Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~823S8
It i~ known to record a video ~i~nal, e.g. a
televi~ion signal, along a s~iral track of a round
recording carrier, a ~o-called video di~c. l~ecording
and reproduction thu~ take place at a con~tant rotational
speed for example 15~0 rpm during reproduction. At such
a constant rotational speed the relative ~peed betw~en
the disc and the recording or reproducing element i~ not
constant. T~lis speed becomes smaller a~ the diameter of
the track decrease~, thu~ towards the inside of the
disc. The recorded waveleng$h tllU9 decreases towards
the centre of the disc for ~ pre~etermined recording
fre4uency. ~mis wffuld not be any disadva~tage in it~elf
if the tran~ducers operated independently of the
15 respective wavelen~th. !~
In practi e howev`er the tran~ducer has a charucter-
i~tic curve according to which its outpu~amplitude ~ :
- . ~ -
decreases as the wavelength drops.~ When recording, this
~: : mean~ that the mechanical~mo~ement~amplitude for a cutting
proce9s wlth a dropping waveleDgt~:is ~maller with a : :
con~bant eontrol voltage ~or the tran8ducer. It i~ al~o
po~sible that, in:fact, the mecbanical de~leotion ampli-
tude-re~in~ the same yet the amplitude of the ~ignal cut
into the disc decrease3 as the wavelength drop~, becau~e
there i~ a lack~of:sharpnes~ of the cutting ~tylu~
~uring repro~uction, the output amplitude of
the electrical signal supplied by the, for example
mechanical-electrical, tra~sducer drops accordingly a~ ~
~ ~,
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the wav~lengtll dro~
l~ecording of th~ vid~o si~nul takes place ~enerully
in the rorm of a fre~uency mo~ulated carrier. As fairly
large wavelengths, i.e. low frequencie~, have u higher
output amplitude according to the ~tated curve of the
tran~ducer than ~mall wavelengths, i.e. high fre~uencie~,
then there is a rise in the lower side band of the
fre~uency modulated carrier. 'l'hereLore it is nece~ury
to lower the lower ~ide band of the frequency modulated
carrier with a filter according to the characteristic
curve. The upper ~id0 band will not be considered in
greater detail below becau~e in genarnl only the lower
side band is utilized duri~g reproduction and the uppar
side band is omitted.
In practice, it has been proved that when there
is this type o~ correction, given a large track diameter,
i~e. at the outer edge of the video di~c where the
a~erage wavelengths are large, the ~harpne~ o~ the
image reproduced is poor and the ~ignal to noise ratio
is relatively smallO On the other hand with a small
track diameter, i~e. at the~inner edge of the di~c the
sharpness is relatively good ~hil~`~h~ ~nter~erence
~pacing is ~all. ~ mus ~harpnes~and interference
. . .
spacing are not constant o~er the entire length of the
recording track.
The invention seeks to provide means by which
the sharpne~s ~and signal to noise ratio may be made as
independent as pos`sible of the respective track diameter
1t~8~358
90 that th~y r~main substuntially unch~ed during
playing of a disc.
l~ccording to tl~e invention, there is provided
a device for recording or re~roducing a video signal
in the form of a frequency modulated carrier on a spiral
; 5 track of u video disc comprising a tr~nsduc~r used
during recording or reproduction nnd having an output
signul whose ~mplitude decreases as the re¢ordèd wave-
length drops and a fre~uency selective filter for
lowering the amplitude of the lower side band of the
: carrier.to an increasing extent as the di~meter of the
track decreases.
Further according:to the in~entlon, there i~
provided a device for recordin~ or reproducing a video
signal along a spiral tr~ck of a video di~c in the ~orm
of a ~requency modulated carrier, wherein the amplitude
of the output signal of the transducer used durlng
recording or reproductio~ decreases~:as the recorded
wavelength drop~ ~nd a fre~uency selective filter is
provld~d ~or lowering the amplitude 4f.~the lower side band
- 20 ~ ~ of the carrier with rospect to the;carrier, characterized
: ~ in-that't'he curve of the ~ilter i~ dependent o~ the
re~pective diameter of the track ~uch tha~t the~lowering
increa8e~ as the diameter of the track decreases.
~ .
A video dlsc~player~is known (German O~fen-
legungsschrift No. 2,503,944) in which,~when there is
spiral scanning, the change in the transmlssion function
(dependence of the amplitude of the ~canned signal on the
fre4uency3 is taken into account by means of a filter as
,
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35B
th~ ~iumet~r of tll~ truck ~ecr~u~es, s~ ilter
lying in the prlt~l of tlle scanned fre~uency Ino~ulate~
curri~r. ~itll this circuit, however, the wllplitude
o~ a ~)ilot sigrnal recorde~ at constant umplitude is
evaluuted ,md the pass region of the filter i~
changed in dependence ther~on. ~irect control of
the decrease in am~litude of the lower side b~nd of
the scu~ned fre~uency modulated currier is not provided
in depend~nce on the respective scanning radius. The
filter does not cause any variable lowering in
amplitude of the lower side band and the res~ective
position of the scanner radially to the vldeo disc is
ulso not directly evaluated. 'l'his ~rrangement does
not deal with holding the shar~ness and interference
spacing as constant as possible over the length o~
the track, is not dealt wlth here.
'~hu~ 7 the varying gradient of the stated curve
of the transducer is taken into consideration witl
large and small wavelengths, so that~ correction is
matched in each case to the re~uireme~ts of a
certain track diameterr 'l'he correction which takes
place and is dependent on the radius, may be used
basically when recording or reproducing or both
simultaneously. ~orrection during recording ~ay also
:
take the distortion brought about by the transducer
curve during reproductio~ into consider~tion eith~r
completely or partially. ~orrection during reproduction
may also either completely or partially balance out
.
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distortion which has occurred as a resul-t of the t.ransducer
curve during recording.
The invention is preferably used with so-called
pressure scanning, as is described in our Canadian Patent No.
923,046 issued March 20, 1973 and our Canadian Patent No.
942,682 issued February 26, 1974. It is not however restricted
to a certain recording method but may be used generally for a
spiral recording having different relative speeds between the
scanner and the disc. The lowering of the lower side band is
generally less during recording than during reproduction.
The invention will now be described in greater
detail by way of example with reference to the drawings in
which:
Figure 1 shows a general circuit diagram of the
arrangement;
Figure 2 shows characteristic curves of the scanner :
for the purpose of illustrating the mode of operation;
Figures 3 and 4 show embodiments for the filters
. used; .
Figure 5 shows a group of curves for the decrease in
accordance with the invention, which decrease is dependent on
radius;
Figure 6 shows the dependence of the decrease on the
radius of the video disc at a frequency of 1 MHz;
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lilZ358
I~'igure 7 Silo~S a furtller group o~ curves ~or
reproduction, and
~`igure 8 shows u curve for recording for the
lowermost side band fre~luency of approximately
1 ~lz~
ln Fi6ure 1 a video disc having u drive dog
is coupled to a shaft 3 of a drive motor 4. 'l'he
video disc 1 rotates above a fixed support 5
on an air cushion 6. Sc~nning take~ place by
: 10 means of a scanner 7 whioh i~ fixed to a carriage
8. 'l'he carriage 8 is pas~ed over the vldeo disc
1 in a radial direction by means of a drive 10 throu~h
- a cord 9, according to the gradient of the spiral
4.'
recording track~ '~he exact guidance of the scanner
takes place by means of the mechanically cut groove
and by means of d resilient mounting of the
scanner 7 on`the carriage 8. lrhe signals are
recorded mechanically on the Yideo disc~1 ln the : :~
form of a fre~uency modulated car~ler for scanning
20 ~ according to the pressure scanning prin~iple. 'l~e
drive 10 is also controlled by the motor 4 as is
indicated by the broken llne 11. T~le signal remo~ed
by the scanner 7 in the form of a carrier 17 frequency
modulated with the video signal is suppled ~ia a line "~
12 to a fllter 13 acting as a correction network. I~
an FM demodulator 14 a video signal 16 is obtained
: at a terminal 15~ e filter 13 serves to raise the .
lower side band of the carrier 17 in order to correct
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~0~ 358
th~ ~r~(luency re~pons~ of tlle sc~nner~
'l'he frequency curve of the filter 13, i.e. the
lowering of the lower side~band is changed in dependence
on the respect1ve diameter,oL the track i.e. the
respective position of the scunner 7 on a radius ~,,
of the video disc ~, us indicated by the variable
resistor 21 in the filter 13. 'l~lis change i~ caused
by the drive 10 via a mechànism indicated by the
broken line 18~ ln addition the variable resi~tor 21
of the filter 13 for example is mechanically coupled
to the radial feed of the carriage 8. 'l'he resistor
.!' .
21 may be a potentiometer the axle of which is
: coupled to the drive of the cord 9. '~le change in
,
: correction may also take place via an element otherthan a variable ohmic re~istor~ Ba~ically the use
of a variable inductance or capacitance (Varicap
diode) is po~sible in an appropriate network.
,,1,.
~ Figure 2 ~how~ the curve of the scanner 7, i.e~
: , the amplitude of the outpu~ signal ~ in dependence on .'
., I " . ~ .
the recorded wavelength, in a ~tandard view for S. When
. there is a constant frequency deviation in the recorded
.. . ... .
carrier, the frequency deviation range 19 shown as a
hatched area occurs at the outer end of the track as a
.....
re~ult of the:lowering relative ~peed towards the inner
part of the disc and the fre~uency deviation range 2U
shown as a hatched area occur~ atl.the inner end of the
track . 'lhese ra~ges are e~ual to one another. ~tarting
frolll tll~ deviation range ~, ir ~ ectr~l line of the
frelIuency Inodulated carrier :is con9idered ~t a ~paci~g
i~ fro~n the centre fre(Iuency toward~ tI~e lower side band
then ~llere is a ri~e in tll~ lower side bund by the amount
~. 'l'Ilus tIIe filter 13 woul~ IIave to lower the lower ~ide
band by tIIis uMount ~t this spectral line. At the
fre~uency deviation 1~, thu~ ut the outer diameter o~
the track when there is an e-lual ~pacing A of the
sp~ctral line from the centre frecIuency, there is only a
rise in the lower side ban~,by the amount ~'. lt can be
seen th~t ~' < B. 'rhus, at ,tlie outer diameter of the
track ~ smaller lowering of:.the lower side band is
.. .;~
neces~ary. This matching of~the lowerlng of the
lower side band in accordance with the respective
diameter of the trar,k durin~,,scanning is carried out by
tlle filter 13 in Figure 1, controlled by the drive 10.
e rise in the,lower side band means a rise in high
fre~uency emphusi~. '~1iS emphasi~ must not be made
~: resettable,but rather the difference in the rise is
resettable. ~ constant rise,can be com~letely desirable,
Fi~ure 3 show~ ~a practical development of the
filter i3. The re~istor 21'~hich i~ varied in dependence
on the radiu~ causes a lowering of the lower side band
dependent on radius. The fre~Iuency modulated carrier ; ~
17 is supplied to the terminal 22 by the scanner 7 while ~ :
~, the output terminal 25 in Figure 1 is connected to the
demodulator 14.
Figure 4 shows another development o~the filter
13.
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~ ur~ 5 sllows u ~rou~ of curve~ and in fuct
lowerin~ of the lower side band of the frequency
modul~ted ci~rrier 17 with ,tlle respective disc radius r
i~S a paramet~r. It muy be se~n that t~le loweringo~
tlle lower side band increases as the rudius 'become
smaller, thus toward~ the inn~r part of the disc.
Figure 6 shows the dep~ndence of lowering of the
lower end of ~he lower side band and in ~'act at a
fre~uenicy of approximately~l MUlz in dependence on the
respec~ive radius as is pro~iuced from Figure 5. It
may be seen that lowering at the inner edge of the
recording track initially changes to ~ v~ry large
~ extent and at the outer edge it change~ to a les~er , ,
'~ extent. This may be obtai~ed by means of special
dimensioning of the filter,',,13, e.g. by means of a
'i¢y
;~ logarithmic potentiometer',~
..
~'igure~7 shows a further;group o~ curves for the
lowering during reproduction which 18 simi;lar ln principle
' to that in ~i~igure 5.
~ Figure 8 ~how~ a curve for recordlng and in
fa~t shows the lowering o~the lowermost side band
:
fre~uency (0.5 - 1 MH~) in dependence on the respective
radiu~ of the recording trackO It may be seen that
th~re the lowering is smaller than during reproduction.
In princlple the filters according to Flgures 3 and 4
may also be used for the lowering during recording.
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