CA1182209A - Method and apparatus for recording a digital information signal in parallel tracks on a record medium without guard bands between at least some adjacent tracks - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Apparatus for performing a method of recording a color video signal on a magnetic tape includes an analog-to-digital converter which samples the video signal at a frequency which is at least three times the color subcarrier frequency of the color video signal and converts the sampled color video signal to digital form; an interface which sequentially distributes the digitized samples to, for example, four channels, each channel including a time base compressor for compressing the digitized samples supplied thereto, an error control encoder for generating error control data from the respective compressed samples and adding the error control data thereto, and a recording processor for adding synchronizing, identifying and address signals to the compressed digitized samples supplied thereto and for code converting the digitized video signal in the form of 8-bit words to a respective 10-bit word code to reduce the low frequency components of the digitized video signal; and four recording transducers, each associated with one of the channels, for recording the digitized video signal from the four channels in a plurality of parallel tracks extending obliquely on the magnetic tape without guard bands between, preferably, any adjacent ones of the tracks and with the digitized video signal being recorded in alternate ones of the tracks with a first azimuth angle and the digitized video signal being recorded in the remaining alternate ones of the tracks with a second azimuth angle which is different from the first azimuth angle.

Description

i ~

BACKGROUND OF THE INVENTION

This invention rela-tes qenerally to a method and apparatus for recording a digi-tized video siqnal on a ma~netic -tape and, more Particularly, is directed -to a me-thod and apparatus for recording a digitized video signal on a magnetie tape with a high recording density.
Conventionally, apparatus for recordin~ a video slgnal on a magne-tic ta~e have been of the analo~, rather than digltal, -type. However, there has been a reeent turn towards development of dlgltal video -tape reeordexs (VTR). Di~ital VTRs have a very hiqh picture quality, whieh enables multlple generatlon dubbing with vlrtuallv no pleture im~airment. .Further, dlgital VTRs provide adjustment free eircuits and self-diagnostic systems which enable easier mai.ntenanee and higher reliability.
With digital VTRs, an analoq video signal is eonverted into digital form by an AJD tanalog-to-digital) eonverter. In partieular, the analog video signal is sampled by eloek pulses having a sampling frecruency which may be, for e~ample, ~ESc, where fse is the color sub-earrier fre~uency of the eolor video signal, resulting in -the analog vicleo signal bein~.eonverted lnto a digitized video signal. eomprised of 8-bit words~ The digitized signal is also coded bv an error eontrol encoder so that errors may be corrected and eoneealed on playback and, it is further coded by a ehannel encoder to achieve high den.sity digital recordinq.

-2-The eoded digitized signal is then recorcled on a magnetic tape by means of a recording amr?lifier. 130wever, it should be appreciated from -the above that the recordinq bit rate, that is, the rate of oceurrence of eaeh bit of the cdigltized video signal, is extremely high. For example, in the above-deseribed embodiment, where -the color sub-carrier frequency fse = 3.58 MHz, the reeording bit rate is equal -to ~fsc times the number of bits per word. In other words, the reeording bit rate is ohtained as follows:

Bit rate = ~ x 3 58 x 106 x 8 = ll~.6 Mb/s.

Because of such high recordinq hit rate, the digit~zecl video signal is not suitable for recording in a sin~le recording ehannel.
Accordingly, it has been proposed to separate the digitized video signal into at least two separate channels prior to recording it on a magnetie tape so as to reduce the recGrding bit rate per ehannel. Typieally, a maqnetic head is assoeiated with eaeh ehannel and all oE the mac~netle heads are ali~ned to reeord the respeetive channels on a magne-tic tape in parallel -tracks extending obliquely on the tape. In order to separate the digitized videc signal into, for example, two ehannels, an interface is provided which distributes alternate 8-bit words of the digitized video signal into the respective channels.
In recording the cligitized vicleo signal in the parallel tracks, it is desirable to increase the siqnal-to-noise (S/N) ratio so that, during reproduetion, a video ~icture oF

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high quali-ty can be obtained, while at the same time, reducing the amoun-t of tape consumption by recordin~ the digitized signal with a high density. Tt should be appreciated that these two ob~ections are contrary to one another. For example, as the track width is decreased so as to obtain such hic~h density recordi.ng, the S/N ratio of the video signal reproduced from the tracks deteriorates.
In like manner, as -the track width is increased which resul-ts .in higher tape consumption, -the S/N ra-tio lncreases.
Therefore, in such previously proposed a~paratus, guard bands have been provlded between adjacent ones o:E the parallel tracks recorded on the magnetic tape so as to avoid cross-talk interference between such adiacent tracks, resulting in a higher S/N ratio. ~lowever, when the track width is ~0~ m, for example, the wldth o the ~uard band between each of the adjacent tracks must be at least ?0~ m, resul-ting in a high tape consumption. IE, on the contrary, the track wid-th is made narrower, tracking errors are apt to occur during the reproduction operation, wherein the heads do not accurately trace the recorded tracks, resulting in a deterioration of the S/N ratio. Also, with a reduction of track width, there necessarily is a reduction in the width of the guard bands, resulting in increased cross-talk interference (noise) from adjacent tracks.

OBJECTS AND SUM~ARY OF THE INVENTION

Accordingly, it is an ob~ect of this invention to provide a method and apparatus for recording a digitized video signal on a ma~netic tane that avoids the above-described ~8;~

dif:Eiculties encountered with -the prior ar-t.
It is another object of this invention -to provide a method and apParatus :Eor recordinq a diqi-tized video siqnal in which the digitized video signal is sequentially distributed to a plurality of channels and then the digitized video signal in each channel is recorded in a plurality oE parallel tracks ex-tending obliquely on a magnetic tape without guard bands between adjacent tracks.
It is still another object oE this inven-tion to provide a method and apparatus for recordinq a digitized video signal in which the video signal, upon being reproduced, has a high signal-to-noise (S/N) ratio.
It is yet another object of -this invention to provide a method and apparatus for recording a digitized video signal in which the digitized video signa:L is recorded with a high recording density in a plurality of parallel tracks exten`ding obliquely on a magnetic tape so as to reduce tape consumption.
I-t is a further object of this inven-tion to provide a method and appara-tus for recoxdi.ng a digitized video signal .in which the digitized video signal is recorded in a plurali-ty of parallel tracks extending oblicluely on a magnetic tape and having a guard band between adjacen-t tracks, with -the digitized video signal in at least some of the tracks being recorded with an azimuth angle which is di~Eerent from other ones oE
the tracks.
In accordance with an aspect of thi~ invention, apparatus for recording a video si(~nal on a magne-tic tape ~2 includes means for converting the video signal into digi-tal form; means for distributing respective portions o:E the digi.tized video signal to at least -two channels; and means for recording the respective portions of the digitized video signal in a plurality of parallel tracks extending obliquely on the magnetic tape without guard bands between a-t least some adjacent ones oE the parallel trac]cs and with the portions of the digitized video signal in some of the parallel -tracks being recorded with an azimuth angle which is di:Eferent from the azimuth angle in other ones of the parallel tracks.
In accordance with another aspec-t of this invention, a method of recording a video signal on a magnetic tape includes the steps of converting -the video signal into digital .~orrn; distributing respective portions of the digitized vldeo signal to at least two channels; and recording the respective portions of the digitized video signal in a plurality of parallel tracks extending obliquely on the magne-tic tape without guard bands between at least some adjacent ones o:E
the parallel tracks and with the portions of the digi-tized video signal in some of the parallel trac]cs being recorded with an azimuth angle which is diEferent :Erom the azimuth angle in other ones of the parallel trac]cs.
In accordance with a further aspect of this invention, the diqital video s.ignal, prior to recording, is code converted, for example, by an 8-to-10 code conversion system, in order to reduce low frequency spectrum components of the digitized video signal so as to improve the S/N ratio of the video signal when reoroduced.

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More particularly there is provided:-Apparatu~ for recording a video ~ignal on amagnetic tape comprising:
means for converting the video signal into digital form;
-means for distributing respective portions o the digitized video signal to at least two channels, each o~ said at least two channels including code converting means for code converting the respective portions of said digitized video signal distributed to the respective channel so as to reduce low frequency components of said digitized video signal; and means for recording the respective portions of said digitized video signal in a plurality of parallel tracks extendiny obliquely on said magnetic tape without guard band~
between at least some adjacent ones of the parallel tracks and w.ith said portions of the digitized video signal in adjacent ones of the parallel tracks without guard bands therebetween being recorded with different azimuth angles.
~ There is also provided:-A method of recording a video signal on amagnetic tape comprising the steps of:
converting the video signal into digital form;
distributing respective portions of the digitized video signal to at least two channels;
code converting the respective portions of said digitized video signal distributed to each channel so as to reduce low frequency components of said digitized video signal;
and recording the respective portions of said digitized video signal in a plurality of parallel tracks extending obliquely on said magnetic tape without guard bands between at least some adjacen~ ones of the parallel tracks and with said portions of the digitized video signal in adjacent ones of the parallel tracks without guard bands therebetween being recorded with different azimuth angles.

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There is further provided: ' A method of recording a video siynal on a mag-netic ta~e comprising the steps of:
converting the video signal into digital form;
distributing respective portions of the digitized video signal to at least three channels, three sequential ones of said parallel tracks including a field interval of video information;
and recording the respective portions of said digitized video signal in a plurality of parallel tracks extending obliquely on said magnetic tape with a guard band provided after every three sequential ones of said parallel tracks and without any guard bands between adjacent ones of the remaining tracks, and with the digitized video signal in the center track of every three sequential ones of said parallel track~ corresponding to a field interval and being recorded with an azimuth angle which is different from the azimuth ~ngle in the remaining ones of the parallel txacks.~

-6b-The above, and other, objects, features and advanta~es of the present i.nvention, will be apparen-t from the Eollowlng detailed description which is to be read in connection with the accompanying drawings.

~RIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram used for explaining the recording of a digitized video signal in parallel -tracks with guard bands between adjacent tracks, accorcling to a prev:iously proposed method of recording a digi-tized video signal;
Fig. 2 is a graphical diagram illustrating the cross-talk characteristics of the previously proposed method of Fig. 1 and the method according to this invention;
Figs. 3A and 3B are schematic diagrams illustrating the tracking hy A magnetic head with apparatus accordinq -to this invention and with previously ~roposed apparatus for recording a digitized video signal;
Figs. ~A-4D are waveform diagrams of various digital.
code converting formats;
Fig. 5 is a graphical diagram of the Erequency spectrum density for the various formats shown in Figs. ~A-4D;
Fig. 6 is a graphical diagram oE the frequency spectrum density illustrating the reduction of low .frequency components by means of an 8-to-1~ code conversion system;
Fig. 7 is a block diagram illustrating a recording section of a digital video tape recorder (VTR) embodying this invention;

Fig. 8 is a hlock diagram illustrating a reproducing 2@~D

section of a digital video tape recorder (VTR) which is complementary to the recording section of Fig. 7, Fig. 9 is a schematic diagram illustrating the positional and azimuth angle relationship be-tween the four magnetic heads of the recording and reproducing sections of Figs. 7 and 8;
Fig. 10 is a schematic diagram of a rotary head assembly included in the digital VTR of Figs. 7 and 8;
Fig. 11 is a schematic plan view of a section of magnetic tape showing tracks in which the signals are recorded by the recording section of Fig. 7 and showing the rela-tion-Silip between the azimuth angles in adjacen-t tracks;
Figs. 12, 13 and 14 are schematic diagrams to which refererce will be made in explaining the digitiza-tion and code arrangement of a video signal for use in a digi-tal VTR
embodying this invention; and Fig. 15 is a schematic plan view of a section of magnetlc tape illustrating the relationship between adjacent tracks in accordance with another embodiment of -this invention.

DET~ILED DESCRIPTION OF THE' PREFERRED EMBODI~lENTS

In order -to facilitate a bet-ter understanding of the presen-t inven-tion, there will first be described the condi.tlons for di.gital recording of a color video signal with a high signal-to-noise (S/N) ratio and a high recording density.
Where a digitized video signal is transmitted, a tolerable bit error rate in the transmission of the digitized 2~9 signal is 1 x 10 7. Since the S/N ra-tio oE a transmission path (where the signal is measured by i-ts pealc-to-peak value and the noise is measured by an effective value) is more -than 20 dB when the bit error rate is sligh-tly less than 1 ~ 10 7, the S/N ratio of a digitized color video signal obtained, during reproduction from a digital VTR, must be larger than 20 dB.
In addition to the requirement for a suEEiciently hicJh S/N ratio, it is also desirable to reduce the tape consumption so as to obtain maximum utilization oE the magnetic tape. This, of course, means that the digital video signal must be recorded with a high bit denslty. In order to obtain such high bit density recording, the number of recorded bits per unit area of.tape S (recording bit density) mùst be high, in which the recording bit densi-ty S is expressed by the following equation:

S = L T ....(1) where L is the line bit density, that is, the number of recordecl bits per unit length in the leng-tl-lwise direction of the track, and T is the track density, that is, the number of recorded bits per uni-t length in the wi.dthwise direction of the track. Generally, as the value of -the line bit densi-ty L
increases, a short wavelength for recording must be utilized.
Assuming that the magnetic layer on the tape is sufficiently thick, it has been determined that the number of magnetic particles which are activated so as to change the 2~

magnetic flux supplied -to the reproducing head increases approximately in propor-tion to the square of the recording wavelength utili~ed. Further, the signal vol-tage generated at the reproducing head increases in proportion to the number of activated magnetic particles, while the noise voltage generated at the reproducing head increases in proportion to the square root of the number of activated magnetic particles. In other words, the signal voltage generated at the reproduced head increases In a proportional manner -to the square of the wavelength and the noise voltage generated at the reproducing head increases in a proportional manner -to the wavelenyth. Thus, if it assumed that the source of noise results only from the tape, tha-t is, the activated magnetic particles thereon, the S/N ratio of the reproduced digitized signal increases in a proportional manner -to the w~avelength. Further, -the S/N ratio for the amplifier system oi the VTR is also proportional to the waveleng-th. I-t should therefore be appreciated that if the track width and the relative speed between the reproducing head and the tape are constant, the S/N ratio increases as -the recordlng wave-length increases. However, it should be appreciated -that this is contrary to the condition of high bit density recording where it is desirable to utilize a short wavelength in order to increase the line bit density L,and consequently, to -thereby increase the recording bit density S.
In regard to the track density T, -the signal voltage and tape noise voltage generated at the reproducing head each decrease in a proportional manner to reductions in the ~2~

track width W. However, if the noise is generated only from the tape, the noise voltage generated at the reproducing head is only in proportion to the square root of the track width W.
In such case, the S/N ratio of -the reproduced digitiz.ed siynal is proportional to the square root of the -track wid-th W.
In regard to the noise from the VTR, the induc-tance of the reproducing head is approximately proportional to the width oE the reproducing head, that is, to the track wid-th W.
When the inductance of the reproducing head is constant, the num~)er of turns of windings on the head are inversely proportional to the square root of trac]c width W. Further, the ma~netic flux linked with the windings o:E the head is proportional to the track width W. It should therefore be appreciated tha-t, with the inductance of the reproducing head maintained at a constant value, the voltage induced in -the reproducing head is proportional to the number of turns N times the magnetic flux ~b intersecting the windings. In other words, the voltage E induced in the reproducing head is proportional to the square root of the -track wid-th W. Further, if the inductance of the reproducing head is cons-tan-t, -tlle n~ise generated by the reproducing head amplifier is also constant. Thus, assuming tha-t the source of noise only resul-ts from the reproducin~ head amplifier, the S/N ratio of the reproduced digitized signal is proportional to the square root of the track width W. If the generated noise from the tape and from the reproducing head amplifier are independent of each other, the S/N ratio of the reproduced digitized signal, as a result of the combined noise from the tape and the ~8Z~Q~

reproducing head ampliEier, is proportional to -the square roo-t of -the traek width W. In other words, reduction of the traek width ~ so as to increase the -track density T results in a deterioration of the S/N ra-tio.
It should be appreciated from the above that the recording bit density S is increased by redueing the traek width W so as to increase the track densi-ty T and by utllizing a short recording wavelength so as -to increase the line bit dènsity L. However, such conditions result in a deterloration of the S/N ratio. I-t should therefore be appreeiated that the eonditlons for increasing the S/N ra-tio while inereasing the reeording bit density S are eontrary -to one another.
In order to eompensate for the above, previously proposed digital video tape recorders have recorded the video signal in a plurality of parallel tracks extending obliquely on a magnetie tape with guard bands between adjacent tracks, as shown in Fig. 1. This results in a reduction of cross--talk noise interference caused by leakage magnetic flux from adjaeent traeks with a eonsequent increase in the S/N ratio.
OE eourse, SUCIl eross-talk interferenee relates only to the noise generated by the tape and no-t crom the reproclucing head ampl.ifier. However, in such ease, if the traclc density T is inereased, that is, the traek width W is decreased, so as to increase the reeording bit density S, the guard bands between adjaeent traeks are also reduced. This results in increased eross-talk noise interference from adjacent tracks. Also, in sueh ease, when the track width W beeomes too narrow, tracing z~

of the tracks by the reproducing heads becomes difficul-t so that lncorrect tracing ls apt to occur with a consequent deterioration of the S/N ratio.
Before proceediny further, the above-mentioned cross-talk interference from adjacent tracks will be discussed. Referring firs-t to Fiy. 1, there is shown a reproducing head 1 having a width W and a plurali-ty of parallel recorded tracks 2 with guard bands between adjacent tracks. The width of the tracks is equal to the head width W
and a magnetized width ~W caused by fringe flux and which is equally divided on both sides of each track so that a fringe flux width ~ W/2 extends in the widthwlse direction on both sides of each track. Given that the width of each ~uard band is equal to x, the wavelength of the recorded signal is ~ , the level of the desired or true recorded signal is E, and the level of the cross-talk signal is ~c' the cross-talk interference component Ct can be expressed by the following equation:

Ct = 20 1Og(Ec/E) = A -~ B ~x/~ dB ---(2) where b aw -bW + ~W b x A = 20 log[ K . ~b e (1-e )e ] ...... (3) K - W + 2~ (l-e b -~) ... (4).

Further, it is assumed that x ~> ~ W and, by experiment, it has been determined tha-t ~W - 0.67 ~ , b ~ 6.~ and B - -60.
If values for the track width W and the guard band width x are chosen as 40~m and 20~ m, respec-tively, from equation (2), when the relative speed of the reproducing head to the tape is 25.59 m/sec, the Erequency characteristic for the theoretical cross-talk component is shown by curve Cl in E'iy. 2. In other words, curve Cl represents the cross-tal]c interference resulting from the two end tracks in Fig. 1 when head 1 traces the center track of Fig. 1. I-t should be appreciated from this curve that the level of the cross-talk interference is subs-tantially increased for low fre~uency components of the video signal.
It should further be appreciated that the reduction of guard band width x and, of trac]c width W, neeessarily results in -the tracks being closer to one ano-ther so as to result in increased cross-talk interference. Therefore, there is a limit to the reduction of guard band width x in order to provide that a picture can be reproduced with good ~uality.
Further, as previously discussed, as the trac]c width W is decreased, it becomes difEicuLt to accura-tely trace each track. In o-ther words, reproducing head 1 is apt to deviate from the desired path of the recording -track. This, of course, results in a subs~antial increase in cross-talk interference from adjacent tracks. Although the tracking aecuracy can be improved by various servo techniques, it is fundamentally determined by the mechanical accuracy of the system which cannot be accurately controlled. In this manner, --1'1-- `

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it should be appreciated that because of mistracking and cross-talk interference from adjacent tracks, -the track width W and guard band width x can only be reduced by a cer-tain amount in order to increase the recording bit density S.
Referring now to Figs. 2 and 3, the basis of the present invention will now be described, which is aimed at obtaining a high recording density while, at the same time, substantially increasing the S/N ra-tio. In accordance with -the present invention, the digi-tized color video signal is distributed to a plurality of channels and the slgnals from -the channels are recorded by recordiny heads associated wi-th each of the respective channels in adjacen-t parallel tracks extending obliquely on a magnetic -tape with the longitudinal edges of the adjacent tracks being in contact with each other so as to eliminate any guard bands -therebe-tween.
Further, the digitized signal is recorded so tha-t the azimu-th angles in adjacent tracks are differen-t from one anotherl with the azimuth angle for each track being defined by the angle hetween the direction of the air gap of the recording head utilized and a reference direction, for example, the directior perpendicular to the longitudinal direction of -the track.
Preferably, the azimuth angles ~ in adjacent tracks are equal, hut opposite, as shown in Fig. 3A. During reproduc-tion, reproducing heads with air gaps having the same direction as those of the respective recording heads trace the respective tracks to reproduce the digitized video signal therefrom. By utilizing such arranyement, cross-talk interference between adjacent tracks is substantially reduced as a resul-t of azimuth ~z~

loss. Such azimuth loss La, during reproduction, as a result of the recording of the video signal in adjacen-t tracks with different azimuth angles, can be expressed as follows:

sin ~AW tan ~

La = 20 log ~ tan ~ d~ ... -(5) where ~ represents -the azimuth angle relative to a reproducing (or recording) head 1 and recordlng track 2. It should be appreciated from e~uation (5) that, if the relative speed of head 1 to the tape is constant, the azimuth loss La lncreases with decreasi.ng wavelength ~, that is, with increasing frequency. Thus, in accordance wi.th another aspect of this invention, the digital video signal is code converted in order to reduce the low frequency spectrum components thereof so as to provide an increased azimuth loss La.
In particular, a specific example will now be illustrated or comparing the recording according to this invention with the previously discussed recording which provides guard bands between adjacent tracks. As shown in Fig. 3A, the digitized video signals from two channels are recorded in adjacent tracks 2 wlth a differential azlmuth angle ~d between the adjacent ~racks which ls selected as 14, and the width W of each track is selected as 60~ m wlth no guard bands therebetween. When a reproduclng head 1 (wlth a 2~

eorrect air gap angle) traces a respective one of tracks 2 of Fig. 3A, the cross-talk component Erom the adjacent -track is shown by eurve C2 in Fig. 2. In comparison, Erom me~sured values, when the track width W is selec-ted as 40~Jm, the wid-th x of eaeh guard band is selected as 20~ m and the azimu-th ang]e ~ for all tracks is selected as 0, as shown in Fig. 3B, and when reproducing head 1 scans one of tracks 2 in Fig. 3B, the actual cross-talk component from the adjacent track is represen-ted by eurve C~ in Fig. 2. I'he above curves C2 and C3 were obtained :Eor the ease where the relative speed oE the reproducing hea~
to the tape was equal. to 25.59 m/sec.
From eurve C2 according -to this invention, for frequencies lower than approximately 2 MHz, -the cross-talk eomponent decreases with lncreasing frequencies up to appro~imately 2 MHz. When the frequency is higher -than 2 MHz, the cross-talk interference between adjacent tracks .increases with increasing frequency due to coupling between the heads and the like. In the actual curve C3 in which the recorded traeks have guard bands -therebetween :Eor frequencles lower than about 200 KHz, the cross-talk curve becomes colncldent with the theoretica1 eurve Cl. Above 200 KHz, curve C3 follows a si.milar pattern to that of eurve C2 in wllich the eross--talk interferenee from adjaeent reeorded traeks decreases wi-th inereasing Erequencies up to about 2 MHz and thereafter, increases with inereasing frequencies. Further, from a eomparison of curves C2 and C3, i-t is seen that, for frequencies lower than about 1 MHz, the cross-talk componen-t, in the ease of azimuth recording according to this invention, is greater than the cross-talk eomponent in the case oE normal recording with guard bands, by only ~ to 6 dB. In the frequency range greater than 1 MHz, curves C2 and C3 are substan-tially coincident so that -the cross-talk components are approximately equal.
It should be appreciated that the tape consumption .is the same for normal recording with guard bands, shown in Fig. 3B, and azimuth recording without guard bands according -to this invention, shown in Fig. 3A. Fur-ther, -the cross-talk interference between adjacent tracks for the two recordings is substantially the same. However, as previously discussed, the S/N ratio of the reproduced digital signal is propor-tional to the square root of the track width W~ Thus, as the track W
is increased, the level of the reproduced signal, and consequently, the S/N ratio, also increases. It should therefore be appreciated that.the overall S/N ratio for the record:ing according to this invention, as shown in Fig. 3A, is higher than that for the recording shown in Fig. 3B. In par-ticular, the S/N ratio for the recording according to this inven-tion is greater than that for -the recording shown in Fig. 3B by an amount 20 log ~ = 1.76 dB.
Further, upon the occurrence of a -trac]cing error by the reproducing head, it should be appreciated that -the S/N
ratio of the reproduced signal for the recording as shown in Fig. 3A is even higher than the aforementioned 1.76 dB over that for the recording shown in Fig. 3B. For example, when reproducing head 1 is displaced so as to trace two adjacent tracks by an e~ual amount, as shown in Figs. 3A and 3B, any deterioration of the S/N ratio for the recording in Fig. 3A

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is substantially reduced as a result of azimu-th loss. However, when reproducing from the recorded tracks shown in Fig. 3B by reproducing head l which equally overlaps the two traclcs, the S/N ratio is 0 dB since the amount of cross-talk interference picked up from the non-desired track is equal tG the level o~
the signal from the track desired to be traced. It should therefore be appreciated that the utilization of azimu-th recordiny with no guard bands between adjacent tracks provides a greatly improved recording over -tha-t previously proposed.
In other words, by utilizing an azimuth recording, -there is obtained a high S/N ratio while also providing high bit density recording.
There is, however, a limit to the value of the azimuth angle ~. In particular, the effective recording wavelength ~e can be expressed as follows:

~e = Acos ~ .... (6) where ~ is the actual recording wavelength utilized. Frorn equation (6), it should be appreciated that the effective recording density is lowered, and consequently, the recording ~is easily effected by spacing and gap loss when -the effective recording wavelength ~ e is small. Since -the effective recording wavelength ~e decreases as the azimuth angle ~ increases, the differential azimuth angle ~d be-tween adjacent tracks cannot be selected too large. It has been ascertained by experiment that the differential azimuth angle 3d is preferably selected in the range of 10 to 30 in order to provide high density reco~.ding.

~8~9 As previously discussed in regard to equation (5~, the azimuth loss La increases as the recording frequency increases. In :Like manner, when the recording frequency is low, the azimuth loss La is also low. This is seen more particularly by curve C2 in Fig. 2 which illustrates an increase in the cross-talk interference with decreasing frequencies below approximately 2 MHz. It should be appreciated that the cross-talk interference between adjacent tracks is considered as a noise signal, in addi-tion to other previously-mentioned noise components, which results in a deteriora-tion of the S/N ratio of the reproduced digital signal. Since the S/N ratio for the reproduced digital signal must be greater than 20 dB, as previously discussed, the level of the cross-talk interference must be lower than approximately -30 dB.
Thus, for example, in the case of azimu-th recording shown by curve C2 in Fig. 2, the level oE the cross-talk interEerence is lower than -30 dB when the recording frequency is in the range of approximately 1 MHz to 25 MHz. However, the digitized video signal converted from the analog video signal includes many components wi-th frequencies less than 1 M~z.
Thus, in accordance with another aspect oE this inven-tion, the occurrence of low frequency signal components of the digitized video signal is reduced so as to subs-tan-tially reduce cross-talk interference which cannot satisfactorily be eliminated by means of azimuth loss.
In particular, the present invention utilizes a code conversion system in which the digitized video signal is code \
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eonverted to eliminate or at least substantially reduce such low frequency eomponents in the digitized signal. Various types of code conversion systems are kno~ in the ar;t. For eY~ample, if the original digitized signal is an NRZ (non-return-to-zero) signal (Fig. 4A), it may be code converted to, for example, a bi-phase code signal ~Fig. ~B), a Miller code signal (Fig. 4C) or an~l2 or modified Miller code signal (Fig.
~D), the frequency speetra of such signals being shown in the graph of Fig. 5, respectively. In the graphical diagram of Fig. S, r represents the bit period, fs represents -the -transmitting frequency (that is, ~he recording bit ra-te), and fn represents the Nyqulst frequency. It should be appreciated that when the digitized signal is converted from the analog signal, it is in parallel form. However, upon reeording, the digitized signal i.s eonverted from parallel form to serial form and the transmitting frequeney fs is the Erequeney of the serial digitized signal. It should further be appreeiated from Fig. 5 that the above eode eonversion systems, that is, bi-phase, Miller and M2, reduce the low frequeney eomponents of the digit:ized signal in comparison to the original NRZ dlgitized signal (Fig. ~A).
In aecordanee with another eode eonversion sys-tem, the digitized signal is eode eonverted in an 8--to-10 code eonversion process, that is, a digitized signal comprised of 8-bit words is converted to a digitized signal comprised of 10-bit words. The broken line in Fig. 6 represents the theoretieal frequency distribution with such 8-to-10 conversion proeess and the solid line represents the actual frequency distribution thereof. Pr~ferably, the block coding is such 2;~

that 28 codes whose DC levels are close ~o zero are selected from 2~ codes of 13-bi words and arranged to have one-to-one correspondence to the original 8-bit codes, as specifically disclosed in de~ail in Patent Application Serial No~ 355,345 file~ July 23, 1980, having a common assignee herewith. By means of this process, the DC level of ~he recorde~ signal is made as close ~o zero as possible, that is; ~D" and "1" bits alternate with each o~her as much as possible. Thus, for example, if f5 equals 38.4 MHz, as shown in Fig. 6, the lower cut-off frequency at which the frequency spectrum is evenly divided in hal~ is approximately 1.3 MHz, and in the frequency range lower than this cut-off frequency the frequency spectrum falls sharply. In this manner, the occurrence of low frequency components of ~he digitized slgnal, that is, components having a frequency below 1.3 MHz which result in the level of cross-talk interference being above -30 dB lFig.
2), is substantially reduced. ~hus, the azimuth loss La is i~ubstantially increased so as ~o more effectively reduce cros5-talk interference from adjacent tracks. In this manner, high density recording is achieved while reproduced digital signals from the recorded ~racks have a high S/N ratio.
There will now be described an apparatus according to this invention for performing the above--described method of recording a digitized video signal in a plurality of parallel tracks extending obliquely on the magnetic tape without guard bands between at least some of the adjacen~ track~ and with the digitized video signal in some of the Darallel tracks being recorded with an azimuth angle which is different from ~he azimuth angle in other ones of the parallel tracks.

,;'-' ''`

.

~2;2~

However, in order to facilitate an better understandi.ng of this aspect o:E the present invention, there will Eirst be described the conditions for digi-tal recording oE, Eor example, an NTSC
color video signal.
The NTSC system color video signal is desirably digitized with the following conditions being established:
1. Since one frame comprises 525 lines, the number o:E lines selected for a first (third) and a second (Eourth) field are 262 and 263, respec-tively. In -the firs-t field, a vertical synchronizing pulse and a horizontal synchronizing pulse are in phase wi-th each other, and the field in whi.ch they are out of phase is considered the second field.
2. The number of sampled picture elemen-ts in each horizon-tal period (H) varies with the sampling frequency (Es) employed. Since the color sub-carrier frequency (fsc) is 455/2 times the horizontal frequency (fH), the numbers oE
sampled picture elements in one horizontal peri.od are as shown in the below Table 1 in the case of fs = 3fsc and in the case of Es = 4fsc Table 1 E
s Even line Odd line Odd frame 682 5~3 3fsc Even frame 633 6~2 Odd frame 910 910 sc Even frame 910 910 Apparatus for performing the previously-described recording arrangement according to the present invention will hereinafter be described wi-th reference to a recording section (Fig. 7) and a playback or reproducing section (Fig. ~) of a digital VTR which will now be described in greater detail. In the digital VTR, a digitiæed video signal is recorded by a rotary head assembly (Fig. 10) in parallel tracks extending obliquely on a magnetic -tape 3 (Fig. 11).
Since the transmitting bit ra-te oF the digital video signal :is high, as previously discussed, four rotary heads lA, lB, lC and lD (Fig. 9) are disposed in close proximi-ty -to each other, and the digitized video signal of one field is distributed -through four channels to such heads and recorded on the magnetic tape in four parallel tracks.
Referring in detail to Fig. 7, it will be seen that an NTSC color video signal to be recorded is applied through an input terminal 11 to an input processor 12. The input processor 12 comprises a clamp circuit and a synchronizing and burst signal separator and supplies the effective or video informatlon portion of the color video signal to an A/D
converter circuit 13. A synchronizing signal and a burs-t signal separated from the color video signal by processor 12 are applied to a master clock generator 21 which is desirably of PLL (phase-locked loop) construction. The master clock generatOr 21 generates clock pulses of the sampling frequency, for example, 4fsc or 4 times the frequency of the burst signal.
The clock pulses from generator 21 and the synchronizing signal are applied to a control signal generator 22 which produces various kinds of timing pulses, identifying signals (ID) for 2~'9 identifying lines, fields/ frames and tracks, and a control signal, such as, a train of sampling pulses.
The A/D converter circuit 13 generally cornprises a sample-and-hold circuit and an A/D conver-ter for conver-ting each sampled output to an 8-bit code which is supplied, in parallel form, to an interface 14. The duration or period of one line (lH) of the NTSC color video signal is 63.5~s and a blanking period therein is 11.1~ s. Accordingly, the period of the effective vldeo region or portion is 52.4~ s.
When the sampling frequency is 4fsc = X2 55 fH~ where fH
is the horizontal frequency, the number of samples in one horizontal period is 910. Further, the number of samples in the effective video region or oortion is 768 samples, as shown in Fig. 12. In consideration of the division oE the video information to be recorded into four channels, the number of effective vldeo samples is selected to be 768 per line or horizontal period with 192 samples being assigned to each channel. In Fig. 12, HD represents the horizontal synchronizing signal and BS represents the burs-t slgnal.
The number of lines forming one field is 262.5H, with a vertical synchronizing period and an equalizing pulse period accounting for 10.5H. Since test signals VIT and VIR
are inserted in the vertical blan~;ing period, they are also regarded as effective video signals. Thus, the number of effective video lines in one field period is selec-ted to be 252.
In other words, an effec-tive frame is selected and may be arranged, for example, so that the first or odd field thereof includes video information in lines 12 263 and the second or even field there~f includes video information in lines 274-525.

~ ~2~9 In this manner, each of the odd and even fields of each frame includes 252 field lines of video information.
The digitized effective video region of -the color video signal is divided by interface 1~ of the digi-tal VTR into four channels. For example, with 768 samples per line, data corresponding to samples (4n-~1) are assigned -to channel A, data corresponding to samples (4n-~2) are assigned to channel B, data corresponding to samples (~n+3) are assigned to channel C, and data corresponding to samples (4n-~4) are assigned to channel D. The da-ta of the four channels are processed in the same manner and only one channel will be described. The data in any one of the channels, for example, channel A, is derived as a record signal for head lA after being applied, in se~uence, to a time base compression circuit 15A, an error correcting or controi encoder 16A, a recording processor 17A and a recording amplifier 18A. The recording amplifiers 18A, 18B, 18C and 18D are connected bv way of a rotary transformer (not shown) to rotary heads lA, lB, lC
and lD, respectively, disposed in close proximity to each other.
The code arrangement of each of the recorded si.gnals respectively provided at heads lA to lD will now be described with re:Eerence to Fig. 14. As there shown, a sub-block SB of the coded digiti~ed signal is composed of 105 samples (840 bits) .in which a block synchronizing signal (SYNC) of three samples ~24 bits), an identifying (ID) and address (AD) signal of two samples (16 bits), information data of 96 samples (768 bits) and CRC (Cyclic Redundancy Check) code of four samples (32 bits) ~822(1 ~

are arranged one after another. The data of one line or horizontal period of the color video signal comprises 192 samples per channel, as previously mentioned, and these samples are divided into two sub-blocks, that is, there are two sub-blocks for each line of each channel, with 96 samples for each sub-block. In other words, each sub-block SB includes data for one-eighth of a line. The block synchronizing signal is used for identlfying the beginning of a sub-bloc]c, whereupon the identifying and address signals, the information da-ta and/or CRC code can be extracted. The identifying signals ID
indicate the channel (track), the frame, the field and the line to which the information data of the sub-block belongs, and the address signal AD represents the address of the respective sub-block. The CRC code is used for the detection of an e~rror in the information data of the respective sub-block.
~ Fig. 13 shows the code arrangement for one field in one channel. In Fig. 13, each reference character S~ 572) indicates one sub-block, with two sub-blocks making up one block or line. Since the effective video region of one field is comprised of 252 lines, as mentioned previously, the data of 252 blocks (50~ sub-blocks) exist in one field.
The video information data of a particular field are sequentially arranged in a 21 x 12 matrix form. Parity data are also provided in connection with the horizontal and vertical directions, respectively, of -the video information data in the matrix. ~ore particularly, on Fig. 13, the parity data for the horizontal direction is shown positioned in the thirteenth column of blocks, and the parity data for the 22~

vertical direction is positioned in the twenty-second row at the bottom. In the thirteen-th column of blocks at the twenty-second row is disposed the vertical parity data for the horizontal pari-ty data. The parity data for the horizontal direction is formed in three ways by 12 sub-blocks respectively taken out of the 12 blocks forming one row of the matrix. In the first row, for example, parity data SB25 is formed by the modulo 2 addition:

[SBl] ~ [SB3] ~ ~SB5] ~ ...... ~ [SB23] = [SB25] .

In the above, [SBi] means only the data in the respecti.ve sub bloclc SBi. In this case, samples belonging -to respec-tive ones of the 12 sub-blocks are each calculated in a parallel, 8-bit form. Similarly, by the modulo 2 addition:

~ [SB2] ~ [SB4] ~ [SB6] ~ ...... ~ [SB24] = [SB26]

parity data [SB26] is formed. The parity data is similarly formed for each of the second to twenty-first rows in the horizontal direction. Enhancement of the error correcting ability results from the fact that parity data is not formed merely by the data of the 24 sub-blocks included in a row, but is formed by the data of 12 sub-blocks positioned at intervals of two sub-blocks in the row.
The parity data for the vertical direction is formed by the data of 21 sub-blocks in each of the first to thirteen columns of blocks. In the first column, parity data [SB547] is formed by the modulo 2 addition:

[SBl] ~ [SB27] ~ ~SB53] ~ .... ..[SB521] = [SB547].

-2~-In this case, samples belonging -to each one of the 21 sub-blocks are calculated in a parallel 8-bit form.
Accordingly, these parity data comprise 105 samples as is also the case with the video data sub-blocks. In the case of transmitting the digitized signal of one field of the above matrix arrangement (22 x 13) as a series of first, second, third, ... twenty-second rows in sequence, since 13 blocks correspond to the length of 12H, a period oE 12 x 22 =
264H is needed for transmitting the digital signal of one field. In other words, since the number of samples in each sub-block SB is 105 and the number of sub-blocks per field in each channel is 572, the number of samples per channel for each Eield ls 105 x 572 = 60,060 samples. Fur-ther, since -there are 4 channels and 910 samples per line, the number of horizontal periods needed for transmitting the video signal of one fteld is (60,060 x 4)/910 = 264H.
Incidentally, if the VTR is of the C-format type, and thus employs an au~iliary head for recording and reproduci~g one part of the vertical blanking period in one field, then a duration of only about 250H can be recorded with a video head. In accordance with the present invention, a duration of 246H, leaving a margin of several H's, has to be recorded in each track, that is, the period of 264H of data to be transmitted is time-base-compressed (with a compression ratio Rt of 41/44) to a period a duration of 246H. Further, a pre-a~ble signal and post-amble signal, each having the transmitting bi-t fre~uency, are inserted at the beginning and the terminating end of the record signal of one field having t~

zz~
the period of 264H. ^~
The time base compression circuit 15 in Fig. 1 compresses the video data with the above-noted compression ratio 41/44 and provides a data blanking period in which the block synchronizing signal, the identifying and address signals and the C~C code are inserted for each sub-block of video data of 96 samples, and at the same time, sets up data blanking periods in which the blocks of the parity data are inserted. The parity data for the horizontal and vertical directions and the CRC code of each sub-block are generated by the error control encoder 16. The block synchronizing signal (SYNC) and the identiEying ~ID) and address (AD) signals are added to the video data in the recording processor 17. The address signal AD represents the previously-noted number (i) of the sub-block. Further, in the recording processor 17 th,ere is provided an encoder of the block coding type which converts the number of bits of one sample from 8 to 10, and a parallel-to-serial converter for serialiæing the parallel 10-bit code. As disclosed in detail in the aforementioned Patent Application Serial No. 365,345, filed July 23, 1980 and having a common assignee herewith, the block coding is such that 28 codes whose DC levels are close to ero are selected from 21 codes of 10-bit words and arranged to have one-to--one correspondence to the original 8-bit codes. By means oE the oregoing, the DC level of the recorded signal is made as close to zero as possible, that is, "0" and "1" alternate with each other as much as possible. Such block coding is employed for preventing degradation of the transmitting waveform on the playback side by substantial DC free transmission. It may also be possible to achieve the same .. ...

results by employing a scramble system utilizing the so-called M-sequence which is substantially random in place of the block coding. It should be appreciated that by means of such code conversioll, the low frequency signal componen~s of the digital video signal are substantially reduced so that, for example, only signal components with frequencies higher than approximately 1.3 MHz are produced, as previously described in regard to Fig. 6. The recording processor 17 converts the code converted digital signal from parallel to serial form and then transmits the sub-blocks sequentially to the respective heads. In the case where each sample comprises 8 bits, the transmitting bit rate per channel, after converting the above 8-bit code to the 10-bi~ code, is-as follows:

(4fsc) x 8 x l4 x 4~4 x 18 ~ 38.4 Mb/sec.

This, of course, is the previously-described frequency f5 in Fig. 6.
The sexially arranged digital signals in each channel are respectively supplied through a recording amplifier 18 to respective rotary maynetic heads lA to lD, which are arranged as shown in Figs. 9 and 10. In particular, each of heads lA to lD has a height selected equal to the track width W.
Further, heads lA and lC are mounted on a rotary drum 5 and aligned in the vertical direction~ith a distance W therebetween, and the other heads lB and lD ar~ also mounted on rotary drum 5 and al~gned in the vertical direction with a distance W there-between. Heads lA to lD are arrangedin close proximity-to one ~ ~Z~19 another so that, for example, head lB (lC) is positloned in the vertical direc-tion between heads lA (lB) and lC (lD).
Further, heads lA and lC are selected to have the same azimu-th angle ~/2, for example,7 in one direction, and heads lB and lD
are selected to have the same azimu-th angle ~/2, for example, 7 in the direction opposite -to -tha-t of heads lA and lC. In this manner, the differential azimuth angle ~d between adjacent tracks is 1~.
Ileads lA to lD are rota-ted together with rotary drum 5 .in synchronism with the color video signal a-t the :Ee.ild frequency, and a magnetic tape 3 con-tacts the peripheral surfaces of heads lA to lD and rotary drum 5 over an angular range of abut 360 in a slant omega (JQ) configuration, and the tape is driven at a constant speed. Accordingly, as shown in Fig. 11, the digitized signals from channels A to D are respectively recorded on tape 3 by heads lA to lD in tracks 2A
to 2D, respectively, each track corresponding to one field.
A control trac]c ~ is also formed at the lower longitudinal edge of tape 3. In this case, the distance W between respective ones of the heads lA to lD is equal to the track width W, so that adjacent tracks 2A to 2D contact each other a-t the longitudinal edges thereof without any guard bands therebetween.
Further, if the rotary radius of each of heads lA -to lD and -the speed of tape 3 are suitably selected, track 2A of each field may contact track 2D of the following field at the respective longitudinal edges thereof, as shown in Fig. 11. Further, since the azimuth angles of the heads are alternately opposed to one another, the azimuth angles of tracks 2A to 2D are also alternately opposed to each other so as to minimize cross-talk 2~
i interference between adjacent tracks.
In the reproducing or playback por-tlon of -the digi-tal VTR, as shown in Fig. 8, the four channels o;E
reproduced signals are derived from reproducing heads lA to lD which scan tracks 2A -to 2D, respectively, corresponding thereto, and are applied through playback amplifiers 31A -to 31D to respective waveform shaping circuits (no-t shown).
Each of the waveform shaping circuits ~includes a playback equallzer Eor increasing the high-frequency component of the reproduced signal and shapes the reproduced signal to a clear pulse signal. Further, each waveform shaping circuit ex-trac-ts a reproducing bit clock synchronized with the pre-amble signal and supplies the reproducing bit clock -to respective playback processors 32A to 32D -together with the data. In each o-f playback processors 3~A to 32D, the serial data is converted to parallel form, the block synchronizing signal is extracted, the data is separated from the block synchronizing signal and from the ID, AD and CRC codes or signals, and further, block decoding or 10-bit -to 8-bit conversion is performed. The resulting data is applied to time base correctors 33A to 33D, respectively, in which time base errors (or axis -Eluc-tuations) ~re removed Erom the data. Each of time base correctors 33A
to 33D iS provided with, for example, four memories, in which reproduced data are sequentially written by clock pulses synchronized with the reproduced data, and the data are sequentially read out from the memories, by reference clock pulses. When the reading operation is likely to get ahead of the writing operation, the memory from which the data has just been read is read again.

The data of each channel is provided from the respective ones of the time base correctors 33A to 33D to respective error correcting decoders 34A to 34D. Each error correcting decoder 34A to 34D includes error detecting and correcting circuits using CRC, horizontal and vertical parities~, a field memory and so on. In particular, each error correcting decoder includes a field memory, and da-ta is written in-to each field memory a-t every sub-bloc]~ SB in response to, for example, the respective address signal AD -there-of. At this time, any error in the data is corrected for every sub~-bloc]c SB of information by -the CRC code and horizontal and vertical parity da-ta. If the error is too great to be corrected by the CRC code and parity data, -the writing in of data of that sub-block SB in the field memory is not performed, and instead, data from the previous field is read out again.
The data from error correcting decoders 34A to 34D
is supplied to respective time base expander circuits 35A to 35D, which returns the data to the original transmitting rate and then applies the data to a common interface 36. I'he i.nterface 36 serves to return the reproduced data of the four channels into a single channel which includes a D/A
converter circuit 37 for conversion oE the data into analog Eorm.
The output from D/A converter circuit 37 is applied to an output processor 38, from which a reproduced color video signal is provided at an output terminal 39. An external reference signal may be supplied to a mas-ter clock generator (not shown), from which clock pulses and a reference 8~

sync..ronizing signal are provided ~o a control signal generator (not shown). The cvn~rol signal genera~or provides control signals synchronized with the external reference signal, such as, varlous ~iming pulses, identifying signals ~or the line~
field and frame, and sample clock pulses. In the reproducing section,~ ~he pxocessing of the signals from heads lA to lD
to the input sides of time base correctors 33A to 33D is timed by ~he clock pulse extracted from the reproduced data, whereas.the processing of the signals from the output sides of the time base correctors 33A to 33D to ~he output terminal 39 is timed by ~he clock pulse from the master clock generakor.
The above recording and reproducing sections shown in Figs~ 7 and 8 are d~scl.osed more particularly in Patent Applicat~on Serial No. 362,045, filed October 9, 1980, having a common assignee herewithO
It should be appreciated that th~ method and apparatus for recording a video signal according to this invention,. as described above, provides that a digi.tized video signal is recorded in parallel tracks with a high recording density in such a manner so as to reduce the tape consumption, resulting in longer periods of recording being possible with a given leng~h of magnetic tape. Further, because the digitized video signal is recorded in parallel tracks without guard bands between adjacent tracks, the tracks are wider so as to increase the S/N ratio. Further, since more information can be recorded on the wider tracks, the recording density on the ta~e can be increased. In ~35-addition, because of -the more efficient utilization of tape by providing wider tracks, there exists a larger tolerance for any tracking er.ror during the reproduction operation.
Since a multi-head apparatus is provided, i-t also may be possible during the reproduction opera-tion to de-tect and correct any tracking error by means of the phase difference between the outputs from, for example, heads lA and lB. It should be appreciated that al.though the presen-t inven-tion has been described in the normal mode of operation, o-ther special reproducing modes may be utilized with this inven-tion, for example, a search mode,in which -the heads scan the tracks when the relative speed between the heads and the tracks is greater -than that for normal recording. Thus, by iden-tifying the channel with the identifying qignal ID, reproduction during such search mode can be carried out even when, for e~ample, head lA, scans track 2C.
~ Although one embodiment of the present invention ¦ has been described above, it should be appreciated that other embodiments within the scope of this inven-tion can be provided.
E`or example, although the digitized video signal was d:ivided into Eour channels and the signal of one field of video inEorma-tion was recorded in four tracks 2A to 2D, the digitized video si~nal may be divided into an odd number of channels, for example, three channels. In such case, -three recording (reproducing) heads are provided, each associa-ted with one of the channels, so that the three heads simultaneously scan tracks 2A to 2C, respectively, to record one field of video information, as shown in FigO 15. In such case, a ~ guard band GB is form~d after every -three sequential tracks I

~22~9 2A to 2C so as to separate each field of video informa-tion on tape 3. However, it shoilld be appreciated -that the azimuth angles in adjacent tracks without guard bands Gs therebetween are different. For example, it may be sufficient for each center track 2B to have the digitized video signal recorded therein with a first azimuth angle and the remaining two tracks 2A and 2C having a digitized video signal recorded thereirl with a second azimuth angle which is different from the first azimuth angle.
E`urther, although it is preferable that the low frequency signal components of the digitized video signal be attenuated by the aforementioned i3-to-10 conversion system, it may be the case that the cross-talk interference between tracks at the outputs of reproduci.ng amplifiers 31A to 31D
is smaller than a predetermined vaiue. In such case, an NRZ
re,cordi.n~ partial response detecting gystem, which will attenuate low frequency signal components in the reproducing section, may be sufficlent to provide a sa-tisfacotry S/N ratio.
Further, it should be appreciated that although a magnetic tape 3 has been utilized in -the preferrecl embodiment of this invention, it may be possible to use a magne-tic disc, magnetic drum or the like.
Having described specific preferred embodimen-ts of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skillecl in -the art without departing from the scope or spirit of -the invention as defined in the appended claims.

Claims (16)

1. Apparatus for recording a video signal on a magnetic tape comprising:
means for converting the video signal into digital form;
means for distributing respective portions of the digitized video signal to at least two channels, each of said at least two channels including code converting means for code converting the respective portions of said digitized video signal distributed to the respective channel so as to reduce low frequency components of said digitized video signal; and means for recording the respective portions of said digitized video signal in a plurality of parallel tracks extending obliquely on said magnetic tape without guard bands between at least some adjacent ones of the parallel tracks and with said portions of the digitized video signal in adjacent ones of the parallel tracks without guard bands therebetween being recorded with different azimuth angles.

2. Apparatus according to claim 1; in which said video signal is a color video signal and said means for converting includes means for sampling said color video signal at a fre-quency which is at least three times the color sub-carrier frequency of the color video signal and analog-to-digital con-verting means for converting the sampled color video signal into digitized form.

3. Apparatus according to claim 2; in which said means for distributing includes interface means for distributing digitized samples of the digitized color video signal from said analog-to-digital converting means sequentially to said at least two channels.

4. Apparatus according to claim 1; in which each of said channels includes time base compression means supplied with respective portions of said digitized video signal from said means for distributing for compressing said respective portions supplied thereto; error control encoding means supplied with said respective portions from said time base compression means for generating error control data from said respective portions supplied thereto and for adding said error control data to the digitized video signal comprised of said respective portions; and recording processor means for adding synchronizing, identifying and address signals to said digitized video signal comprised of said respective portions from said erorr control encoding means; and said means for recording includes transducer means associated with each channel for recording the output from the respective recording processor means for each channel in one of said plurality of parallel tracks.

5. Apparatus according to claim 4; including four channels and in which said means for recording includes four transducers, each associated with a respective one of said four channels for recording the output from the recording processor means of the respective channel in one of said plurality of parallel tracks, with the digitized video signal in alternate ones of said parallel tracks being recorded with an azimuth angle which is different from the azimuth angle in the remaining alternate ones of the parallel tracks and without any guard bands between any adjacent ones of said parallel tracks.

6. Apparatus according to claim 5; further including a rotary drum assembly adapted for rotatable movement, and in which said four transducers are secured to said rotary drum assembly and adapted to rotate therewith, a first set of two of said transducers having an air gap with a first azimuth angle and separated by the width of one of said parallel tracks in the vertical direction of said guide drum assembly, and a second set of the other two of said transducers having an air gap with a second azimuth angle different from said first azimuth angle and separated by the width of one of said parallel tracks in the vertical direction of said guide drum assembly, with the vertical position of one of said transducers of said first set corresponding to a position between said two transducers of said second set and with the vertical position of one of said transducers of said second set corresponding to a position between said two transducers of said first set.

7. Apparatus according to claim 1; in which said digitized video signal is comprised of a plurality of 8-bit words and each of said code converting means converts each of said 8-bit words to a respective 10-bit word from a 10-bit word code.

8. Apparatus according to claim 1; in which each of said code converting means substantially eliminates components of said digitized video signal with frequencies lower than approximately 1 MHz.

9. A method of recording a video signal on a magnetic tape comprising the steps of:
converting the video signal into digital form;
distributing respective portions of the digitized video signal to at least two channels;
code converting the respective portions of said digitized video signal distributed to each channel so as to reduce low frequency components of said digitized video signal;
and recording the respective portions of said digitized video signal in a plurality of parallel tracks extending obliquely on said magnetic tape without guard bands between at least some adjacent ones of the parallel tracks and with said portions of the digitized video signal in adjacent ones of the parallel tracks without guard bands therebetween being recorded with different azimuth angles.

10. The method according to claim 9; in which said video signal is a color video signal and further including the step of sampling said color video signal at a frequency which is at least three times the color sub carrier frequency of the color video signal; and said step of converting includes the step of converting the sampled video signal into digital form.

11. The method according to claim 10; further including the steps of compressing said respective portions of said digitized video signal distributed to each of said at least two channels; generating error control data from said respective compressed portions in each channel; adding said error control data to the respective compressed portions in each channel;
and adding synchronizing, identifying and address signals to said respective compressed portions with said error control data in each channel, prior to said step of recording.

12. The method according to claim 9; in which said step of recording includes the step of recording the respective por-tions of said digitized video signal in said plurality of paral-lel tracks without guard bands between any adjacent ones of said parallel tracks and with the digitized video signal in alternate ones of said parallel tracks being recorded with a first azimuth angle and the digitized video signal in the remaining alternate ones of said parallel tracks being recorded with a second azimuth angle which is different from said first azimuth angle.

13. The method according to claim 12; in which said step of distributing distributes the respective portions of the digitized video signal to four channels and four sequential ones of said parallel tracks includes a field interval of video information.

14. A method of recording a video signal on a mag-netic tape comprising the steps of:
converting the video signal into digital form;
distributing respective portions of the digitized video signal to at least three channels, three sequential ones of said parallel tracks including a field interval of video information;
and recording the respective portions of said digitized video signal in a plurality of parallel tracks extending obliquely on said magnetic tape with a guard band provided after every three sequential ones of said parallel tracks and without any guard bands between adjacent ones of the remaining tracks, and with the digitized video signal in the center track of every three sequential ones of said parallel tracks corresponding to a field interval and being recorded with an azimuth angle which is different from the azimuth angle in the remaining ones of the parallel tracks.

15. The method according to claim 9; in which said video signal is comprised of a plurality of 8-bit words and said step of code converting includes the step of converting each of said 8-bit words to a respective 10-bit word from a 10-bit word code.

16. The method according to claim 9; in which said step of code converting substantially eliminates components of said digitized video signal with frequencies lower than approxi-mately 1 MHz.