting the amount of light (see Japanese 
Patent Provisional Publication No. 52-76003); 9 and 19, half-silvered 
mirrors; 10, an optical modulator for the main information; 11, a 
terminal; 7, 12, 19 and 27, reflectors; 13 and 14, cylindrical lenses; 15 
and 25, slit members; S1 and S2, slits; 16, 24, 26 and 28, lenses; 20, an 
objective lens; 21 and 34, spots; 22, an optical modulator for a tracking 
control signal; 23, a terminal; 17 and 29, a polarizing prism; 30 and 31, 
position-deviation detectors; 32 and 33, control devices; and arrows Y1 
and Y2 indicate the directions of displacement of the lens due to control. 
Detailed structure and operation of the arrangements designated at 
references 5 to 33 in FIG. 4 are described in detail in Japanese Patent 
Provisional Publication No. 54-123916, and therefore, further description 
is omitted. 
To the terminal 23 of the optical modulator 22 for the tracking control 
signal is applied tracking signals fp1 and fp2, and a rotational phase 
reference signal fp3, etc. are applied from signal generators 36 to 38 via 
a switching circuit 35, while the main information signal, which has been 
frequency modulated, is applied to the terminal 11 of the main information 
signal optical modulator 10. 
The reference numeral 39 is a signal source of the composite color video 
signal; SP, an interference signal-adding circuit, one example of which 
has been shown in FIG. 1; 40, a source of an audio signal to be attached 
to the composite color video signal; 41, an adder; 42, an oscillator; 43, 
a frequency modulator; and 44, a recording amplifier; and the output 
signal from the recording amplifier 44 is applied to the terminal 11 of 
the main information signal optical modulator 10 as the main information 
signal. 
On the master disk D, recording tracks are made in the form of a pit 
arrangement by the main information signal, and tracking signals fp1 and 
fp2 having different frequencies are recorded in the form of a pit 
arrangement in such a manner that the tracking signals fp1 an fp2 are 
alternatively switched at an interval of one revolution of the master disk 
D between two adjacent tracks of the above-mentioned main information 
signal, while the rotation phase reference signal is recorded at the 
switching positions between the above-mentioned two tracking signals fp1 
and fp2. 
In this way, a master disk of no-guide groove video disks according to the 
reproduction method of the type of electrostatic 
capacitance-variation-detection (so called VHD method), is formed. From 
this master disk video disks (recorded recording media) may be produced in 
the same manner as well known producing methods of phonograph records. 
Although a recording apparatus for a master disk of video disks of VHD 
method has been shown in FIG. 4, of course other type video disks may be 
produced by producing a master disk of video disks which can be optically 
reproduced without recording tracking signals. 
When a video disk, on which a composite color video signal produced by the 
device for adding the copy-proof interference signal according to the 
present invention has been recorded in a given form, is played back by a 
video disk player to supply a reproduced signal to a monitor image 
receiver, it is possible to reproduce a satisfactory color TV picture on 
the monitor image receiver. However, when the reproduced signal from the 
video disk player is once recorded by a home-use VTR, and when a 
reproduced signal from the home-use VTR is applied to the monitor image 
receiver, it is impossible to reproduce a satisfactory color TV picture on 
the monitor image receiver, for instance, in a VTR of a particular sort, 
only nonpractical color pictures can be reproduced from the monitor image 
receiver with the reproduced signal from the home-use VTR due to color 
confusion, and in another type home-use VTR, only black and white pictures 
can be reproduced on the monitor image receiver. Namely, in any of 
home-use VTRs, when the reproduced signal from the video disk is once 
recorded by a home-use VTR, and the reproduced signal from the VTR is 
applied to the monitor image receiver, it is impossible to obtain a 
practical color picture. 
Next, will be described the reasons that it is impossible to obtain a 
satisfactory color TV picture by a monitor image receiver with a 
reproduced signal from a home-use VTR after the composite color video 
signal, to which an interference signal has been added in the vicinity of 
the horizontal synchronous signal Ph as shown in FIGS. 3(b) to (j), is 
once recorded by the home-use VTR. 
FIG. 5 is a block diagram of a portion of a home-use VTR according to the 
above-mentioned PS method, on reproduction, and FIG. 6 is a block diagram 
of a portion of a home-use VTR according to the above-mentioned PI method, 
on reproduction. In FIGS. 5 and 6, the reference numeral 45 is a low pass 
filter; 46, 53, 60 and 68, frequency converters; 47 and 61, band pass 
filters; 48 and 62, 1H delay circuits; 49 and 63, burst-sampling circuits; 
50 and 64, phase comparators; 51 and 65, 3.58 MHz oscillators; 52, a 3.58 
MHz VCO; 66, a 3.57 MHz VCO; 54 and 67, phase-shift circuits; 55 and 74, 
input terminals for signals indicative of the position of the rotary head; 
56, a 40-times multiplier; 69, a 44-times multiplier; 57 and 72, 
synchronizing separation circuits; 58 and 73, input terminals of 
reproduced luminance signal; 59, an ACC circuit; 70, an H/2 killer 
circuit; and 71, a flip-flop. 
In a home-use VTR according to either PS method or PI method, a low 
frequency conversion carrier chrominance signal, which has been 
phase-shifted by a given amount on recording, is phase-shifted, on 
reproduction, in an opposite direction to that on recording, and the 
above-mentioned operation on reproduction is effected in the portion shown 
in FIG. 5 in a home-use VTR according to the PS method, and in a portion 
of FIG. 6 in a home-use VTR according to the PI method. In a VTR according 
to either method, on the above-mentioned restoring operation of phase on 
reproduction, the horizontal synchronous signal included in the reproduced 
luminance signal is multiplied by the 40-times multiplier 56 or 44-times 
multiplier 69 to be used after separation by the synchronizing separation 
circuit 57 or 72. 
Therefore, if an interference signal, such as shown in FIGS. 3(b) through 
1(j), has been added in the vicinity of the horizontal synchronous signal 
of the signal reproduced by a home-use VTR, the operation of the portion 
of the circuit arrangement of FIG. 5 or FIG. 6 is disturbed by the 
interference signal so that correct phase-restoring operation will not be 
performed. As a result, correct color TV pictures would not be reproduced 
by a monitor image receiver when such a reproduced signal from a home-use 
VTR is supplied to the monitor image receiver. 
Especially, in a home-use VTR, shown in FIG. 6, according to the PI method, 
the operation of the H/2 killer circuit 70 would be unstable when 
reproducing a composite color video signal, to which an interference 
signal such as shown in FIGS. 3(b) to (j) has been added, and therefore, 
satisfactory reproduced pictures would not be obtained when the reproduced 
signal is applied to a monitor image receiver. 
FIGS. 7(a) through 7(h) are waveform charts for explaining the condition 
that the operation of the H/2 killer circuit 70 becomes unstable. FIG. 
7(a) shows a train of horizontal synchronous signals having no 
interference signal, where pulses Pe, Pe . . . of FIG. 7(a) are 
equalization pulses. 
FIG. 7(b) is a waveform chart at the output side of the H/2 killer circuit 
70 under the condition that the normal pulse train of FIG. 7(a) is applied 
to the H/2 killer circuit 70, and FIG. 7(c) is a waveform chart showing 
the output waveform of the flip-flop 71 in the case that the output signal 
from the H/2 killer circuit 70 corresponds to FIG. 7(b). 
In the case that an interference signal has been added in the vicinity of 
the horizontal synchronous signal of the composite color video signal, in 
either case, that the signal to be applied to the H/2 killer circuit 70 is 
of FIG. 7(d) (the case that the interference signal is also added in the 
vertical blanking interval) or of FIG. 7(f) (the case that the 
interference signal is not added in the vertical blanking interval), the 
waveform of the output side of the H/2 killer circuit 70 would be 
disturbed as shown in FIG. 7(e) and FIG. 7(g). Therefore, the output 
waveform of the flip-flop 71, which operates by being triggered by the 
output signal of the H/2 killer circuit 30, becomes irregular as shown for 
instance, in FIG. 7(h), and accordingly, phase-shifting condition in the 
phase-shifter 67 would be totally confused. 
Although the adding position of such an interference signal, which is 
capable of disturbing the operation of the H/2 killer circuit 70, may be 
any place in a portion between a midway portion in the pulse width of the 
horizontal synchronous signal Ph and a half portion of the video signal 
period which precedes the horizontal synchronous signal, since it is 
necessary to avoid an adding condition that the interference signal 
appears in the reproduced picture, addition of the interference signal 
should be done at a point between the midway portion in the pulse width of 
the horizontal synchronous signal and a point which preceds the leading 
edge of the horizontal synchronous signal 4 to 5 microseconds. 
Next, in the case that the peak portion of the horizontal synchronous 
signal is fixed at a predetermined potential by using a pulse clamping 
circuit when recording by a home-use VTR, since the interference signal, 
which has been added to the horizontal synchronous signal, disturbs the 
clamping operation of the composite color video signal in the pulse 
clamping circuit, only reproduced pictures, whose horizontal 
synchronization has been disturbed, are obtained by a monitor image 
receiver when such a composite color video signal reproduced from such a 
home-use VTR is applied to the monitor image receiver. 
FIG. 8 is a block diagram showing an example of the recording system of a 
home-use VTR equipped with a pulse clamping circuit, and FIGS. 9(a) to 
9(c) are waveform charts for the description of the operation of the 
circuit arrangement of FIG. 8. 
In FIG. 8, the reference numeral 75 is an AGC circuit; 76, a low pass 
filter; 77, a preemphasis circuit; 78, a pulse clamping circuit; 79, a 
white clipper; 80, a dark clipper; 81, an FM modulator; 82, a 
synchronizing separation circuit; and 83, a clamping pulse generating 
circuit. 
In FIG. 8, the composite color video signal applied to the terminal 84 is 
applied via the AGC circuit 75 to the high pass filter 85 and low pass 
filter 76, and in the high pass filter 85, the chromatic signal in the 
composite color video signal is extracted to be sent to a color processing 
circuit which is not shown, and on the other hand, in the low pass filter 
76, a signal (FIG. 9(a)) comprising a luminance signal component and a 
composite color video signal is applied to the preemphasis circuit 77. The 
preemphasis circuit 77 reinforces the high frequency component of the 
given signal applied thereto to supply the same to the clamping circuit 
78. 
The clamping circuit 78 fixes the potential of the peak portion of the 
horizontal synchronous signal to a predetermined potential, and this is 
essential for setting the reference frequency of an FM signal wave by 
fixing the D.C. level of the luminance signal to a predetermined potential 
on frequency modulation. The white clipper 79 is provided in connection 
with the clamping circuit 78 for preventing the inversion on signal 
recording, and the dark clipper 80 may be provided in connection with the 
clamping circuit 78. 
A clamping pulse, which is applied to the clamping circuit 78, is generated 
by the clamping pulse generating circuit 83, on the basis of the 
horizontal synchronous pulse which has been separated from the 
synchronizing separation circuit 82. The clamping pulse Pc is one, as 
shown in FIG. 9(b), which is retarded 1 microsecond or so from the leading 
edge of the horizontal synchronous signal Ph and has a pulse width of 1 
microsecond or so. 
Namely, equalization pulses each having a pulse width which is narrower 
than the horizontal synchronous signal, reside in the vertical blanking 
interval of the composite color video signal, and it is necessary that the 
clamping pulse is positioned at a time point which is 1 microsecond behind 
the leading edge of the pulse to be clamped, and has a pulse width of 1 
microsecond or so in order to fix the equalization pulses to a 
predetermined potential by the pulse clamping circuit 78. 
In the case that the clamping operation in the clamping circuit 78 is 
performed by the clamping pulse Pc shown in FIG. 9(b), if the signal to be 
clamped is one to which the interference signal Ps1 has been added in the 
horizontal synchronous signal Ph as shown in FIG. 9(a), it is a matter of 
course that the clamping operation in the clamping circuit 78 with respect 
to the signal to be clamped is effected in connection with the peak 
portion of the interference signal Ps2, and in this case, the signal to be 
clamped is clamped in such a manner that the line CL--CL in FIG. 9(a) is 
fixed to a predetermined potential. 
Since the dark clipper 80, which is provided in connection with the 
clamping circuit 78, operates so that signal portions below a 
predetermined level are clipped on the basis of the reference level 
CL--CL, in the case that the clamping level is determined as CL--CL of 
FIG. 9(a), most portions of the horizontal synchronous signal are removed 
by the dark clipper 80, and therefore the signal applied from the clamping 
circuit 78 to the FM modulator 81 assumes a state as shown in FIG. 9(c). 
Therefore, it is apparent that only horizontal synchronization disturbed 
reproduced pictures are reproduced when signals recorded and reproduced by 
a home-use VTR equipped with such a recording system are applied to a 
monitor image receiver. 
In the recording system having the arrangement shown in FIG. 8, the 
operation of the clamping pulse generating circuit is disturbed in the 
presence of the interference signal in the horizontal synchronous signal, 
so that produced clamping pulse becomes abnormal, resulting in abnormal 
clamping operation of the clamping circuit 78. 
From the foregoing description, it will be understood that the technique of 
adding one or more interference signals to the composite color video 
signal in the vicinity of the horizontal synchronous signal according to 
the present invention provides a recorded recording medium which is 
substantially copy-proofed because only nonpractical pictures, such as 
scrambled or confused color pictures or black and white pictures, are 
obtained when intending to reproduce the recorded information after being 
recorded to a VTR. Since the amplitude of the interference signal added to 
the composite color video signal is a little greater than the height of 
the horizontal synchronous signal, and since the base line of the 
interference signal corresponds to the peak of the negative going pulse of 
the horizontal synchronous signal, the dynamic range of the composite 
color video signal is not widened at all. Therefore, it is possible to 
readily emit a reproducing signal having satisfactory S/N from a 
reproducing player of the composite color video signal-recorded recording 
medium. Since the present invention provides the above-described 
copy-proof technique, it is possible to readily invalidate steal-copying 
from video disks, video tapes or the like by home-use VTRs. 
In addition, it is useful to further completely prevent steal-copying by 
VTRs by a new interference signal to the reproducing signal emitted from a 
reproducing player by providing an interference signal generating device, 
such as written in the specifications of Japanese patent applications Nos. 
55-75348 and 55-100047, in the reproducing player of composite color video 
signal-recorded recording medium according to the present invention. 
Moreover, in practicing the present invention, an interference signal whose 
peak portion slightly projects beyond the peak portion of the horizontal 
synchronous signal may be added to the composite color video signal. 
As described in the above, according to the present invention the 
aforementioned conventional problems can be satisfactorily resolved, so 
that video disks, video tapes or the like, which can readily invalidate 
steal-copying by home-use VTRs, can be provided. 
The above-described embodiments are just examples of the present invention, 
and therefore, it will be apparent for those skilled in the art that many 
modifications and variations may be made without departing from the spirit 
of the present invention.