FR2543775A1 - SYSTEM FOR RECORDING A DIVISION MULTIPLEXED VIDEO SIGNAL IN TIME - Google Patents

Abstract

THE RECORDING SYSTEM INCLUDES MEANS 11-31 FOR GENERATING MULTIPLEX VIDEO SIGNALS BY TIME DIVISION, AND MEANS 34, 36-39 FOR FREQUENCY MODULATION. RECORDING MEANS 38, 40, 41A, 42A, 60A RECORD THE MODULATED FREQUENCY SIGNAL IN SUCH MANNER THAT THE CARRIER FREQUENCIES OF THE FREQUENCY MODULATED SIGNALS RECORDED ON TWO ADJACENT TRACKS DIFFER FROM ONE OF THE OTHER BY AN ODD MULTIPLE FROM 14 HORIZONTAL SCAN FREQUENCY.

Description

The present invention relates generally to systems

  recording apparatus for recording a time division multiplexed video signal and more particularly to a recording system which records a time division multiplexed video signal on a recording medium by forming tracks with a unit which is a natural multiple of a frame and in which one of two kinds of signals

  of compressed time-based color difference, trans-

  alternatively sequentially online for

  each period of horizontal scanning, a signal of syn-

  horizontal tracking and a compressed time-based luminance signal or an uncompressed time-based luminance signal corresponding to a horizontal scan period are time-division multiplexed within a horizontal scan period in

  the video signal multiplexed by division in time.

  For the recording of a video signal, it is known

  the system of recording and reproduction azimuthal.

  In this system, the video signal is frequency modulated and a frequency modulated video signal is recorded on a magnetic recording medium, for example

  by forming tracks on the recording medium.

  To improve the utilization efficiency of the support of

  recording, it is conventional to record mutually adjacent tracks by means of heads having air gaps oriented in angular directions of different azimuths, leaving or not leaving

  narrow guard strips between adjacent tracks.

  However, to reduce in a large proportion the noise resulting from crosstalk due to the adjacent track

  in this azimuth recording and reproduction system

  the recording tape must be chosen in such a way that the frequency-modulated video signal occupies a high frequency range in which the effect of

  Azymutal loss by misalignment of azimuth is considerable.

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  In addition, it is essential to use the frame correlation by recording the frequency-modulated video signal such that the positions in which a horizontal sync signal is recorded on the mutually adjacent tracks are aligned in the direction of the width of the frame. the track This alignment of

  positions when recording the synchronization signal

  horizontal alignment is sometimes called H. alignment.

  The reason for this provision is the following:

  The noise that occurs in the demodulated signal when noise is mixed in the modulated video signal

  frequency is what is known as the triangular noise

  The suppression of this noise in the demodulated signal therefore has a great importance for the noise whose frequency is close to the carrier frequency and, on the other hand, is of less importance when the

  noise frequency deviates from the carrier frequency.

  On the other hand, there is virtually no azimuthal azimuthal loss effect for the signal in the low frequency range. As a result, the frequency modulated component that has been modulated by the horizontal synchronization and that exists within the low frequency range of the modulated video signal in-frequency is reproduced as crosstalk from the adjacent track The component

  Frequency Modulated which is reproduced as a diapha-

  from the adjacent track may be mixed within the frequency-modulated video signal reproduced from the desired track. When crosstalk from the adjacent track is mixed in the reproduced frequency modulated video signal, the component frequency modulated which is modulated by the video part and which exists in the high frequency range at a frequency close to the carrier frequency and the noise resulting from the crosstalk can be suppressed according to the principle of the triangular noise indicated above However , the frequency-modulated component

  which is modulated by the horizon synchronization signal

  tale has a frequency that is distinct from the carrier frequency and the noise result of crosstalk, in this case, can not be suppressed in a very effective manner. When reading a recording medium on which a track pattern has been recorded in which there is no alignment H, there is no correlation between the frequency-modulated video signal reproduced in FIG. from the desired track and the crosstalk component that is reproduced from the adjacent track and the carrier frequency of the reproduced frequency-modulated video signal and the carrier frequency of the crosstalk component are not generally close to one of the other In some cases, the carrier frequency of the frequency-modulated video signal reproduces and the carrier frequency of the crosstalk component are separated by a maximum frequency deviation. It is therefore impossible to suppress the noise level that is due. to the crosstalk that appears in the demodulated video signal,

  When registration takes place under conditions

  such that there is alignment H, that is to say that

  positions in which the synchronization signal

  horizontally is recorded on the adjacent tracks are aligned in the direction of the width of the track, the information that is very similar and are separated from each other by a frame are aligned in the mutually adjacent tracks In this case, the frequency of the frequency-modulated video signal that is reproduced

  from the desired track and the frequency of the

  In these conditions, a beat component of the difference between the two preceding frequencies becomes practically zero, and it is then possible to practically eliminate the noise due to the crosstalk Because, in particular, the frequency-modulated components which are modulated by the signal

  horizontal synchronization are recorded on each

  cune of the tracks with the same frequency, the noise due to the frequency modulated component which is modulated by the horizontal synchronization signal and is reproduced from the adjacent track as crosstalk can be eliminated. Under these conditions, to virtually eliminate the noise due to crosstalk from the adjacent runway

  in the recording and azimuth reproduction system

  Ideally, the recording should be such that there is an alignment H in the recorded track model. However, a recording apparatus and

  (a VCR) which is designed to perform

  kill the recording during a normal mode so that there is alignment H in the track pattern

  recorded on a magnetic tape can not be

  to kill the recording in such a way that there is

  H in the track pattern recorded on the magnetic tape during a long recording

  eg VCR time In this mode of recording

  the length of a drum and the number of frames recorded on a track remains the same as in the case of the normal recording mode, but the speed of movement of the magnetic tape is lower than the speed of the recording. the magnetic tape at the time of the normal recording mode and heads having a smaller track width than the track width of heads used at the time of the mode are used.

  normal recording, so that a recording

  longer than recording at the time of normal recording using the same

length of magnetic tape.

  When reading the magnetic tape below,

  a track pattern in which there is no line

  H, the reproduced image leaves much to be desired because of the interference of beat duration due to crosstalk from the adjacent track, as has been seen. So far, so-called carrier interleaving method F 1 has been used to visually reduce the crosstalk interference interference from the adjacent track. In this FM carrier interleaving method, the carrier frequencies FM between the mutually adjacent tracks are treated to differ from one another by an odd multiple of half the horizontal scan frequency As there is a linear correlation (correlation for each of the horizontal scan periods) in the video signal ,

  the process of nesting the FM carriers reduces visual-

  beating interference using the characteristic

  according to which the crosstalk phase is reversed for each horizontal scan period (1 H> when the FM carrier frequency of the FM video signal reproduced from the desired track and the FM carrier frequency of the crosstalk component from the adjacent track are processed to differ from each other by an odd multiple

  half of the horizontal scan frequency.

  For some time, as a result of rapid progress

  in the semiconductor technology, in

  precision and in the manufacture of mini-

  and in similar areas, it has become possible to significantly improve the image quality of the reproduced image obtained in the recording and reproducing apparatus and to reduce the

  overall dimensions and the weight of the recording apparatus

  and reproduction The reduction of dimensions

  of the tape cassette and the diameter of the drum.

  boun has a considerable influence on reducing the overall dimensions and decreasing the weight of the recording and reproducing apparatus and the speed of movement of the magnetic tape must be reduced to reserve the recording time wanted for a compact type magnetic tape cassette. To obtain a high-quality reproduced image in the recording and reproduction equipment, the size and weight of which are reduced

  registration and reproduction have been proposed.

  For example, a recording and reproducing apparatus has been proposed for subjecting two kinds of color difference signals, obtained

  by frequency demodulating the chroma carrier signal

  minance, to a time base compression, and also to submit to a time base compression

  the luminance signal In this recording device

  reproduction and reproduction, time-based signals

  award-winning are division multiplexed in time and the time division multiplexed video signal

  is modulated in frequency and recorded on the support of

  At the time of reproduction, an inverse signal processing of the signal processing performed at the time of recording is performed so as to obtain a reproduced composite color video signal which is suitable for the original standard system. registration and reproduction of this type is described for example in the French patent application

published under No. 2,115,443.

  In the recording and reproduction apparatus above, the difference in

  bands of the luminance signal and the difference signals

  color and the device intervenes in such a way that the color difference signals that have the band

  the narrowest are transmitted in the period of

  In other words, one of the color difference signals that is transmitted within a horizontal scanning period (1 H) is subjected to a time base compression corresponding to about 20% of In addition, for the band to be used effectively, the luminance signal is subjected to a time base compression of about 80% of 1 H, so as to occupy a band that is in the same range as the band. of the compressed time-based color difference signal, and is transmitted In addition, the two color difference signals are time-division multiplexed, as an in-line sequential signal, in which the two color difference signals are transmitted. alternately every 1 H, with the compressed time-based luminance signal The time-division multiplexed video signal is sent to a frequency modulator and an output signal emitted by the frequency modulator is t recorded on the media

  At the moment of reproduction, a processing

  signals from the processing of the signals actually

  killed at the time of registration is made to obtain

  a composite color video signal reproduced

  registration and reproduction used in this

  registration and reproduction is hereinafter referred to

  below by the term TIMEPLEX system.

  In the TIMEPLEX system which transmits the time division multiplexed video signal, there is no period during which the luminance signal and the

  signal of color difference are transmitted simultaneously

  In the case of the color video signal of the NTSC system and the color video signal of the PAL system, there may be mutual interference and moire between the luminance signal and the color difference signals, because the luminance signal and However, this reciprocal interference and moire do not occur in the TIMEPLEX system. In addition, the compressed time-based luminance signal and the color difference signal at the same time do not occur in the TIMEPLEX system. based

  of compressed time used in the TIMEPLEX com-

  both have a power distribution in which the energy is high in the low frequency range and low in the high frequency range. In other words, the compressed time-based luminance signal and the difference signal of the color-based compressed time take a signal format that is suitable for

  Frequency modulation It is therefore possible to obtain

  a strong modulation index and the signal-to-noise ratio can be significantly improved In addition, it is possible

  to effectively use the transmission band.

  However, the division multiplexed video signal

  in time obtained on the basis of the system TIMEPLEX com-

  takes the sequential color difference signal into

  line and therefore does not have a linear correlation.

  In these circumstances, even when the imbrication process

  FV carrier arrangement described above and making it possible to differ from the odd multiple of a half-frequency of horizontal scanning the carrier frequencies Flv

  in mutually adjacent tracks is applied directly

  In this case, there is still a problem that it is impossible to visually reduce the crosstalk interference due to crosstalk from the

adjacent track.

  The object of the invention is thus to enable the realization

  of a time-division multiplexed video signal recording system that is new

  effective and in which the difficulties referred to above

above were measured.

  Another object of the invention is to provide a recording system which records a video signal,

  multiplexed by division in time and modulates in frequency

  recording on a recording medium by forming tracks with a unit which is a natural multiple of a frame and in which one of the two kinds of compressed time-based color difference signals which are transmitted alternately sequentially in line at each horizontal scanning period, a horizontal synchronization signal and a compressed time-based luminance signal or an uncompressed time-based luminance signal corresponding to a horizontal scanning period are time division multiplexed in a period of horizontal scanning

  in the time division multiplexed video signal.

  The recording system according to the present invention

  makes the recording in such a way that the frequencies

  carrier frequencies of video signals multiplexed by

  frequency-modulated time division which are recorded

  on tracks mutually adjacent to each other on the recording medium differ from each other by an odd multiple of 1/4 of the frequency

horizontal scanning.

  In the recording system according to the invention, it is possible to invert the phase of a component of

  demodulated signal of a division multiplexed FM video signal

  over time that is reproduced from the tape

  neighbor and is mixed in the division multiplexed signal

  time that is reproduced from a track

  wanted both periods of horizontal scanning.

  Therefore, in the system according to the invention, it is possible

  to visually reduce crosstalk interference interference, both for the luminance

  and for the color difference signal.

  Various other features of the invention

  from the detailed description which follows.

  Embodiments of the subject of the invention are shown, by way of non-limiting example, in the appended drawing. Fig. 1A is a block diagram of a portion of an embodiment of a time division multiplexed video signal recording system.

according to the invention.

  Fig. 1B is a block diagram of a first embodiment of the remainder of the essential part of the system shown in Fig. 1A, and of a reproduction system. Figs 2 (A) to 2 (F) represent waveforms

  understanding the functioning of the system

  schematically in fig 1 A. Figs 3 (A) and 3 (B) each represent an example

  waveform of a color input video signal

  in the system shown diagrammatically in FIG. 1A and an exemplary waveform of a video signal

output from this system.

  FIG. 4 is a perspective view showing a situation in which a rotary drum and the

  analogous devices are in contact with a magnetic tape

  tick. Fig. 5 shows an example of a track pattern

  formed by the recording system according to the invention.

  Fig. 6 is a block diagram of a second embodiment of the remainder of the essential part of the system shown in Fig. 1A and a reproduction system. Fig. 7 is a circuit diagram showing an embodiment of a non-amplification circuit

  linear system shown diagrammatically in FIG 6.

  Fig. 8 shows an example of a characteristic of

  frequency of the circuit shown in FIG.

  As shown in Fig. 1A, a color video signal from the SECAM system, shown in Fig. 2A, is sent to

  an input terminal 11 This color video signal is applied

  low-pass filter 12, in which a luminance signal is separated, and is also sent to a

  decoder 13 in which a chromium carrier signal

  nance is separated and then demodulated as a difference signal

sequential color online.

  In the in-line sequential color difference signal, there is a predetermined difference between a DC current level bl of an achromatic color portion (unmodulated carrier portion) having a width of 4.9 juice and located in a rear bearing within a horizontal scanning period (1 H) in which a color difference signal (BY) is transmitted, and a DC level b 2 of a

  achromatic color part (non-modular carrier part

  lée) having a width of 4.9 ps and located in a bearing

  rearward within 1 H in which the dif-

  color (R Y) is transmitted, as indicated

  Fig. 2 (B). The reason for this is that a frequency of sub-

  chrominance carrier of the chromium carrier signal

  nance is 4.25 M Hz in the color difference signal transmission line (BY) and a chrominance subcarrier frequency of the chrominance carrier signal in the transmission line of the color difference signal (RY) is not 4.25 M Hz but 4.406 M Hz The sequential in-line color difference signal is subject to a DC level shift, so that the DC level of the color part The achromatic signal of one of the color difference signals coincides with the DC level of the achromatic color portion of the other color difference signal, before being sent to an analog-to-digital converter (AD) 15 by the color difference signal. intermediate of a low-pass filter 14 An output signal of the converter AN 15 is sent to a circuit

memory 16.

  On the other hand, the luminance signal is separated from the input color video signal of the SECAM system in the low-pass filter 12. This luminance signal is sent to a separation circuit 17 of the synchronization signal.

  in which a horizontal synchronization signal

  The horizontal synchronization signal is

  separate output signal of the signal separation circuit 17

  horizontal synchronization is sent to a

  18, the pulse signal from a low-pass filter 12 is also sent to an AN converter 19

  in which the luminance signal is subjected to a

  analog-digital version The output signal of the con-

  AN 19 is sent to the memory circuits 20 and 21 The memory circuits 16, 20 and 21 each consist of a random access memory (MEV) and an address counter The device 18 for generating control pulses emits different pulses control circuit and sends the control pulses to the converters AN 15 and 19.9 to the switching circuits 22, 25 and 27 and to the digital-to-analog conversion circuits (NA) 23 and 24. control pulses emits a write clock pulse and a read clock pulse, with a predetermined timing and with a repetition frequency

  predetermined, and sends these clock pulses to

  and in the memory circuits 16, 20 and 21. In other words, the control pulse forming device 18 sends an 8 M Hz write clock pulse, for example, to one circuits

  20, 21, so as to record in one of the cir-

  20 or 21, a luminance signal corresponding to

  is 1 hour long and is transmitted indoors

  a video duration of 52 juices At the same time, the

  The control pulse forming circuit 18 sends a read clock pulse of 10 M Hz, for example, to the other memory circuit 20 or 21 immediately after the transmission of a compressed time-based color difference signal. corresponding to 1 H (52 ps) has been performed, so as to read, in the other memory circuit 20 or 21, a luminance signal recorded in

  memory which corresponds to 1 H and has been transmitted 1 H aupa-

  The read clock pulse is sent to the other memory circuit 20 or 21 for a period which excludes from the duration of 1 H a serial transmission period in which the horizontal synchronization signal and the compressed time-based color difference are transmitted Reading and writing in the memory circuits 20 and 21 are performed alternately every 1 H In addition, the switching circuit 22 which is connected to the output sides of the memory circuits 20 and 21 is switched in response to a control pulse from the control pulse forming device 18 for selectively passing an output signal of the memory circuit 20 or 21 which performs the read operation. that a luminance signal which has undergone a time base compression of 4/5 is obtained intermittently from

  of the switching circuit 22 without loss of information.

  This compressed time-based luminance signal from the switching circuit 22 is subjected to a digital-to-analog conversion in the conversion circuit NA 23 and is converted into a signal shown in FIG. 2. On the other hand, the signal of color difference

  online sequential is subject to an analog-to-

  digital in the converter AN 15 before being sent to the memory circuit 16 The sequential in-line color difference signal which is transmitted in a video duration of 52 ps in 1 H (64 s) is written in the circuit

  memory 16 in response to a register clock pulse

  2 M Hz, for example, this enrollment clock pulse being received from the training device 18

  control pulses After a predetermined period of time

  (eg 1.6 ps) from the moment this operation

  Enrollment ration is completed, a color difference signal which has undergone a time base compression of 1/5 is read in the memory circuit 16 in response

  to a reading clock pulse of 10 M Hz, for example

  This read clock pulse from the control pulse forming device 18

  in this case, the duration of a reading is 10.4 ps.

  The compressed time-based in-line sequential color difference signal from the memory circuit 16 is digital-to-analog converted in the conversion circuit NA 24 and then sent to the

  terminal 25a of the switching circuit 25 A level of

  of the achromatic color part of the sequential online color difference signal, which was

  sampled and maintained in the device 18 of

  control pulses, is applied to a terminal 25 B of the switching circuit 25 The switching of the circuit

  switching 25 is controlled by a pulse of

  of the control pulse forming device 18, so that the switching circuit 25 is switched and connected to the terminal 25a from the end of the period during which the DC level (reference level

  colored) is applied to the ends of the terminal 25b.

  The switching circuit 25 therefore selectively produces a signal shown in Fig. 2 (C) in which the compressed time-based in-line sequential color difference signal of the conversion circuit 24 is division multiplexed in the time, immediately after the color reference level, and sends this signal

  selectively produced to the switching circuit

  27 by means of a low-pass filter 26.

  The conversion circuits NA 23 and 24 each comprise

  a lock gate and an associated NA converter.

  The switching circuit 27 receives the compressed time-based luminance signal shown in Fig. 2 (E) and derived from the conversion circuit NA 23 through

  a low-pass filter 28 Moreover, the switching circuit

  27 also receives a multiplexed signal comprising a horizontal sync signal having a width of about 4 ps, as shown in Fig. 2 (D) and a discrimination burst signal shown in Fig. 02 (F) and having a frequency of 1.6 M Hz for example This multiplexed signal is produced in the training device 18

  control pulses from the synchronization signal

  and the discrimination burst signal generated in the control pulse generating device 18 The discriminating burst signal

  nation is used to discriminate signals from different

  color difference (B-Y) and (R-Y) When a difference

  level of direct current between the color portion achro-

  in the color difference (RY) and (BY) signals is eliminated by moving the DC level of the achromatic color portion in one of the color difference signals so as to coincide with the DC level of the achromatic color part in the other color difference signal, and that the recording and reproduction takes place in a situation in which the difference in DC level is eliminated, discrimination must be made to determine that a obtained color difference signal is one of the two color difference signals, so as to obtain the original chrominance carrier signal by means of a single frequency modulator in the reproduction system. In other words , the difference in DC level between the achromatic color parts in the two color difference signals must be restored before the signal of porteu original chrominance can be obtained by the frequency modulator in the system

  In these circumstances, when recording

  and reproduction occur while the difference

  the DC level above is maintained, the burst signal of discrimination is not necessary

  since the discrimination information that allows the dis-

  between the two difference signals of

  is transmitted to them as a difference in current level

continued.

  Switching of the switching circuit 27 is

  This is caused by a pulse from the control pulse generating device 18. As a result, the switching circuit 27 outputs a multiplexed signal.

  division in the time in which the synchronization signal

  horizontal or multiplexed signal from the control pulse forming device 18, the output signal of the lowpass filter 26 and the output signal of the low-pass filter 28 are multiplexed by division in time in sequence with a duration In other words, for a duration of 1 h, the output signal of the switching circuit 27 is a time division multiplexed signal comprising the horizontal synchronization signal from the training device 18. control pulses, the output signal of the low-pass filter 26 and the signal of

  output of the low-pass fi lter 28 The synchronization signal

  horizontal direction and the discrimination burst signal generated in the control pulse generating device 18 are multiplexed in the multiplexed signal from the pulse generator 18

command.

  When a color video signal from the SECAM system having

  the shape of a color bar signal like the one shown in

  sensed in Fig. 3 (A) is sent to the input terminal 11, a video signal multiplexed by division in time,

  shown in Fig. 3 (B), is transmitted by the communication circuit

  As shown in FIG. 3 (B), a discriminating burst signal S is multiplexed with a signal

  horizontal synchronization H 2 every 1 H (64 us).

  In the time division multiplexed video signal represented by Fig. 3 (B), synchronization signals

  horizontal lines H 1 and H 2, levels L 1 and L 2 of

  color (the DC level of the

  achromatic color of the respective color difference signals), compressed time-based color difference (RY) signals C and (BY) C and a compressed time-based luminance signal YC are transmitted sequentially in line The time division multiplexed video signal shown in FIG.

  FIG. 3 (B) is passed through a circuit 29 of FIG.

  the signal supplied to the terminal 32 is sent to an automatic gain control circuit (AGC) shown in FIG. fig IB, and the signal level is set to one level

  predetermined by the AGC circuit 33.

  The video signal multiplexed by division in time

* which comes from the circuit (AGC) 33 is sent to a modula-

  frequency converter 34 and a recording circuit 35.

  Frequency modulator 34 frequency-modulates a carrier that has a carrier frequency ft when there is no input to the frequency modulator 34 and no frequency modulation by the division-multiplexed video signal in the frequency modulator 34. time from the circuit (AGC) 33, so that the carrier varies between a first

  predetermined frequency and a second predetermined frequency

  The carrier takes the first frequency when the carrier is frequency modulated by the sync peak level of the time division multiplexed video signal and takes the second predetermined frequency when the carrier is frequency modulated by the peak white level. The time divide multiplexed video signal A time dividing multiplexed FM video signal, provided by a frequency modulator 34, is sent to a frequency converter 36 in which a frequency conversion is performed in such a way that the a frequency component can be obtained (f + f) f being a first frequency c ol 02

  oscillation of a signal from an oscilla-

  The output signal of the frequency converter 36 is sent to a frequency converter 38 in which a frequency conversion is performed so that a frequency component fc + f 0) f 02 can be obtained. 02 6 as a second local oscillation frequency of a signal coming from a

local oscillator 39.

  The first local oscillation frequency f 01 and the second local oscillation frequency f 02 are chosen in such a way that the frequency difference

  (f 01 f 02) is an odd multiple of 1/4 of a frequency

  horizontal scanning time of the time division multiplexed input video signal In the example shown in FIG. 3 (B), the horizontal scanning frequency f H is equal to 15 625 K Hz. Under these conditions, the carrier frequency of the time division multiplexed FM video signal provided by the frequency converter 38 differs from the carrier frequency of the PM video signal

  multiplexed by time division, provided by the conversion

  frequency converter 34, a frequency difference (f 01 f 02) which is an odd multiple of 1/4 of the horizontal scanning frequency f H The time division multiplexed output FM video signal from the converter frequency 38 is sent to a circuit

  when the two frequencies of

  which differ from each other by an odd multiple of 1/4 of the horizontal scanning frequency f H are

  neighbors of each other and that the frequency conversion

  quence occurs only in a frequency converter.

  In a single stage, it is difficult to separate and filter the time-division multiplexed FM video signal of a desired carrier frequency in a filter circuit because the signal frequency

  division multiplexed FM video in time and frequency

  local oscillation are close to each other.

  This is the reason why frequency converters

  However, in principle, it is possible to send the local oscillation frequency (fo 01 f 02) to a single frequency converter and to obtain the division multiplexed video signal F 4. in time having the desired carrier frequency. A first time division multiplexed FM video signal having a carrier frequency of fc provided by the recording circuit 35 after having

  been subjected to signal processing such as an ampli-

  The invention is directed to a magnetic head 41a. A second time division multiplexed FM video signal having a carrier frequency that differs from the carrier frequency fc by an odd multiple of 1/4 of the frequency

  f horizontal scanning, provided by the recording circuit

  record 40, is sent to a magnetic head 42a.

  As shown in FIG. 4, the magnetic heads 41a and 42a are mounted on the plane of rotation of an upper rotary drum 56 at an angular distance of 1800

  from each other The magnetic heads 41a and 42 have

  air gaps oriented in different azimuths with respect to each other.

  is guided by guide pins 57 and 58 as indicated by

  4 and wraps obliquely around the upper rotary drum 56 and a lower fixed drum 59 on an angular sector of about 1800 along an

  guide strip of the magnetic tape which extends obli-

  on the lower fixed drum 59 The magnetic tape

  60 a is moved in a situation in which it is pinched between a capstan and a nip roller which are not shown in FIG. 4 In FIG. 4, the upper rotary drum 56 rotates in the opposite direction

clockwise.

  The magnetic heads 41a and 42a shown in FIG. 4, of a known video recorder with two rotating heads, produce video tracks t A1 at t A 11 and at 1 to t B 11 on the magnetic strip 60a, as shown in FIG. Fig. 5 These video tracks t 1 i t t Al and 1 at t B 11 have a track width TW and have an interval between tracks TP without guard band (or with an extremely narrow guard band). The video signal is multiplexed In fact, there is a thin recording superposition area on the track and the time dividing multiplexed video signal F 4 corresponding to a single video track. little more than one frame is recorded on a

  However, even in this case, the information provided

  video that are separated from each other by

  an interval of one frame are recorded in

  related to each other on the mutual tracks.

  The video tracks t A A 2 A t 9 o A

  of the magnetic tape 60a are formed by the head magn 6

  41 a and video tracks t BI Pt B 2 9 t B 3 o o t B 1 l

  of the magnetic strip 60a are formed by the magnetic head

  Under these conditions, between two adjacent video terminals formed on the magnetic tape 60a, the first time division multiplexed FM video signal is recorded by the magnetic head 41a on one of the two adjacent video tracks and the second time division multiplexed video signal is recorded by the magnetic head 42a on the other video track. The carrier frequencies F 4 in the two adjacent tracks therefore differ by an odd multiple of 1/4 of the frequency

f horizontal scanning.

  In FIG. 5, the magnetic strip 60 a is displaced in the direction of the arrow A. As is known, a track

  audio t 1 is formed by an audio head and a speech track

  T 2 is formed by a control head, at the same time

  video tracks described above.

  ticks 41a and 42a perform scanning in the direction of arrow B.

  The description below relates to the functioning

  a reproduction system that reproduces the time division multiplexed video signal that has been

  recorded under the conditions described above.

  Fig. 1B shows the recording of a signal

  recorded on a magnetic tape 60b by the same recording system as the magnetic tape 60a The first time division multiplexed FM video signal which is reproduced from the magnetic tape 60b by a magnetic head 41b which exhibits an air gap having

  the same azimuth angle as the air gap of the magnetic head

  4 is amplified to a predetermined level in a reproduction amplifier 43 and is then sent to a switching circuit 44. On the other hand, the second time division multiplexed FM video signal which is reproduced from the magnetic strip 60b by a magnetic head 42b which has a gap having

  the same azimuth angle as the air gap of the magnetic head

  that 42A is sent to a frequency converter 46

  through a reproduction amplifier 45

  frequency converter 46 performs a frequency conversion

  quence so that it gives a frequency component which is the sum of the carrier frequency (f Rc + f 01) f 02 J of the second time division multiplexed FM video signal and the second local oscillation frequency As a result, the time division multiplexed FM video signal provided by the frequency converter 46 has a carrier frequency of (f + 1). frequency converter 47 performs another frequency conversion to provide a frequency component which is the sum of the carrier frequency (fc + f 01) of the time division multiplexed FM video signal reproduced and supplied by the frequency converter 46 and the first local oscillation frequency f 1 provided by the local oscillating circuit 37 The multiplexed video signal

  by division in the reproduced time provided by the conversion

  frequency weaver 47 therefore has a frequency of

carrier f.

  The switching circuit 44 switches to alternately provide the passage of the video signal

  division multiplexed in time reproduced which pre-

  sense a carrier frequency of f and is provided by c the reproduction amplifier 43 and the video signal

  division multiplexed in time reproduced which pre-

  the carrier frequency of fc and is provided by the frequency converter 47, at each

  scanning a track, and produces a multi-

  plexed by division in the continuous reproduced time Ce

  division multiplexed video signal over time

  The continuous output provided by the switching circuit 44 is sent to a frequency demodulation circuit 48 in which a frequency demodulation is performed such that it gives the division multiplexed video signal in the reproduced time shown in FIG. 3 (B). ) To eliminate the frequency component (f 01 f 02) which is an odd multiple of 1/4 of the horizontal scanning period f H, the reproduced time division multiplexed video signal from the frequency demodulation circuit 48 is sent in a low-pass filter 49 and in a high-pass filter 50 to divide the frequency band into a range of low frequencies and

  a range of high frequencies The high frequency signal

  What happens from the high-pass filter 50 and which includes the frequency component (f 01 f 02) is sent to an addition circuit 52 via a delay circuit 51 of 2 H The high frequency signal which comes from the filter high pass 50 is also sent directly to the addition circuit 52. The delay circuit 51 of 2 H and the addition circuit 52 form a comb filter.

  the phases of the frequency components which are

  odd digits of 1/4 of scan frequency f H

  horizontal and are inside the high frequency signal

  As a result of the high pass filter 50 differing for each 2 H period, it is possible to obtain at the output of the addition circuit 52 a high frequency signal which has been removed from the frequency component (fol f 02 ) which is an odd multiple of 1/4 of the

  frequency f H horizontal scanning.

  The high frequency signal which has been removed from the frequency component (f 01 f 02) and supplied by the addition circuit 52, and a low frequency component supplied by the low pass filter 49 are sent.

  to a composition circuit 53 The compositing circuit

  53 produces a reproduced time division multiplexed video signal which has been removed from the parasitic frequency component (fo f 2) and this video signal

01 02

  division multiplexed in the reproduced time is sent to an output terminal 55 passing through a video signal output circuit 54. The time division multiplexed video signal reproduces and from the output terminal 55 is sent to a signal circuit. time base dilation (not shown) where the time base is expanded and returned to the initial time base and the time division multiplexed video signal

  reproduced is transformed into a luminance signal reproduced

  duit and into a sequential line color difference signal reproduces the color difference signal

  reproduced line sequential is then coded and trans-

  formed into a chrominance carrier signal of the desired standard system, and is then multiplexed with the reproduced luminance signal to provide a reproduced standard system color video signal as the color video signal shown in Fig. 3A, for example standard system color video signal is sent to a control display apparatus (not shown) and

  displayed as a reproduced color image.

  Although the crosstalk component from

  the adjacent track is reduced by the az

  mismatch by azimuth, the crosstalk component

  still remains in the division multiplexed FM video signal

  reproduced time from the switching circuit

  As has been seen, the two kinds of color difference signals are subjected to time base compression and sequentially transmitted online in the time division multiplexed video signal,

  so that there is no linear correlation (correlates

  for each duration of 1 h) and that there is a correction

  For these conditions, the period of the correlation N is not 1 / fH, but 2 / fH On the other hand, as we have seen, the difference between the

  Fi carrier frequencies in the two adjacent tracks

  is an odd multiple of f / 4, I 1 results in H the phase of the crosstalk component being inverted every other line and the interference of beat (noise)

  due to crosstalk can be reduced visually.

  The effect of the visual reduction of crosstalk interference due to crosstalk is obviously important for the portion of the luminance signal included in FIG.

  video signal multiplexed by time division, reproduced

  but the influence of the visual reduction of the inter-

  Crosstalk interference is also important for color difference (R-Y) signals

  and (B-Y) included in the multiplexed video signal

  in time, because the crosstalk beat time interference has a two-line shift ratio for the difference signals

of color (R Y) and (B-Y).

  The description below relates to a second

  embodiment of the recording system according to the invention shown in FIGS. 6 and 7 In FIG. 6, the parts which are identical to the parts already shown in FIG. 1B are designated by the same references and

  are not the subject of a new description In the

  case of FIG. 6, the time division multiplexed signal provided by the AGC circuit 33 is sent to

  a circuit 61 for forming a differential voltage.

  On the other hand, on the basis of a pulse which is in phase with the rotation phase of the magnetic heads 41a and 42a and is applied to an input terminal 62, a switching pulse forming circuit 63 produces a square wave whose period is equal to two track scan periods. This square wave which is produced by the switching pulse forming circuit 6 is sent as a switching pulse to the training circuit 61. The time division multiplexed input video signal is therefore added to a predetermined voltage at each scan period of a track and is sent to a frequency modulator 64.

  by the circuit 61 forming a different voltage

  Thus, for example, the sync peak level of the time division multiplexed video signal from the differential voltage forming circuit 61 is alternately shifted to

  up or down (increased and decreased) by the

  predetermined resolution above each scan period of a track (for example a frame). Under these conditions,

  between two adjacent frames, the peak level of syn-

  chronization differs from the predetermined tension.

  predetermined resolution is chosen such that the FM carrier frequency corresponding to the peak level of synchronizations within the time division multiplexed FM output video signal from the frequency modulator 64 differs by an odd multiple of 1 / 4 of the frequency f H of horizontal scanning between

two adjacent frames.

  Under these conditions, the first multi-frequency FM video signal

  time-division-keyed having the FM carrier frequency of fc and the second time-division multiplexed FM video signal having the FM carrier frequency which differs from the carrier frequency fc

  an odd multiple of ff / 4 are provided alternately

  by the frequency modulator 64 with a period equal to one scan period of a track (with a period of one frame in the case envisaged). The output FM video signal, multiplexed by time division, provided by the Frequency modulator 64 is sent to the recording circuits 35 and 40. The recording is thus performed in such a way that the FMI carrier frequencies of the time division multiplexed FM video signals are recorded on two adjacent tracks. of the magnetic tape 60 has different one by

  ratio to the other of an odd multiple of f H / 4.

  The following description relates to the functioning

  As shown in FIG. 6, the reproduced time division multiplexed video signal from the frequency demodulator 48 is supplied to a voltage difference compensation circuit 65 because the peak sync level of the

  division multiplexed video signal over time

  provided by the frequency demodulator 48 alternately up and down the predetermined voltage for each frame The voltage difference

  is eliminated in the compensation circuit 65 of diff 6

  in response to a pulse of

  tation (square wave) which is emitted by the switching pulse formation circuit 63 and has a period of

  It follows from this that a multi-purpose video signal

  plexed by division in the reproduced time and in which the synchronization peak level is set to a specific voltage, is obtained from the voltage difference compensation circuit 65 and is sent to the low pass filter 49 and the pass filter. high 50 The output signal of the high-pass filter 50 is sent to

  a nonlinear amplification circuit 66.

  The nonlinear amplification circuit 66 is

  truce for example as shown in Fig 7 As shown in Fig 7, an input terminal 70 is connected to the base of a transistor Q 1 NPN type via a capacitor Ct A point o s makes the connection between the collector of the transistor Q 1 and a collector resistor R 1 is connected to the cathode of a diode D and to the anode of a diode D 2 via a

  circuit comprising a capacitor C 2 and a resistor R 2.

  An anode of the diode D 1 and a cathode of the diode D 2 are connected together to a fixed terminal of a variable resistor VR The cursor of the variable resistor VR is

  connected to the base of an NPN-type transistor Q 2 through the

  A point o is the connection between the collector of transistor Q 2 and a collector resistor R is connected to an output terminal 71 via a capacitor C 4. R 4 and R 5 are resistances of

  polarization of the base for the transistor Q 1 and the resistors

  R 7 and R 8 are base biasing resistors for transistor Q 2 R resistors 6

  and R 9 are transmitter resistances for the transistors

  corresponding tors Q 1 and Q 2 In the nonlinear amplification circuit 66 described above, the output signal of the high-pass filter 50

  which is supplied to the input terminal 70 is sent to the

  sistor Q 1 via the capacitor C 1 o

  An amplified signal is provided by the collector of the

  Q 1 and is sent to the cathode of the diode D 1 and the anode of the diode D 2 through the circuit comprising the capacitor C 2 and the resistor R 2 A circuit constituted by the diodes D 1 and D 2 mounted in parallel exhibits high resistance when the level of the input signal is low and has low resistance when the level of the input signal is high. The variable resistor VR therefore provides a signal whose

  the attenuation depends on the level of the input signal.

  The parasitic frequency component which is a multi-

  odd pf of f H / 4 is mixed as crosstalk from

  of the track adjacent to the divide multiplexed video signal.

  in time reproduced increases markedly

  tionally to the tracking error of magnetic heads.

  ticks 41b and 42b relative to the desired video track.

  When the maximum tracking error is 10%,

  for example, the spurious component is less than

than 20 db.

  It is therefore possible to eliminate the above parasitic frequency component by setting the characteristic of the nonlinear amplification circuit 66 so as to increase the attenuation of a signal below

  db and to decrease the weakening of a signal

above 20 db.

  The constants of the circuit elements in the case of the nonlinear amplification circuit 66 shown in FIG. 7 are the following, for example when the

  source voltage Vcc is + 9 volts.

CAPACITORS

  C 1 = C 3 = C 4 = 47%; C 2 = 220 P F

RESISTANCE

  R 1 = R 9 = 1 Kfl; R 2 = 195 K; R 3 = 2.92 Ifl; R 4 = R 7 = 39 F R 5 = R 8 = 10 KL; R 6 = 470 L and VR = 4.7 Kfl Under these conditions, when the amplitude of the input signal applied to the input terminal 70 reaches a level

  maximum (the assumed maximum level is assumed -

  0 db), the nonlinear amplification circuit 66 has a frequency characteristic which is indicated by a

  curve I in FIG. 8 and sets the gain at 2 M Hz per unit.

  In addition, when the amplitude of the input signal applied to the input terminal 70 takes levels of 10 d B,

  d B and 30 d B, the non-amplification circuit

  linear 66 has frequency characteristics which are respectively indicated by the curves II, III and IV of FIG. 8 and reduces the gain when the level

input signal decreases.

  When the parasitic frequency component is multiplexed with the level signal higher than 20 d B, it is impossible to completely eliminate this parasitic frequency component. However, the existence of this parasitic frequency component does not pose any problem from the point of view. visual view The high frequency signal which is obtained from the collector of the transistor Q 2, in the nonlinear amplification circuit 66 shown

  in FIG. 7, is sent to the composition circuit 53, represented

  6, via the capacitor C 4 and the output terminal 71. The high frequency signal coming from the collector of the transistor Q 2 is therefore composed, in the composition circuit 52, with the bass signal.

  frequency from the low-pass filter 49.

  In this second embodiment of the invention, it is also possible to visually reduce the crosstalk interference due to crosstalk from the adjacent track, this crosstalk mixing with the time division multiplexed video signal. reproduced as in the case of the first embodiment described above. The present invention is not limited to the embodiments described above. Thus, for example, the luminance signal contained in the time dividing multiplexed input video signal may be a luminance signal at a time. uncompressed time base that has not undergone time base compression, the rate

  compression of the time base of the difference signals

  A color difference signal can still undergo base-time compression for about 20% of the duration of 1 H, and a signal of luminance that has not undergone time-base compression can be transmitted in the remainder of the time remaining In both cases, the image reproduced

  that is obtained will not be perfect, but the image reproduces

  In addition, the elements or signals which determine the oscillation frequencies of the frequency modulators 34 and 64 can be switched for each scan period of a track of the division multiplexed input video signal in the time of in such a way that one obtains alternately two carrier frequency species which differ from each other by an odd multiple of f H / 4 during each period

  In this case, it is not necessary to

  In addition, although not directly related to the present invention, the amplification circuit is linear 66 can be used instead of the comb filter constituted by the delay circuit 51 of 2 H, and by the addition circuit 53, and instead it is possible to use the comb filter instead of the amplification circuit

non linear 66.

  Moreover, the present invention can obviously be applied in the case where the recording is performed by transforming a color video signal of the NTSC system or a color video signal of the PAL system into a time division multiplexed video signal based on the

TIMEPLEX system.

  In addition, the present invention is not limited to the embodiments described and shown in detail

  many variations and modifications can be

  without departing from the purpose and framework of the invitation.

Claims (6)

  1 Recording system for recording   of a time division multiplexed video signal, said recording system comprising recording means for recording a signal on a track of a recording medium for each unit which is an integer multiple of a frame , characterized in that it comprises: means (11-31) for producing division multiplexed video signals in this time   making it possible to produce a video signal mu multiplexed by   vision in time in which one of the two species   of time-based color difference signals   awarded which are alternatively transmitted in a   online sequencing at each scan period   zontal, a horizontal synchronization signal and a corresponding compressed time-based luminance signal   at a horizontal scanning period or a light signal   * nancial time base of which a part of   the luminance information has been eliminated, are respec-   multiplexed by time division within the   during a period of horizontal scanning, and the means   (34, 36-39, 61, 63, 64) frequency modulation pro-   a frequency-modulated signal by frequency modulating   a carrier by the time division multiplexed video signal, said carrier having a carrier frequency which alternately takes one of two frequencies which differ from each other by an odd multiple of 1/4 of the horizontal scanning frequency for each of the units which is an integer multiple of a frame;   in that the means (38, 40, 41a, 42a, 60a) for recording   record the frequency modulated signal from the frequency modulation means on a track of a recording medium for each unit which is multiple   integer of a frame; and that the frequency-modulated signal   is recorded in such a way that the carrier frequencies of the frequency-modulated signals recorded on the   two adjacent tracks differ from one another   odd tip of 1/4 of the horizontal scan frequency-   2 Recording system according to the claim   1, characterized in that the frequency modulation means comprises a frequency modulator (34) frequency modulating the carrier by the time division multiplexed video signal and providing a first frequency modulated signal and means (3 G -39> of   frequency conversion circuit converting to frequency   quence the first signal modulated in frequency by a   frequency which is an odd multiple of 1/4 of the frequency   horizontal scanning and giving a second   frequency modulated signal; in that the means of recording   The recording includes two heads (41a, 42a) alternately scanning the recording medium for each unit which is an integer multiple of a frame; in that the first head (41a) receives the first frequency-modulated signal and records this first signal on the recording medium; and in that the second head   (42a) receives the second frequency modulated signal and   register this second signal on the recording medium.   3 Registration system according to the claim   2, characterized in that the means of the frequency conversion circuit comprise a first circuit   (36, 37) providing a component   health of frequency which is the sum or the difference of the   first signal modulated in frequency and a first frequency   local oscillation frequency, and a second frequency conversion circuit (38, 39) providing the sum or difference of a second local oscillation frequency which differs from the first local oscillation frequency by an odd multiple of 1 / 4 of the horizontal scan frequency and an output signal frequency   of the first frequency conversion circuit.   4 Registration system according to the   cation 1, characterized in that the modulation means   frequency means comprise means (61, 63) for   the DC level receiving the division multiplexed video signal over time to   the DC level of the multi-   plexed by time division up and down a predetermined voltage for each unit which is an integer multiple of a frame, and a frequency modulator (64) frequency modulating a carrier by the video signal multiplexed by division in time from the DC-level moving means; and in that the frequency modulator performs a frequency modulation such that it provides a frequency modulated signal whose frequency is an odd multiple of 1/4 of the horizontal scan frequency when the carrier is frequency modulated   by the predetermined DC voltage.   Recording system according to claim 1, characterized in that the means which produces the time division multiplexed video signal comprise means (11, 12) providing a luminance signal, means (11, 13> providing an in-line sequential color difference signal, first time base compression means (18-23) which receives the luminance signal to compress the luminance signal;   time base so as to provide the light signal.   based on compressed time, a circuit (17, 18) pro-   the horizontal synchronizing signal, second time base compression means (15, 16, 18, 24, 25) receiving the sequential in-line color difference signal and compressing the time base of this signal with a rate of time base compression with which one of the compressed time compressed color signals is transmitted, for a specified time, by subtracting from a horizontal scanning period the sum of the transmission times during which a part of of the compressed time-based luminance signal corresponding to a horizontal scanning period and the horizontal synchronization signal are transmitted, and switching means (18, 27 31) producing output signals of the first and second synchronization means. compression of the time base and the horizontal synchronization signal by   multiplexing these signals by division over time.   6 Registration system according to the   5, characterized in that the first means of   time base compression include a first con-   an analog-to-digital converter (19) receiving the luminance signal and transforming the luminance signal into a digital signal, two memory circuits (20, 21) receiving both the digital output signal of the first   analog-digital converter and performing alternating   a write operation and a read operation for each of the horizontal scanning periods so as to write in the digital output signal of the first analog-to-digital converter and to read the digital signal written, means (18, 22) assuring the alternating reading of the digital signal recorded in the first and the second memory circuit at each period   horizontal scanning on the basis of a first pulse   reading clock voltage having a frequency greater than that of a first registration clock pulse   and a first digital-to-analog conversion circuit (23)   logic converting the read signal from the first and   second memory circuit (20, 21) into an analog signal.   to produce the compressed time-based luminance signal, and that the second time-base compression means comprises a second analog-to-digital converter receiving the signal.   of sequential color difference in line and trans-   forming said signal into an analogue signal; a third memory circuit (16) receiving the digital output signal of the second analog-to-digital converter and recording the digital output signal of the second analog-to-digital converter in a video duration within a horizontal scanning period and reading the digital signal recorded for the remaining time within the same horizontal scanning period, means <22) making the third memory circuit (16) perform a registration operation   based on a second registration clock pulse   tion and having it carried out subsequently through this third   firing a read operation on the basis of a second read clock pulse having a frequency higher than that of the second write clock pulse and a second digital-to-analog converting circuit (24) transforming the signal reading   from the third memory circuit to an analog signal   logic so as to produce alternately the two kinds of color difference signals based on   compressed time for each horizontal scan period.   7 Registration system according to the   cation 5, characterized in that the circuit which produces the horizontal synchronization signal comprises a circuit part producing a discrimination signal which is used to discriminate the transmission times of the two kinds of color difference signals to   compressed time base for a period of horizontal scanning   every two zonal signals and producing a multiplexed signal in which a discrimination signal is multiplexed with   the horizontal synchronization signal.